Ever since intermittent fasting became a Kourtney Kardashian-endorsed health fad, skeptics have pressed a question: Could its benefits simply be the result of caloric restriction?
If you limit the time in which you eat each day, you are probably consuming less food period. Maybe the drop in pounds — plus some of the side benefits seen in intermittent fasters, like lower levels of insulin and higher levels of human growth hormone — are the result of the oldest weight loss strategy: eating less.
A clinical trial, published last week in the lofty New England Journal of Medicine, tasked more than 100 people with restricting their caloric intake for 12 months. It did not find any meaningful difference in outcomes for one segment of the study that also practiced intermittent fasting.
What’s New — Both groups limited their diets, to 1500 to 1800 calories a day for men and 1200 to 1500 calories a day for women. (The average person in China, where the study was conducted, eats about 3,000 calories a day, about 600 less than the average American.) One group, making up about half the participants, also limited their eating to a window of eight hours each day, mimicking one type of intermittent fasting.
The weight loss measurements “were not significantly different in the two groups,” the study authors write. At the 12 month-mark, those in the intermittent fasting group had:
- lost an average of 17.6 pounds, versus 13.8 for those who merely restricted calories
- experienced an average reduction in body mass index of 2.9, versus 2.3
- underwent an average reduction of waste circumference was 3.5 inches, versus 2.8
- underwent an average change in body fat of 4.3 percent, versus three for the control group
The differences were middling. The study authors concluded the “time-restricted-eating regimen did not produce greater weight loss than the regimen of daily calorie restriction.”
The researchers also tested a few other health measures, including blood pressure, glucose levels, and lipid levels. There were no noteworthy differences in those either.
How They Did It — Researchers in Guangzhou, China, recruited 139 participants, all in the obese category of the BMI, with an average of 31.5.
All agreed to the same caloric restrictions. The participants received nutritional counseling and protein shakes to stay on track. Sixty-nine out of 139 also limited their eating to 8 a.m. to 4 p.m. As planned, the two groups had similar caloric deficits during the study.
The study had a good retention rate; 135 of the 139 original participants completed a six-month program and 118 held on for another six months.
Why It Matters — Some researchers have proposed a variety of benefits supposedly exclusive to intermittent fasting (IF) or explanations for why giving your body a long break from digestion has intrinsic benefits.
IF could decrease appetite by slowing your metabolism. Some researchers also think it could align your digestion with your internal clock and create a smoother process by allowing the cells to process what you have already eaten before getting hit with another intake of glucose. This break could give cells a chance to work on other tasks, like breaking down toxins and repairing tissue damage.
“time-restricted–eating regimen worked as an alternative option for weight management”
Some studies have linked IF to reductions in biomarkers for metabolic diseases, like diabetes, and increases in markers for cardiovascular health, and it might increase human growth hormone.
Does any of that mean that intermittent fasting is better than just eating fewer calories for health in humans, particularly for weight loss and relief from the negative effects of obesity? Science is still working on it.
But the researchers say that IF works as a strategy if it helps with the greater goal of eating less. From the study:
Even so, our findings suggest that the time-restricted–eating regimen worked as an alternative option for weight management. We speculate that these data support the importance of caloric intake restriction when adhering to a regimen of time-restricted eating.
