Importance Increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance. Fructose ingestion produces smaller increases in circulating satiety hormones compared with glucose ingestion, and central administration of fructose provokes feeding in rodents, whereas centrally administered glucose promotes satiety. Objective To study neurophysiological factors that might underlie associations between fructose consumption and weight gain. Design, Setting, and Participants Twenty healthy adult volunteers underwent 2 magnetic resonance imaging sessions at Yale University in conjunction with fructose or glucose drink ingestion in a blinded, random-order, crossover design. Main Outcome Measures Relative changes in hypothalamic regional cerebral blood flow (CBF) after glucose or fructose ingestion. Secondary outcomes included whole-brain analyses to explore regional CBF changes, functional connectivity analysis to investigate correlations between the hypothalamus and other brain region responses, and hormone responses to fructose and glucose ingestion. Results There was a significantly greater reduction in hypothalamic CBF after glucose vs fructose ingestion (–5.45 vs 2.84 mL/g per minute, respectively; mean difference, 8.3 mL/g per minute [95% CI of mean difference, 1.87-14.70]; P=.01). Glucose ingestion (compared with baseline) increased functional connectivity between the hypothalamus and the thalamus and striatum. Fructose increased connectivity between the hypothalamus and thalamus but not the striatum. Regional CBF within the hypothalamus, thalamus, insula, anterior cingulate, and striatum (appetite and reward regions) was reduced after glucose ingestion compared with baseline (P<.05 significance threshold, family-wise error [FWE] whole-brain corrected). In contrast, fructose reduced regional CBF in the thalamus, hippocampus, posterior cingulate cortex, fusiform, and visual cortex (P<.05 significance threshold, FWE whole-brain corrected). In whole-brain voxel-level analyses, there were no significant differences between direct comparisons of fructose vs glucose sessions following correction for multiple comparisons. Fructose vs glucose ingestion resulted in lower peak levels of serum glucose (mean difference, 41.0 mg/dL [95% CI, 27.7-54.5]; P<.001), insulin (mean difference, 49.6 μU/mL [95% CI, 38.2-61.1]; P<.001), and glucagon-like polypep-tide 1 (mean difference, 2.1 pmol/L [95% CI, 0.9-3.2]; P=.01). Conclusion and Relevance In a series of exploratory analyses, consumption of fructose compared with glucose resulted in a distinct pattern of regional CBF and a smaller increase in systemic glucose, insulin, and glucagon-like polypeptide 1 levels.

Obesity is a worldwide epidemic resulting in part from the ubiquity of high-calorie foods and food images. Whether obese and nonobese individuals regulate their desire to consume high-calorie foods differently is not clear. We set out to investigate the hypothesis that circulating levels of glucose, the primary fuel source for the brain, influence brain regions that regulate the motivation to consume high-calorie foods. Using functional MRI (fMRI) combined with a stepped hyperinsulinemic euglycemic-hypoglycemic clamp and behavioral measures of interest in food, we have shown here that mild hypoglycemia preferentially activates limbic-striatal brain regions in response to food cues to produce a greater desire for high-calorie foods. In contrast, euglycemia preferentially activated the medial prefrontal cortex and resulted in less interest in food stimuli. Indeed, higher circulating glucose levels predicted greater medial prefrontal cortex activation, and this response was absent in obese subjects. These findings demonstrate that circulating glucose modulates neural stimulatory and inhibitory control over food motivation and suggest that this glucose-linked restraining influence is lost in obesity. Strategies that temper postprandial reductions in glucose levels might reduce the risk of overeating, particularly in environments inundated with visual cues of high-calorie foods. IntroductionGlucose is an important regulatory signal and the primary fuel source for the brain (1). Specialized glucose-sensing neurons located in the hypothalamus, hindbrain, and forebrain are important in the control of glucose homeostasis and feeding behavior (1, 2). Transient declines in blood glucose increase hunger and therefore mobilize an individual toward food consumption (3, 4), particularly high-sugar (5) and high-fat foods (6). Further, hypoglycemia provokes a physiological stress response to mobilize the individual toward seeking food and restoring glucose levels (6). While the role of hindbrain and hypothalamic neuronal responses in hypoglycemia and maintaining energy homeostasis is well characterized (1, 2, 7), the specific neural mechanisms mediating the motivational drive for food under mild hypoglycemic conditions are not known. We hypothesized that a reduction in circulating glucose, to levels commonly observed several hours after glucose ingestion in healthy individuals (8), would activate brain reward and motivation pathways, including the striatum and insula, while concomitantly increasing desire for high-calorie foods.To test this hypothesis, we performed functional MRI (fMRI) studies in 14 healthy (9 nonobese and 5 obese) subjects 2 hours after ingestion of a standardized lunch. Subjects viewed high-calorie food, low-calorie food, and non-food images while lying in the scanner during a stepped hyperinsulinemic euglycemic-hypo-

