Weight loss of at least 5% (preferably at least 10%) of initial body weight is recommended for people with MAFLD to decrease liver fat and improve cardiometabolic risk factors, with greater amounts of weight loss typically producing greater improvements.^[3] As such, it’s unsurprising that decreases in liver fat were greater in the HPLG group, considering they lost more body weight.

The greater weight loss in the HPLG group may be a product of differences in protein intake between groups. Protein intake increased from 19% of energy intake at baseline to 34% of energy intake at the end of the study in the HPLG group, while the control group reportedly consumed 22% of energy intake from protein at the end of the study.

Evidence suggests that protein is more satiating than carbohydrate or fat.^[4] Protein consumption has been shown to suppress appetite, decrease ghrelin (a hunger-promoting gastrointestinal hormone), and increase satiety-inducing gastrointestinal hormones (e.g., GLP-1, cholecystokinin) in the short term.^[5] Additionally, ad libitum higher-protein diets have been shown to induce unintentional weight loss,^[6]^[7] and lower-protein diets have been shown to result in increased energy intake.^[8]^[9] In the long term, many studies have reported greater weight loss with higher-protein diets, compared to lower-protein diets.^[4]

Virtually any diet that produces a sustained decrease in energy intake is effective for reducing liver fat,^[10] and as noted above, higher-protein diets may be a particularly effective option for achieving this feat. Nonetheless, a handful of studies have investigated whether higher-protein diets are advantageous for reducing liver fat independent of their effect on body weight.

A 6-week trial published in 2017 found that a high-protein diet (30% of energy from protein, 40% carbohydrate, and 30% fat) rich in either animal or plant protein reduced liver fat by 36–48% from baseline.^[11] Additionally, there were minimal changes in body weight, which were not correlated with reductions in liver fat. However, a major limitation of this trial was the absence of a control group.

In a 6-week crossover trial published in 2019, participants received five meals per day providing equivalent energy content but different amounts of macronutrients: either 30% of energy from protein, 30% carbohydrate, and 40% fat (high-protein diet) or 17% of energy from protein, 50% carbohydrate, and 33% fat (control diet).^[12] The high-protein diet reduced liver fat compared to the control diet (−2.4% vs. +0.2%), and there were nonsignificant changes in body weight in both conditions.

In a third trial published in 2020, participants were randomized to consume a hypocaloric diet (1500–1600 kcal/day) providing either 10% of energy from protein (low-protein diet) or 30% of energy from protein (high-protein diet) for 3 weeks.^[13] There was also a separate cohort that consumed a hypocaloric diet (1,200-1,500 kcal/day) containing 20–22% of energy from protein (moderate-protein diet). Despite similar weight loss between groups, liver fat decreased from baseline by 42.6% and 36.7% in the high-protein and moderate-protein groups, respectively, whereas liver fat did not change in the low-protein group.

The precise mechanisms by which protein may positively affect liver fat are unclear, but evidence suggests that a high-protein diet can modulate metabolic pathways involved in hepatic fat uptake and storage, as well as de novo lipogenesis (i.e., the creation of fat from nonfat sources).^[13]^[11]

Based on the available evidence, a high-protein diet may be effective for people with MAFLD in two different ways. First, it may suppress appetite, making it easier to adhere to a hypocaloric diet, which is required to reduce liver fat and improve cardiometabolic risk factors. Second, even in the context of equivalent weight loss, a hypocaloric high-protein diet may be more effective than other hypocaloric diets for reducing liver fat, but further research is needed to confirm this hypothesis.

Low-Glycemic-Index Diet

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