I've been in an #Itscomplicated relationship with the ketogenic diet since the time when it was cool to actually use that status on Facebook. I can still remember that paradigm-shifting evening (circa 2010), clicking away in forums dedicated to the fringe low carb world, when a key word illuminated my screen. It was a concept I'd been searching for, yet didn't even know existed: ketosis. Of course, I'd probably seen it quite a few times in my obsessive research regarding the science of fat burning, but this was the first time I saw it in relation to another key concept rendering it ludicrously applicable: ketostix. Ya see, apparently, I could measure my level of fat burning with urine analysis strips, which would magically change colors in the presence of ketones like Fun Dip. Say what???

Fueled by this "scientific" evidence of liberated fat stores, I would subsequently embark on an ultra low carb endeavor in which I chased the chemtrails of urinary ketones and entered the culinary world of cream cheese by the spoonful, faux cauliflower "mashed potatoes" (before they were even *slightly* a thing), a 6 month fling of only chicken and coconut oil (true statement), and a moment of tears at getting "kicked out" of ketosis by an iHop omelet. (There's batter in them there eggy waters!)

Needless to say, I've been there, done that. And am still sort of doing it... but not really. Well.... #Itscomplicated

WHAT IS KETO?

Keto refers to "ketosis," a metabolic state in which the body - lacking dietary fuel (primarily from carbohydrates) - begins running primarily on fats (dietary and/or body fat), as well as a supplemental substrate known as ketones. While ketones are typically generated within the body, they're also now available in more "ready" forms like MCT oil and actual (expensive) ketone esters. Ketosis is a natural, inherent metabolic state which allows the body to cope with "starvation" from a lack of carbohydrate fuel, and historically arose as a response to actual periods of famine, since hunter-gather humans would often go much longer between meals than we do today.

So while ketosis is not starvation, it is, nevertheless, known as a sort of "starvation metabolism," if that makes sense. And while that may sound scary, it's actually completely natural, and provides the body with a very steady fuel source of fat and ketones, rather than fluctuating carb intakes. In today's overweight, ever-satiated (yet oddly "hungry") society, keto can therefore be an effective weight loss method, since it forces the body into the crème de la crème fat burning state, pumped up and ready to use body fat for fuel, rather than relying on constant snacks and sugar.

THE EVOLUTION OF THE KETOGENIC DIET 

Ok, this is sort of a farce, since the history of keto is sort of the history of being human. As just discussed, before the days of processed foods and grains, we naturally consumed substantially less carbs, and likely entered periods of ketosis quite often (without butter in our coffee or an array of delicious #fatbombs, just saying.) For its more modern manifestation, in the 1920s, the ketogenic diet became a therapeutic approach as an insanely effective means of treating epilepsy. (A 2000 review found that the ketogenic diet reduced more than 90% of seizures in almost half of children tested, and more than 50% in the other half.)

With growing interest and the revelation of many health benefits of the ketogenic state, keto got pushed to the limelight in the 1970s, with Dr. Atkin's Diet Revolution and the birth of the Atkins era. To this day, modern diet figures (think for example, Jimmy Moore) champion this high fat, low carb ketogenic approach.

Another more recent trend in the keto history was a keto diet not necessarily dependent on high fat per se, but rather simply focused on low carb, with moderate fat and moderate protein, à la the Ketogains community, founded by Luis Villasenor.

Another keto manifestation involves advocates of strictly whole foods-based "Paleo" approaches to keto, as well as advocates of ketosis who achieve it via intermittent fasting, but which may contain more carbs in one's "eating window" (and which may or may not be "Paleo" in spirit.) For the Paleo-ish approach, with perhaps a bit of fasting, think people like Robb Wolf's Paleo Solution, Mark Sisson's Primal Blueprint, Dave Asprey's Bulletproof Diet, and of course my own What When Wine. 

As you can see, there's many manifestations of keto, lots of overlap, and numerous contradictions. You could be Paleo but not keto, keto but not Paleo, Paleo AND keto, achieve ketosis via IF yet not be "low carb," do Atkins Paleo-style, do Atkins and be literally anti-Paleo, etc. Heck, you could even eat HIGH carb but slather your food in MCT oil, and register ketones. Whew!

In any case, limiting carbs at some point (be it through dietary macros or fasting) is typically key for the diet (many advocate 20 grams or less per day), while the amount of fat and protein can be adjusted based on the protocol, as broken down below. (Note: "Net carbs" refers to the total carbohydrate content of a food, minus the fiber.)

Therapeutic Ketogenic Diet 

~ 5% Carbs, ~ 20% protein, ~75- 80% fat. Typically no restrictions on the type of food.

Atkins 

Induction phase: <20 grams of net carbs per day, with gradually increased carb intakes through "phases" from there, up to ~80-100 net carbs per day. No hardcore restrictions on types of foods, though recommendations are made.

Ketogains

< 30 grams net carbs per day, with individual fat/protein macros based on one's body weight, activity level, and goal weight. No hardcore restrictions on types of foods, though recommendations are made.

Paleo Keto 

​A more lenient carb approach based on whole foods to reach moments of ketosis, either consistently, or at points through the day/days. This often features a diet of whole meats, veggies, nuts, and healthy fats, with perhaps occasional low carb fruits like berries.

Intermittent Fasting (IF)

Variable amount of carbs consumed in one's eating window, which may or may not lead to ketosis in the fasted state. The idea is that once a person depletes their glycogen stores with enough consistent fasting (often in a One Meal A Day, or OMAD pattern), they will enter ketosis daily.

