4:3 intermittent fasting produces greater weight loss vs. daily calorie restriction

Key takeaways:

• Adults who fasted 3 nonconsecutive days a week lost more weight vs. those assigned to daily calorie restriction.
• The best dietary intervention is one patients will “adhere to long term,” a researcher said.

A 4:3 intermittent fasting intervention produced greater weight loss over a year in adults with overweight or obesity vs. daily caloric restriction, according to results of a randomized clinical trial published in Annals of Internal Medicine.

The NIH-funded study additionally showed that participants who underwent intermittent fasting achieved greater cardiometabolic health.

Danielle M. Ostendorf, MS, PhD, CEP, an assistant professor at The University of Tennessee, Knoxville, told Healio that the “exciting” findings align with the researchers’ hypothesis that intermittent fasting would yield more weight loss “because we thought that focusing calorie counting only 3 days a week, instead of doing it every day, would make it easier to adhere to the dietary strategy over time.”

Several prior analyses have shown the potential effectiveness of various intermittent fasting patterns, like 5:2 intermittent fasting, for weight loss.

Intermittent fasting is often confused with time-restricted eating, but there is a difference between the two patterns, Ostendorf said.

“Time-restricted eating involves limiting food intake to an 8-to-10-hour window where you only eat during that window of time and then you fast outside during that time,” she said. “It’s done every single day and it’s done consistently.”

In contrast, intermittent fasting “is a more periodic and significant fast, and it involves cycling between complete or near-complete energy restriction on the fast days and then eating your normal amount of calories on the nonfast days,” Ostendorf noted.

In the randomized clinical trial, Ostendorf and colleagues assigned 165 participants (73.9% women; mean age, 42 years) to either restrict their energy intake by 80% on 3 nonconsecutive days weekly and make healthy food and portion choices on nonfast days (4:3 intermittent fasting) or restrict their energy intake by 34.3% every day for 12 months. Across the week, both groups averaged the same targeted energy deficit of 34.3%.

The intervention groups received a comprehensive behavioral weight loss program, a fitness center membership, and were recommended to build up their exercise levels to at least 300 minutes a week by the 6-month mark, Ostendorf said.

A total of 125 participants completed the trial, with the 4:3 intermittent fasting group having lower attrition vs. the calorie restriction group at 12 months (19% vs. 29.6%).

The researchers reported that 4:3 intermittent fasting participants showed a greater reduction in weight (–7.7 kg; 95% CI, –9.6 to –5.9) vs. daily calorie restriction participants (–4.8 kg; 95% CI, –6.8 to –2.8) at 12 months.

Overall, 58% and 38% of 4:3 intermittent fasting participants achieved weight loss of at least 5% and 10% at 12 months, respectively.

In comparison, 47% of daily calorie restriction participants achieved at least 5% weight loss at 12 months, whereas 16% achieved at least 10% weight reduction.

Ostendorf and colleagues added that 4:3 intermittent fasting participants showed more favorable changes in cardiometabolic measures like systolic BP, HbA1c, low-density lipoprotein cholesterol levels and fasting glucose levels at 12 months.

The 4:3 intermittent fasting intervention was also safe, with just four mild diet-related adverse events occurring over the study period.

The researchers acknowledged study limitations, including a limited ability to generalize the results to diverse groups, children, older adults, adults with CVD or diabetes and people with obesity who may not have access to comprehensive weight loss programs.

“It’s important to note that we did see a lot of individual variability in both the fasting group and daily caloric restriction group.” Ostendorf told Healio.

As a result, “the best dietary weight loss strategy is going to be one that a person feels they can stick to and adhere to long term,” she said. “I think what this study shows is that there is this additional evidence-based dietary weight loss strategy for people to consider and choose from.”