If you eat very little one day, do you overeat the following days?

When undertaking a weight-loss program via dietary restriction, a person has two options: daily or intermittent calorie restriction. Daily calorie restriction (CR) generally involves around 20-50% reduction in energy intake every day, based on the caloric needs for weight maintenance, while intermittent CR refers to a greater reduction in energy intake one to four days per week with unrestricted food consumption on the other days. Weight loss is often similar^[1] with continuous and intermittent CR, though intermittent CR may be more effective for retaining lean mass^[2]. Furthermore, a secondary analysis^[3] of a one-year randomized clinical trial (the A TO Z study) comparing popular weight loss diets (Atkins, Zone and Ornish) found that adherence to the given diet may be more important than the diet itself in supporting successful weight loss.

A key factor in adherence to diet (and in turn, sustained weight loss) is hunger, which would suggest that the long-term success of an intervention might depend on how it affects appetite. Two key hormones involved with hunger sensations are described in Figure 1: ghrelin^[4] and glucagon-like peptide 1^[5] (GLP-1), which can respectively increase or decrease appetite to balance out longer-term changes in energy balance.

Figure 1: Actions of GLP-1 and Ghrelin

There is a paucity of research in lean individuals looking at the effects of short periods of severe energy restriction on appetite hormones, similar to what would be seen during intermittent fasting regimens. Many research studies focus on weight loss methods for people who are obese and trying to lose weight. Perhaps less appreciated is the gradual accumulation of body fat throughout adulthood that eventually puts lean adults into the obese category. Accordingly, the aim of this recent study was to examine the effect of acute energy restriction (25% of estimated energy requirements) on hormonal markers of appetite regulation, subjective hunger, and ad libitum food intake in lean individuals, compared with a control diet providing adequate energy intake. The researchers hypothesized they would observe an increase in ghrelin and decrease in GLP-1, along with increased ad libitum energy intake after the acute energy restriction.

Undertaking repeated bouts of intermittent energy restriction is a proven method of weight loss, but its effects on appetite-regulating hormones in lean individuals are not well understood. This study set out to examine the effect of acute energy restriction on objective and subjective markers of appetite regulation, compared with a control diet.