Choosing Your Keto 

​If you're wondering which protocol will get you into ketosis the fastest, then severely cutting carbs, like the historical therapeutic approach, Atkins Induction Phase, or Ketogains macros, is likely the way to go. If you want to really jumpstart ketosis, throw in some fasting with that.

On the other hand, simply following a Paleo and/or IF lifestyle, can condition your body over time to readily switch between fuel substrates of carbs and fats, leading to a metabolic state known as "fat adaptation." 

You can also just slather your food in MCT oil and generate ketones, but this will not be a state of carb-depleted ketosis.

So... what's the most "natural" option on the keto menu?

From my perspective, the high fat ketogenic diet for epilepsy is fairly novel, as arguably no cultures subsisted on such a diet full time, with the exception of perhaps the Inuit - an Arctic population with a diet rich in fatty meat (think whales and seals and polar bears!) as well as occasional berries and such. I say perhaps, because recent findings indicate the Inuit actually harbored genes which made them less likely to enter ketosis. Talk about complicated! (See Chris Masterjohn's discussion of the concept: Inuit Genetics Show Us Why Evolution Does Not Want Us In Constant Ketosis for more on that.) Ketogains, on the other hand, is arguably more similar to our actual historical diet, since it isn't all about splattering food in fat, but rather focuses on simply lowering carbs and (often) upping protein, typically resulting in eating meat, nuts, and veggies. And lastly, I personally believe Paleo and/or intermittent fasting (depending on the foods chosen for the eating window) to be most in line with our historical nature, since such approaches can create a state of metabolic flexibility, in which the body oscillates between carb and fat burning naturally, rather than trying to "force" it into a state of constant ketosis.

KETONES

Ketone bodies are an alternate fuel source naturally generated by the body in its fat burning, ketogenic state, and include acetoacetate, β-hydroxybutyrate, as well as acetone. This acetone -the same compound found in many nail polish removers - is one of the reasons people can experience "keto breath" when adapting a ketogenic diet, as excess ketones can be excreted via the breath.

Ketones can directly enter the cell mitochondria for fuel, unlike glucose from carbohydrates, which require an intermediate conversion step. Ketones also generate more energy than glucose, with fewer toxic by-products like reactive oxygen species and free radicals. And while 100 grams of glucose yields around 8.7 kilograms of ATP (a “currency” of intracellular energy), 100 grams of ketones create around 10.5 kilograms of ATP.  This means fueling on ketones rather than carbs = more energy for you! We'll look at more benefits of ketones and ketosis in a bit!

Got Ketosis? 

Ketosis is often defined as registering ketones at a minimum of .5 mmol, with a "golden" range of 1.5- 3 mmol. That said, it's been argued that the mere presence of ketones  indicates one is in ketosis, and levels can fluctuate based on the individual and their keto history.

Subjectively, there are quite a few ways you can infer you're knock knock knockin' on keto's door. These include an odd sweet taste in one's mouth, the aforementioned stereotypical "keto breath" (described as everything from nail polish remover to dog breath), as well a complete lack of sugar cravings, and feelings of sustained energy.

Fancying more concrete signs? I hear ya! After all, I'm sort of definition #testallthethings.  Thankfully, you can 100% confirm if you are, in fact, producing ketones. Here are your options:

Testing Options

Urine Strips: Ketone urine analysis strips turn a certain color (like pink to purple) depending on the presence of ketones. Pros: Urine testing is cheap and painless. Cons: Urine strips indicate ketones you excreted, but not necessarily used. While they can be great for indicating when you first "get into" ketosis as a newbie, they or may not be reliable indicators beyond that, as the body becomes more adept at actually using ketones, and not excreting as much. People often get disheartened when they don't register ketones on the strips, or don't register them at high levels, when really, it could be because they're mostly using, rather than excreting them.

Breath Testing: Breath meters (like the popular Ketonix) can also measure the presence of ketones in your breath. Pros: Breath testing is non-invasive, more reliable than urine, and doesn't require refill strips. Cons: Like urine tests, breath testing may simply indicate ketones excreted, but not necessarily utilized. That said, a 2002 study did find that breath tasting pretty accurately correlated to levels of β-hydroxybutyrate and acetoacetate, whereas urine tests were only equally reliable for β-hydroxybutyrate.

Blood Testing: Blood tests for ketones are arguably the most consistent and best way to check ketone levels. I wholeheartedly recommend the Keto Mojo for this! Cons: Blodd testing is the most pricey testing method, requires strip refills, and you also gotta prick yourself! Pros: Blood testing is hands down the most reliable indicator of ketosis, as it indicates what ketones are active in your blood, and how much! Thankfully, the super awesome Keto Mojo meter has also made it more affordable!

Why Are My Numbers Low?

Measuring ketones can be everything from exciting to disheartening to utterly misleading. This is because registering ketones indicates your body is making them (unless you supplemented with MCT oil, for example), but they do not necessarily indicate if your body is using them. The levels registered can also vary widely: less is not always bad, and more is not always better! When the body first adjusts to ketones, it has a tendency to produce a ton, without utilizing them so well. The over-spill is often excreted in the breath and urine. Keto-goers are often disheartened when initially high ketone readings drop as they progress on the diet. But this is not necessarily because they're not making ketones, but rather because their body has become better adept at fully utilizing ketones.

Because of this, I advocate using measuring devices in the genesis of your keto experimentation to know when you actually enter keto, and perhaps afterwards to see how various foods affect your ketogenic state, but I don't suggest measuring all the ketones, all the time. Do the diet that makes you feel good, and don't sweat the small stuff!

