Alternate-day fasting cuts insulin levels, resistance in half
Alternate-day fasting lowered levels of fasting insulin and insulin resistance to a greater degree than calorie restriction among adults with overweight or obesity and insulin resistance, according to findings published in Obesity.
“A key question that remains unknown is whether [alternate-day fasting] produces superior changes in glucoregulatory factors compared with [calorie restriction] in populations at risk for developing diabetes (ie, insulin-resistant individuals with overweight and obesity),” Krista A. Varady, PhD, associate professor in the department of kinesiology and nutrition at University of Illinois at Chicago, and colleagues wrote. “These preliminary findings show that intermittent fasting may be more effective than daily [calorie restriction] to lower insulin resistance in adults at risk for developing diabetes.”
Varady and colleagues examined changes in fasting insulin, insulin resistance as calculated via the homeostatic model assessment of insulin resistance, BMI, fat mass, lean mass and several other metrics over a 12-month period among a cohort of 43 adults with a baseline BMI of at least 25 kg/m2 and insulin resistance. During the 12 months, alternate-day fasting was practiced by 11 participants (mean age, 43 years; 81.8% women), calorie restriction was practiced by 17 participants (mean age, 42 years; 76.5% women) and the remaining 15 maintained their regular dietary routine (mean age, 41 years; 73.3%).
Alternate-day fasters had to reach 125% of their required caloric intake in one day and drop intake to 25% of energy needs on the next day, with this pattern continuing for the first 6 months, after which the ratios switched to 150% and 100%. Calorie restriction was defined by limiting caloric intake to 75% of energy requirements in the first 6 months and to 100% in the final 6 months, according to the researchers.
After 12 months, participants who followed an alternate-day fasting regimen reduced body weight by 8% compared with those on the routine regimen (P < .0001). The researchers noted that those who restricted calories lost 6% of body weight compared with those who did not adjust their diets (P < .0001) and that this reduction was similar to the alternate-day fasters.
However, there was a 52% reduction in fasting insulin at 12 months among alternate-day fasters vs. a 14% reduction among the calorie restrictors (P < .05). At the same time point, insulin resistance declined by 53% for those fasting on alternate days and by 17% for those restricting calories (P < .05).
“Taken together, these findings suggest that fasting generally produces superior reductions in insulin resistance compared with daily [calorie restriction] despite similar weight loss,” the researchers wrote. “Moreover, it is likely that these effects may be more pronounced in participants who display higher levels of insulin resistance at baseline.”
The researchers further noted that those assigned to alternate-day fasting did not thoroughly adhere to the regimen, with intake on fast days higher than recommended and intake on feast days lower than recommended.
“Participants consistently struggled to stick to their fast-day calorie goals, which puts into question the sustainability and tolerability of [alternate-day fasting] long term,” the researchers wrote. “On the other hand, it is interesting that [alternate-day fasting] participants consumed almost twice as many calories on fast days but still observed greater metabolic effects compared with [calorie restriction] participants. This suggests that simply reducing energy intake by [approximately] 1,000 kcal/d a few days per week may have significant metabolic benefits.” – by Phil Neuffer
Disclosure: Varady reports author fees from Hachette Book Group.