This article was first published in The Montreal Gazette.
It’s hard to know how to eat right these days. Last month, claims that intermittent fasting doubled your risk of cardiovascular death were dominating the news cycle. In my previous column, I explained why that probably wasn’t true and why most people need not worry. But I am dubious about the many claims made about intermittent fasting, especially when it comes to weight loss.
Intermittent fasting, or time-restricted eating as it is sometimes called, is popular and trendy among the movers and shakers of pop culture. The rich and famous swear by it and there are more than a few examples of people who have used it to lose a considerable amount of weight. It can also be useful for controlling blood sugar and improving insulin resistance, which can help reduce the need for diabetes medications.
The benefits are clear. But what is less clear is whether there is anything inherently special about intermittent fasting or whether it is just one more diet among many. Intermittent fasting is clearly more convenient for many people. Its basic premise is to limit food consumption to a 12- or 10- or 8-hour window (different people espouse different protocols). Unlike many other diets it doesn’t require calorie counting, avoiding specific foods, or any change to meal preparation. You just have to watch the clock.
But while intermittent fasting is more convenient, it isn’t necessarily better. In one study, compared to a regular diet, intermittent fasting didn’t result in greater weight loss after one year. It also didn’t improve any other metabolic outcomes like blood pressure, cholesterol or insulin resistance. The data on its effectiveness is inconsistent.
But the burning question in the field is whether intermittent fasting has any inherent benefit beyond simple calorie restriction. Some believe that intermittent fasting is simply a way to eat less whereas others believe that the timing of when you eat matters as well.
A recent study in the Annals of Internal Medicine sought to answer this very question by performing a special randomized controlled trial. Forty-one patients were randomly assigned to time restricted-eating or calorie restriction, but for the three-month study period participants got their food from a special study metabolic kitchen. So rather than just being told to do this or that, they were supplied with all the food they were supposed to eat, thus minimizing the chance of diverging from the study protocol.
The benefit of this approach is that both groups got the same number of daily calories, the only difference being when they consumed them. The intermittent-fasting group could eat only between 8 a.m. and 6 p.m., with 80 per cent of those calories taken in before 1 p.m. The calorie-restriction group could eat liberally throughout the day.
Both groups lost over two kilograms (five pounds), but the weight loss was nearly identical in both. Measures of blood glucose and insulin resistance were also not different between groups. The conclusions drawn from this study were that when calories are held constant, intermittent fasting doesn’t lead to more weight loss than simply eating less throughout the day. In other words, intermittent fasting works by reducing calorie intake. Nothing more, nothing less.
Intermittent fasting is popular (for now) because of its relative simplicity and straightforward messaging. It does lead to (modest) weight loss, but you could probably do equally well by just eating less consistently throughout the day.
For some people, time-restricted eating will be easy and intuitive, whereas for others it will be hard and unsustainable. Ultimately, the best diet is the one you can stick with and the one that gets you to eat less overall.
There are many outlandish claims about the health benefits of intermittent fasting. But in the end, it seems like it’s just another way to eat less, which we should all be doing anyway.