HEALTH BENEFITS

Numerous studies have shown the ketogenic diet to benefit a variety of health condition and disease states, despite many a doubter's accusations of the necessity of carbs. These health benefits may be due to a myriad of potential reasons, including the foundational concept of the anti-inflammatory benefits of a fat-burning metabolism, increased mitochondrial energy production, blood sugar control, as well as other mechanisms discussed below (and who knows what else!)

Blood Sugar & Insulin Control

Perhaps this goes without saying, but the ketogenic diet can be epic for balancing blood sugar levels, especially for those who deal with insulin issues, or struggle with diabetes or pre-diabetes. Across the board, studies often find that the keto diet improves insulin sensitivity and glucose tolerance. Unless you have a pre-existing condition which renders you unable to properly utilize ketones for fuel, it's pretty hard to NOT reach stable blood sugar levels on a ketogenic diet, seeing as how you're not taking in sugar to begin with! It's just like, not a thing. (That said, some people do experience elevated blood sugar levels on keto, which can be due to things like elevated stress hormones, or perhaps a state of slight insulin "resistance," since the body begins, in a way, "preserving" the blood sugar it does have, to put it very casually.)

Brain Health

Keto can provide superstar support for the brain. While the brain does require a very minimal amount of glucose for fuel, that amount is minute, and when a person is "fat-adapted," even less so! (By the way, the brain is the only organ requiring this glucose, with the exception of cells which have no mitochondria, such as some in the eyes.) In fact, the brain actually functions much better on ketones, which are consistent and "clean burning,"  generating far less oxidative stress and byproducts, than the more "dirty" burning glucose.

Numerous studies have shown the ketogenic diet can be highly effective for treating brain injury, such as from stroke and brain trauma. As indicated in a recent scoping review, the keto diet may also minimize inflammation in the brain while improving energy utilization. In the same vein, ketosis may be particularly effective for preventing brain cancer, as well as Alzheimers, which is considered by some to be "diabetes of the brain."

Inflammation & Pain Relief

In down-regulating glucose metabolism, the ketogenic diet is highly anti-inflammatory in nature, reducing oxidative byproducts from energy generation. To this point, researchers in a recent study in Nature Communication found they could replicate the anti-inflammatory effects of the ketogenic diet by using the 2-deoxyglucose (2DG) molecule to stop glucose metabolism. The result? Essentially a wipe out of inflammation. (Which infers a lot about glucose metabolism!)

The anti-inflammatory effects of ketosis can yield a multitude of benefits, since chronic inflammation is often the root cause of many degenerative diaereses and ailments we experience today. (Unfortunately, taking pain pills only masks the problem, while not addressing the underlying cause). It therefore comes as no surprise that being in a state of ketosis may reduce all sorts of pain, from inflammation to neurpathic to even thermal pain. Pain can also be due to increased activity of neurons, which the ketogenic diet may, for lack of a better word, "calm down." (This is also a proposed mechanism for how the ketogenic diet treats epilepsy). Ketosis may also enhance the body's secretion of adenosine, which can further relieve pain.

Cancer

From a mechanistic perspective, utilizing a ketogenic diet for cancer makes a lot of sense. It has been postulated that many types of rogue cancerous cells can only utilize glucose and lactate as their main source of fuel. Since a ketogenic diet switches the body to utilizing fatty acids and ketones, this can effectively starve cancer cells, or at the very least make them more susceptible to treatments like chemotherapy. Recent research indicates that the ketogenic diet harbors great potential as a therapeutic approache to cancer, though it is likely most effective at present as a preventative measure. It's also pertinent to look at the specific type of cancer, which may determine reactions to a ketogenic intervention. (It's even possible the ketogenic diet might increase tumor growth for a few, very specific manifestations of cancer.) That said, a 2018 review concluded that the "ketogenic diet in cancer patients is safe and feasible as an adjuvant therapy," but did note that adherence to the diet for at least 3 to 4 weeks was necessary.

Anti-Aging

A major factor of aging is the oxidative byproducts from cellular processes, as well as increased inflammation in general. Since the ketogenic diet can substantially reduce inflammation, it can therefore be a potential therapeutic approach for longevity. Of course things are tricky, since we don't have studies on long term ketogenic diets. For supreme anti-aging potential, I suggest making your ketogenic diet (or any diet in general) rich in anti-aging, nourishing, whole foods brimming with antioxidants! Think: grass-fed animals, organic greens, chocolate, coffee, perhaps some wine and berries, etc.

KETO &  THE MICROBIOME

Many a naysayer will often raise an eyebrow at the ketogenic diet's effects on the gut microbiome, insisting the need for carbs and fiber to support our little buggers. But is this necessarily the case? Not necessarily...

For starters, a ketogenic diet does not necessitate reduced fiber intake. While you can totally do keto #carnivore style, the ketogenic diet is often rich in low carb veggies. And in general, any approach which reduces inflammation and improves the health of a person, tends to create beneficial changes in the gut microbiome. Such lifestyle changes include weight loss, exercise, and - maybe for you - the ketogenic diet!

Furthermore, the gut microbiome is insanely complicated and unique to the individual -  dependent one one's genetics, gut status, and a myriad of other factors, including diet of course. (See my post A Probiotic's Purpose: All About Gut Bacteria, Fiber, Histamine, IBS, FODMAPS, And More! for more on that!) While we're learning more about the gut microbiome each and every day, it's becoming increasingly clear just how unclear the whole matter is. Different healthy populations will feature vastly different microbiomes, based on their ancestry, environment, and food choices. We're seeing that more gut bacteria isn't always better, and some studies even show that "increased bacterial diversity" associates with health issues. (Perhaps the most common manifestation of the problems of too much bacteria is a condition known as SIBO, or "small intestinal bacteria overgrowth." You can learn more on that here: Is Your IBS Caused By SIBO? Get ALL The Info!)

