The beneficial effects of Mediterranean diet over low-fat diet may be mediated by decreasing hepatic fat content.

BACKGROUND & AIM: It is unclear if a reduction in hepatic fat content (HFC) is a major mediator of the cardiometabolic benefit of lifestyle intervention, and whether it has prognostic significance beyond the loss of visceral adipose tissue (VAT). In the present sub-study, we hypothesized that HFC loss in response to dietary interventions induces specific beneficial effects independently of VAT changes. METHODS: In an 18-month weight-loss trial, 278 participants with abdominal obesity/dyslipidemia were randomized to low-fat (LF) or Mediterranean/low-carbohydrate (MED/LC + 28 g walnuts/day) diets with/without moderate physical activity. HFC and abdominal fat-depots were measured using magnetic resonance imaging at baseline, after 6 (sub-study, n = 158) and 18 months. RESULTS: Of 278 participants (mean HFC 10.2% [range: 0.01%-50.4%]), the retention rate was 86.3%. The %HFC substantially decreased after 6 months (-6.6% absolute units [-41% relatively]) and 18 months (-4.0% absolute units [-29% relatively]; p <0.001 vs. baseline). Reductions of HFC were associated with decreases in VAT beyond weight loss. After controlling for VAT loss, decreased %HFC remained independently associated with reductions in serum gamma glutamyltransferase and alanine aminotransferase, circulating chemerin, and glycated hemoglobin (p <0.05). While the reduction in HFC was similar between physical activity groups, MED/LC induced a greater %HFC decrease (p = 0.036) and greater improvements in cardiometabolic risk parameters (p <0.05) than the LF diet, even after controlling for VAT changes. Yet, the greater improvements in cardiometabolic risk parameters induced by MED/LC were all markedly attenuated when controlling for HFC changes. CONCLUSIONS: %HFC is substantially reduced by diet-induced moderate weight loss and is more effectively reduced by the MED/LC diet than the LF diet, independently of VAT changes. The beneficial effects of the MED/LC diet on specific cardiometabolic parameters appear to be mediated more by decreases in %HFC than VAT loss. LAY SUMMARY: High hepatic fat content is associated with metabolic syndrome, type 2 diabetes mellitus, and coronary heart disease. In the CENTRAL 18-month intervention trial, a Mediterranean/low-carbohydrate diet induced a greater decrease in hepatic fat content than a low-fat diet, conferring beneficial health effects that were beyond the favorable effects of visceral fat loss. ClinicalTrials.gov Identifier: NCT01530724.

Intrahepatic fat, abdominal adipose tissues, and metabolic state: magnetic resonance imaging study.

BACKGROUND: Intrahepatic fat (IHF) is best known to associate with waist circumference (WC) and visceral adipose tissue (VAT), but its relation to abdominal subcutaneous adipose tissue is controversial. While IHF ≥ 5% dichotomously defines fatty liver, %IHF is rarely considered as a continuous variable that includes the normal range. In this study, we aimed to evaluate %IHF association with abdominal fat subdepots, pancreatic, and renal-sinus fats. METHODS: We evaluated %IHF, abdominal fat subdepots, %pancreatic, and renal-sinus fats, among individuals with moderate abdominal obesity, using 3-Tesla magnetic resonance imaging. RESULTS: Among 275 participants, %IHF widely ranged (0.01%-50.4%) and was lower in women (1.6%) than men (7.3%; P < .001). In an age, sex, and WC-adjusted models, VAT area (P < .006) was directly associated with %IHF, while superficial-subcutaneous adipose tissue proportion was inversely associated with %IHF (P < .006). In these models, renal-sinus fat was positively associated with %IHF (P = .005). In an age, sex, WC, and VAT-adjusted models, elevated liver enzymes, glycemic, lipid, and inflammatory biomarkers were associated with increased %IHF (P < .003 for all). In these models, the associations remained robust even within the normal range strata of IHF < 5% for triglycerides and chemerin (P ≤ .004 for all). For the diagnosis of fatty liver, the joint area under the curve of WC, alanine-aminotransferase, triglycerides/high-density lipoprotein cholesterol, and homeostasis model assessment of insulin resistance was 0.84(95% CI, 0.79-0.89). CONCLUSIONS: Intrahepatic fat is differentially associated with abdominal fat subdepots. Intrahepatic-fat as a continuous variable could be predicted by specific traditional parameters, even within the current normal range, and partially independent of VAT.

The effect of long-term weight-loss intervention strategies on the dynamics of pancreatic-fat and morphology: An MRI RCT study.

