Alternate-day fasting may soften the metabolic hit of weight regain in rats
In obese rats, calorie cutting and low-fat diet swaps raised dyslipidemia and cell stress when a high-fat diet returned. Alternate-day fasting looked safer.
Summary
Most people who lose weight regain it, and yo-yo dieting may raise diabetes and heart risk. Researchers in Brazil made male rats obese with a high-fat diet for 8 weeks. They then tried one of four approaches for 6 weeks: staying on the diet, eating 30% less of it, alternating fasting and feeding days, or switching to low-fat chow. Finally, all rats got unlimited high-fat food for 4 weeks. Every strategy slowed weight gain, but all rats regained quickly once it stopped. Rats that had cut calories or switched to low-fat chow showed worse blood lipids, weaker antioxidant and anti-inflammatory responses in liver and fat tissue, and more stress in lymph nodes. Alternate-day fasting appeared to give partial protection. This is early animal work, but it suggests how someone loses weight may affect what happens if the weight returns.
Detailed Summary
Weight regain is the norm after dieting. Nearly half of people regain all lost weight within 12 months, and only about 11% keep off 5 kg after five years. Repeated loss and regain, or weight cycling, has been linked to higher diabetes and cardiovascular risk, sometimes exceeding that of stable obesity. This study asked whether the weight-loss strategy used changes the metabolic consequences once old eating habits return.
Male Wistar rats (n = 32) ate a lard-based high-fat diet (HFD) for eight weeks to induce obesity and glucose intolerance. They were then split into four groups for six weeks: continued ad libitum HFD (n = 8), continuous caloric restriction with 30% less HFD (R-HFD, n = 9), alternate-day fasting with 24 hours of free HFD alternating with 24 hours of fasting (ADF-HFD, n = 9), and diet replacement with ad libitum low-fat chow (ad lib-LFD, n = 6). In the final four weeks, all groups had free access to HFD again.
All three interventions slowed weight gain during phase two (relative weight gain, one-way ANOVA F3,28 = 13.22, P < 0.0001). Once HFD was unrestricted, each intervention group gained more weight than the continued-HFD group (F3,28 = 8.268, P = 0.0004). By week 18, body weight, Lee Index (a rodent BMI analogue), epididymal fat percentage (about 2.6-3.0%) and liver mass (about 3.0-3.1% of body weight) did not differ between groups. R-HFD was the only group whose Lee Index rose between weeks 14 and 18.
Metabolic differences emerged despite similar final weights. Rats switched to low-fat chow showed a delayed glucose response by week 18, with higher glycemia at 30 minutes than the ad lib-HFD and R-HFD groups (P < 0.05). Their glucose area under the curve did not differ significantly, and fasting glycemia was unchanged. Insulin was modestly lower in the ad lib-LFD and R-HFD groups. The authors report that continuous restriction and diet replacement increased susceptibility to dyslipidemia over time, and impaired liver and fat antioxidant and anti-inflammatory responses. They also report greater lymph node stress, assessed through heat shock protein 70 (HSP70), a chaperone linked to antioxidant defense, NF-kB control and cellular senescence.
ADF showed no such pattern and appeared to confer partial protection during rebound. In phase three, ADF-HFD and R-HFD rats ate the least, while the low-fat chow group ate more than all others. Intake therefore does not fully explain the metabolic differences. The authors speculate that ADF may better preserve metabolic homeostasis, but the data do not establish a mechanism.
Several caveats apply. This is a rodent study in males only, with small groups (the diet-replacement group finished with six animals) and a model in which restriction was defined relative to HFD intake. Rats were sacrificed at a single time point, and the results (including the lipid data, which were truncated in the text available here) need replication in females and in human weight-regain trials. The findings are hypothesis-generating rather than a basis for clinical advice.
Key Findings
- All three interventions slowed weight gain during the 6-week intervention phase (relative weight gain ANOVA F3,28 = 13.22, P < 0.0001) in obese male rats (n = 32).
- After unrestricted high-fat diet returned, every intervention group gained more weight than the continued-HFD group (F3,28 = 8.268, P = 0.0004), showing rapid rebound.
- Final body weight, Lee Index, epididymal fat (about 2.6-3.0%) and liver mass (about 3.0-3.1%) did not differ between groups, so metabolic differences were not explained by body size.
- Rats previously switched to low-fat chow showed a delayed glucose response at 30 minutes by week 18, higher than ad lib-HFD and R-HFD groups (P < 0.05).
- Continuous restriction (30% less HFD) and diet replacement increased susceptibility to dyslipidemia under renewed HFD, with weaker liver and fat antioxidant and anti-inflammatory responses.
- Continuous restriction and diet replacement heightened lymph node stress on return to unlimited obesogenic diet, whereas alternate-day fasting appeared partially protective.
- R-HFD was the only group whose Lee Index increased between weeks 14 and 18, even though it had among the lowest energy intakes.
Methodology
Male Wistar rats (n = 32) ate a lard-based high-fat diet for 8 weeks, then were assigned to ad lib-HFD (n = 8), 30% restricted HFD (n = 9), alternate-day fasting (n = 9) or ad libitum low-fat chow (n = 6) for 6 weeks, followed by 4 weeks of free HFD. Outcomes included body weight, Lee Index, glucose tolerance tests, serum lipids, insulin, liver enzymes, liver histology, hematologic inflammation ratios, oxidative stress markers (TBARS, SOD, catalase) and HSP70 in plasma and tissues. Analyses used one-way and repeated-measures two-way ANOVA with Tukey or Šídák post-tests, and Kruskal-Wallis for non-parametric data. Sample size was calculated for body weight (power 80%, alpha 5%).
Study Limitations
The study used only male rats in a high-fat-diet model, with small groups (the diet-replacement group ended with six animals), so findings may not translate to women or to humans. Restriction was defined relative to HFD intake, and tissues were sampled at a single end point, limiting mechanistic inference. Conflict-of-interest information was not included in the provided text.
Enjoyed this summary?
Get the latest longevity research delivered to your inbox every week.
Enter your email to subscribe: