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Intermittent Fasting Versus Other Calorie-Counting Diets

A recent study casts doubt on the concept that when you eat is more important than what you eat.

This article was originally posted in the Montreal Gazette.

There are some very good science-driven ways to lose weight. People who need to lose weight for medical reasons can turn to both bariatric surgery and medications to help achieve that weight loss. Obviously, a healthy diet and lifestyle factors are an important aspect of any weight-loss strategy, which is why so much ink has been spilled on the concept of dieting. However, despite the many dietary fads that have come and gone over the years, there is no convincing evidence that any one outperforms the other.

The reality is that all diets are more or less equally effective and differences between various diets are minimal. Some may be more appealing to certain groups of people, but on average they tend to perform equally well in large populations.

In recent years, time-restricted-eating, also known as intermittent fasting, has become de rigueur. The central idea behind this concept is that when you eat is more important than what you eat. The theory centres around the somewhat vague idea that eating at certain times is less likely to promote the rise in insulin and other hormones that contribute to weight gain.

But such theories mean little without demonstrable proof that any such diet leads to weight loss. It must be shown that the diet du jour not only helps people lose weight, but also outperforms standard diets in some measurable way.

Which is why the recent publication of a study in the New England Journal of Medicine is particularly interesting. In the study researchers randomized 139 patients to time-restricted-eating or regular calorie restriction. Those doing time-restricted-eating could only eat between the hours of 8 a.m. and 4 p.m., whereas the other group could eat whenever they liked. Both groups were required to limit themselves to 1,800 calories per day for men and 1,500 calories per day for women. In effect, the researchers were testing whether skipping dinner and not eating at night resulted in superior weight loss. While this is common advice from various self-proclaimed experts, the data from this trial suggests that it doesn’t actually work.

Dropouts in this trial were quite low. Around 85% of the patients made it to the one-year follow-up. And while both groups lost weight, the difference between them was minimal. At 12 months, the difference between groups was less than two kilograms and statistically meaningless given the margin of error. What’s more, there was no difference in blood pressure, cholesterol, waist circumference or percent body fat between the two groups. As such, nothing of clinical importance was gained by the time restriction.

Critics will suggest that the timing of the restriction explains the negative study. But previous studies have tried other versions of this diet. In 2020, the TREAT randomized trial tested a time-restriction-diet that limited eating from noon to 8 p.m., essentially an instruction to skip breakfast. It, too, failed to show any difference in weight loss, though it was a shorter-term study that only lasted three months.

Some people may find that some version of this time-restricted-eating diet already fits their schedule and way of life. There are a fair number of people who skip breakfast routinely and some people generally avoid late-night meals, preferring to eat earlier in the day. In the end, there does not appear to be a right or wrong way to eat in terms of timing. When diets work, it is because people eat less food. Skipping a meal, which is essentially what these diets get you to do, will make you eat less if you persist with the strategy long term. But which meal you skip, whether it is breakfast, lunch or dinner, doesn’t seem to matter. So the best advice when it comes to diets is to find the one you can stick with. That’s the only way they work.


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