Effects of Acute Iso- and Hypocaloric Carbohydrate Restriction on Liver Fat and Glucose and Lipid Metabolism.

Context: Liver fat is reduced within days after a low-carbohydrate diet substituted with fat to maintain isocaloric conditions.

Objective: Investigate the effect of matched carbohydrate restriction during isocaloric and hypocaloric conditions on liver fat and postprandial glucose and lipid metabolism.

Design: Cross-over randomized clinical trial.

Setting: Research unit.

Participants: 15 participants with overweight/obesity (BMI 32.5 [31-34] kg/m2, median [IQR]).

Intervention: Three dietary interventions; 1) two days of isocaloric control diet (CON), 2) two days of CON followed by two days of carbohydrate-restriction (∼60 g/day) during very-low calorie conditions (VLCD), and 3) two days of CON followed by two days of isocaloric conditions with low carbohydrate (∼60 g/day), high-fat (LCHF) diet.

Main outcome measure: Liver fat measured using 1H-magnetic resonance spectroscopy.

Results: Liver fat was -16% [-34;4] (median [IQR]) after LCHF relative to after CON (p=0.020), but did not differ between VLCD and CON. Fasting plasma concentrations of triacylglycerol, glucose, and insulin were lower after both LCHF and VLCD compared with after CON. However, postprandial plasma glucose concentrations were higher and insulinogenic index lower after both LCHF and VLCD.

Conclusion: Two days of LCHF led to lower liver fat, which was not observed after VLCD. This demonstrates the dynamic regulation of liver fat and the beneficial role of substituting carbohydrates with fat to maintain energy provision. Both LCHF and VLCD had positive effects on fasting parameters for glucose metabolism, however, both diets impaired early beta-cell response resulting in deterioration in glucose handling during the meal test.