Is there any potential danger in the "temporary fast", a popular weight loss strategy in recent years?

 Intermittent fasting (Intermittent fasting) is a very popular weight loss strategy. One of the subdivided dieting methods is called "time-limited eating", that is, eating within a fixed eating window. For people who lose weight, "eating within a limited time" is a relatively less painful and easier way to do, so it is widely respected. But a new study recently found that "eating within a limited time" may have little effect and may also cause muscle loss. This article is translated from the New York Times, the original title is "A Potential Downside of Intermittent Fasting", I hope to inspire you.

Intermittent fasting is a popular weight loss strategy. But a new study found that a popular intermittent fasting method called “time-restricted eating” has minimal weight loss and has a potential negative effect: muscle loss.

The new study, published in JAMA Internal Medicine, is one of the most rigorous studies to validate limited-time diets. Time-limited diet requires fasting for 12 hours or more a day. Many followers of this diet usually skip breakfast and eat between about noon to 8 pm, which means they fast for 16 hours a day. This method of weight loss has been promoted in best-selling weight loss books, and is sought after by many celebrities.

Research over the years has shown that practicing this diet can make you lose meat in a short time and improve metabolic health, although most of the data comes from animal experiments or small experiments in a relatively short period of time. Experts say that this diet is effective because it allows people to eat whatever they want, as long as they eat it within a short period of time, so that they can consume fewer calories.

But the new study found that those who are assigned to fast for 16 hours a day and eat between noon and 8 pm, the so-called 16:8 diet, hardly get any weight loss results. During the three-month study, they lost an average of 2 to 3.5 pounds (approximately 1.54 kg)-only slightly more than the control group, and most of what they lost was not fat, but including muscle. "Lean pieces" inside.

Although muscle loss during weight loss is normal, the fasting group lost more muscle than expected. This has to make people worry, because muscle has many health benefits, it can prevent people from falling and becoming disabled as they age, and it can also reduce mortality. In addition, muscles can also promote metabolism, helping to prevent the weight lost during dieting from rebounding in the future. Researchers speculate that one cause of muscle loss may be that fasting causes people to eat less protein.

The author of this study and a cardiologist at the University of California, San Francisco, Dr. Ethan Weiss, was surprised by these new findings. Since 2014, Weiss has implemented a limited-time diet, eating between noon and 8pm every day. But when he analyzed the data and saw the results of his research, he stopped daily fasting and restarted his breakfast.

He said: "My prejudice is that it is feasible to eat within a limited time, and I am doing this myself, so I was shocked by the result."

But some experts warned that this study was too short to be a weight loss test. They said that if the study time is longer and there are more participants, the fasting group is likely to show greater weight loss. They also pointed out that previous studies have shown that people can perform better if they consume most of their calories earlier in the day, that is, when our bodies can metabolize food better. If we skip breakfast, then eating a lot in the afternoon and evening will violate our biological clock.

For example, studies have found that if a relatively fat adult eats more breakfast, moderate lunch, and less dinner than eating less with breakfast and more dinner, he can lose more weight and reduce heart rate. Risk factors for vascular disease.

Courtney Peterson (Courtney Peterson) is a researcher at the University of Alabama at Birmingham who studies intermittent fasting. He did not participate in this new study. He believes: "It may be that the effect of limited time eating is better than we thought. It’s smaller, or if you eat earlier, the effect will be better. There is no conclusion yet.”

Many cultures in the world practice fasts for religious or spiritual reasons. But fasting has become popular for health reasons. Previous small studies have shown that doing so can prolong lifespan and have extensive benefits for metabolism, such as improving cholesterol levels and reducing insulin resistance. Some other common forms of intermittent fasting include alternate-day fasting, which means that the calorie intake does not exceed 500 calories every other day; and a 5:2 diet, which means eating normally five days a week and fasting for two days.

However, it is difficult for many people to spend a whole day without food. Krista Varady, a professor of nutrition at the University of Illinois, Chicago, found in her research that, compared with other forms of fasting, limited time eating has a slower weight loss effect, but it usually It is the most acceptable form of fasting. Varady believes that people tend to eat 300 to 500 calories less per day while restricting the eating time window. She said: "The best part is that there are no restrictions on eating during the window. People don't have to count carbohydrates or calories, and they don't have to change their diet lists."

Varadi said she plans to start a one-year limited-time diet study in the near future. She said: "I found this diet very popular, but there are so few studies on it."

Studies have shown that mice that eat high-fat and high-sugar foods 24 hours a day are prone to gain weight and get sick. If the time to eat the same food is limited to an 8-hour window, obesity and metabolic diseases can be prevented. After learning this, Weiss became interested in limited-time diets. According to his own experience, it is not very difficult to skip breakfast and eat between noon and 8 pm.

He wanted to see if this diet could be an easy way for people to lose weight, so in the current study, he and his colleague Dylan Lowe designed an experiment: They recruited 116 overweight and obese adults People and divide them into groups. One group served as a control group and ate three structured meals a day. The other group ate between noon and 8 pm. Outside the 8-hour window, only non-calorie beverages such as tea and black coffee were allowed.

The researchers chose noon to 8 pm because it is more acceptable to society. Participants can skip breakfast in the morning, but in the evening they may sit down for dinner with family or friends. "We want to make this as easy as possible and as practical as possible," Weiss said.

The researchers gave each participant a digital weight scale to track their weight changes over 12 weeks. They also asked 50 participants in the "fasting group" and "three meals a day group" to visit their laboratory four times during the study to measure their fat and muscle mass, blood sugar levels, and energy expenditure.

In the end, the fasting group lost an average of 2 pounds, only half a pound more than the control group. The researchers found that most of the metabolic indicators of the fasting group hardly improved. Although they did lose more weight, 65% of the weight lost in the fasting group came from muscles, which was two times the normal weight loss. Times more.

Weiss said that the loss of muscle in the fasting group was probably due to skipping breakfast every day, which led to a decrease in their protein intake. But this can be avoided: other studies have found that people can maintain muscles during fasting by doing resistance training and consuming more protein during eating. Weiss said that these findings need further research, but he is still skeptical about limited-time diets.

He said: "This is a short study, but for me, it is enough to make me doubt the effectiveness of this diet method. Even if it is really effective, the effect is very small."


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