Caloric Restriction Compared to Alternate-Day Fasting on Insulin Resistance 

Caloric restriction vs alernate day fasting: is one more effective than the other for people who have obesity?

A question that researchers have asked is, “Does alternating fasting days have a better effect than caloric restriction in people that are at increased risk of developing type 2 diabetes?”  The purpose of this study was to compare alternating fasting days to caloric restriction to understand the effects of both body weight and glucose regulation in patients that have obesity or overweight and have insulin resistance. 

In this study, researchers assessed 43 patients who had the following baseline characteristics: a body mass index (BMI) of at least 25 mg/m2 and insulin resistance.  These subjects were examined for a 12-month time period for changes in insulin resistance and fasting insulin. These levels were calculated using the homeostatic model assessment for BMI, insulin resistance, lean mass, fat mass, and several other metric factors.  Of the 43 patients, 11 of them were assigned to the alternating fasting day group. Within this group, the mean age was 43 years and about 82% of them were women. The calorie restriction group consisted of 17 subjects that had a mean age of 42 years and about 77% were women.  The remaining 15 subjects were in the control group where they remained on their regular diet routine. The control group had a mean age of 41 years and about 73% were women. 

For patients in the alternate day fasting, they were required to reach 125% of their required caloric intake within one day and drop their caloric intake by 25% of energy for the next day, and this arrangement was to continue for 6 months.  After the 6 months ended, the ratio for the alternating day fasters had changed to 150% and 100%, respectively. For subjects in the caloric restriction group, they had to lower their caloric intake by 75% of the needed energy required for the first 6 months and then 100% for the remaining 6 months.

After the completion of the 12 months, patients within the alternate day fasting group had a reduction of 8% in body weight when compared to those who continued their routine daily diet (P < 0.0001).  When researchers compared subjects who didn’t change their daily routine to those that reduced caloric intake they saw a 6% decrease in body weight (P < 0.0001) in favor of those who changed caloric intake.  There was a 6% body weight reduction in subjects that alternated daily fasting compared to those that reduce caloric intake. 

When comparing fasting insulin, there was a 52% reduction in subjects with alternate day fasting compared to a 14% reduction in subjects with reducing caloric intake (P < 0.05).  Also, insulin resistance was decreased by 53% in subjects with alternate day fasting compared to 17% in subjects with the decreased caloric intake (P < 0.05). Other factors remained unchanged when comparing the different groups to each other.  These factors include lean mass, visceral fat mass, LDL-C, HDL-C, triglycerides, blood pressure, C‐reactive protein, tumor necrosis factor α, and interleukin 6 values.

The researchers concluded that alternate day fasting had a superior effect at reducing fasting insulin and insulin resistance when compared to decreasing the daily caloric intake.  However, they both had a similar incidence of decreasing body weight. Further studies should investigate if alternate day fasting and increased exercise will further decrease insulin resistance, fasting insulin, and body weight.

Practice Pearls:

• Alternate day fasting can decrease fasting insulin and insulin resistance in patients who have overweight or obesity and have insulin resistance.
• There is no difference in weight reduction when comparing alternate day fasting and reduction in caloric intake.
• Other factors such as lean mass, visceral fat mass, LDL-C, HDL-C, triglycerides, blood pressure, C‐reactive protein, tumor necrosis factor α, and interleukin 6 values were unchanged when comparing the different groups.

K, Gabel. “Alternate-Day Fasting Cuts Insulin Levels, Resistance in Half.” Healio, https://www.healio.com/endocrinology/obesity/news/online/{095f9279-939a-4ff8-ab20-13a85b0b667a}/alternate-day-fasting-cuts-insulin-levels-resistance-in-half.

Gabel, Kelsey, et al. “Differential Effects of Alternate‐Day Fasting Versus Daily Calorie Restriction on Insulin Resistance – Gabel – 2019 – Obesity – Wiley Online Library.” Obesity, John Wiley & Sons, Ltd, 22 July 2019, https://onlinelibrary.wiley.com/doi/abs/10.1002/oby.22564.

Maya Rudolph, Fourth Year PharmD Candidate, Florida A&M University, College of Pharmacy & Pharmaceutical Sciences