At similar weight loss, dietary composition determines the degree of glycemic improvement in diet-induced obese C57BL/6 mice

<div><p>Background</p><p>Achieving weight loss is the cornerstone of the treatment of the metabolic consequences of obesity, in particular of glucose intolerance.</p><p>Objective</p><p>To determine whether improvement in glucose control depends on dietary macronutrient composition of the diet at identical weight loss.</p><p>Materials and methods</p><p>Twenty-two weeks old diet-induced obese C57BL/6 mice lost weight through caloric restriction on normal chow (R-NC) or high fat diet (R-HF). Control mice were fed normal chow (LEAN) or high fat diet (OBESE) ad libitum. Body weight and composition were assessed after 8 weeks of dietary intervention. Glucose homeostasis was evaluated by intraperitoneal glucose tolerance tests (IPGTT). Epididymal white adipose (eWAT) and hepatic tissues were analyzed by immunohistochemistry and RT-qPCR.</p><p>Results</p><p>By 30 weeks of age, the body weight of the mice on R-NC (31.6±1.7g, mean±SEM) and R-HF (32.3±0.9g) was similar to LEAN mice (31.9±1.4g), while OBESE mice weighed 51.7±2.4g. Glucose tolerance in R-NC was better than in LEAN mice (69% AUC IPGTT, P 0.0168) whereas R-HF mice remained significantly less glucose tolerant (125% AUC IPGTT, P 0.0279 vs LEAN), despite identical weight loss. The eWAT pads and adipocyte size were similar in LEAN and R-NC mice, while the eWAT pad size of R-HF was 180% of R-NC (P < 0.0001) and the average adipocyte size of R-HF mice was 134% of R-NC fed mice (P 0.0285). No LEAN or R-NC mice had hepatic steatosis, in contrast to 28.6% of R-HF mice. Compared to OBESE mice, inflammatory markers were lower in eWAT and liver tissue of R-NC, but not in R-HF mice. Measures of visceral adiposity correlated well with glucose tolerance parameters.</p><p>Conclusions</p><p>In mice, caloric restriction on a normal chow diet improved glucose tolerance significantly more when identical weight loss was achieved on a high fat diet.</p></div

Macronutrient composition.

<p>Macronutrient composition.</p

Correlations between body composition, glucose parameters, epididymal white adipose tissue (eWAT) size, hepatic steatosis and ALT levels.

<p>Correlations between body composition, glucose parameters, epididymal white adipose tissue (eWAT) size, hepatic steatosis and ALT levels.</p

Energy expentidure components as obtained in automated cages for indirect calorimetry.

<p>Respiratory exchange rate (a), oxygen consumption (b), heat production (c) and ambulatory activity (d) (n = 6–8 per group). Data are presented as mean±SEM * P<0.05; ** P<0.01 *** P<0.001 **** P<0.0001.</p

Characteristics of epididymal white adipose tissue (eWAT) upon different weight loss interventions.

<p>Relative weight of eWAT pads (n = 11–15 per group) (a) Adipocyte size (b) as based on microscopic H&E stained sections of eWAT of LEAN (c), R-NC (d), R-HF (e) and OBESE (f) mice (magnification 20x, scale bars indicate 100μm). Average adipocyte surface in eWAT tissue samples (n = 6–9 per group, G) and relative mRNA expression levels of TNF-alpha (g) and MCP-1 (h) in eWAT (n = 6–8, per group). Data are presented as mean±SEM. * P<0.05; *** P<0.001.</p

Body weight and body composition.

<p>Body weight evolution (a) and caloric intake (b) LEAN (white circles), R-NC (light grey upward triangles), R-HF (dark grey downward triangles) and OBESE (black circles) mice. N = 11 for LEAN and OBESE, n = 15 for R-NC and R-HF. Body weight (c) and body composition, expressed as fat percentage (d) and lean mass (e) as measured by DXA at 30 weeks of age (n = 6 per group). Data are presented as mean±SEM * P<0.05; ** P<0.01 *** P<0.001 **** P<0.0001.</p

Characteristics of liver tissue upon different weight loss interventions.

<p>Relative liver weight (n = 11–15 per group) (a) Serum alanine aminotransferase (ALT) levels (n = 6–9 per group) (b) and hepatic triglyceride (TG) content (n = 6 per group) (c). H&E stained sections of liver tissue from LEAN (d), R-NC (e), R-HF (f) and OBESE (g) mice (magnification 10x, scale bars indicate 200μm). Steatosis (h), Inflammatory activity (i) and Fibrosis (j) score and Relative frequency of liver disease (n = 11–15 per group) (k); Relative mRNA expression levels of TNF-alpha (n = 6–8 per group) (l). Data are presented as mean±SEM. * P<0.05; *** P<0.001.</p

Glucose homeostasis parametes upon weight loss interventions.

<p>Blood glucose (n = 11–15 per group) (a) and serum insulin levels (n = 6 per group) (b) after 6h fasting. Intraperitoneal glucose tolerance test, and calculated AUC (n = 8 per group) (c, d) Insulin tolerance test and calculated AUC (n = 6 per group). Data are presented as mean±SEM. * P < 0.05; *** P < 0.001 **** P < 0.0001.</p

Regression equations and 95% CI to convert TSH levels of centre 5 and 6 to Autodelphia method.

<p>Centre 5: Liège; Centre 6: Louvain en Woluwé. CI confidence interval.</p

Bland Altman plot of comparison of Method 1 (Autodelphia) used by centre 1,2,3,4 versus Method 2 (ELISA commercial Biorad) used by centre 5.

<p>Mean difference: −3.854 mU/L (CI −4.291 to −3.417 mU/L) (left) and method 1 (Autodelphia) used by centre 1,2,3,4 versus method 3 (ELISA) used by centre 6; mean difference: −1.470 mU/L (CI −1.692 to −1.249 mU/L) (right).</p