The aim was to determine whether fed VLDL and chylomicron (CM) triacylglycerol (TAG) production rates are elevated in metabolic syndrome (MetS). Eight men with MetS (BMI 29.7 ± 1.1) and eight lean age-matched healthy men (BMI 23.1 ± 0.4) were studied using a frequent feeding protocol. After 4 h of feeding, an intravenous bolus of ²H₅-glycerol was administered to label VLDL1, VLDL2, and TAG. ¹³C-glycerol tripalmitin was administered orally as an independent measure of CM TAG metabolism. Hepatic and intestinal lipoproteins were separated by an immunoaffinity method. In MetS, fed TAG and the increment in TAG from fasting to feeding were higher (P = 0.03 and P = 0.04, respectively) than in lean men. Fed CM, VLDL1, and VLDL2 TAG pool sizes were higher (P = 0.006, P = 0.03, and P < 0.02, respectively), and CM, VLDL1, and VLDL2 TAG production rates were higher (P < 0.002, P < 0.05, and P = 0.06, respectively) than in lean men. VLDL1, VLDL2, and CM TAG clearance rates were not different between groups. In conclusion, prandial hypertriglyceridemia in men with MetS was due to an increased production rate of both VLDL and CM TAG. Since both groups received identical meals, this suggests that in MetS the intestine is synthesizing more TAG de novo for export in CMs.

Context: Alterations of protein turnover may contribute to the progressive decline of muscle mass with aging. Objective: Our objective was to examine the effects of near-physiological recombinant human GH and/or testosterone (T) administration to older men on whole body protein kinetics and muscle gene expression. Design, Settings, and Participants: A 6-month randomized, double-blind, placebo-controlled trial in 21 healthy elderly men aged 65–75 yr, was performed. Participants were randomized to receive placebo GH and placebo T, rhGH and placebo T (GH), T and placebo GH (T), or rhGH and T (GHT). Interventions: The leucine rate of appearance (index of proteolysis), nonoxidative leucine disposal rate (an index of protein synthesis), and leucine oxidation rate were measured with an infusion of l-[1-¹³C] leucine. Muscle biopsies for the measurement of gene expression were performed. Body composition and aerobic capacity (maximal oxygen capacity) were measured. Results: Serum IGF-I levels increased significantly with GH and GHT (P < 0.001) compared with placebo. T increased significantly only in the T group (P = 0.028). Leucine rate of appearance and nonoxidative leucine disposal rate increased with GH (P = 0.015, P = 0.019) and GHT (P = 0.017, P = 0.02), but leucine oxidation did not change significantly in any treatment group. Midthigh muscle mass and maximal oxygen capacity increased (P < 0.04) with GHT only. Expression of muscle function genes did not change significantly, but the within-group comparisons revealed a significant increase of androgen receptor expression in the GHT group (P = 0.001). Conclusion: This study showed that 6-month treatment with low-dose GH alone or with T in healthy elderly men produces comparable increments in whole body protein turnover and protein synthesis.

Background and Aims: Exercise is recommended for the management of metabolic dysfunction‐associated steatotic liver disease (MASLD), yet effects on liver histology remain unknown, especially without significant weight loss. We aimed to examine changes in surrogate measures of liver histological response with exercise training.Methods: We conducted a post hoc pooled analysis of three randomised controlled trials (duration: 12–20 weeks) comparing aerobic exercise interventions with controls. The primary outcome measure was a ≥30% relative reduction in (MRI‐measured) liver fat, as a surrogate measure of liver histological response (the threshold necessary for fibrosis improvement). Secondary outcome measures were changes in other biomarkers of liver fibrosis, anthropometry, body composition and aerobic fitness.Results: Eighty‐eight adults (exercise: 54, control: 34; male: 67%) were included with mean (SD) age 51 (11) years and body mass index 33.3 (5.2) kg/m². Following the intervention, exercise had ~5‐fold (OR [95%CI]: 4.86 [1.72, 13.8], p = .002) greater odds of ≥30% relative reduction in MRI‐measured liver fat compared with control. This paralleled the improvements in anthropometry (waist and hip circumference reduction), body composition (body fat, visceral and subcutaneous adipose tissue) and aerobic fitness (V̇O₂peak, ventilatory threshold and exercise capacity). Importantly, these effects were independent of clinically significant body weight loss (<3% body weight).Conclusion: Exercise training led to clinically meaningful improvements in surrogate serum‐ and imaging‐based measures of liver histological change, without clinically meaningful body weight reduction. These data reinforce the weight‐neutral benefit of exercise training and suggest that aerobic training may improve liver fibrosis in patients with MASLD.