In any case, it is unlikely that the ketogenic diet would permanently "damage" your gut microbiome, if such is your worry. A fascinating 2013 study, "Diet rapidly and reproducibly alters the human gut microbiome," found that bacteria populations changed significantly within a few days of abrupt dietary change. The researchers took subjects who historically ate either a plant or animal-based diet, and switched things up to see what would happen. The plant-based diet in the study consisted of grains, legumes, vegetables, and fruits, while the animal diet featured meat, eggs, and cheese. The researchers found that a mere day after the new food reached the participants' gut bacteria, things began shifting. Specifically, those on the animal-based diet began featuring more bacteria which breakdown protein and bile, while the plant-eaters got more bacteria feasting on fiber and carbohydrates. Interestingly, the animal diet (which produced more abrupt shifts than the plant diet) also increased gene activity for vitamin biosynthesis, as well as the potential for degrading carcinogens found in charred meat.

These changes notably occurred even when the people had been following the opposite diet for years. And when the participants switched back to their normal diet, the gut bacteria adapted within two days. Those consuming the animal-based diet also registered urinary ketones by day 2, making this study quite applicable to our current discussion! So while a ketogenic diet may quickly affect your gut bacteria, it will likely do so in a way which simply makes you more adept at getting nutrition from your food! Yey! In any case, if you do decide to stop keto, your gut bacteria can definitely go back to a similar version of the way they were.

(As an unrelated but fascinating side note, the researchers also noted that those on the animal, but not plant-based, diet experienced a significant loss of weight, despite the same amount of calories. Granted, this could have been due to water retention, but I still find it noteworthy.)

KETO AND WEIGHT LOSS

Perhaps the keto diet's most heralded benefits is its tendency to spur weight loss. This makes sense, since the diet switches the body into a primarily fat-burning mode. Beyond that, the diet can be highly satiating, so participants often underconsume calories, even if unintentionally. Of course, this welcomes in the oft-discussed argument of whether keto causes weight loss purely from its fat-burning metabolic state, or if the lost pounds are entirely due to calorie restriction. Some even advocate that one simply cannot gain fat at all when fully ketogenic, as the body will simply waste excess calories.

A proposed mechanism for how the keto diet may help seizures, is by up-regulating energy generation in the brain, enhancing  mitochondrial function. This may also increase the amounts of adenosine, which - in addition to its tendency to reduce seizures - is known as the neurotransmitter which makes you sleepy, and is blocked by caffeine. The keto diet may also up-regulate cortisol, encouraging a state of alertness and fat burning. (Contrary to popular belief, cortisol is not bad all the time - you just need it in the proper amounts at the proper times!)

Research also indicate the ketogenic diet may increase the use of polyunsaturated fats for fuel in the body, shuttling them from fat stores to the liver and brain. (Since people typically aren't consuming the majority of their fats on a ketogenic diet from PUFAs, but rather from saturated fats and MCTS, these large amounts of circulating PUFAS in the bloodstream on a keto diet insinuate they're likely coming from body fat, rather than dietary intake.)

In any case, it's hard to deny that thousands of people have experienced epic weight loss with keto. As a 2018 decade long review concluded, "the effects of  [the ketogenic diet] on extra energy expenditure and weight loss are undeniably strong," even if the precise mechanisms are vague at presence. (The study's researchers put their bets on increased energy expenditure, possibly by increased oxygen). Other studies show ketosis down-regulates appetite hormones, and may even increase leptin, the hormone which makes you feel full. Basically, the keto diet can be the crème de la crème of appetite suppression, which is just what many people need for weight loss.

Better yet, keto typically supports the "right" kind of weight loss, with studies consistently finding that low carb approaches typically preserve lean muscle, while also regulating blood and metabolic profiles.

As for my personal thoughts on the matter, I think a keto diet often works best for weight loss in those who are overweight or obese, with ample fat stores to tap into. It's like opening the combination lock to a secret safe full of money which has just been sitting there, waiting to be used! Once that storage is used up, however, be it 20 or 200 lbs later, a person may find they function better with more carbs, or at least require more fat in their diet to sustain their new body, since they don't have as much "reserve" fuel.

For a nice analysis of tons of studies looking at low carb and ketogenic diets and weight loss, check out this post: 23 Studies on Low-Carb and Low-Fat Diets — Time to Retire The Fad.

KETO AND EXERCISE

When it comes to the keto diet and exercise, studies (and individual reactions) are mixed. For some, keto totally boosts performance, for others... not so much. (At least not in the short term.)

Endurance 

On the endurance side of things, the ketogenic diet tends to be quite beneficial. If you think about it, it really makes a lot of sense. After all, the average human being has enough stored energy in the form of body fat to walk a thousand miles, so you'd think going and going should be easy, right? So why do we get so tired? Why is going and going so difficult? As one of my favorite study quotes puts it (because when you're me, you actually have a list of #favoritestudyquotes): "An apparent paradox of long-distance running is that even the leanest athletes store enough fat to power back-to-back marathons, yet small carbohydrate reservoirs can nevertheless catastrophically limit performance in endurance exercise."

The fat-burning endurance conundrum is because the body typically fancies running primarily on glucose from carbohydrates as fuel. Our glucose availability, however, is limited to our most recent meal, as well as relatively-small glycogen stores: depending on the individual, around 100 grams in the liver and around 400 grams in the muscles. When you're accustomed to running on such sugar stores, the body will get tired and resist tapping into fat stores. It's the whole "hitting the wall" feeling. In fact, the brain can make you hit the wall even before near glycogen depletion, sort of like if your iPhone stopped working at 10% battery. (Which I swear happens more and more with each "update." Alas!)

