Objective: To assess how intrahepatic fat and insulin resistance relate to daily fructose and energy intake during short-term overfeeding in healthy subjects. Design and methods: The analysis of the data collected in several studies in which fasting hepatic glucose production (HGP), hepatic insulin sensitivity index (HISI), and intrahepatocellular lipids (IHCL) had been measured after both 6-7 days on a weight-maintenance diet (control, C; n ¼ 55) and 6-7 days of overfeeding with 1.5 (F1.5, n ¼ 7), 3 (F3, n ¼ 17), or 4 g fructose/kg/day (F4, n ¼ 10), with 3 g glucose/ kg/day (G3, n ¼ 11), or with 30% excess energy as saturated fat (fat30%, n ¼ 10). Results: F3, F4, G3, and fat30% all significantly increased IHCL, respectively by 113 6 86, 102 6 115, 59 6 92, and 90 6 74% as compared to C (all P < 0.05). F4 and G3 increased HGP by 16 6 10 and 8 6 11% (both P < 0.05), and F3 and F4 significantly decreased HISI by 20 6 22 and 19 6 14% (both P < 0.01). In contrast, there was no significant effect of fat30% on HGP or HISI. Conclusions: Short-term overfeeding with fructose or glucose decreases hepatic insulin sensitivity and increases hepatic fat content. This indicates short-term regulation of hepatic glucose metabolism by simple carbohydrates.

Dietary protein may play an important role in the prevention of metabolic dysfunctions. However, the way in which the protein source affects these dysfunctions has not been clearly established. The aim of the current systematic review was to compare the impact of plant- and animal-sourced dietary proteins on several features of metabolic syndrome in humans. The PubMed database was searched for both chronic and acute interventional studies, as well as observational studies, in healthy humans or those with metabolic dysfunctions, in which the impact of animal and plant protein intake was compared while using the following variables: cholesterolemia and triglyceridemia, blood pressure, glucose homeostasis, and body composition. Based on data extraction, we observed that soy protein consumption (with isoflavones), but not soy protein alone (without isoflavones) or other plant proteins (pea and lupine proteins, wheat gluten), leads to a 3% greater decrease in both total and LDL cholesterol compared with animal-sourced protein ingestion, especially in individuals with high fasting cholesterol concentrations. This observation was made when animal proteins were provided as a whole diet rather than given supplementally. Some observational studies reported an inverse association between plant protein intake and systolic and diastolic blood pressure, but this was not confirmed by intervention studies. Moreover, plant protein (wheat gluten, soy protein) intake as part of a mixed meal resulted in a lower postprandial insulin response than did whey. This systematic review provides some evidence that the intake of soy protein associated with isoflavones may prevent the onset of risk factors associated with cardiovascular disease, i.e., hypercholesterolemia and hypertension, in humans. However, we were not able to draw any further conclusions from the present work on the positive effects of plant proteins relating to glucose homeostasis and body composition.

Excess fructose intake causes hypertriglyceridemia and hepatic insulin resistance in sedentary humans. Since exercise improves insulin sensitivity in insulin-resistant patients, we hypothesized that it would also prevent fructose-induced hypertriglyceridemia. This study was therefore designed to evaluate the effects of exercise on circulating lipids in healthy subjects fed a weight-maintenance, high-fructose diet. Eight healthy males were studied on three occasions after 4 days of 1) a diet low in fructose and no exercise (C), 2) a diet with 30% fructose and no exercise (HFr), or 3) a diet with 30% fructose and moderate aerobic exercise (HFrEx). On all three occasions, a 9-h oral [13C]-labeled fructose loading test was performed on the fifth day to measure [13C]palmitate in triglyceride-rich lipoprotein (TRL)-triglycerides (TG). Compared with C, HFr significantly increased fasting glucose, total TG, TRL-TG concentrations, and apolipoprotein (apo)B48 concentrations as well as postfructose glucose, total TG, TRL-TG, and [13C]palmitate in TRL-TG. HFrEx completely normalized fasting and postfructose TG, TRL-TG, and [13C]palmitate concentration in TRL-TG and apoB48 concentrations. In addition, it increased lipid oxidation and plasma nonesterified fatty acid concentrations compared with HFr. These data indicate that exercise prevents the dyslipidemia induced by high fructose intake independently of energy balance.

Supplementation with essential amino acids blunts the fructose-induced increase in IHCL but not hypertriglyceridemia. This is not because of inhibition of VLDL-[(13)C]palmitate production. This trial was registered at www.clinicaltrials.gov as NCT01119989.

Coffee consumption attenuates hepatic insulin resistance but not the increase of IHCLs induced by fructose overfeeding. This effect does not appear to be mediated by differences in the caffeine or chlorogenic acid content. This trial was registered at clinicaltrials.gov as NCT00827450.