Intermittent fasting is all the rage due to its potential health benefits, and now a new review shows this style of eating really does produce weight loss and may even improve certain markers of heart health.
Intermittent fasting is an umbrella term for several diets that alternate between feasts and fasts. The 5:2 diet involves eating normally five days of the week and restricting your calories on the other two days. Alternate-day fasting calls for a fast day-feast day-fast day pattern. In contrast, time-restricted eating refers to eating only during specific time windows each day.
"The new study demonstrates that the different forms of intermittent fasting, i.e., alternate-day fasting, the 5:2 diet and time-restricted feeding, are all effective weight loss interventions for people with obesity," said study author Krista Varady, director of the Human Nutrition Research Unit at the University of Illinois, in Chicago.
"Intermittent fasting may be an effective means of lowering heart disease risk by decreasing blood pressure, low-density lipoprotein [LDL] or 'bad' cholesterol, and triglycerides," she said. What's more, these diets may help prevent type 2 diabetes by lowering insulin resistance and fasting insulin levels.
Most of these benefits likely stem from weight loss.
"All of these regimens induce a calorie restriction of 15% to 30% daily, which results in weight loss," Varady said. "When an obese person loses weight, they almost always see reductions in LDL cholesterol, triglycerides, blood pressure and insulin resistance."
For the review, the researchers analyzed 11 studies that comprised 130 trials of various intermittent fasting regimens. When the investigators looked at all of the studies as a whole, intermittent fasting did produce weight loss and improvements in risk factors for heart health. However, only alternate-day fasting and the 5:2 diet resulted in a clinically significant weight loss of more than 5%, the study showed.
The findings were published online Dec. 17 in JAMA Network Open.
So, should you or shouldn't you jump on the intermittent fasting bandwagon, and if you do, which method is right for you?
Two experts who were not involved with the study agreed that it's too early to make any blanket recommendations.
"The study provides strong evidence that some, but not all, of the regimens result in weight loss and related decreases in body mass metrics and improvements in cardiometabolic risk factors, such as cholesterol levels, blood pressure and measures of insulin resistance," said Benjamin Horne. He is the director of cardiovascular and genetic epidemiology at the Intermountain Heart Institute in Salt Lake City, Utah.
The methods in this study that showed the most profound benefits tend to be the most difficult to follow, he noted. "Future studies should evaluate the ability of the average person to adhere to these regimens, because it is unclear that they are sustainable over the long term," Horne said.
The study also could not address if intermittent fasting reduces heart attacks or strokes or extends longevity. "It is unknown whether the average person can adhere to any of the four intermittent fasting regimens for a long enough period of time [years or decades] to affect those outcomes," Horne added.
And importantly, he asked, can weight loss can be sustained without continuing the regimen?
There are also safety considerations. "The hype surrounding intermittent fasting may be leading to harms to unsuspecting people who want to achieve better health," Horne explained, "especially people with diagnosed chronic diseases and asymptomatic health conditions."
New York City dietician Robin Foroutan isn't a fan of the difficult-to-stick-with intermittent fasting regimens that showed the greatest benefits in this study.
"I only recommend time-restricted eating and fasting-mimicking diets," said Foroutan. Fasting-mimicking diets work by tricking your body into thinking that you're fasting even though you're still eating. These methods are easier to follow so people are more likely to stay the course.
The bottom line? Always talk to your doctor before starting a new eating regimen, she said.
The Academy of Nutrition and Dietetics has more on the various types of intermittent fasting.
SOURCES: Krista Varady, PhD, professor, nutrition, and director, Human Nutrition Research Unit, University of Illinois, Chicago; Robin Foroutan, MS, RDN, dietitian, New York City; Benjamin Horne, PhD, director, cardiovascular and genetic epidemiology, Intermountain Heart Institute, Salt Lake City, Utah; JAMA Network Open, Dec. 17, 2021, online