On the ketogenic diet, however, the body runs primarily on fat, so there's no wall to hit! Being "keto-adapted" can boost endurance, decrease inflammation, increase maximal oxygen uptake (VO2max), and hasten recovery to boot! As noted in "The Effects of a Ketogenic Diet on Exercise Metabolism and Physical Performance in Off-Road Cyclists," "Most studies with endurance athletes have indicated that prolonged ketosis results in an adaptation, after which free fatty acids become the major metabolic fuel, and carbohydrate utilization is markedly reduced during moderate, but exhausting exercise." Furthermore, as discussed in Ori Hofmekler's Maximum Muscle, Minimum Fat: The Secret Science Behind Physical Transformation, practicing resistance training in lower carb states can build muscle fibers which particularly use more fat for fuel.

While there are tons of studies on the subject, here are just a few to show how simultaneously promising yet complicated the matter is:

• A case study of 10 athletes who followed a keto diet without regulating calories found the subjects became better at using fat for fuel, even at more intense workouts, and also lost more weight. They also reported feeling better overall, mentally and physically, and recovered faster, with less inflammation. They originally felt less energetic, but ultimately more energetic, particularly when they exercised. That said, brief bits of actual high intensity exercise was harder to perform.
• A 2014 study of ketogenic diets in 8 trained, off-road cyclists, found the diet benefited endurance, boosted body composition and blood profiles, decreased inflammation, and supported fat-fueled activity. That said, high intensity exercise performance was reduced, which the study credited to decreased glycogen stores. (But check out the next bullet point!)
• A 2015 study found that elite endurance athletes who ate a low (10%) carb diet, burned double the fat while exercising at high effort for 3 hours on a treadmill, compared to athletes eating a higher (59%) carb diet. Interestingly, the low carb athletes stored and used comparable amounts of glycogen to the carb-based athletes.
• A 2017 case study of 5 athletes found that, although the keto diet slightly decreased "time to exhaustion," the athletes experienced enhanced well-being and recovery. As the study concluded, "Despite performance decrements and some negative experiences, athletes were keen to pursue a modified low-carbohydrate, high-fat eating style moving forward due to the unexpected health benefits they experienced."

High Intensity

While the fitness world may be increasingly embracing the benefits of fat-burning metabolisms for enhanced endurance, high intensity stuff is a smidge more iffy. This is because quick bursts of activity typically utilize muscle glycogen - energy stored in the muscles from carbohydrates. While some keto advocates maintain that keto-fueled high intensity is indeed plausible (if not superior) given an adequate adaption period, the majority seem to be a bit more hesitant. As noted in a 2014 study, while a ketogenic diet can boost endurance performance and body composition, it notably "decreases the ability to perform high intensity work, due to decreased glycogen muscle stores and the lower activity of glycolytic enzymes, which is evidenced by a lower LA concentration and a maximal work load during the last 15 min of the high intensity stage of the exercise protocol."

In. other words, a ketogenic diet might make high intensity activity more difficult, but I don't think it makes it impossible. And interestingly, a recent study actually found that athletes on a low carb diet used similar amounts of glycogen as those on a high carb diet, so it really is likely a matter of finding what works for you personally. 

KETO AND HORMONES

Perhaps the greatest and potentially most appropriate fear surrounding the keto diet, involves its effects on hormones, especially when it comes to the female side of things.

Fertility

Despite common fears of low carb wrecking women's hormones, the ketogenic diet might actually encourage fertility in women who suffer menstrual irregularities due to being overweight, or due to polycystic ovary syndrome (PCOS), the most prevalent endocrine disturbance in females, which yields metabolic, reproductive, and psychological problems. These positive hormonal effects may be because the ketogenic diet can create a healthier overall metabolic state, and generate beneficial hormonal changes as a consequence. A 2017 systemic review looking at a low carb diet's effects on fertility, concluded that "reducing carbohydrate load can reduce circulating insulin levels, improve hormonal imbalance and resume ovulation to improve pregnancy rates compared to usual diet," but did note a lack of research for non-PCOS infertility.

Studies on lower carb diets have also found beneficial hormonal changes affecting fertility outcomes. In 2017, researchers at the Delaware Institute for Reproductive Medicine (DIRM) in Newark conducted a trial looking at women utilizing in vitro fertilization, and found that, while 11% of those following a "high carb" diet became pregnant, 58% in the low carb group became pregnant. For even more keto-fertility studies, check out this link.

That said, many of the studies analyzing carb content and fertility use "low carbohydrate" diets with around less than 45% carbs, which may or may not be actually "ketogenic," so perhaps a better comparison would be to look at studies on fasting, which are much more likely to yield a metabolic state of ketosis. These have also found neutral or even beneficial hormonal effects on women, especially those with PCOS. A 2010 Ramadan study specifically analyzing fasting and menstrual cycles found no significant negative effects. Another 2013 Ramada study aimed to investigate fasting’s effects on nervous system factors such as cortisol, catecholamines, and sex hormones, and found that fasting proved therapeutic for the PCOS women, decreasing levels of the stress hormones cortisol and noradrenaline. (The researchers were interested in fasting's effects on these hormones, since a proposed mechanism for PCOS is a shutdown of the reproductive system due to increased nervous system activity.)

And ironically, dietary restriction resulting in ketogenic states, might even extend fertility by preserving female ovaries. Mice put on alternate day fasting protocols experience menstrual cycles later in life than mice who eat normally, and Dutch women who suffered starvation during World War II ultimately experienced no change in fertility (despite fluctuations during the war), and in fact bore children who were, in turn, more fertile.

