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"Obesity - metabolism"
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Genetic studies of body mass index yield new insights for obesity biology
Obesity is heritable and predisposes to many diseases. To understand the genetic basis of obesity better, here we conduct a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), a measure commonly used to define obesity and assess adiposity, in up to 339,224 individuals. This analysis identifies 97 BMI-associated loci (
P
< 5 × 10
−8
), 56 of which are novel. Five loci demonstrate clear evidence of several independent association signals, and many loci have significant effects on other metabolic phenotypes. The 97 loci account for ∼2.7% of BMI variation, and genome-wide estimates suggest that common variation accounts for >20% of BMI variation. Pathway analyses provide strong support for a role of the central nervous system in obesity susceptibility and implicate new genes and pathways, including those related to synaptic function, glutamate signalling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.
A genome-wide association study and Metabochip meta-analysis of body mass index (BMI) detects 97 BMI-associated loci, of which 56 were novel, and many loci have effects on other metabolic phenotypes; pathway analyses implicate the central nervous system in obesity susceptibility and new pathways such as those related to synaptic function, energy metabolism, lipid biology and adipogenesis.
Genetic correlates of obesity
In the second of two Articles in this issue from the GIANT Consortium, Elizabeth Speliotes and collegues conducted a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), commonly used to define obesity and assess adiposity, to find 97 BMI-associated loci, of which 56 were novel. Many of these loci have significant effects on other metabolic phenotypes. The 97 loci account for about 2.7% of BMI variation, and genome-wide estimates suggest common variation accounts for more than 20% of BMI variation. Pathway analyses implicate the central nervous system in obesity susceptibility including synaptic function, glutamate signaling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.
Journal Article
Dietary supplementation with inulin-propionate ester or inulin improves insulin sensitivity in adults with overweight and obesity with distinct effects on the gut microbiota, plasma metabolome and systemic inflammatory responses: a randomised cross-over trial
ObjectiveTo investigate the underlying mechanisms behind changes in glucose homeostasis with delivery of propionate to the human colon by comprehensive and coordinated analysis of gut bacterial composition, plasma metabolome and immune responses.DesignTwelve non-diabetic adults with overweight and obesity received 20 g/day of inulin-propionate ester (IPE), designed to selectively deliver propionate to the colon, a high-fermentable fibre control (inulin) and a low-fermentable fibre control (cellulose) in a randomised, double-blind, placebo-controlled, cross-over design. Outcome measurements of metabolic responses, inflammatory markers and gut bacterial composition were analysed at the end of each 42-day supplementation period.ResultsBoth IPE and inulin supplementation improved insulin resistance compared with cellulose supplementation, measured by homeostatic model assessment 2 (mean±SEM 1.23±0.17 IPE vs 1.59±0.17 cellulose, p=0.001; 1.17±0.15 inulin vs 1.59±0.17 cellulose, p=0.009), with no differences between IPE and inulin (p=0.272). Fasting insulin was only associated positively with plasma tyrosine and negatively with plasma glycine following inulin supplementation. IPE supplementation decreased proinflammatory interleukin-8 levels compared with cellulose, while inulin had no impact on the systemic inflammatory markers studied. Inulin promoted changes in gut bacterial populations at the class level (increased Actinobacteria and decreased Clostridia) and order level (decreased Clostridiales) compared with cellulose, with small differences at the species level observed between IPE and cellulose.ConclusionThese data demonstrate a distinctive physiological impact of raising colonic propionate delivery in humans, as improvements in insulin sensitivity promoted by IPE and inulin were accompanied with different effects on the plasma metabolome, gut bacterial populations and markers of systemic inflammation.
Journal Article
Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake
The carbohydrate–insulin model of obesity posits that high-carbohydrate diets lead to excess insulin secretion, thereby promoting fat accumulation and increasing energy intake. Thus, low-carbohydrate diets are predicted to reduce ad libitum energy intake as compared to low-fat, high-carbohydrate diets. To test this hypothesis, 20 adults aged 29.9 ± 1.4 (mean ± s.e.m.) years with body mass index of 27.8 ± 1.3 kg m
−2
were admitted as inpatients to the National Institutes of Health Clinical Center and randomized to consume ad libitum either a minimally processed, plant-based, low-fat diet (10.3% fat, 75.2% carbohydrate) with high glycemic load (85 g 1,000 kcal
−1
) or a minimally processed, animal-based, ketogenic, low-carbohydrate diet (75.8% fat, 10.0% carbohydrate) with low glycemic load (6 g 1,000 kcal
−1
) for 2 weeks followed immediately by the alternate diet for 2 weeks. One participant withdrew due to hypoglycemia during the low-carbohydrate diet. The primary outcomes compared mean daily ad libitum energy intake between each 2-week diet period as well as between the final week of each diet. We found that the low-fat diet led to 689 ± 73 kcal d
−1
less energy intake than the low-carbohydrate diet over 2 weeks (
P
< 0.0001) and 544 ± 68 kcal d
−1
less over the final week (
P
< 0.0001). Therefore, the predictions of the carbohydrate–insulin model were inconsistent with our observations. This study was registered on ClinicalTrials.gov as
NCT03878108
.
