Compared with SFA intake, n-6 PUFAs reduce liver fat and modestly improve metabolic status, without weight loss. A high n-6 PUFA intake does not cause any signs of inflammation or oxidative stress. Downregulation of PCSK9 could be a novel mechanism behind the cholesterol-lowering effects of PUFAs. This trial was registered at clinicaltrials.gov as NCT01038102.

Excess ectopic fat storage is linked to type 2 diabetes. The importance of dietary fat composition for ectopic fat storage in humans is unknown. We investigated liver fat accumulation and body composition during overfeeding saturated fatty acids (SFAs) or polyunsaturated fatty acids (PUFAs). LIPOGAIN was a double-blind, parallel-group, randomized trial. Thirty-nine young and normal-weight individuals were overfed muffins high in SFAs (palm oil) or n-6 PUFAs (sunflower oil) for 7 weeks. Liver fat, visceral adipose tissue (VAT), abdominal subcutaneous adipose tissue (SAT), total adipose tissue, pancreatic fat, and lean tissue were assessed by magnetic resonance imaging. Transcriptomics were performed in SAT. Both groups gained similar weight. SFAs, however, markedly increased liver fat compared with PUFAs and caused a twofold larger increase in VAT than PUFAs. Conversely, PUFAs caused a nearly threefold larger increase in lean tissue than SFAs. Increase in liver fat directly correlated with changes in plasma SFAs and inversely with PUFAs. Genes involved in regulating energy dissipation, insulin resistance, body composition, and fat-cell differentiation in SAT were differentially regulated between diets, and associated with increased PUFAs in SAT. In conclusion, overeating SFAs promotes hepatic and visceral fat storage, whereas excess energy from PUFAs may instead promote lean tissue in healthy humans.

BackgroundDifferent healthy food patterns may modify cardiometabolic risk. We investigated the effects of an isocaloric healthy Nordic diet on insulin sensitivity, lipid profile, blood pressure and inflammatory markers in people with metabolic syndrome.MethodsWe conducted a randomized dietary study lasting for 18–24 weeks in individuals with features of metabolic syndrome (mean age 55 years, BMI 31.6 kg m−2, 67% women). Altogether 309 individuals were screened, 200 started the intervention after 4-week run-in period, and 96 (proportion of dropouts 7.9%) and 70 individuals (dropouts 27%) completed the study, in the Healthy diet and Control diet groups, respectively. Healthy diet included whole-grain products, berries, fruits and vegetables, rapeseed oil, three fish meals per week and low-fat dairy products. An average Nordic diet served as a Control diet. Compliance was monitored by repeated 4-day food diaries and fatty acid composition of serum phospholipids.ResultsBody weight remained stable, and no significant changes were observed in insulin sensitivity or blood pressure. Significant changes between the groups were found in non-HDL cholesterol (−0.18, mmol L−1 95% CI −0.35; −0.01, P = 0.04), LDL to HDL cholesterol (−0.15, −0.28; −0.00, P = 0.046) and apolipoprotein B to apolipoprotein A1 ratios (−0.04, −0.07; −0.00, P = 0.025) favouring the Healthy diet. IL-1 Ra increased during the Control diet (difference −84, −133; −37 ng L−1, P = 0.00053). Intakes of saturated fats (E%, beta estimate 4.28, 0.02; 8.53, P = 0.049) and magnesium (mg, −0.23, −0.41; −0.05, P = 0.012) were associated with IL-1 Ra.ConclusionsHealthy Nordic diet improved lipid profile and had a beneficial effect on low-grade inflammation.

ContextSaturated fatty acid (SFA) vs polyunsaturated fatty acid (PUFA) may promote nonalcoholic fatty liver disease by yet unclear mechanisms.ObjectiveTo investigate if overeating SFA- and PUFA-enriched diets lead to differential liver fat accumulation in overweight and obese humans.DesignDouble-blind randomized trial (LIPOGAIN-2). Overfeeding SFA vs PUFA for 8 weeks, followed by 4 weeks of caloric restriction.SettingGeneral community.ParticipantsMen and women who are overweight or have obesity (n = 61).InterventionMuffins, high in either palm (SFA) or sunflower oil (PUFA), were added to the habitual diet.Main Outcome MeasuresLean tissue mass (not reported here). Secondary and exploratory outcomes included liver and ectopic fat depots.ResultsBy 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.ConclusionsSFA 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.