The Thyroid

The thyroid is sort of like the central governor for metabolism, and thyroid hormones (including the storage form T4 and active form of T3) function like keys which unlock the mitochondrial-energy producing potential of cells. You want your thyroid functioning on par if you want to, quite honestly, feel energetically ready for anything. (Check out my post How To Fix Your Thyroid And Find Your Life for more details on the thyroid!)

Hypo/hyper elephant in the room time! Does keto negatively affect the thyroid? Advocates of keto will often proclaim that either A: It doesn't. or B. Any reduction in thyroid hormones is simply because the body is functioning better metabolically, and so requires less thyroid hormone in the first place. Arguments are also made (and indeed, supported by scientific literature), that overall lower thyroid hormone production may correlate to increased lifespan, similar to calorie restriction.

I've been on the fence about this whole issue myself.

From a historical perspective, we often consumed way less carbs as hunter-gatherers, and were often ketogenic for many spiels, and arguably our thyroids were dandy. That said, it's also possible certain populations who more regularly consumed ketogenic diets, would rely more on "whole" animal products, and thus ingest natural thyroid hormones from the thyroid glands of animals. {Tangent: I recently went to Whole Foods to buy some chicken necks for bone broth, and asked if the necks still contained the thyroid gland. The guy looked at me like I was an alien and said he had never, in his 8 years of working there, been asked such a question. It happens.)

On the guy side of things, I haven't seen too much literature supporting detrimental effects on male thyroid production. For example, a 2002 study looked at a 6 week low carb diet (8% carbs) in 12 normal-weight, healthy men, compared to 8 control men. It found the diet decreased insulin, and actually increased the storage and free forms of T4 hormone (11 and 13 % respectively), while not significantly affecting T3 uptake, or many other hormones for that matter. (The keto men also lost significant fat loss, yet increased lean body mass.)

On the other hand, studies have shown that T3 production from T4 can decrease in fasting individuals, and a recent 2017 study found a keto diet implemented for epilepsy in 120 kids (half of each gender), resulted in hypothyrodiism in 20 of the children. (Ironically, despite being only 17% of the children, the study concluded that the ketogenic diet, "causes thyroid malfunction.")

A 1985 study also looked at liquid low carb diets higher in either fat or protein, to see how they would affect hormones. Both had 35% carbs, and used either 10% protein and 55% fat, or 35% protein and 30% fat. While this is sort of a wonky set-up in my opinion, and the diets notably used polyunsaturated fats (rather than the potentially more beneficial MCTs, monounsaturated fats, or perhaps even saturated fat), in any case, the researchers found that T3 decreased more on the high fat than the high protein diet, but that, also interestingly, TSH declined on both... which indicates increased thyroid function. Go figure. (The TSH is like your thermostat, and it raises when the pituitary gland senses you need more thyroid hormone, but drops when your pituitary senses you have adequate or even need less thyroid hormone.) As a side note, the study also found that the high protein version lead to higher insulin levels after the meal, but lower glucose levels later, compared to the high fat diet. The higher fat diet, on the other hand, decreased serum triglycerides more.

I'd definitely like to see more studies on the ketogenic diet's effect on the thyroid. In any case, while it seems that keto is often benign, or even beneficial, for the thyroid, I definitely encourage those following a keto diet to keep tabs on their thyroid status. I'd also wager that keto practiced via an intermittent fasting pattern, in which you dip into ketosis for a bit during the day, but consume more carbs in the eating window, might be more supportive of the thyroid.

MCTs

MCTs, or "medium chain fatty acids," are a form of fatty acid with less than 10 carbon atoms per chain, which are rapidly metabolized into ketones. They're found naturally in things like breast milk and coconuts, and also available as refined, supplemental oils. Unlike other fats, MCTs are actually not processed through the lymph system, but rather are shuttled straight through the portal vein to the liver, giving them instant energy potential like a carb, without affecting blood sugar. Pretty nifty!

Most commercially available MCT oils are a blend of the c8 (Caprylic acid) and c10 (Capric acid) varieties. (Side note: Caprylic acid is quite notable for its epic antimicrobial properties!) That said, some versions of commercially available MCT oils are straight up C8, which are processed the fastest, and thus argued to be even more "ketogenic" in potential. ​

Studies on MCTS are fairly consistent, though at times conflicting. MCTs are known for their thermogenic effect, and purported "inability," or at least extreme unlikelihood, to be stored as body fat, since they're readily used as fuel by the liver. And indeed, most studies (and there are a LOT of them) often find that substituting other forms of fat with MCTs, often results in greater fat loss (or less weight gain in an overfeeding situation), especially when long chain fatty acids (LCTs) are replaced with MCTs. This greater weight loss can occur even when the same amount of calories are consumed.

For example, a 2008 study looked to see what would happen when 31 overweight individuals consumed similar calorie -restricted diets, with either 18-24 grams per day of olive oil or MCT oil. (Olive oil was chosen for comparison because it is liquid at room temperature like MCTs, and has the leg up of being associated itself with weight loss.) The woman in the study consumed 1500 calories per day, while the men consumed 1800. They were all given "study muffins" which secretly contained 10 grams of their assigned oil, and were also given 8-14 grams of olive or MCT oil for cooking, amounting to around 12% of their total daily energy. The researchers found that the MCT oil lead to greater fat loss, including around the abs specifically.