In an inpatient, randomized controlled crossover trial, participants consumed 550–700 kcal day
−1
fewer calories when following a plant-based, low-fat diet with a high glycemic load compared with an animal-based, low-carbohydrate diet with a low glycemic load; weight loss was comparable between the two diets and there were no significant differences in hunger or enjoyment of the meals.
Journal Article
Overeating Saturated Fat Promotes Fatty Liver and Ceramides Compared With Polyunsaturated Fat: A Randomized Trial
Saturated fatty acid (SFA) vs polyunsaturated fatty acid (PUFA) may promote nonalcoholic fatty liver disease by yet unclear mechanisms.
To investigate if overeating SFA- and PUFA-enriched diets lead to differential liver fat accumulation in overweight and obese humans.
Double-blind randomized trial (LIPOGAIN-2). Overfeeding SFA vs PUFA for 8 weeks, followed by 4 weeks of caloric restriction.
General community.
Men and women who are overweight or have obesity (n = 61).
Muffins, high in either palm (SFA) or sunflower oil (PUFA), were added to the habitual diet.
Lean tissue mass (not reported here). Secondary and exploratory outcomes included liver and ectopic fat depots.
By design, body weight gain was similar in SFA (2.31 ± 1.38 kg) and PUFA (2.01 ± 1.90 kg) groups, P = 0.50. SFA markedly induced liver fat content (50% relative increase) along with liver enzymes and atherogenic serum lipids. In contrast, despite similar weight gain, PUFA did not increase liver fat or liver enzymes or cause any adverse effects on blood lipids. SFA had no differential effect on the accumulation of visceral fat, pancreas fat, or total body fat compared with PUFA. SFA consistently increased, whereas PUFA reduced circulating ceramides, changes that were moderately associated with liver fat changes and proposed markers of hepatic lipogenesis. The adverse metabolic effects of SFA were reversed by calorie restriction.
SFA markedly induces liver fat and serum ceramides, whereas dietary PUFA prevents liver fat accumulation and reduces ceramides and hyperlipidemia during excess energy intake and weight gain in overweight individuals.
Journal Article
Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study
Metabolic syndrome is characterized by a constellation of comorbidities that predispose individuals to an increased risk of developing cardiovascular pathologies as well as type 2 diabetes mellitus1. The gut microbiota is a new key contributor involved in the onset of obesity-related disorders2. In humans, studies have provided evidence for a negative correlation between Akkermansia muciniphila abundance and overweight, obesity, untreated type 2 diabetes mellitus or hypertension3–8. Since the administration of A. muciniphila has never been investigated in humans, we conducted a randomized, double-blind, placebo-controlled pilot study in overweight/obese insulin-resistant volunteers; 40 were enrolled and 32 completed the trial. The primary end points were safety, tolerability and metabolic parameters (that is, insulin resistance, circulating lipids, visceral adiposity and body mass). Secondary outcomes were gut barrier function (that is, plasma lipopolysaccharides) and gut microbiota composition. In this single-center study, we demonstrated that daily oral supplementation of 1010A. muciniphila bacteria either live or pasteurized for three months was safe and well tolerated. Compared to placebo, pasteurized A. muciniphila improved insulin sensitivity (+28.62 ± 7.02%, P = 0.002), and reduced insulinemia (−34.08 ± 7.12%, P = 0.006) and plasma total cholesterol (−8.68 ± 2.38%, P = 0.02). Pasteurized A. muciniphila supplementation slightly decreased body weight (−2.27 ± 0.92 kg, P = 0.091) compared to the placebo group, and fat mass (−1.37 ± 0.82 kg, P = 0.092) and hip circumference (−2.63 ± 1.14 cm, P = 0.091) compared to baseline. After three months of supplementation, A. muciniphila reduced the levels of the relevant blood markers for liver dysfunction and inflammation while the overall gut microbiome structure was unaffected. In conclusion, this proof-of-concept study (clinical trial no. NCT02637115) shows that the intervention was safe and well tolerated and that supplementation with A. muciniphila improves several metabolic parameters.
