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Why don’t diets work?

The importance of a holistic approach grounded in biology

By Dr Sean Wharton, MD, PharmD, FRCP(C)
Internal Medicine Specialist
Adjunct Professor McMaster University and York University, Ontario, Canada
Diplomat of the American Board of Obesity Medicine

In the field of obesity management, the #1 treatment recommended to those trying to lose weight is to go on a diet.  All kinds of diets have been prescribed, always with the promise that this diet is better than the previous diet and will lead to long-lasting weight loss. Well, we all know how that story ends. 

Why calorie restriction alone isn’t enough

Most people can achieve some short-term weight loss, only to regain it all and a few more pounds.  So why don’t diets work?  There is a real challenge here, as the only way to achieve sustained weight loss is with caloric restriction over the long term, leading to the natural assumption that a calorie-restricted diet should be the key. However, there is a fundamental flaw here.

Let’s use an analogy.  To win the 100-metre dash, you have to run fast.  Therefore, one would think that if you just work on moving your legs faster then you should win. Why doesn’t that simple advice work?  Maybe there are other determining factors; perhaps it’s a matter of not just trying to run faster, but trying to run with a better technique, to run smoother. Maybe it’s creating a vision of victory and a mental attitude of winning that will eventually lead to running faster and winning.  There are many more aspects to winning this race than just telling someone to run faster.

Therefore, for weight loss, maybe it’s not just about the diet (eating less), but instead we can achieve the lower calories as a byproduct of the effective strategies put in place to achieve the goal of weight management. To understand what the effective strategies are, we need to take into account human biology, physiology and psychology.

Healthy sustainable eating should be a goal not a particular diet

In the new Canadian Obesity Guidelines, we used evidence-based medicine to look at effective dietary interventions for long-term weight loss and found no evidence of any particular diet.  We did find evidence for dietary interventions to treat conditions such as hypertension and heart disease. This approach is called ‘medical nutrition therapy’ and we should use it to treat conditions, or prevent conditions where there is evidence for its use. If there is no evidence, then healthy sustainable eating should be a goal.

We need a holistic approach grounded in biology to achieve long-term weight loss

When it comes to weight management, we will still need calorie restriction. Just like, if the track star wants to win, they will need to run fast, therefore that goal is still evident; however, it needs to be achieved through specific means, not just thinking that ‘moving legs faster’ is enough.

Similarly, to achieve lower calories, there are effective methods stemming from our understanding of biology and including psychological intervention, pharmacotherapy and bariatric surgery.  All of these interventions act within the brain neurochemistry to create the ability to achieve long-term calorie restriction.

Weight management should remove the idea of diets alone and engage in healthy eating when there are no specific medical concerns and the use of medical nutrition therapy for specific medical conditions. Individuals can achieve lower calories if they follow the current therapeutic interventions of psychological interventions, pharmacotherapy and bariatric surgery.

HQ20OB00207, Approval date: December 2020

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