Other studies find similar results, but sometimes with caveats. For example:

• A 2003 study which looked at overweight women who consumed diets of 40% fat, with 30% of the total diet being either MCT or LCT, found the MCTs increased energy expenditure and fat oxidation more than LCTs, but this notably did not affect their actual body fat percentages. (So yeah... not sure what to take from that?)
• A 2001 study in healthy men and women who consumed 60 grams of fat per day, either in the form of MCT or LCT, found the MCT lead to significantly greater fat loss, but only in those with a BMI > 23. In other words, MCTs might be great for stimulating fat burning, if you've got a lot of fat to lose.
• A 1999 study of 12 healthy women who consumed 32% of their diet as either MCTs or LCTs, found that MCTs significantly increased metabolism and energy expenditure after 7 days, but not after 14 days, insinuating that the body might adjust to MCT fuel, like any fuel really.
• A 2003 study of 24 healthy, overweight men comparing olive oil to MCT oil in the participants' diets, found that MCTs resulted in greater weight loss over 28 days, but only increased metabolism and fat oxidation significantly in the beginning of the trial.

MCTs' Metabolic Mechanisms 

The proposed mechanisms for why MCTS encourage weight loss are similar to the ketogenic diet in general: MCTs stimulate thermogenesis (fat burning) and decrease appetite.

For example, a 1996 study of 8 healthy men in a human respiratory chamber (think: crème de la crème of #control, in which participants are insanely monitored and their exact calorie intake and burning is measured), found that MCTs did, in fact, increase the patients metabolism by around 5%. (The patients ingested around 30 grams per day of either MCT or LCT.) Due to changes in their noradrenaline levels, the researchers postulated this thermogenic effect could be due to increased nervous system activity. (Other studies have shown that MCT rich diets can increase GABA levels as well, so things are definitely happening in the nervous system!)

MCTs have also been shown to increase satiety, with participants in studies often consuming less calories in subsequent meals following a meal rich in MCTs. But the weird thing? Studies can't really pinpoint any specific hormone or mechanism for this. In fact, a a majority of the studies analyzing how MCTs versus LCTs affect satiety-related hormones in subjects, often find that MCTS do not notably stimulate hunger-suppressing hormones. Very odd. Still, MCT oils seem to decrease appetite on a larger, rather than acute, basis.

Some even argue that MCTs literally cannot be stored as fat, as they are immediately turned into the energy in the liver. That said, studies have found MCTs in the blood circulation of those on high MCT oil diets, so that might not necessarily be the case. In any case, it is notable that in overfeeding studies, MCT-rich diets typically lead to less weight gain than other forms of fats, as previously discussed.

MCTs Effects On Keto Induction

Some people wonder if ingesting MCTs will somehow speed up their "entry" into ketosis (and all its glorious mood and health benefits), and also if MCT oil supplementation can aid any potentially bumpy "transitions" to veto-land. Well guess what: a 2018 study looked at just that! (There's seriously a study for everything these days!) The researchers compared the effects of ketogenic diets with or without MCT oil in 28 healthy adults, and measured their ketone and blood sugar levels, as well as symptoms of "keto induction," which include headache, various forms of GI distress, bad breath, muscle cramps or weakness, skin rashes, and difficulty concentrating. They found that MCTs did in fact create higher ketone levels all the time, and at a potentially faster rate than without such supplementation. MCts also slightly aided the negative induction side effects, except for digestive distress (which I'm guessing was a disaster pants situation, due to MCTs' famous loose-bowel instigating effect, to put things nicely.) The effects of MCTs on mood weren't certain.

On the epilepsy health side of things, a 2016 study looked at MCT-supplemented ketogenic diets, created to make the therapeutic dietary protocol more bearable for epileptic patients by fostering a ketogenic state, while allowing more carbs. The paper notes such diets have been found to be equally effective as non-MCT supplemented therapeutic keto approaches. (It also notes that seizure rates in animal studies do not correlate with the levels or degrees of ketosis, which I take as evidence that we should probably stop stressing about how high our ketones measure.)

MCT Takeaways 

Whew! This whole MCT thing could have been a post itself. In any case, here are my current takeaway thoughts:

• MCTs can be a bit "misleading" on a ketogenic diet, because they can create extremely high ketone level readings, yet do not necessarily mean you're generating ketones from body fat, if such is your goal. Ketones from MCT do not = ketones from your body fat.
• That said, smart use of MCT oil can stimulate thermogenesis and a fat-burning state, especially if you're overweight and/or just beginning a keto or lower carb protocol.
• You might gain weight if you add thousands of calories in the form of MCTs to your diet, but it will probably result in less weight gain than adding other forms of fat.
• MCTs can be a great supplement for brain performance, especially the C8 only version.
• I like to view MCTs not as food per say,  but rather like a supplemental hack for weight loss and performance, if used correctly.

P.S. - I've got some great RECIPES utilizing MCT oil in What When Wine, like my Immune-Boosting Italian Dressing!

FAQ

As the co-host of the top iTunes podcast, The Intermittent Fasting Podcast, I know there are a ton of keto questions out there. We get them daily. So while this could turn into a blog post in and of itself, here are some biggies.

Is Keto Paleo?

People often say they're trying to decide between keto OR Paleo. Listen guys.  You can do Paleo in a keto style, and you can do keto in a paleo style. However, you can also do Paleo and not be keto, or you can do keto and not be Paleo. They are not necessarily the same thing. Keto involves the metabolic state of ketosis, typically created from carb depletion. Paleo involves eating whole foods, and eschewing grains, processed foods, and oftentimes legumes and dairy. Here are some examples of what that might look like:

• Keto Paleo: Meat, Leafy Greens, Nuts, Oils, Occasional Berries
• Keto But NOT Paleo: Lots Of Dairy, Processed Low Carb "Goodies"
• Paleo But NOT Keto: A Diet High In Fruits And/Or Starches

Can Too Much Protein Kick You Out Of Ketosis?

