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Do saturated fats fatten up your liver?

Overfeeding can contribute to non-alcoholic fatty liver disease, but does the type of macronutrient that's consumed also play a role?

Study under review: Saturated Fat Is More Metabolically Harmful for the Human Liver Than Unsaturated Fat or Simple Sugars

Introduction

About one in four[1] people in the world have non-alcoholic fatty liver disease (NAFLD), a condition characterized by an excessive (more than 5%) infiltration of the liver with fat (steatosis) due to non-alcoholic causes. It is strongly associated[2] with metabolic problems, such as type 2 diabetes, cardiovascular disease, and nonalcoholic steatohepatitis (liver fat accumulation accompanied by inflammation). You can see some statistics about NAFLD’s prevalence illustrated in Figure 1.

Liver fat content originates[3] primarily from adipose tissue (59%), with lesser contributions from hepatic de novo lipogenesis (DNL, the creation of fatty acids within the liver; 26%), and dietary fat (15%). Still, the roles of DNL and dietary fat in NAFLD have raised questions about how macronutrient composition affects its development.

Mechanistic studies[4] have demonstrated that high-sugar diets increase both DNL and liver fat, at least under conditions of calorie excess. Similarly, at least one study[5] has compared the effects of overeating saturated fats (SFAs) or polyunsaturated fats (PUFAs), and found that liver fat increased more with SFA despite similar weight gain between groups.

Ceramides, which are major components of cell membranes derived from SFAs, are a possible explanation for SFA-induced NAFLD due to their involvement in[6] insulin resistance (IR). This, in turn, interferes with glucose metabolism and increases hepatic gluconeogenesis[7] (glucose production by the liver). On top of that, evidence suggests that some lipid-induced inflammatory signals[8], possibly stimulated by gut microbiota-driven endotoxemia[9] or a crosstalk[10] between gut microbiota and dietary lipids, are stimulating ceramide biosynthesis.

Most of the data regarding the relationship between NAFLD-associated IR and ceramides is from animal studies, and there have not been many studies comparing overfeeding of SFA, unsaturated fatty acids (monounsaturated FA (MUFA) and PUFA), and simple sugars on liver fat content. The study under review aimed to determine the influence of hypercaloric diets with different macronutrient and FA compositions on measures of NAFLD and its associated IR.

Non-alcoholic fatty liver disease (NAFLD), an abnormal buildup of fat within the liver, affects 25%of the global population. It is strongly associated with metabolic dysfunction, and diet is known to play a role in its development. The study under review assessed how hypercaloric diets of different macronutrient and fatty acid (FA) compositions would influence measures of NAFLD and its associated insulin resistance (IR).

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Other Articles in Issue #46 (August 2018)