Intermittent fasting diets have become very popular in the past few years as they can produce clinically significant weight loss at least in the short term. However, the long-term effects of intermittent fasting on weight management are still poorly understood because the majority of studies to date have followed patients for short durations (8 to 12 weeks).
To better understand the role of intermittent fasting in weight loss, a team from the University of Illinois Chicago (UIC) reviewed research on intermittent fasting to provide insights into its effects on the body and to provide advice for incorporating these diets into everyday life. They also presented recommendations for future research in a paper recently published in Nature Reviews Endocrinology.
The 3 main forms of intermittent fasting were reviewed:
- Alternate-day fasting — consuming 0-500 calories on alternating feast days
- 5:2 diet — 2 fast days and 5 feast days per week
- Time-restricted eating — eating only during a prescribed time window each day
These diets produce mild to moderate weight loss, a 3% to 8% decrease from baseline, over short durations of 8 to 12 weeks, wrote lead author Krista Varady, PhD, professor of nutrition at the UIC College of Applied Health Sciences.
Intermittent fasting is on par with traditional calorie-restricted diets for weight loss, the researchers found. Some studies have shown that intermittent fasting improves cardiometabolic risk factors such as blood pressure, levels of LDL cholesterol and triglycerides, insulin resistance, and hemoglobin A1c HbA1c , while other studies show no benefit on these parameters.
The authors conclude that intermittent fasting is generally safe, producing few gastrointestinal, neurologic, hormonal, or metabolic effects, the researchers noted.
The study also dispelled some myths about intermittent fasting. “The main myth is people are going to feel weak and not be able to concentrate during fasting. We’ve shown it is the opposite: they actually have a better ability to concentrate,” Dr Varady said, adding the increased energy may be an evolutionary response to the need to seek food during lean times.
Additionally, current research shows that intermittent fasting does not harm metabolism. “With any diet, as you lose weight, your metabolism, like your calorie needs, will go down because they’re correlated tightly with your muscle mass. As you lose weight, people tend to lose a little bit of muscle. But fasting doesn’t tank your metabolism at all. We’ve shown that it is the same that would happen with traditional dieting,” Dr Varady said.
The review outlines areas for future research on intermittent fasting. “We really do need long-term data to see if people can do intermittent fasting for the long term,” Dr Varady said. “I get lots of emails from people saying that they have been on the diet for 10 to 15 years, and it reversed their type 2 diabetes, and they lost 60 pounds, and it was the only diet they could stick to. That is always nice to hear, but we need actual data to support that.”
Support for the study was provided by the National Institute of Diabetes and Digestive and Kidney Diseases (R01DK119783).
Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Clinical application of intermittent fasting for weight loss: progress and future directions. Nat Rev Endocrinol. 2022 Feb 22. doi:10.1038/s41574-022-00638-x