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There's No Single True Path to Weight Loss

While some people feel very strongly about the low-fat vs. low-carb debate, the evidence base is very messy.

This article was first published in The Montreal Gazette.

I was once asked why I don’t go out and write a diet book to make some easy money. It seems like it would be fairly simple. There are dozens of diet books out there, though many of them blatantly contradict each other. The only real problem seems to be choosing the particular diet to promote as the true one path to weight loss. That’s actually surprisingly difficult, given that there really is no good evidence that one diet is better than another.

For simplicity, we can lump diets into a few categories: low-fat, low-carb, high-protein, low calorie, very-low-calorie, or alternate day fasting diets. To confuse matters, some diets borrow principles from various categories and so the keto diet, paleo diet, carnivore diet and the like advocate high protein and various degrees of low carb strategies.

The question then becomes, is one diet superior to another? The short is answer is no. A 2014 meta-analysis in the Journal of the American Medical Association reviewed 48 trials and found that all diets led to weight loss when compared to no diet. The low-carb diets did slightly better than the low-fat diets at six months, with 8.73 vs. 7.99 kilograms lost. The wrinkle is that at 12 months some of that lost weight was regained and the difference between low-fat and low-carb diets (7.25 vs. 7.27 kg) essentially disappeared.

While some people feel very strongly about the low-fat vs. low-carb debate, the evidence base is very messy. A recent study in the BMJ suggested low-carb diets were better while just a few months earlier, a study in JAMA suggested they were not. Whatever your position on the issue, you can find a study that supports it, as long you are willing to ignore the contradictory evidence.

Alternate-day fasts have become very popular recently, but they don’t necessarily perform any better than a classic low calorie diet. Low calorie and very low calorie diets promise to not just help you lose weight, but also to help you live longer. Unfortunately, much of the data comes from animal studies, and the short-term weight loss seen with calorie restriction tends to disappear long term.

The issue with every diet is that many people regain some or all of the lost weight with time. One problem is that some fad diets are simply not sustainable long term. Another problem is that weight loss inevitably leads to loss of lean body mass, which in turn leads to less energy expenditure. Essentially, as you diet and lose weight, your body needs fewer calories for everyday activities (what is often termed as your metabolism slowing down), and weight loss plateaus. One large trial in the New England Journal of Medicine found that high protein diets were better for keeping the weight off, but the difference between the low and high protein groups amounted to less than 1 kg.

For anyone truly interested in losing weight in the New Year, a series of small but sustained interventions may end up having a greater long-term impact. Eliminating high calorie drinks can have a substantial effect on weight control. Most people know that sodas are especially high in sugar and calories, but they often don’t realize that fruit juices, alcohol and even flavoured coffees have a deceptively high calorie count. Just cutting out these non-essentials from your diet can cut hundreds of calories from your daily intake. Let other people agonize over the latest diet. If you want to lose weight, don’t drink your calories. Drink water.


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