In rodent models, obesity and hyperglycemia alter cerebral glucose metabolism and glucose transport into the brain, resulting in disordered cerebral function as well as inappropriate responses to homeostatic and hedonic inputs. Whether similar findings are seen in the human brain remains unclear. In this study, 25 participants (9 healthy participants; 10 obese nondiabetic participants; and 6 poorly controlled, insulin- and metformin-treated type 2 diabetes mellitus (T2DM) participants) underwent 1H magnetic resonance spectroscopy scanning in the occipital lobe to measure the change in intracerebral glucose levels during a 2-hour hyperglycemic clamp (glucose ~220 mg/dl). The change in intracerebral glucose was significantly different across groups after controlling for age and sex, despite similar plasma glucose levels at baseline and during hyperglycemia. Compared with lean participants, brain glucose increments were lower in participants with obesity and T2DM. Furthermore, the change in brain glucose correlated inversely with plasma free fatty acid (FFA) levels during hyperglycemia. These data suggest that obesity and poorly controlled T2DM progressively diminish brain glucose responses to hyperglycemia, which has important implications for understanding not only the altered feeding behavior, but also the adverse neurocognitive consequences associated with obesity and T2DM.

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Background and Aims Peroxisome proliferator‐activated receptor (PPAR)‐γ agonists decrease hepatic/visceral fat (VF) and improve necroinflammation despite subcutaneous (SC) fat weight‐gain. Understanding the impact of changes in VF, VF‐to‐SC fat distribution (VF/SC) and adiponectin (ADPN) levels in relation to histological improvement after weight‐loss or pioglitazone is relevant as novel PPAR‐γ agonists are being developed for treating non‐alcoholic steatohepatitis (NASH). Methods Fifty‐five patients with NASH received a −500 kcal/d hypocaloric diet and were randomized (double‐blind) to pioglitazone (45 mg/d) or placebo for 6‐months. Before and after treatment patients underwent a liver biopsy and measurement of hepatic/peripheral glucose fluxes, hepatic/adipose tissue‐IR and, in 35 patients, hepatic and VF/SC‐fat was measured by magnetic resonance spectroscopy/imaging. Data were examined by multivariable statistical analyses combined with machine‐learning techniques (partial least square discriminant analysis [PLS‐DA]). Results Both pioglitazone (despite weight‐gain) and placebo (if weight‐loss) reduced steatosis but only pioglitazone ameliorated necroinflammation. Using machine‐learning PLS‐DA showed that the treatment differences induced by a PPAR‐γ agonist vs placebo on metabolic variables and liver histology could be best explained by the increase in ADPN and a decrease in VF/SC, and to a lesser degree, improvement in oral glucose tolerance test‐glucose concentrations and ALT. Decrease in steatosis and disease activity score (ballooning plus lobular inflammation) kept a close relationship with an increase in ADPN (r = −.71 and r = −.44, P < .007, respectively) and reduction in VF/SC fat (r = .41 and r = .37, P < .03 respectively). Conclusions Reduction in VF and improved VF/SC‐distribution, combined with an increase in ADPN, mediate the histological benefits of PPAR‐γ action, highlighting the central role of fat metabolism and its distribution on steatohepatitis disease activity in patients with NASH.