1 September 2017


In his Obesity Notes blog, Dr Arya Sharma recently reviewed a year-long randomised controlled study by John Trepanowski and colleagues that showed alternate day fasting is evidently no better in producing superior adherence, weight loss, weight maintenance, or cardio-protection compared to good old daily calorie/kilojoule restriction (which also produces modest long-term results at best).

“It seems that every year someone else comes up with a diet that can supposedly conquer obesity and all other health problems of civilization. In almost every case, the diet is based on some “new” insight into how our bodies function, or how our ancestors (read – hunters gatherers – never mind that they only lived to be 35) ate, or how modern foods are killing us (never mind that the average person has never lived longer than ever before), or how (insert remote population here) lives today with no chronic disease. Throw in some scientific terms like “ketogenic”, “gluten”, “anti-oxidant”, “fructose”, or “insulin”, add some level of restriction and unusual foods, and (most importantly) get celebrity endorsement and “testimonials” and you have a best-seller (and a successful speaking career) ready to go.

Hunter gatherers

The problem is that, no matter what the “scientific” (sounding) theories suggest, there is little evidence that the enthusiastic promises of any of these hold up under the cold light of scientific study. Therefore, I am not the least surprised that the same holds true for the much hyped “alternative-day fasting diet”, which supposedly is best for us, because it mimics how our pre-historic ancestors apparently made it to the ripe age of 35 without obesity and heart attacks.

The alternate day fasting group in the year-long randomised controlled study published in JAMA Internal Medicine had significantly more dropouts than both the daily calorie restriction and control group (38% vs. 29% and 26% respectively). Mean weight loss was virtually identical between both intervention groups (around 6kg).

Purists of course will instantly criticize that the study did not actually test alternative-day fasting, as more people dropped out and most of the participants who stayed in that group actually ate more than prescribed on fast days, and less than prescribed on feast days – but that is exactly the point of this kind of study – to test whether the proposed diet works in “real life”, because no one in “real life” can ever be expected to be perfectly compliant with any diet. In fact, again, as this study shows, the more “restrictive” the diet (and, yes, starving yourself every other day is “restrictive”), the greater the dropout rate.

Unfortunately, what counts in real life is not what people should be doing, but what people actually do. The question really is not whether or not alternate-day fasting is better for someone trying to lose weight but rather, whether or not “recommending” someone follows an alternate-day fasting plan (and them trying to follow it the best they can) is better for them. The clear answer from this study is “no”. So why are all diets the same (in that virtually all of them provide a rather modest degree of long-term weight loss)?

My guess is that no diet (or behaviour for that matter) has the capability of fundamentally changing the body’s biology that acts to protect and restore body fat in the long-term. Irrespective of whether a diet leads to weight loss in the short term and irrespective of how it does so (or how slow or fast), ultimately no diet manages to “reset” the body-weight set point to a lower level, that would biologically “stabilize” weight loss in the long-term. Thus, the amount of long-term weight loss that can be achieved by dieting is always in the same (rather modest) ballpark and it is often only a matter of time before the biology wins out and we put all the weight back on.

Clearly, I am not holding my breath for the next diet that comes along that promises to be better than everything we’ve had before. My advice to patients is: do what works for you, but do not expect miracles – just find the diet you can happily live on and stick to it.”

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Dr Sharma 
Dr Sharma is Professor of Medicine and Chair in Obesity Research and Management at the University of Alberta, Edmonton, Canada. He is also the Clinical Co-Chair of the Alberta Health Services Obesity Program. He has authored and co-authored more than 350 scientific articles and has lectured widely on the etiology and management of obesity and related cardiovascular disorders and is regularly featured as a medical expert in national and international TV and print media and maintains a widely read obesity blog at www.drsharma.ca.