Intermittent fasting: ‘Feast or famine’ is sometimes a fitness focus

In a recent column, I told you about a review of intermittent fasting as a method for weight control, which is a topic I am returning to here.

Another study recently published in the New England Journal of Medicine suggests that daily fasting with caloric restriction may not lead to shedding more pounds than just cutting back on calories.

Over the course of a year, study participants who ate only from 8 a.m. to 4 p.m. did not lose significantly more weight than individuals who ate whenever they wanted to eat. Nor did they achieve significantly greater improvements in other obesity-related health measures like body mass index (BMI) or metabolic risk.

They noted that daily fasting has gained popularity because it is a weight-loss strategy that is simple to follow. However, the long-term effectiveness and safety of time-restricted eating as a weight-loss strategy are still uncertain.

It is generally accepted that the ideal BMI is less than 25. So, the researchers recruited 139 adult patients with BMIs between 28 and 45. Individuals with serious medical conditions, such as malignant tumors, diabetes, chronic kidney disease, and others were excluded. Other exclusion criteria included smoking, ongoing participation in a weight-loss program, gastro-intestinal surgery within the prior year, use of medications that impact energy balance and weight, and planned or current pregnancy.

All participants were advised to eat calorie-restricted diets, with ranges of 1,500-1,800 calories per day for men and 1,200-1,500 calories per day for women. To determine the added impact of fasting, participants were randomized in a 1:1 ratio into time-restricted (fasting) or non-time-restricted (non-fasting) groups, in which fasting participants ate only during an eight-hour window from 8 a.m. to 4 p.m. Non-fasting participants ate whenever they wanted but consumed the same total calories per day.

At six months and one year, participants were re-evaluated for changes in weight, body fat, BMI, lean body mass and metabolic risk factors, including glucose level, triglycerides, blood pressure and others.

At one-year follow-up, 118 participants (84.9%) remained in the study. Although members of the fasting group lost slightly more weight on average than those in the non-fasting group (mean, 17.6 pounds vs. 13.9 pounds), the difference between groups was not statistically significant.

Most of the other obesity-related health measures also trended toward favoring the fasting group, but again, none of these improvements was statistically significant.

The data suggest that caloric intake restriction explained most of the beneficial effects of a time-restricted eating regimen. But time-restricted eating may be a viable and sustainable approach for a person who wants to lose weight.

The results of the trial suggest that caloric restriction combined with time restriction is an approach that is as safe, sustainable and effective for weight loss as calorie restriction alone. However, it may need to be combined with intensive coaching and monitoring such as that which took place in the study in order to get the best results.

Although it was the longest time-restricted eating trial to date, a true control group with no caloric or time restrictions was lacking. Nor was there a group where time was restricted, but no caloric restriction was imposed during the “feast” portion of the “fasting-feasting” time restriction program.

Combining caloric restriction with time-restricted eating sort of defeats the appeal of a time-restricted diet to many people as well as making it more difficult to sustain if and when the person’s weight control goal has been achieved.

Earlier studies have suggested that just limiting the eating window to eight hours per day results in people naturally cutting out 300-500 calories per day. That may be why so many people like time-restricted eating so much.

On a personal level, I have chosen an eating window of noon to 8 p.m. instead of the 8 a.m. to 4 p.m. pattern used in the study. Although I have tried to avoid overt gluttony, I also have not been trying to specifically limit the number of calories consumed during the “feast” period of each day.

As always, if you are planning any intervention like a time- and/or calorie-restricted diet, you should consult with your health care provider to help you to do it safely.