Time Restricted Feeding as a Means to Control Obesity?

Time restricted eating, variously referred to as alternate day fasting (ADF), has a number of dietary variation but the overall goal is the limiting of caloric intake. It would seem obvious that if one reduces their total daily caloric intake, and/or increases the level of physical activity, that there can only be healthful benefits. Numerous double-blinded studies on when one eats, not only how much one eats, have demonstrated clinical benefits.

In a recent study published in the journal, Nutrition, several overweight and obese females were examined over the course of eight weeks to determine the effects of time and calorie restricted eating on weight reduction and numerous other clinical parameters of health.

Metabolic and behavioral effects of time-restricted eating in women with overweight or obesity: Preliminary findings from a randomized study

At the beginning of the study each participant was screened for body weight, resting metabolic rate, metabolic profile, and symptoms of mood and eating disorders and then again at the conclusion of the eight week study. The control participants were placed on the same calorie restricted diets but were not restricted as to time at which they could eat. The time restriction part of the study involved an eight hour window of each day where the participants could eat and a 16 hour period where food intake was restricted. The time restricted participants were divided into two subgroups where one subgroup consumed their first meal at 8:00am (08:00 h) and last meal at 4:00pm (16:00 h) and the other subgroup consumed their first meal at 12:00 noon (12:00 h) and last meal at 8:00pm (20:00 h).

As for the diets themselves, the macronutrient composition ranged from 40% to 45% for carbohydrate, 30% to 35% for lipid, and 20% to 25% for protein. The calorie restriction for each participant was determined from each individuals estimated energy requirement which took into account the level of activity of each participant.

At the conclusion of the eight week study an analysis of changes in body weight, fat mass, fat-free mass, and total body water was done for comparison between the time restricted participants and those with no eating time restriction. The calorie restriction, in and of itself, was associated with body weight reduction in both groups with the time restricted participants showing an average of 9.5 lbs (4.3 kg) lost and the non-time restricted participants showing an average of 3.3 lbs (1.5 kg) lost. When comparing body fat mass and free fat mass reductions the time restricted diet proved to provide a more pronounced level of loss compared to the non-time restricted diet.

There was no difference between the two groups with respect to resting metabolic rate, oxygen consumption and respiratory quotient, RQ (basal metabolic rate when estimated from carbon dioxide production). No difference in either group was shown for serum glucose, total cholesterol, non-esterified fatty acids, and ketone bodies.

The take home from this study is that, whereas, time restriction on eating does lead to a greater level of body mass reduction than calorie restriction alone, the benefits of calorie restriction cannot be dismissed. A limitation to this study is that it compared two groups of equally calorie restricted diets to time of feeding, it did not utilize a control group that was restricted in ad libitum feeding but not calorie restricted.