Is intermittent fasting better than chronic calorie restriction? Only if you actually do it!

In his keynote talk at Low Carb Houston, Dr. Andreas Eenfeldt recently stated that showering only gets you clean if you actually do it. He used this obvious example to highlight the trouble with studies that proclaim one method is no better than another, but then document that only a fraction of the subjects was compliant with the intervention. Thus the conclusion could be that the intervention was difficult for the subjects to maintain, but the conclusion should not be that the intervention did not work.

A recent study in The American Journal of Clinical Nutrition falls prey to the same problem. German investigators evaluated the effects of intermittent calorie restriction, defined as 5 days per week of normal eating with 2 days at 25% of baseline calorie intake, versus chronic calorie restriction, defined as 80% reduction in daily caloric intake, versus no change in caloric consumption (control group) in 150 overweight or obese adults.

After 50-weeks, they found no meaningful difference in the primary endpoint of genetic expression in adipose cells. They also claimed there was no difference in weight loss, BMI or waist circumference between intermittent and chronic calorie restriction. Does this negate all the positive anecdotal experience in favor if intermittent fasting?

Definitely not. Looking further into the data tells us another story.

Between weeks 2 and 7, there was 80% compliance with the intermittent calorie restriction protocol. At the 12-week mark, there was better weight loss for this group — about 7% of body weight — compared to the chronic calorie restriction group — roughly 5% of body weight. By the end of the 50-week trial, however, there was no longer a significant difference between intermittent and chronic calorie restriction. Interestingly, the compliance with the 5:2 intermittent calorie restriction protocol at week 50 was a paltry 21%.

When only 21% of the subjects complied with the intermittent calorie restriction, can we really claim it is no better than chronic calorie restriction? Of course not. Instead, we have to decipher why so few subjects maintained compliance.

We don’t know for sure, but the study did encourage “low-fat dairy,” with only one serving of meat or fish per day. As a result, the subject’s diets showed “an overall increase in protein and carbohydrate intake relative to total energy intake, paralleled by reductions in fat.” Would they have fared better with a low-carb, high-fat diet? Anecdotal experience would say “yes,” but this study did not investigate this question.

In the end, this study does little to help us understand the differential effects of intermittent and chronic calorie restriction. It does, however, suggest that intermittent calorie restriction is challenging for those following a higher-carb, low-fat diet. Instead, we are likely to see better compliance and thus better outcomes with a high-fat, low-carb diet and intermittent fasting. You can hear more about this strategy from The Diet Doctor Podcast interview with Megan Ramos from IDMProgram.com.

Thanks for reading,
Bret Scher, MD FACC

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