A heated debate in the keto community is whether or not protein can kick you out of ketosis. While protein does not contain carbohydrates, excess protein can be converted to glucose via a processes called gluconeogenesis - which means, quite literally, the generation of glucose. That said, gluconeogensis happens anyway in ketosis, since some cells in the body do require glucose for function, including red blood cells and a small percent of the brain. It is also postulated that gluconeogensis likely happens on an as needed, rather than automatic, basis. I also believe the amount of glucose generated from excess protein - even large amounts of such - is unlikely to kick one out of ketosis.

That said, protein is insulinogenic, meaning it can create an insulin response, and often times a potent one at that! I believe this is a key reason people often feel like protein "kicks them out" of ketosis. Just speaking personally here, but I've found the insulinogenic response of protein, especially if not paired with enough satiating fat, can create an intense feeling of hunger, thanks to the insulin release. I therefore think a super high protein, low fat, low carb diet may create hunger and blood sugar issues for some people, while not necessarily being "anti-ketosis."

Do Calories Matter?

Oh boy.  This is a biggie. Some will say you literally cannot gain weight from excess calories when ketotic. Others say it's all about calories, and ketosis actually results in weight loss from naturally reduced caloric intake due to decreased appetite. My personal thoughts on the matter? There's way more to weight loss and weight gain than calories. There's hormones and water and fat and types of fat and hunger and lack of hunger and thermogenesis and thyroid and metabolism and #allthethings. You can eat less calories than you "should" burn, and not lose weight. You can also eat more calories than you "should" burn, and not gain weight. It happens. I say don't stress about it. Focus instead on the types of foods which leave you satisfied and not craving. Make these foods whole foods (refined foods are more likely to make you gain weight - just saying!) If you do, indeed, eat 10,000 calories on a keto diet, chances are you might gain weight. Or maybe you won't. Interestingly, many studies looking at isocaloric diets with various macronutrient profiles, find people lose more on low carb than low fat diets, despite the same amount of calories. So again, I say forget calories! Focus on your mitochondria and health and performance, and the rest should fall in line from there. (That said, just so you don't feel cheated in this answer, please check out the MCT section, for more on how the types of fat affect fat storage. And for a very thorough discussion of how calories are used in the body, check out The Calorie Conundrum, in my book What When Wine: Lose Weight and Feel Great With Paleo-Style Meals, Intermittent Fasting, and Wine.)

Recipes?

For some pretty epic recipes created by the talented chef Ariane Resnick, I refer you to my book, What When Wine: Lose Weight and Feel Great With Paleo-Style Meals, Intermittent Fasting, and Wine! It's got 50 Paleo-friendly recipes, all of which indicate if they're low carb, keto, vegetarian, low-FODMAP, and more!!

SO WHAT DOES IT ALL MEAN?

Ok, if you made it through this epic post - which Google is informing me takes over an hour to read  - I applaud you! I also imagine you may be motivated by some newfound keto-high, or desperately searching for reasons to continue with your keto attempts and achieve said rumored keto-high. In any case, the time has come for my final thoughts on the fatty matter! While I’ve obviously got a LOT of 'em, here are my current key beliefs, subject to change with new research and experience of course.

My Keto Takeaways

• The keto diet may be particularly beneficial for those who struggle with insulin dysregulation, blood sugar issues, pre-diabetes, and/or diabetes.
•  If you’ve got a lot of weight to lose, keto may be great for you, especially if you haven’t tried it before. But if you’re already at an average or lean weight, you might function better on a higher carb intake. 
• There are different versions of keto. You, for example, may do better on a lower fat, higher protein keto approach, or vice versa.
• Getting your genetic profile may reveal whether or not you're inclined to function better on higher fat or higher carb. That said, a recent study did find that genetics do not seem to matter when it comes to weight loss, when "healthy" low fat versus low carb diets are followed, despite the researchers earlier findings to the contrary. So who knows!
• There aren’t really any historical populations who were 24/7 keto, with the exception of the Inuit. (Which is also complicated, as mentioned.) However, that doesn’t invalidate the keto concept as a modern diet hack. After all, there weren’t any long term vegan populations either, or historical populations experimenting with piracetams, red light therapy, vibration machines, or all the other modern life/health hacks we've got today.

What I Do

So where do I currently fall on the whole keto-experimentation thing?

Not gonna lie, I really want to be a keto gal. Like really. I often imagine myself in this perpetual flow state of keto zen, sipping on MCTs and laughing in the face of an apple. Yet, while I’ve been keto in the past for months on end, I’m honestly having difficulty returning to it 24/7 at this present point in my life. For reals. I’ve tried quite a few times recently, and failed.

 Ya see, when I first went keto those many moons ago, I was coming from a Standard American Diet at a much higher weight (about 50 lbs more!), and indeed saw a myriad of benefits, the most revolutionary of which was likely the complete loss of a perpetual need for feeding. The stabilized mood, fading acne, and of course, actual weight loss (finally!) further fueled my keto fire. But when I introduced more carbs a few years later in my newfound Paleo paradigm, I saw even more benefits: radiating skin, a feeling of uber-hydration, decreased residual inflammation, the disappearance of headaches, and much more.

I’ve also experienced two very telling times in which I broke my keto-ness with carbs, in two very different scenarios, and which yielded two very different results. The first time was pre-Paleo, right before competing on the ABC game show Spell-Mageddon, about a few years after adopting low carb. I figured shocking my system with a granola bar might provide an epic energy boost and fuel me to game show stardom. All it did was make me feel crappy; I got literally wiped out on the show; dominated the publicity Getty images in ways I'd rather not remember; and ultimately ran back to keto with open arms. (Note to self: No. More. Game. Shows. Ever.)