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Alternate Day Fasting Is No Better Than Any Other Fad Diet



It seems that every year someone else comes up with a diet that can supposedly conquer obesity and all others 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”, “guten”, “anti-oxidant”, “fructose”, or “insulin”, add some level of restriction and unusual foods, and (most importantly) get celebrity endorsement and “testemonials” and you have a best-seller (and a successful speaking career) ready to go.

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.

Thus, a year-long randomised controlled study by John Trepanowski and colleagues, published in JAMA Internal Medicine, shows that alternate day fasting is evidently no better in producing superior adherence, weight loss, weight maintenance, or cardioprotection compared to good old daily calorie restriction (which also produces modest long-term results at best).

In fact, the alternate day fasting group 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 (~6 Kg).

Purists of course will instantly critisize 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 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.

@DrSharma
Edmonton, AB

9 Comments

  1. Dear Dr. Sharma,

    Will the inner body-weight set point ever be overwritten? What after 1y/2y/5y/10y/20y adhering to a diet and maintaining the same weight?

    Best regards,

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    • There is no robust scientific evidence that the body weight set point can be permanently altered to regulate weight at a lower set point – bariatric surgery sort of does this but when you reverse the surgery, the weight comes back – nothing “permanent” about it.

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      • Thank you

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  2. Fully agree with this. So frustrating to see many people saying this is a long term solution to weight struggles. There is nothing magical about skipping meals, and it results in short term deprivation.

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  3. I haven’t read the study and work with people having betabloc disorders. In general, seems like LCHF or ketogenic nutrition not only has a great effect on weight loss but on metabolic fuctions, energy, hunger signals, etc. It also seems quite sustainable with the patients I follow. Fasting every two days will be extremely challenging for a person who it consumming a lot of CHO…not those that are LCHF adapted.

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  4. I believe that the determination defines your body to diets the fasting helps yes but and I need to have attitude to achieve good results I liked the article very good

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  5. In my life (I am 65)I have gone a total of at least 300 days with no food at all. These were mostly single days, but sometimes I’d go two or more. The reason for this was that I was poor and too proud to go to a homeless shelter to eat. Sometimes I would pull out garbage bags from the backs of restaurants, and eat other people’s unfinished meals.

    Anyway, this wildly disorganized style of eating, with frequent fasting, did not seem to harm my physical health. (My mental health was a little disordered, and probably still is, not that I’ve ever sought treatment for it.) What I learned then is something that I cannot actually teach anyone, including Dr. Sharma, and that is that going hungry for short periods is not harmful. You don’t even feel much in the way of food cravings.

    Now, in old age, I probably eat about a thousand calories a day. I have not eaten either breakfast or lunch in twenty years. I just don’t care about food, and you can’t get me to eat a full Canadian meal, because I just can’t get it in me.

    And I’m healthy. I’m six foot five, about a hundred and eighty, and I can run a half mile in just under three minute. I am not on any medication at all, which is probably rare for a Canadian my age.

    The biggest problem with fat people is that they love to eat. Watch the food channel some time, and it’s one lover of food after another. Eating is their greatest joy. Moreover, they seem to think that human beings cannot endure more than ten hours without eating before suffering severe damage. These people need to learn that eating for fun is a modern luxury, and has no basis in biological necessity.

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  6. Y’know, Dr. Sharma, your basic premise on this blog seems to be, very few people can lose weight and keep it off because it’s just too tough. It’s a good thing you’re not am Alcoholics Anonymous sponsor, because you’d be telling you sponsored subjects that “the body” would always sabotage their efforts to quit drinking.

    Look: the laymen have it right here. People are too fat because they eat too much food. If people want to weight less they must eat leas food. Probably quite a bit less.

    I keep posting (and being denied) on your blog because, in my experience, once you learn to go hungry, hunger is not particularly stressful. Except that what people are feeling is not hungry. I’ll bet most Canadians have never been hungry, and have no idea what it feels like. No, what people are feeling when they think they are hungry (because they skipped breakfast, or something minor like that) is a compulsion to feel the pleasure of eating.

    How did you get through medical school if you have such a poor opinion of the need for discipline? Nobody can hold a job without willingly enduring a certain amount of fatigue, embarrassment and fear. So nobody can also endure longings for food? That’s just absurd.

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  7. I read your piece on this topic on GI News from the University of Sydney. I agree that the real world aspect of the compared diets is important, as you point out. In the preliminary section of your piece, however, you refer to hunters gatherers and make the comment, “never mind that they only lived to be 35.” While I do agree that human longevity has increased, the 35 years you cite is, I believe, misleading as it is calculated on life expectancy from birth, not the upper end of life expectancy for those who reached maturity. Those who lived through multiple childhood illnesses and infections were capable of lifespans approximately as long as those currently enjoyed. To ignore the lower incidence and prevalence of certain diseases that plague modern civilization in hunter gatherers or similar by citing an irrelevant and inaccurate lifespan is not helpful.

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