Journal Article
Fibroblast Growth Factor 21 Mediates Specific Glucagon Actions
Glucagon, an essential regulator of glucose homeostasis, also modulates lipid metabolism and promotes weight loss, as reflected by the wasting observed in glucagonoma patients. Recently, coagonist peptides that include glucagon agonism have emerged as promising therapeutic candidates for the treatment of obesity and diabetes. We developed a novel stable and soluble glucagon receptor (GcgR) agonist, which allowed for in vivo dissection of glucagon action. As expected, chronic GcgR agonism in mice resulted in hyperglycemia and lower body fat and plasma cholesterol. Notably, GcgR activation also raised hepatic expression and circulating levels of fibroblast growth factor 21 (FGF21). This effect was retained in isolated primary hepatocytes from wild-type (WT) mice, but not GcgR knockout mice. We confirmed this link in healthy human volunteers, where injection of natural glucagon increased plasma FGF21 within hours. Functional relevance was evidenced in mice with genetic deletion of FGF21, where GcgR activation failed to induce the body weight loss and lipid metabolism changes observed in WT mice. Taken together, these data reveal for the first time that glucagon controls glucose, energy, and lipid metabolism at least in part via FGF21-dependent pathways.
Journal Article
Gut microbiota metabolites, amino acid metabolites and improvements in insulin sensitivity and glucose metabolism: the POUNDS Lost trial
ObjectiveAlterations in gut microbiota have been linked to host insulin resistance, diabetes and impaired amino acid metabolism. We investigated whether changes in gut microbiota-dependent metabolite of trimethylamine N-oxide (TMAO) and its nutrient precursors (choline and L-carnitine) were associated with improvements in glucose metabolism and diabetes-related amino acids in a weight-loss diet intervention.DesignWe included 504 overweight and obese adults who were randomly assigned to one of four energy-reduced diets varying in macronutrient intake. The 6-month changes (Δ) in TMAO, choline and L-carnitine levels after the intervention were calculated.ResultsGreater decreases in choline and L-carnitine were significantly (p<0.05) associated with greater improvements in fasting insulin concentrations and homeostasis model assessment of insulin resistance (HOMA-IR) at 6 months. The reduction of choline was significantly related to 2-year improvements in glucose and insulin resistance. We found significant linkages between dietary fat intake and ΔTMAO for changes in fasting glucose, insulin and HOMA-IR (pinteraction <0.05); a greater increase in TMAO was related to lesser improvements in the outcomes among participants who consumed a high-fat diet. In addition, ΔL-carnitine and Δcholine were significantly related to changes in amino acids (including branched-chain and aromatic amino acids). Interestingly, the associations of ΔTMAO, Δcholine and ΔL-carnitine with diabetes-related traits were independent of the changes in amino acids.ConclusionOur findings underscore the importance of changes in TMAO, choline and L-carnitine in improving insulin sensitivity during a weight-loss intervention for obese patients. Dietary fat intake may modify the associations of TMAO with insulin sensitivity and glucose metabolism.Trial registration numberNCT00072995.
Journal Article
Regulation of abdominal adiposity by probiotics (Lactobacillus gasseri SBT2055) in adults with obese tendencies in a randomized controlled trial
Background/Objectives: In spite of the much evidence for the beneficial effects of probiotics, their anti-obesity effects have not been well examined. We evaluated the effects of the probiotic Lactobacillus gasseri SBT2055 (LG2055) on abdominal adiposity, body weight and other body measures in adults with obese tendencies. Subjects/Methods: We conducted a multicenter, double-blind, randomized, placebo-controlled intervention trial. Subjects (n=87) with higher body mass index (BMI) (24.2–30.7 kg/m2) and abdominal visceral fat area (81.2–178.5 cm2) were randomly assigned to receive either fermented milk (FM) containing LG2055 (active FM; n=43) or FM without LG2055 (control FM; n=44), and were asked to consume 200 g/day of FM for 12 weeks. Abdominal fat area was determined by computed tomography. Results: In the active FM group, abdominal visceral and subcutaneous fat areas significantly (P<0.01) decreased from baseline by an average of 4.6% (mean (confidence interval): −5.8 (−10.0, −1.7) cm2) and 3.3% (−7.4 (−11.6, −3.1) cm2), respectively. Body weight and other measures also decreased significantly (P<0.001) as follows: body weight, 1.4% (−1.1 (−1.5, −0.7) kg); BMI, 1.5% (−0.4 (−0.5, −0.2) kg/m2); waist, 1.8% (−1.7 (−2.1, −1.4) cm); hip, 1.5% (−1.5 (−1.8, −1.1) cm). In the control group, by contrast, none of these parameters decreased significantly. High-molecular weight adiponectin in serum increased significantly (P<0.01) in the active and control groups by 12.7% (0.17 (0.07, 0.26) μg/ml) and 13.6% (0.23 (0.07, 0.38) μg/ml), respectively. Conclusion: The probiotic LG2055 showed lowering effects on abdominal adiposity, body weight and other measures, suggesting its beneficial influence on metabolic disorders.
Journal Article