Alternate Day Fasting Effectiveness Not Affected By Meal Timing

Alternate day fasting (ADF) can be an effective weight loss strategy, but optimal meal timing on fast days has not been thoroughly examined. Kristin Hoddy, graduate student in the Department of Kinesiology and Nutrition at the University of Illinois-Chicago, shared evidence that meal timing does not affect weight loss or heart disease risk markers. The results were drawn from a small study of individuals with obesity who trialed a variety of approaches to ADF meal timing, conducted by UIC’s Associate Professor of Kinesiology and Nutrition Krista Varady and presented on November 7, 2014 at Obesity Week in Boston, MA.

ADF is an approach to calorie restriction for weight loss that has been growing in popularity, and presents an approach to calorie restriction that may increase adherence. Some proponents of ADF also advocate maximizing the number of hours spent in the fasting state; this often means that one small meal is eaten at midday on fast days. However, this eating schedule may be incompatible with work or family schedules, and may reduce adherence. Whether the timing of a meal — or even eating several smaller meals – during fast days affects weight loss and cardiometabolic markers had not been well studied.

Hoddy, a co-investigator, explained that Varady’s group examined alternating fast days and days with unrestricted eating. For fast days, participants consumed about 25% of metabolic energy needs, or 500-600 Kcal for most individuals. On “feast” days, participants ate ad libitum, with no caloric restrictions.

Meals for fast days were provided to study participants. A typical fast day meal for participants eating one meal daily would consist of a small frozen entrée, a vegetable such as baby carrots, a small dessert portion, and low-fat yogurt.

Participants (n=74, mostly female, mean BMI=30 kg/m2), were randomized into three groups: one group (ADF-L) had a lunchtime meal on fasting days, one group (ADF-D) had their meal between 6:00 and 8:00 pm, and one group (ADF-SM) divided food on fast days into three small meals, with breakfast, lunch and dinner of about 100, 300, and 100 Kcal each. Participants were sedentary, and individuals with diabetes, a history of cardiovascular disease, or taking medication for weight loss or glucose or lipid control were excluded.

All participants had a two-week run-in before beginning the intervention to ensure weight was stable, and maintained the ADF for eight weeks. For all three groups, body weight was reduced significantly (p<0.001), with the ADF-L group losing a mean of 3.5 +/- 0.4 kg, the ADF-D group losing a mean of 4.1 +/- 0.5 kg, and the ADF-SM group losing a mean of 4.0 +/- 0.5 kg. There was no significant difference in weight loss between groups.

Investigators also tracked fat mass reduction and reduction in visceral fat; these were significant (p<0.001) and comparable in all groups. Though there was no significant change in plasma lipid levels in any group, low-density lipoprotein (LDL) particle size increased in all groups (1.3 +/- 0.5 Å, p<0.05). Measures of blood glucose control and insulin resistance were also unchanged across groups.

Hoddy noted that alternate day fasting represents an effective approach to reducing body weight, fat mass, and visceral fat mass, though the present study did not see improvement in cardiometabolic markers or glucose control. Since the timing of meals did not affect results, Hoddy advised clinicians to counsel their patients to be flexible with meal timing if they choose this approach to calorie restriction. Incorporating a flexible approach to ADF may promote adherence to this weight loss strategy.