Background: The dysfunction of energy metabolism in white adipose tissue (WAT) induces adiposity. Obesogenic diets that are high in saturated fat disturb nutrient metabolism in adipocytes. This study investigated the effect of an isocaloric high-fat diet without the confounding effects of weight gain on the gene expression of fatty acid and carbohydrate transport and metabolism and its genetic inheritance in subcutaneous (s.c.) WAT of healthy human twins. Methods: Forty-six healthy pairs of twins (34 monozygotic, 12 dizygotic) received an isocaloric carbohydrate-rich diet (55% carbohydrates, 30% fat, 15% protein; LF) for 6 weeks followed by an isocaloric diet rich in saturated fat (40% carbohydrates, 45% fat, 15% protein; HF) for another 6 weeks. Results: Gene expression analysis of s.c. WAT revealed that fatty acid transport was reduced after one week of the HF diet, which persisted throughout the study and was not inherited, whereas intracellular metabolism was decreased after six weeks and inherited. An increased inherited gene expression of fructose transport was observed after one and six weeks, potentially leading to increased de novo lipogenesis. Conclusion: An isocaloric dietary increase of fat induced a tightly orchestrated, partially inherited network of genes responsible for fatty acid and carbohydrate transport and metabolism in human s.c. WAT.

Background/Objectives: Emerging data support evidence of the essential role of glucagon for lipid metabolism. However, data on the role of dietary fat intake for glucagon secretion is limited. This analysis investigated whether altering nutritional fat intake affects glucagon levels in healthy subjects. Methods: A total of 92 twins (age: 31 ± 14 years, BMI: 23 ± 3 kg/m²) consumed two 6-week diets: first a low-fat, high-carbohydrate diet (LFD) followed by an isocaloric high-fat, low-carbohydrate diet (HFD). In total, 24 twins (age: 39 ± 15 years, BMI: 24 ± 2 kg/m²) continued with a high-protein diet (HPD). Clinical investigations were performed after 6 weeks of the LFD, after 1 and 6 weeks of the HFD and after 6 weeks of the HPD. Results: The LFD caused a significant decrease in fasting glucagon (−27%, p < 0.001) compared to baseline. After 6 weeks of the HFD, glucagon increased (117%, p < 0.001 vs. LFD), while free fatty acids decreased. Six weeks of the HPD further increased glucagon levels (72%, p = 0.502 vs. HFD), although fasting amino acid levels remained constant. Fasting insulin and HOMA-IR moderately increased after one week of the HFD, while six weeks of the HPD significantly decreased both. The fasting glucagon-to-insulin ratio decreased during the LFD (p < 0.001) but increased after the HFD (p < 0.001) and even further increased after the HPD (p = 0.018). Liver fat, triglycerides and blood glucose did not increase during the HFD. The heritability of glucagon levels was 45% with the LFD. Conclusions: An HFD increases glucagon levels and the glucagon-to-insulin ratio under isocaloric conditions compared to an LFD in healthy lean subjects. This rise in glucagon may represent a metabolic response to prevent hepatic steatosis, as glucagon increases have been previously shown to induce hepatic fat oxidation.

Introduction: Offspring exposed to high fat diet (HFD) during pregnancy (IU) and lactation (L) are at risk of developing obesity in adulthood. Inhibition of glucose dependent insulinotropic polypeptide receptor signaling (Gipr^-/-) in mice is protective of HFD induced obesity. We reported that Gipr^-/- exposed to HFD during IU/L are no longer protected from diet induced obesity in adulthood. We now tested the hypothesis if these programming effects are due to altered promoter methylation of key genes of lipid metabolism which causes a decrease in gene expression. Methods: Female GIP receptor heterozygous (Gipr^+/-) mice were fed either HFD or control (C) diet prior to mating with Gipr^+/- male mice and during IU/L. Male Gipr^-/- offspring were kept on normal chow for 22 weeks after weaning, followed by HFD for additional 20 weeks. This resulted into Gipr^-/- exposed to either C (KO Ciu-HF) or HFD (KO HFiu-HF) during IU/L and HFD later in adulthood. Wild type (WT) male mice fed C diet during IU/L and HFD in adulthood served as controls (WT Ciu-HF). At 45 weeks of age, body fat content, adipocyte size and expression and DNA-methylation of genes of fatty acid oxidation in muscle were analyzed. Results: KO HFiu-HF had increased body fat content (P < 0.05) and larger adipocytes (P < 0.005) compared to KO Ciu-HF. Gene expression of PPARα (2.45-fold) and CPT-1β (1.53-fold) was massively increased in KO Ciu-HF compared to WT Ciu-HF mice (P < 0.05), but down regulated by 45.2% for PPARα and by 41.0% for CPT-1β in KO HFiu-HF compared to KO Ciu-HF (P < 0.05) in muscle. One CpG-site for PPARα and three CpG-sites for CPT-1β showed a decrease in methylation in KO Ciu-HF compared to WT Ciu-HF and a renewed increase in KO HFiu-HF as seen in WT Ciu-HF. CpG-methylation correlated inversely with gene expression. Conclusion: HFD during IU/L induces epigenetic modifications leading to decreased peripheral fatty acid oxidation that reverses the protection of diet induced obesity in Gipr^-/- mice.

