The metabolic consequences of 'yo-yo' dieting are markedly influenced by genetic diversity

Abstract

Background: Weight loss can improve the metabolic complications of obesity. However, it is unclear whether insulin resistance persists despite weight loss and whether any protective benefits are preserved following weight regain (weight cycling). The impact of genetic background on weight cycling is undocumented. We aimed to investigate the effects of weight loss and weight cycling on metabolic outcomes and sought to clarify the role of genetics in this relationship.

Method: Both C57BL/6 J and genetically heterogeneous Diversity Outbred Australia (DOz) mice were alternately fed high fat Western-style diet (WD) and a chow diet at 8-week intervals. Metabolic measures including body composition, glucose tolerance, pancreatic beta cell activity, liver lipid levels and adipose tissue insulin sensitivity were determined.

Results: After diet switch from WD (8-week) to chow (8-week), C57BL/6 J mice displayed a rapid normalisation of body weight, adiposity, hyperinsulinemia, liver lipid levels and glucose uptake into adipose tissue comparable to chow-fed controls. In response to the same dietary intervention, genetically diverse DOz mice conversely maintained significantly higher fat mass and insulin levels compared to chow-fed controls and exhibited much more profound interindividual variability than C57BL/6 J mice. Weight cycled (WC) animals were re-exposed to WD (8-week) and compared to age-matched controls fed 8-week WD for the first time (LOb). In C57BL/6 J but not DOz mice, WC animals had significantly higher blood insulin levels than LOb controls. All WC animals exhibited significantly greater beta cell activity than LOb controls despite similar fat mass, glucose tolerance, liver lipid levels and insulin-stimulated glucose uptake in adipose tissue.

Conclusion: Following weight loss, metabolic outcomes return to baseline in C57BL/6 J mice with obesity. However, genetic diversity significantly impacts this response. A period of weight loss does not provide lasting benefits after weight regain, and weight cycling is detrimental and associated with hyperinsulinemia and elevated basal insulin secretion.

Fig. 1. Effect of weight loss on metabolic outcomes in C57BL/6 J mice.

a Weight loss study design, (b–g) metabolic outcomes at 16 wk time point including (b) fat mass, (c) fasting insulin, (d) insulin at 15 min time point during glucose tolerance test (GTT) (e) fasting glucose, (f) GTT results and area under the GTT curve, (g) ex-vivo 2-deoxyglucose (2DG) uptake basal (0 nM) and insulin stimulated (10 nM) into adipose tissue. Error bars are SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs AOb (n = 6–16/group). All statistical analysis was conducted using ANOVA. WL: Weight loss, AOb: Always having Obesity.

Fig. 2. Effect of weight cycling on metabolic outcomes in C57BL/6 J mice.

a Weight cycling experimental design for 24-week study duration, b group means for body weight over 24 weeks, (c) group means for fat mass over 24 weeks, (d–h) metabolic outcomes at 24 week time point including (d) fasting insulin, (e) insulin at 15 min during glucose tolerance test (GTT), (f) fasting glucose, (g) GTT results and area under the GTT curve, (h) ex-vivo glucose uptake basal (0 nM) and insulin stimulated (10 nM) into adipose tissue. Error bars are SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs chow, #p < 0.05 vs LOb, $p < 0.05 vs AOb (n = 6–16/group). All statistical analysis was conducted using ANOVA. LOb Later onset obesity, WC Weight cycling, AOb Always having obesity.

Fig. 3. Effect of weight cycling on metabolic outcomes in DOz mice.

a Experimental design for DOz mice study. Group means over 24 weeks for (b) body weight, (c) fat mass. Group means at 16 weeks time point for (d) fasting glucose, (e) GTT results (f) area under the GTT curve, (g) fasting insulin, (h) insulin at 15 min during GTT. Group means at 24 weeks time point for (i) fasting glucose, (j) GTT results, (k) area under the GTT curve, (l) fasting insulin, (m) insulin at 15 min during GTT. Error bars are SEM. Statistical analysis was conducted using two-sample T-tests for (c, d, f, i, k, l) or Mann–Whitney U-test where groups had unequal variances or outliers (g, h). *p < 0.05, **p < 0.01, ***p < 0.001 (n = 30–32/group). LOb Later onset obesity, WC Weight Cycling.

Fig. 4. Weight Cycling responses and energy intake in DOz and C57BL/6 J mice.

Fat mass loss (%) following switch from WD to chow for (a) DOz mice and (b) C57BL/6 J mice. Fat mass loss (%) = -(fat mass week 16 - fat mass week 8) / (fat mass week 8 - fat mass week 0). Adjusted weight over 24 weeks in (c) DOz mice and (d) C57BL/6 J mice. Adjusted weight = weight / initial weight (g). Opaque lines are group averages per week, translucent lines are individual values per week. e Experimental design for the DOz mice energy intake study. f Group means over 6 weeks for Average daily energy intake (kcal). Energy intake was measured for 3 consecutive days every 2nd week and averaged to gauge the average daily energy intake per mouse for weeks 2, 4, and 6. Error bars are SEM. NS not significant, *p < 0.05, **p < 0.01, ***p < 0.001 (n = 14–16 / group for C57BL/6 J study, n = 30–32/group for DOz study, n = 19–20 / group for DOz energy intake study). All statistical analysis was conducted using two-sample T-tests. LOb Later onset obesity, WC Weight Cycling.

Fig. 5. Effect of weight cycling on insulin secretion in C57BL/6 J and DOz mice.

Islet insulin secretion in chow, LOb, WC and AOb C57BL/6 J mice following (a) low dose (2.8 mM) or (b) high dose (16.7 mM) glucose, (c) Homeostasis Model Assessment of beta cell function (HOMA-B) in LOb (orange) and WC (blue) DOz mice, (d) plasma FFA in chow, LOb, WC and AOb C57BL/6 J mice after a 6 h fast, (e) plasma FABP4 levels in chow, LOb, WC and AOb C57BL/6 J mice. All measurements taken at 24 week time point. *p < 0.05, **p < 0.01 vs chow, #p < 0.05 vs AOb, $p < 0.05 vs LOb (n = 6–32/group) Statistical analysis was conducted using ANOVA (a, b, d, e) or Mann–Whitney U-test (c). LOb Later onset obesity, WC Weight cycling, AOb Always having Obesity.