Eating only within an eight-hour window during the day works about as well as calorie counting for weight loss, a one-year trial has found. The results suggest that fasting diets work simply by causing people to eat less overall, says at the University of Illinois Chicago, rather than offering any specific weight-loss benefits.
Fasting diets, also sometimes called intermittent fasting or time-restricted eating, have grown in popularity in recent years as an alternative way to lose weight than traditional calorie counting.
One of the most commonly practised versions involves eating all meals and snacks within an eight-hour window, often between midday and 8.00pm, as it lets people have their evening meal with their families, says Varady.
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Her team asked 90 people with obesity to follow this practice, to go on a calorie-counting diet or to continue their usual eating habits, for six months. Those in the calorie-counting group were asked to eat 25 per cent fewer calories than the amount that a dietitian calculated would maintain their weight, based on their starting weight and activity levels. They were all were asked to fill out a seven-day food diary every three months.
The dieting phase was followed by a six-month period aimed at weight maintenance, when the fasting group could slightly relax their rules, to keep their food intake within a 10-hour window. The calorie counters were allowed to eat 100 per cent of their calculated daily calorie requirements.
By the end of the year, both the intermittent fasters and the calorie counters were eating 400 fewer calories a day and had lost about 5 kilograms more than those in the control group.
Many people report finding intermittent fasting easier than calorie counting, says Varady. “It’s a nice alternative to to not have to vigilantly monitor everything you’re eating and just look at the clock and let the time do the same thing for you. It’s probably the reason that [intermittent fasting] has become so popular.”
A previous study found that intermittent fasting plus calorie counting led to similar amounts of weight loss as calorie counting alone – but this only included Chinese adults. The new trial was carried out in a racially diverse group of people, including one third who were African American and nearly half who were Hispanic.
at the British Dietetic Association says the results support the idea that different kinds of weight loss diets work usually through the same effect: restricting energy intake. “The diet that you can stick to works best,” he says.
Annals of Internal Medicine