Background/Objectives: Emerging data support an essential role of glucagon for lipid metabolism. However, data on the role of dietary fat intake for glucagon secretion is limited. This analysis investigated whether altering nutritional fat intake affects glucagon levels in healthy subjects. Methods: 92 twins (age: 31±14 years, BMI: 23±3 kg/m2) consumed two 6-week diets: first a low fat, high carbohydrate diet (LFD) followed by an isocaloric high fat, low carbohydrate diet (HFD). 24 twins (age: 39±15 years, BMI: 24±2 kg/m2) continued with a high protein diet (HPD). Clinical investigation days were performed after 6 weeks of LFD, after 1 and 6 weeks of HFD and after 6 weeks of HPD. Results: The LFD caused a significant decrease of fasting glucagon (-27 %, p<0.001) compared to baseline. After 6 weeks of HFD glucagon increased (117 %, p<0.001 vs. LFD) while free fatty acids decreased. 6 weeks of HPD further increased glucagon levels (72 %, p=0.502 vs. HFD) although fasting amino acid levels remained constant. Fasting insulin and HOMA-IR moderately increased after one week of HFD, while 6 weeks of HPD significantly decreased both. The fasting glucagon-to-insulin ratio decreased through LFD (p<0.001) but increased after HFD (p<0.001) and even further after HPD (p=0.018). Liver fat, triglycerides and blood glucose did not increase during the HFD. The heritability of glucagon levels was 45% with the LFD. Conclusions: A HFD increases glucagon levels and the glucagon-to-insulin ratio under isocaloric conditions compared to a LFD in healthy lean subjects. This rise in glucagon may represent a favorable metabolic response as neither glucose levels nor insulin resistance or liver fat showed clinically relevant increases.

Introduction: The clock gene machinery coordinates numerous metabolic processes to adapt physiological responses to light-dark and feeding regimens. However, in humans it is unknown whether clock genes participate in nutrient-induced metabolic and inflammatory responses. Herein, we hypothesized that the switching from high carbohydrate – low fat diet to a low carbohydrate – high fat (LC/HFD) isocaloric diet affects the molecular circadian clock and potentially alters diurnal rhythms in fat metabolism and inflammation in human monocytes. Methods: To evaluate this, we analyzed diurnal pattern of gene expression in monocytes of 29 non obese healthy twins using a three-time-point rhythm prediction method. Results: Diurnal oscillations of core clock genes (PER1, PER2, PER3 and TEF) and inflammatory genes (CD14, CD180, NFKBIA, and IL1B) were altered by LC/HFD within one or six weeks. LC/HFD also affected the expression of non-oscillating genes contributing to energy metabolism (SIRT1) and fat metabolism (ACOX3, IDH3A). Further, the expression of clock genes PER1 – 3 and TEF correlated with blood cholesterol levels and with expression of metabolic and inflammatory genes and were highly concordant among monozygotic twins. In vitro experiments confirmed direct effects of plasma FFA levels on the clock gene expression. Conclusion: In summary, our results suggest for the first time that the dietary fat and carbohydrate content alters the function of peripheral circadian clock in humans as well as diurnal rhythms of genes contributing to inflammation.