There were no significant differences in mean weight loss between the alternate-day fasting group versus the calorie restriction group after 6 months of intervention, relative to the control group: -6.8% (95% CI -9.1% to -4.5%) versus -6.8 (95% CI -9.1% to -4.6%), reported Krista A. Varady, PhD, of the University of Illinois at Chicago, and colleagues.
Findings were consistent when the groups were followed through a year, after a 6-month maintenance phase: -6.0% (95% CI -8.5% to -3.6%) versus -5.3% (95% CI -7.6% to -3.0%), they wrote in JAMA Internal Medicine.
During the year-long, randomized clinical trial, the two intervention groups experienced no significant differences among secondary endpoints, which included blood pressure, heart rates, triglycerides, fasting glucose, fasting insulin, insulin resistance, C-reactive protein, and homocysteine concentrations.
Although total cholesterol levels did not significantly differ between groups, in relation to the control, means levels of HDL cholesterol were significantly higher among the alternate-day fasting group compared with the calorie restrictive group after 6 months of the weight loss phase (6.2 mg/dL, 95% CI 0.1- 12.4 mg/dL).
However, there were no significant differences between both intervention groups for HDL cholesterol levels after 12 months (1.0 mg/dL, 95% CI -5.9 to 7.8 mg/dL).
Alternatively, mean levels of LDL cholesterol were significantly higher in the alternate-fasting group after 12 months when compared with the calorie-restrictive group (11.5 mg/dL, 95% CI 1.9-21.1 mg/dL). However, this difference was not displayed at 6 months into the trial.
The authors highlighted the growing popularity of alternate-day fasting regimens with the primary goal of weight loss, particularly over the past few years. They explained this type of diet "involves a fast day where individuals consume 25% of their usual intake (approximately 500 kcal), alternated with a "feast day" where individuals are permitted to consume food ad libitum."
They noted that some of the current literature, mostly consisting of short-term studies, have reported improvements in regards to insulin sensitivity, lipid profiles, and blood pressure, and well as weight loss.
The single-center study included 100 people with obesity, with a mean BMI of 34, randomized into three groups: the alternate-day fasting group, calorie restrictive group, and a control.
The weight-loss phase consisted of the first 6 months of intervention. During this time, the alternate-day fasting group was instructed to consume 25% of baseline energy during lunch on fasting days, alternative with feast days, which involved consuming 125% of baseline energy over three meals. The calorie-restrictive group were consumed 75% of baseline energy over three meals, each day. During the first 3 months of the weight-loss phase, meals were provided to the participants, which were in accordance with the American Heart Association guidelines.
During this phase, Varady's group found adherence to the regimen was particularly tougher in the alternate-day fasting group, paired with a higher drop-out rate, which may have resulted in "a possible selection bias between groups." They noted this group tended to consume more than was prescribed on fasting day, as well as eating less than prescribed on feast days, writing "it appears as though many participants in the alternate-day fasting group converted their diet into de facto calorie restriction as the trial progressed."
Alternatively, the researchers reported that participants in the calorie-restrictive group had greater adherence to the prescribed energy intake targets.
The last 6 months of the study consisted of a weight-maintenance phase, where all participants were told to maintain his or her weight, continuing through the completion of the trial. The research group assessed body weight measures each month, while fat, visceral fat, and lean mass were measured every 6 months. Daily energy expenditure was assessed through doubly labeled water. Blood samples were drawn to assess secondary outcomes.
The study had some limitations, including the short duration of the maintenance phase at 6 months, and a control group that received no counseling, and less attention from study personnel, relative to the intervention groups, which may have confounded the findings.
Also, "the dropout rate was higher than anticipated, our power to detect the hypothesized difference of 5% weight loss between the intervention groups at month 6 decreased from 80% to 60%. The higher dropout rate in the alternate-day fasting group may have also introduced a possible selection bias between groups," the authors acknowledged."
Although the trial's findings reported that "alternate-day fasting may be less sustainable in the long term, compared with daily calorie restriction, for most obese individuals," this type of diet still may appeal to some individuals, despite the higher rates of dissatisfaction reported among this group during the trial, the authors noted.
"It will be of interest to examine what behavioral traits (eg., ability to go for long periods without eating) make alternate-day fasting more tolerable for some individuals than others," they wrote. "Future work in this area should examine whether this lack of adherence to alternate-day fasting is due to cognitive, environmental, and/or physiological factors."
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