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The New Obesity Guidelines Are Big on How Little We Know

sharma-obesity-fat-dietingYesterday saw the online release of new obesity management guidelines – the results of an enormous amount of work by those involved.

In my first cursory study of this 70 page document, what leaps out at me are two important treatment options that are not discussed: exercise and pharmacotherapy – both, to me, essential components of obesity management.

However, what also stands out is the rather poor level of evidence that exists for virtually all of the dietary recommendations.

Thus, the valiant attempt to answer the question regarding comparative efficacy/effectiveness of diets of differing forms and structures (macronutrient content, carbohydrate and fat quality, nutrient density, amount of energy deficit, and dietary pattern) or other dietary weight loss strategies (e.g., meal timing, portion-controlled meal replacements) in achieving or maintaining weight loss in overweight and obese individuals, yielded surprisingly little.

After exhaustively reviewing virtually all of the existing studies that compares one dietary approach to another, the only recommendation for which the level of evidence to support it was rated as “high” is that “high protein” diets with 25% to 30% of energy derived from protein (compared to the typical 15%) are no more effective in promoting weight loss when both diets are calorie-restricted (500–750 kcal/day deficit).

If that was not disappointing enough to those who believe that high-protein diets lead to more weight loss (they don’t), the evidence for other approaches is even more disillusioning, as it consistently ranges between “low” and “insufficient”.

Thus, low fat approaches appear no better than high-fat (strength of evidence: “moderate”), while the evidence in support of low-calorie diets, complex vs. simple carbs, glycemic load, Mediterranean-style diets, lower-fat lacto-ovo-vegetarian or vegan-style, or lower fat high dairy/calcium with added fiber and/or low glycemic index/load foods, use of liquid and bar meal replacements, or even very low calorie approaches is largely “insufficient” to make any reasonable recommendations in favour of any of these strategies versus any other.

Not that people do not lose on any or all of these diets as long as they are “energy restricted” – of course they do!

But, what is lacking is evidence that any of these countless dietary approaches confer any meaningful advantage (in terms of amount of weight lost, metabolic benefits or sustainabilty of weight loss) compared to any other.

So, whilst millions of “bestseller” diet books may continue to make millions for their authors and publishers by touting one revolutionary weight loss solution after another, they are essentially closer to religious belief systems than scientific fact.

It appears after all, that the single recommendation that best summarizes all of the actual evidence on diet and weight management boils down to “eat less” – and we all know how effective that recommendation turns out to be.

So, do we really need any  more dietary studies on weight management? After all, if these questions have not been answered conclusively by the last 100 studies (some of them rather large and conducted by some of the best researchers in the field), why would anyone expect conclusive answers from the next 100 studies?

Perhaps it is time to acknowledge that there is perhaps really no difference between different dietary approaches to weight management or that such a difference, even if it does exist, is virtually impossible to ever conclusively “prove” in humans – let alone in clinical practice.

In light of this evidence (or rather lack of it), it is hard to see how dietary practitioners manage to maintain any level of enthusiasm for “dietary approaches” to weight management that extoll anything other than reducing calories.

Obviously, this sobering state of affairs is unlikely to dispel the firm “beliefs” that certain diet strategies are superior to others for managing weight or reducing weight-associated health risks.

Perhaps, what we need to accept, is that there simply is no “superior” dietary approach to managing your weight – it’s whatever works best for you.

Atlanta, GA


  1. I will read the full report once it is publicly available, although with 70 pages and your summery, it might be more skimming than reading. I suspect that I will see what I normally see when large meta-studies are presented– a whole lot of methodological noise. It is not at all uncommon to lose important data when you look at multiple comprehensive studies all at once. Quite often the differences in study designs wipe out any meaningful information when they are all compiled into one “study”. As a reader of your blog, I am well aware of your predisposition toward not emphasizing one macronutrient over another. I would agree with you that there is plenty of evidence that weight loss can be achieved through simply reducing calories, however, there is plenty of evidence through numerous individual studies that would support a different conclusion, one that would favor the Mediteratian diet or the low carb diet. I could cite many of these studies, but I am sure you have already seen them. Last year’s study published in the New England Journal of Medicine with the lead author of Meir J. Stampfer which compared the low-carb, low-fat and the Mediterranean diet comes to mind, but there are many others. I suspect that this topic is nowhere near exhausted by these recommendations and researchers will continue to try to support their “religious beliefs” as you put it, meanwhile the rest of us are left to navigate these very muddy waters with eat less and move more as pretty much the only meaningful message out of these pages. Since we know how effective this advice it to most people, after thirteen years of research, I would say the whole endeavor is starting to remind me of a Monty Python skit.

