Intermittent fasting doesn't work for weight loss: study

The longest and most thorough study looking at time-restricted eating found that it is no more more effective than regular calorie restriction.

Maija Kappler 4 minute read April 22, 2022
Young woman with scale look into fridge

intermittent fasting isn't a practice that will work for every person all the time. GETTY

Intermittent fasting isn’t an effective weight-loss technique, according to the longest and most thorough study published on the topic.

The study, published Wednesday in the New England Journal of Medicine, followed 139 patients considered obese over a period of one year. They were put on a calorie-restricted diet of 1200 to 1500 calories a day for women and 1500 to 1800 calories a day for men. The one significant difference was that one group was instructed to only eat between 8 a.m. and 4 p.m., while the other group could eat the same number of calories at any point during the day.

Changes in weight ‘weren’t significant’

Researchers found that after a full year of eating that way, “changes in weight were not significantly different in the two groups.” The group that just restricted calories lost a mean of 6.3 kg (14 pounds) while the time-restriction group lost 8 kg (18 pounds). There were also no major differences in waist circumferences, BMI, body fat, body lean mass, blood pressure, or other health markers like blood glucose levels or insulin sensitivity between the two groups.

“Among patients with obesity, a regimen of time-restricted eating was not more beneficial with regard to reduction in body weight, body fat, or metabolic risk factors than daily calorie restriction,” the researchers concluded.

Fasting has a long history as a part of religious or political practices, but it became popular as a health and weight loss strategy within the last decade. There are a wide variety of kinds of fasts, from eating only between certain hours to taking several days off normal eating patterns. U.K. doctor Michael Mosley helped popularize the idea in the early 2010s with the 5:2 diet, which involves a cycle of eating normally for five days and then restricting calories to just 500 to 600 for two days.

Previous studies on intermittent fasting — none of which have involved as large a sample size or as long a study period — have shown both benefits and drawbacks to the practice.

One 2016 study looked at 59 people who did “alternate day fasting,” where they rotated between one day of eating and one day of fasting for eight weeks and found that the participants did lose weight and also lowered their insulin level, which led to faster weight loss — something the new study contradicted.

Intermittent fasting can be easier to follow than a regular diet because it involves less calorie-counting, Healthline suggests. Nutritionist Katelan Sottosanti echoed that sentiment to Philadelphia Magazine in 2020: “I think people like it because it comes off as easy and makes them feel like they are in control of their food, rather than the other way around,” she said. “Individuals will set their own eating window and make their own food choices within the chosen time frame, making it adaptable to busy schedules or lifestyles.”

But like any calorie-restrictive diet, intermittent fasting also comes with the potential for people to emerge even heavier and less healthy. Many diets “work” in the short term, with people losing weight for a while — but when restrictions are too difficult to follow, bingeing is a common response.

Restricting food can be self-defeating

“Restricting food groups or demonizing things like sugar can lead to feelings of deprivation that often manifest as overeating or bingeing farther down the line,” registered nutritionist Laura Thomas told Shape. “It’s really self-defeating.” That’s the reason somewhere between 80 and 95 per cent of people who diet end up gaining all the weight back — and sometimes even more, because of the changes to their metabolic system.

“Research tells us that yo-yo dieting can negatively affect your metabolism,” endocrinologist and obesity specialist Dr. Marcio Griebeler told the Cleveland Clinic. “It doesn’t matter the diet: low-carb, low-fat, ketogenic, whatever. We see rebound weight gain almost every time.”

The new study doesn’t necessarily advise people who feel intermittent fasting works for them should stop. The practice may work for some people — but in the same way the keto diet has diehard defenders but is definitely not for everyone, intermittent fasting isn’t a practice that will work for every person all the time, either. Nutrition and weight are highly specific to individual people’s bodies, environments and circumstances, and healthy eating can look very different for different people.

“The safest eating habit is one that is sustainable,” registered dietitian Gal Cohen also told Philadelphia. Often, I see clients try to cut out whole food groups, jump on the latest fad diet bandwagon, or follow what’s worked for their friends, only to realize that approach isn’t working for their body. My advice: If it’s not something you can see yourself doing long-term, it’s not for you.”

Maija Kappler is a reporter and editor at Healthing. You can reach her at mkappler@postmedia.com
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