A common fear with intermittent fasting is that, by temporarily restricting your eating, you’ll become ravenously hungry and end up overeating way more than you would normally, doing more harm than good. Come meal time, all hell will break lose as you stuff your face to oblivion. Nobody needs that!
But is this case?
While doing research for my next book on intermittent fasting, I came across an interesting study on the subject. Published in the 2013 British Journal of Nutrition, the study was called “The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women.” (Gotta love how medical journal titles are always straight to the point!)
The study compared the effects of 3 “energy restriction” diets in 115 overweight women:
- A daily Normal Low Calorie Diet (CR) providing 75% of basic calorie needs: This was a Mediterranean style diet with 25% protein, 45% carbs, and 30% fat.
- A 2 day per week Low Carb IF Diet (IF) providing 30% of basic calorie needs: The patients ate a normal Mediterranean style diet for 5 days, then would have 2 days in a row eating just 30% of their normal calories.
- A 2 day per week IF Diet With Unlimited Protein & Fat (IF+PF) providing 30% of their basic calorie needs: The patients ate a normal Mediterranean style diet for 5 days, then would have 2 days in a row eating unlimited protein & fat. Interestingly, it was expected the protein + fat diet would cause the women to automatically “self-limit” their calorie intake. I find this to be a vast, very telling assumption about the weight loss potential inherent in a low carb, high fat diet. But that’s beside the point.
(Note: I provided my own acronyms – the ones in the study were too confusing.)
The Study Found:
- Both IF diets provided significantly greater weight loss than the normal calorie restriction diet. The IF diet yielded 65% weight loss and the IF+PF diet yielded 58% weight loss, while the CR diet yielded 40% weight loss.
- Both IF diets also saw greater reductions in body fat specifically, compared to mere calorie restriction. This supports the idea that IF promotes fat burning, while sparing lean muscle tissue. Yey!
- Both IF diets lowered insulin levels more than the normal calorie restriction diet.
- All groups saw increased ketone levels. (But that’s for another day!)
But what I found most interesting?
In what the study calls a “carry over” effect, the women on the intermittent fasting protocols spontaneously decreased their calorie intakes on their “normal” eating days. Although they were told to eat “euenergetic” diets providing maintenance calories, they would eat significantly less than that. On average, the IF group ate 1366 calories rather than their prescribed 1987 calories, and the IF+PF group ate 1538 calories rather than their prescribed 2021 calories. In fact, the amount the IF groups were willingly eating on their “free” days mirrored the enforced restricted days of the calorie restriction group. Oh hey!
Intermittent fasting protocols may encourage people to willingly eat less in general, even when not specifically fasting. Intermittent fasting does not seem to encourage binging and overeating, but, if anything, yields unintentional calorie restriction. (Nor does it create unhealthy eating thoughts, as discussed in my recent post, Does Intermittent Fasting Encourage Eating Disorders?)
The only thing to fear, is fear itself!