Labelling molecules with stable isotopes to create tracers has become a gold-standard method to study the metabolism of lipids and lipoproteins in humans. There are a range of techniques which use stable isotopes to measure fatty acid flux and oxidation, hepatic fatty synthesis, cholesterol absorption and synthesis and lipoprotein metabolism in humans. Stable isotope tracers are safe to use, enabling repeated studies to be undertaken and allowing studies to be undertaken in children and pregnant women. This review provides details of the most appropriate tracers to use, the techniques which have been developed and validated for measuring different aspects of lipid metabolism and some of the limitations of the methodology.

Background: Dyslipidaemia and lipodystrophy have been described in treated HIV patients and in a small percentage of untreated HIV patients. Lipodystrophy in these patients has been shown to be associated with a lower expression of low density lipoprotein (LDL) receptors. Methods: We have investigated the effect of antiretroviral treatment with either a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI) on body fat distribution and LDL apolipoprotein B (apoB) kinetics in 12 HIV-negative controls and 52 HIV-infected patients, including antiretroviral treatment-naive (TN) patients ( n=13) and patients taking two nucleoside analogues plus either a PI ( n=15) or an NNRTI ( n=24). Results: LDL cholesterol was not different between groups. Compared with the controls, LDL apoB absolute synthetic rate (ASR) and fractional catabolic rate (FCR) were lower and residence time (RT) was higher in the PI and NNRTI groups ( P<0.05). In the TN patients, LDL ASR was lower ( P<0.05) and there was a trend for a lower FCR and higher RT compared with the controls ( P=0.07). LDL apoB pool size was greater in the PI group compared with the controls ( P<0.05). In the PI group, patients on ritonavir (RTV)-containing regimens had a lower LDL apoB ASR ( P=0.009) and a trend to a lower LDL apoB FCR and increased RT compared with non-RTV-containing PI regimens ( P=0.05). There was a positive correlation between LDL apoB FCR and limb fat/lean body mass ( P=0.004) in all subjects. Conclusions: Decreased LDL FCR, despite unchanged LDL cholesterol, was demonstrated in both treated and untreated HIV patients. It was more marked with RTV-containing regimens and was associated with reduced limb fat. The increased LDL RT may lead to an increased risk of atherogenesis thus contributing to the risk for cardiovascular disease in these patients.

Dietary fructose has been linked to an increased post-prandial triglyceride (TG) level; which is an established independent risk factor for cardiovascular disease. Although much research has focused on the effects of fructose consumption on liver-derived very-low density lipoprotein (VLDL); emerging evidence also suggests that fructose may raise post-prandial TG levels by affecting the metabolism of enterocytes of the small intestine. Enterocytes have become well recognised for their ability to transiently store lipids following a meal and to thus control post-prandial TG levels according to the rate of chylomicron (CM) lipoprotein synthesis and secretion. The influence of fructose consumption on several aspects of enterocyte lipid metabolism are discussed; including de novo lipogenesis; apolipoprotein B48 and CM-TG production; based on the findings of animal and human isotopic tracer studies. Methodological issues affecting the interpretation of fructose studies conducted to date are highlighted; including the accurate separation of CM and VLDL. Although the available evidence to date is limited; disruption of enterocyte lipid metabolism may make a meaningful contribution to the hypertriglyceridaemia often associated with fructose consumption.