The New Obesity Guidelines Are Big on How Little We Know
Yesterday 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.