For people who are overweight or have obesity, intermittent fasting may lead to better weight loss results than counting and limiting calories every day.
“This is an important finding and shows that adults may be more successful at losing more weight with the 4:3 intermittent fasting strategy compared to daily calorie restriction,” says co-lead study author Danielle Ostendorf, PhD, an assistant professor in the department of kinesiology, recreation, and sports studies at the University of Tennessee, Knoxville.
Dr. Ostendorf adds, “Achieving a 5 percent loss of original body weight is associated with clinically meaningful health benefits,” including improvements in blood pressure and HDL “good” cholesterol, as well as fasting glucose and hemoglobin A1C levels (measurements related to diabetes).
Intermittent Fasting Outperformed Calorie Restriction for Weight Loss
For the yearlong trial, researchers recruited 165 overweight and obese adults; 125 completed the study. The participants were between ages 18 and 60, and were roughly split into two groups:
- A 4:3 intermittent fasting group
- A calorie-restriction group
Those in the intermittent fasting group had no calorie limits four days a week. They could eat whatever they wanted, but were encouraged to make healthy food choices. Then, on three nonconsecutive days, these participants had to make an 80 percent reduction in their average energy intake.
For most people, the easiest way to reach that 80 percent goal would be to take in only 500 calories.
People in the calorie-restricted group had to cut their daily calorie intake by one-third, which would equal a middle-range intake of about 1,650 calories per day.
All participants received a free gym membership, group-based behavioral support, and instruction in calorie counting. The researchers encouraged them to exercise for at least 300 minutes per week and to get their calories in a ratio of 55 percent carbohydrates, 15 percent protein, and 30 percent fat.
At 12 months, participants in the 4:3 intermittent fasting group had lost an average of 7.6 percent of their body weight — compared to a weight loss of 5 percent in the calorie restriction group.
In the intermittent fasting group, 58 percent achieved weight loss of at least 5 percent, versus 47 percent in the calorie restriction group.
With the intermittent fasters, study authors also noted slightly more favorable changes in systolic blood pressure, total and LDL “bad” cholesterol levels, and fasting blood sugar.
“A modest loss of 5 to 10 percent body weight can translate to an improvement in lifestyle and comorbid conditions [like heart disease and diabetes], with more benefits seen with more weight loss,” says Theresa Gentile, RDN, a spokesperson for the Academy of Nutrition and Dietetics.
“In general, the greater one’s BMI [body mass index], the greater the risk of comorbid conditions,” she says.
The 4:3 Intermittent Fasting Plan Worked Better Than the 5:2
There are several types of intermittent fasting diets, with previous studies paying particular attention to the effects of the 5:2 program (five days of normal eating and two days of extreme calorie restriction each week).
“The new study is unique as it uses a 4:3 intermittent fasting schedule,” says Gentile, who was not involved in the research. “Most previous studies on intermittent fasting compared to daily caloric restriction have not found significant weight loss in the intermittent fasting group.”
Intermittent Fasting May Take Some Getting Used To
The researchers reported that many participants in the intermittent fasting group initially struggled during the three days of severe calorie restriction, with at least one participant describing the 4:3 plan as “dreadful.”
But many participants said it got much easier over time — it just took a while to adjust, says Victoria Catenacci, MD, co-lead author of this study and an associate professor of medicine in the division of endocrinology, metabolism, and diabetes at the University of Colorado Anschutz Medical Campus.
“As with any dietary strategy, we observed a high level of individual variability, meaning that many participants were successful using the 4:3 intermittent fasting approach, whereas many were less successful,” she says. “The best approach is going to be the one that a person thinks they can stick with long-term.”
While fasting can be challenging, Gentile suggests that it might be easier than calorie restriction.
“Firstly, it’s mentally easier than micromanaging every calorie every day,” she says. “Secondly, your hunger and satiety [fullness] hormones may adapt to the schedule, allowing you to be less hungry on your lower-calorie days.”
Gentile notes that the study was limited by its relatively small participant size, but deserves further investigation.
Intermittent Fasting Tips
Dr. Catenacci and Ostendorf offer this advice to help make intermittent fasting easier:
- Gradually build toward three fasting days. Researchers gave participants time to adjust, so they started out fasting one day a week, built up to two days, and then three.
- One meal a day may be easier than spreading out snacks. Participants found it was easier to have all their calories in one sitting on fasting days. Anecdotally, participants said they never felt full if they spread out their calories throughout the day.
- Hydration is key. Drinking calorie-free beverages like black coffee and sparkling water throughout the day can help fight hunger while supporting bodily function and maintaining energy levels.
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