Shahar Madjar, MD, Journal columnist

I have written here on several occasions about intermittent fasting for weight loss.

But it seems that there is always more to say about diets in general and intermittent fasting in particular.

In a study published in the prestigious New England Journal of Medicine, a new question was examined: is intermittent fasting in combination with caloric restriction better than caloric restriction alone.

Here are a few words about each of these diets:

Caloric restriction has been the recommended diet for the treatment of obesity. The idea is simple: consume fewer calories than you spend and weight loss will follow. Unfortunately, implementing the idea isn’t as simple. It requires focus and determination. It calls for some degree of obsessiveness. Calories need to be counted, portions to be controlled. Caloric restriction diets are therefore difficult to sustain over time.

Time restriction of food consumption (also known as intermittent fasting) seems easier. No more calorie accounting, or portion control. Instead, limit the number of hours in which food is consumed. A popular regimen is the 7-11 regimen in which dieters are encouraged to fast between 7 PM and 11 AM on the following day. Like in the case of caloric restriction, the idea here is also clear: restricting the number of hours in which food is consumed would invariably lead to a reduction in caloric intake, and, potentially (this hasn’t been proved beyond reasonable doubt) will jump-start the body into a new phase of higher metabolic activity and faster weight loss.

Nearly all the studies on intermittent fasting resulted in weight loss (2.5-9.9% of body weight) and also in a decrease in fat mass. However, studies comparing intermittent fasting to caloric restriction didn’t fully support the superiority of one diet over another. One such study (79 participants) showed that both groups lost a similar amount of weight (6.8% of body weight at 6 months) and that their fat mass and fat distribution were similar.

Which brings me to this new study I alluded to at the opening of this article. The study was conducted in Guangzhou, China in collaboration with researchers from Tulane University in New Orleans. It examined the question of whether caloric restriction in combination with time restriction (intermittent fasting) is superior to caloric restriction alone.

The researchers randomly divided the 139 participants into two groups. Both groups received dietary counseling including instruction booklets and sample menus. Both groups were instructed to write a daily dietary log and to take photographs of the food they consumed.

All the participants met with a health coach every two weeks and attended health education sessions monthly. Participants in both groups were instructed to limit their caloric intake (1,500-1,800 calories a day for men and 1,200-1,500 calories a day for women).

There was one important difference, though, between the groups: participants in one group were instructed to stick with caloric restriction alone while the other group was advised to stick to the same caloric restriction regimen and to also limit their caloric intake to an 8-hour period a day, from 8 AM to 4 PM.

Despite the intense, rigorous regimen, most participants (about 85%) adhered to their respective regimens during the 12-month study period. Both groups lost a significant amount of weight (8 kg in the time and caloric restriction, and 6.3 kg in the caloric restriction group). From a statistical standpoint, this difference wasn’t significant. Similarly, there was no statistical difference between the groups in terms of their waist circumferences, BMI, body fat, body lean mass, blood pressure, serum glucose levels, and metabolic risk factors for cardiovascular disease.

As I was reading the article, I wondered why the researchers chose to limit themselves to these two groups (caloric restriction diet vs. caloric and time-restricted diet). I felt that including a third group in which participants would be assigned to time restriction diet (without caloric restriction) would have allowed the research to compare three different regimens: caloric restriction, time restriction, and combined calorie and time restriction).

As designed, the study reinforces what we have already known and adds some important, new information. We already know that sticking to a diet, whether time-restricted or calorie-restricted, would lead to significant weight loss. Based on this new study, we now know that adding time restriction to caloric restriction is not significantly better than caloric restriction alone. The study also suggests that most of the weight loss in time-restricted diets may be attributed, simply, to reduced caloric intake.

EDITOR’S NOTE: Shahar Madjar, MD, MBA, is a urologist and an author. He practices at Schoolcraft County Memorial Hospital in Manistique, and at Baraga County Memorial Hospital in L’Anse. Find his books on Amazon. Contact him at smadjar@yahoo.com.