BACKGROUND & AIMS: The ability to mobilize pancreatic-fat and the meaning of decreased fat in the pancreas remain controversial. We followed the dynamics of pancreatic-fat and its morphology during various long weight-loss induced lifestyle-interventions. METHODS: In isolated workplace with monitored/provided lunch, we randomly assigned healthy persons with abdominal obesity or dyslipidemia for one of two 18-month equal-caloric diets: low-fat (LF) or Mediterranean/low-carbohydrate (Med/LC, with provided 1oz walnuts/day), with or without added moderate exercise (supervised gym membership). We used magnetic-resonance-imaging to quantify pancreatic-fat and morphology. RESULTS: At baseline, 277 eligible participants (mean age = 48 years; 88% men; pancreatic-fat = 17.4 ± 5.1%) had higher pancreatic-fat in men (17.7 ± 4.9% vs 14.9 ± 5.5% in women; p = 0.004). Following 18-month intervention (adherence = 86.3%) and moderate weight-loss (mean = -3.0 ± 5.5 kg), pancreatic-fat decreased moderately but significantly (-0.26 ± 2.18% units; p = 0.049). Med/LC diet induced a greater decrease in pancreatic-fat compared to LF (p = 0.043), and the combination of Med/LC diet + exercise exhibited the highest reduction (-0.69% units) as compared to LF diet without exercise (+0.12%units; p = 0.027 between groups). In multivariate regression models, after further adjusted for visceral adipose-tissue (ΔVAT), pancreatic-fat loss associated with both decreases in pancreatic-morphology ratio (perimeter divided by area; beta = 0.361; p < 0.001) and superficial-subcutaneous adipose-tissue loss (beta = 0.242; p = 0.001), but not with changes in intrahepatic-fat (beta = -0.034; p = 0.638). Pancreatic-fat loss associated with increased intake of polyunsaturated-fat (beta = -0.137; p = 0.032), as with improved high-density lipoprotein-cholesterol (HDL; beta = -0.156; p = 0.023) and triglycerides/HDL ratio (beta = 0.162; p = 0.015), independently of ΔVAT, but not with glycemic-control parameters (e.g. HbA1c, HOMA-IR and HOMA-beta; p > 0.2 for all). CONCLUSIONS: Pancreatic-fat loss is mainly associated with improved lipid, rather than glycemic profiles. Med/LC diet, mostly with exercise, may benefit pancreatic-fat loss. Pancreatic-morphology could serve as a biomarker of pancreatic-fat state. (ClinicalTrials.gov identifier: NCT01530724).

Intramyocellular triacylglycerol accumulation across weight loss strategies; Sub-study of the CENTRAL trial.

BACKGROUND: Intramyocellular triacylglycerol (IMTG) is utilized as metabolic fuel during exercise and is linked to insulin resistance, but the long-term effect of weight loss strategies on IMTG among participants with abdominal fat, remain unclear. METHODS: In an 18-month trial, sedentary participants with abdominal fat/dyslipidemia were randomized to either a low-fat (LF) or Mediterranean/low-carbohydrate (MED/LC) diet (including 28g·day-1 of walnuts). After 6-months, the participants were re-randomized to moderate intense physical activity (PA+) or non-physical activity (PA-). Magnetic resonance imaging (MRI) was used to quantify changes of IMTG, abdominal sub-depots, hepatic and intermuscular fats. RESULTS: Across the 277 participants [86% men, age = 48 years, body-mass-index (BMI) = 31kg/m2, visceral fat = 33%] 86% completed the 18-m trial. At baseline, women had higher IMTG than men (3.4% vs. 2.3%, p<0.001) and increased IMTG was associated with aging and higher BMI, visceral and intermuscular fats, HbA1c%, HDL-c and leptin(p<0.05), but not with intra-hepatic fat. After 18 month of intervention and a -3 kg mean weight loss, participants significantly increased IMTG by 25%, with a distinct effect in the MED/LCPA+ group as compared to the other intervention groups (57% vs. 9.5-18.5%, p<0.05). Changes in IMTG were associated with visceral and intermuscular fat, metabolic syndrome, insulin and leptin (p<0.05 for all), however, these associations did not remain after adjustment for visceral fat changes. CONCLUSIONS: Lifestyle strategies differentially affect IMTG accumulation; combination of exercise with decreased carbohydrate/increased unsaturated fat proportion intake greatly increase IMTG. Our findings suggest that increased IMTG during diet-induced moderate weight loss may not be directly related to cardiometabolic risk. TRIAL REGISTRATION: ClinicalTrials.gov NCT01530724.