Intermittent fasting received't enable you to drop some weight, as a UCSF examine suggests


Dr. Ethan Weiss, a cardiologist at the University of California at San Francisco, has been experimenting with intermittent fasting for seven years. The health fad of restricting eating to certain periods of time hit the mainstream after a number of promising studies in mice suggested it could be an effective strategy for weight loss in humans.

So Weiss decided to try it himself by limiting his own food to eight hours a day. After seeing that he had lost a few pounds, many of his patients asked him if it could work for them.

In 2018, he and a group of researchers started a clinical study to investigate them. The results published on Monday surprised him.

The study found "no evidence" that limited time eating works as a weight loss strategy.

People instructed to eat at random times each day within a strict eight-hour window of time and skip eating in the morning lost an average of about 2 pounds over a 12-week period. Subjects who ate with permitted snacks at normal meal times lost 1.5 pounds. The difference was not "statistically significant" according to the UCSF research team.

"I hoped to show that what I've been doing for years is working," he said over the phone. "But as soon as I saw the data, I stopped."

Some indications of muscle mass loss

Intermittent fasting, once a trend among self-proclaimed "biohackers" who use diet and lifestyle changes to improve their health, has become increasingly prevalent over the past decade. Instagram influencers regularly weigh the trend down, and super-fit celebrities like Hugh Jackman have said this helps them get fit for film roles. In Silicon Valley, entrepreneur Kevin Rose launched an app called Rise that people can use to monitor their fasting. In doing so, he found that the scientific data is "getting pretty exciting". Twitter CEO Jack Dorsey and actress Jennifer Aniston are also famous fans.

With so many stars touting its benefits, intermittent fasting was the most used diet search on Google in 2019, according to Google Trends data.

But the scientific evidence in humans is still thin. The UCSF study, titled TREAT, led by Weiss and PhD student Derek Lowe, aimed to fill some gaps in research with a randomized controlled trial.

As of 2018, they recruited 116 overweight or obese people. All participants were given a Bluetooth scale and asked to exercise as usual.

Weiss suggests that the placebo effect could have caused both groups to lose weight: Many people will be more careful about what they eat when taking part in a nutrition study, which means they are more likely to choose healthier foods.

Going forward, consumers should be increasingly skeptical of any nutritional study that claims weight loss benefits without a control group.

There may also be a potential downside to intermittent fasting. A smaller percentage of participants were asked by the researchers to be on site to perform more advanced tests, including changes in fat mass, lean mass, fasting glucose, fasting insulin, and so on. Through these measurements, the researchers discovered that people who ate for limited periods of time appeared to lose more muscle mass than the control group. Weiss says the result is not final, but he hopes to do more studies later.

More studies are also needed to show whether intermittent fasting is safe for people over 60 or for people with chronic conditions like diabetes and medication.

Even so, Weiss is not yet ready to write off intermittent fasting completely – there may be benefits in fasting at different times of the day. In Weiss' study, participants skipped food in the morning. He did not study the effects of missing meals at night.

But at the moment he won't recommend it to his patients.

"Just losing weight doesn't mean good things will happen for your health," he explained.


Katherine Clark