Differential weight loss with intermittent fasting or daily calorie restriction in low- and high-fitness phenotypes

Abstract

New findings: What is the central question of this study? How does intrinsic aerobic capacity impact weight loss with 50% daily caloric restriction and alternate-day fasting? What is the main finding and its importance? Intermittent fasting is effective for weight loss in rats with low fitness, which highlights the importance of how intermittent fasting interacts with aerobic fitness.

Abstract: Recent interest has focused on the benefits of time-restricted feeding strategies, including intermittent fasting, for weight loss. It is not yet known whether intermittent fasting is more effective than daily caloric restriction at stimulating weight loss and how each is subject to individual differences. Here, rat models of leanness and obesity, artificially selected for intrinsically high (HCR) and low (LCR) aerobic capacity, were subjected to intermittent fasting and 50% calorie restrictive diets in two separate experiments using male rats. The lean, high-fitness HCR and obesity-prone, low-fitness LCR rats underwent 50% caloric restriction while body weight and composition were monitored. The low-fitness LCR rats were better able to retain lean mass than the high-fitness HCR rats, without significantly different proportional loss of weight or fat. In a separate experiment using intermittent fasting in male HCR and LCR rats, alternate-day fasting induced significantly greater loss of weight and fat mass in LCR compared with HCR rats, although the HCR rats had a more marked reduction in ad libitum daily food intake. Altogether, this suggests that intermittent fasting is an effective weight-loss strategy for those with low intrinsic aerobic fitness; however, direct comparison of caloric restriction and intermittent fasting is warranted to determine any differential effects on energy expenditure in lean and obesity-prone phenotypes.

Keywords: adiposity; alternate-day fasting; body composition; high- and low-capacity runners; intrinsic aerobic capacity; male; rat.

Figure 1.. Body weight and composition in male high-capacity runners (HCR) and low-capacity runners (LCR) subjected to 21 days of 50% calorie restriction (CR).

50% CR induced a significant loss of (A) body weight, (B) fat mass, and (C) lean mass. There was significantly greater loss of lean mass in HCR than LCR subjected to 50% CR and non-significant trend for greater weight loss in HCR than LCR (p = 0.051); † (over bar) significant loss in 21-day CR rats compared to control ad libitum-fed rats; * (in legend) HCR significantly different from LCR during 21-day CR; Mean ± SD, p < 0.05.

Figure 2.. Body weight and composition in male high-capacity runners (HCR) and low-capacity runners (LCR) subjected to 7 weeks of intermittent fasting (IF).

LCR lost significantly more of their baseline (A) body weight and (B) fat mass than HCR on IF. (C) There was no significant difference in the percent of lean mass lost from baseline between HCR and LCR; *significantly more loss in LCR than HCR; Mean ± SD, p < 0.05.

Figure 3.. Weekly food intake across 7 weeks of intermittent fasting (IF) in high-capacity runners (HCR) and low-capacity runners (LCR).

(A) HCR and LCR significantly reduced their food intake from baseline. HCR ate more than LCR at baseline and during each week of IF. (B) HCR showed a greater reduction from baseline food intake at weeks 1, 2, 4, and 7. (C) ANCOVA, compared to LCR, HCR showed a significantly greater reduction in food intake for a given weight loss. # (over vertical bar) significant interaction between time and phenotype; * (in legend) HCR significantly different from LCR, Mean ± SD, p < 0.05.

Figure 4. Body weight and composition during fed and fasted days of intermittent fasting (IF) in high-capacity runners (HCR) and low-capacity runners (LCR).

(A) LCR had higher fed- and fasted-day body weights than HCR in each week of IF. (B) HCR and LCR fat mass did not differ between phenotype during weeks 6 (on a fasted day; p = 0.06) or 7 (on a fed day; p = 0.08). (C) LCR had more lean mass than HCR at both weeks 6 (fasted) and 7 (fed). (D) LCR lost more fat mass than HCR during both weeks 6 (fast) and 7 (fed). (E) LCR lost more lean mass than HCR during week 7 (fed), but not week 6 (fast) of IF. † (over bar) significantly more fasted and fed lean mass in LCR than HCR; * (in legend) or * (over error bar) significantly more in LCR than HCR, Mean ± SD, p < 0.05.

Figure 5.

Relative change in body composition with 50% calorie restriction (50% CR) and intermittent fasting (IF) in male high- and low-capacity runners (HCR, LCR).