High-protein Diet More Effectively Reduces Hepatic Fat Than Low-protein Diet Despite Lower Autophagy and FGF21 Levels

Chenchen Xu; Mariya Markova; Nicole Seebeck; Anne Loft; Silke Hornemann; Thomas Gantert; Stefan Kabisch; Kathleen Herz; Jennifer Loske; Mario Ost; Verena Coleman; Frederick Klauschen; Anke Rosenthal; Volker Lange; Jürgen Machann; Susanne Klaus; Tilman Grune; Stephan Herzig; Olga Pivovarova-Ramich; Andreas F. H. Pfeiffer

Disclosures

Liver International. 2020;40(12):2982-2997. 

In This Article

Abstract and Introduction

Abstract

Background and Aims: Non-alcoholic fatty liver disease (NAFLD) is becoming increasingly prevalent and nutrition intervention remains the most important therapeutic approach for NAFLD. Our aim was to investigate whether low- (LP) or high-protein (HP) diets are more effective in reducing liver fat and reversing NAFLD and which mechanisms are involved.

Methods: 19 participants with morbid obesity undergoing bariatric surgery were randomized into two hypocaloric (1500–1600 kcal/day) diet groups, a low protein (10E% protein) and a high protein (30E% protein), for three weeks prior to surgery. Intrahepatic lipid levels (IHL) and serum fibroblast growth factor 21 (FGF21) were measured before and after the dietary intervention. Autophagy flux, histology, mitochondrial activity and gene expression analyses were performed in liver samples collected during surgery.

Results: IHL levels decreased by 42.6% in the HP group, but were not significantly changed in the LP group despite similar weight loss. Hepatic autophagy flux and serum FGF21 increased by 66.7% and 42.2%, respectively, after 3 weeks in the LP group only. Expression levels of fat uptake and lipid biosynthesis genes were lower in the HP group compared with those in the LP group. RNA-seq analysis revealed lower activity of inflammatory pathways upon HP diet. Hepatic mitochondrial activity and expression of β-oxidation genes did not increase in the HP group.

Conclusions: HP diet more effectively reduces hepatic fat than LP diet despite of lower autophagy and FGF21. Our data suggest that liver fat reduction upon HP diets result primarily from suppression of fat uptake and lipid biosynthesis.

Introduction

Non-alcoholic fatty liver disease (NAFLD), which is defined by excessive triglyceride accumulation in more than 5% of the hepatocytes, is becoming increasingly prevalent and causes serious global health problem as it affects 20%-30% of Western populations.[1] The chronic and progressive stage of NAFLD, non-alcoholic steatohepatitis (NASH), dramatically increases the risks of irreversible fibrosis, cirrhosis and even hepatocellular carcinoma (HCC).[2] Nowadays, caloric restriction is a widely accepted treatment for NAFLD. However, it has not been fully resolved which macronutrient composition is most effective in reducing liver fat content. For instance, high-protein (HP) diets have been proven to increase energy expenditure, decrease blood glucose levels, promote fat oxidation and consequently support weight loss, and reduce liver fat in mouse and human studies.[3–6] Low-protein (LP) diets, on the other hand, were also shown to increase energy expenditure and improve glucose homeostasis, despite an elevated food intake, in several mouse studies.[7–10]

Increased fibroblast growth factor 21 (FGF21) expression and secretion,[7] and increased hepatic autophagy[11,12] may contribute to ameliorate metabolic responses to LP diets. At present, there are contradictory results regarding autophagy and lipid degradation. Singh et al[13] found that 'lipophagy' represents an essential pathway for the degradation of lipid droplets, while Shibata et al[14] reported that autophagy was involved in the formation and growth of lipid droplets resulting in potentially opposite effects. In addition, the elevation of endogenous FGF21 secretion has also been shown to prevent diet-induced obesity and insulin resistance in skeletal muscle-specific autophagy-deficient mice[15] and has been proposed to reflect a protective response in order to improve metabolic parameters in metabolic disorders.[16] On the other hand, HP diets might suppress liver lipogenesis at the molecular level[17–19] to reduce liver fat. Furthermore, mitochondrial dysfunction may contribute to developing NAFLD through the formation of ROS[20] and the depletion of ATP levels.[21]

In this clinical study, we aimed to clarify whether LP or HP diets exert greater effects on liver fat reduction and to investigate their molecular mechanisms during dietary intervention. For this, we performed a 3-week dietary intervention in 19 participants with morbid obesity and an indication of NAFLD prior to bariatric surgery and collected blood and liver tissue samples during surgery. We hypothesized that LP and HP diets might induce liver fat reduction via different mechanisms. We suggested that LP diets in contrast with HP intakes would induce autophagy, FGF21, and thus reduce liver fat content, and that HP diets might trigger increased mitochondrial activity and fatty acid β-oxidation, or decrease liver lipogenesis.

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