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  2. Dear Dr. Sharma, I think many things are under-researched or not researched at all, sometimes deliberately (tactical avoidance), sometimes because of bias, sometimes from lack of funding support, and sometimes because the scientific model has limits. Nevertheless, lack of causal evidence does not need to mean seeking the lowest common denominator in treating obesity. There is more to weight loss than “eat less, exercise more.” I agree that there is not sufficient evidence for dietary pronouncements, but I do think there is sufficient correlative data to suggest that some foods appear addictive to some patients or seem to trigger binge eating or otherwise inappropriate eating behaviours. I also think there is sufficient correlative data to suggest that high nutrient food, lower in fat, salt and sugar, and richer in vitamins and minerals (and higher in wholegrain fibre) are wiser choices, and less prone to trigger excessive eating behaviours. They are wiser because they add significant functional value whilst reducing caloric impact. I wonder about data that suggests that higher protein levels do not increase the probability of weight loss, but seem to stay silent about other possibly important health benefits, such as reduced muscle loss and organ damage for patients experiencing rapid weight loss. I think more interest and study needs to go towards the psychology and sociology of obesity, and consideration of an addictions model for treatment in cases where binge eating or addiction-like behaviours seem to be driving excessive caloric intake. I would also think that there is sufficient correlative data to suggest that keeping food logs, counting calories and staying away from high-calorie foods may make it easier for obese patients trying to arrest weight gain or attempt weight-loss. In other words, whilst the evidence is soft, our resolve must harden so we may take what we do know, and what is correlatively probable, and pursue wise treatment. We have a growing understanding of the profound and often permanent changes body chemistry and processes undergo for the morbidly obese, and we are getting a much stronger picture of the neurology of addiction as they apply to substances normally understood as “food”. Science is not wise, but physicians can be. Let’s not throw in the towel.

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  3. Dr. Sharma,

    Could you comment on the 52 wk Optifast Diet which incorporates meal replacements with behavioral change, and nutrition counselling? How effective is this for patients in keeping the weight off vs other diets that you researched?

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  4. ANTIBOBESITY DRUGS? NO Thanks!! This CANNOT be the solution!
    As an example: Novartis 2002 finished all activities on obesity research, despite a key discovery by the Team I was leading: we came to the conclusions that the body is too smart to be overdriven by a drug! This means that any NO TOXIC effect on food intake lasts only few days and is counterbalanced by other endogenous food intake regualtors!

    There is another unmentioned topic in the new guidelines: the American Paradox: e.g. the high prevalence of obesity rate in USA (35.7 %) by a daily total calories intake from fast food of 11.3% (both average values at different ages)!!!
    Or with other words: even the USA-Americans get obese by eating (too many calories) from “healthy” foods!

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  5. THANK YOU Dr Sharma! Your post is very timely for I have been trying different dietary approaches to weight loss and not getting much out of it except for craving whatever a particular diet cuts out. Right then, back to moderation and walking the dogs.

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  6. I was also disappointed to see the new guidelines hardly mentioned physical activity in the management of physical activity. Physical activity may not be an effective way to lose weight, but it nonetheless plays a role in the management of obesity (prevention, weight loss maintenance, ingestive behaviour etc.).

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  7. I’ve always felt that the “best” diet is the one you can actually stick with long term, and the one that leaves you feeling satisfied, not deprived. I think the balance of macro nutrients *would* play a role in that, but perhaps that balance would vary from one person to another.

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  8. Hi Arya, did you find any guidelines for what dietary+physical activity approach would be the most healthy way to lose weight (with quick eye bolling, I didn’t). Rather than concentrating on weight loss alone, I would have liked to see evidence for preventing loss of lean body mass. Best regards from Finland!

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  9. “German theoretical physicist Werner Heisenberg, Nobel laureate for the creation of quantum mechanics, distanced himself from positivism by saying: ‘The positivists have a simple solution: the world must be divided into that which we can say clearly and the rest, which we had better pass over in silence. But can any one conceive of a more pointless philosophy, seeing that what we can say clearly amounts to next to nothing? If we omitted all that is unclear we would probably be left with completely uninteresting and trivial tautologies.'”

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