Myths and facts about the role of diet in metabolic dysfunction-associated steatotic liver disease

Abstract

Metabolic dysfunction-associated steatotic liver disease (MASLD) has become a leading cause of liver-related morbidity worldwide. Despite broad consensus on the importance of diet in managing the disease, numerous myths and misconceptions persist among patients, healthcare professionals, and the general public. This article aims to critically review the main myths and facts surrounding the role of diet in MASLD, in light of the most current scientific evidence.

Key Words: Metabolic dysfunction-associated steatotic liver disease; Non-alcoholic fatty liver disease; Diet; Nutrition; Fatty liver; Metabolic disease; Lifestyle; Myths

Core Tip: This review article summarizes the main misconceptions about diet and metabolic dysfunction-associated steatotic liver disease and presents practical, evidence-based recommendations that help patients and professionals make science-based, informed decisions.

INTRODUCTION

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), is characterized by the accumulation of fat in the liver individuals without significant alcohol consumption, it is commonly associated with metabolic disorders such as obesity, type 2 diabetes, and dyslipidemia[1]. The substantial global increase in cases of this chronic liver disease has spurred research efforts to develop pharmacological treatments with regulatory approval for this clinical condition[2]. Despite advancements in drug development, dietary interventions remain the cornerstone of management, though confusion persists about what is truly effective and constitutes myth[3]. This article aims to distinguish fact from fiction based on current scientific evidence and to serve as an educational resource for the general public (Table 1).

Table 1 Summary of myths and facts.

Myth	Main message
All carbohydrates are harmful	The type of carbohydrate matters. Complex carbohydrates rich in fiber are protective, while excessive consumption of simple sugars, especially fructose, is associated with increased hepatic lipogenesis
Fats should be eliminated from the diet	The quality of fat is more important than quantity. Monounsaturated and polyunsaturated fats have anti-inflammatory and hepatoprotective effects, while trans fats and saturated fats should be minimized
Only the number of calories matters, not the quality of food	Isocaloric diets with different nutritional compositions have distinct effects on liver health. Diet quality impacts steatosis regardless of caloric balance
Any weight loss already improves MASLD	Although modest weight loss (3%-5%) can reduce hepatic steatosis, a reduction of ≥ 7%-10% is necessary to achieve regression of inflammation and fibrosis
People with normal weight don't need to worry about their diet	MASLD can also affect individuals with normal BMI ("lean MASLD"), representing up to 20% of cases and equally susceptible to disease progression
Intermittent fasting is contraindicated	Strategies such as intermittent fasting can promote weight loss, improve insulin sensitivity, and reduce liver fat when properly guided and monitored
Supplements and "superfoods" can cure MASLD	There is no dietary supplement or isolated food with robust evidence of efficacy in reversing MASLD; none can replace a comprehensive dietary and behavioral approach
Herbal teas and supplements are always safe and help "cleanse" the liver	Most herbal substances lack scientific evidence of efficacy and may cause liver toxicity. Many cases of acute hepatitis and liver failure are associated with "natural" supplements
Coffee is harmful for people with fatty liver	Black coffee has hepatoprotective effects and may slow disease progression. Drinking 2-3 cups per day is potentially beneficial for most patients with MASLD
Iron-rich foods should be avoided when ferritin is elevated in MASLD	Elevated ferritin levels in MASLD patients usually reflect inflammation and insulin resistance rather than true iron overload. Dietary iron restriction is rarely indicated
Red meat can be consumed freely in MASLD	Excessive consumption of red meat, especially when processed or prepared at high temperatures, has been associated with worsening hepatic steatosis and inflammation
Gluten and lactose must be eliminated from the diet in MASLD	The exclusion of gluten and lactose is not routinely recommended unless the patient has a confirmed diagnosis of celiac disease, lactose intolerance, or non-celiac gluten sensitivity
There is a "safe" dose of alcoholic beverage	Even small amounts of alcohol can have a harmful effect on the liver in patients diagnosed with hepatic steatosis. Total abstinence is recommended for individuals with hepatic steatosis

MASLD: Metabolic dysfunction-associated steatotic liver disease; BMI: Body mass index.

MYTH 1

All carbohydrates are harmful: False. The type of carbohydrate is important. Complex carbohydrates, that are rich in fiber, such as whole grains, fruits, and vegetables - are considered protective. On the other hand, excessive consumption of simple sugars, especially fructose found in sweetened beverages and various processed foods (such as high-fructose corn syrup), is strongly associated with increased hepatic lipogenesis[4,5].

MYTH 2

Fats should be eliminated from the diet: False. The quality of fat consumed is more important than the quantity. Monounsaturated and polyunsaturated fats, such as those found in olive oil, avocados, and fatty fish, have anti-inflammatory and hepatoprotective benefits. Conversely, while trans fats should be avoided, the intake of saturated fats should be limited[6]. Some intake of saturated fat (up to 7% of total dietary lipid calories) is necessary for cell membrane structure and lipid metabolism[7].

In contrast, in 2024, Xu et al[8] found that monounsaturated fatty acids (MUFAs) may be more lipogenic than saturated fatty acids (SFAs). The study, which used Mendelian randomization, suggests that MUFAs do not play the same central role as SFAs in direct, lipid-mediated liver damage. The researches propose an epigenetic mechanism: MUFAs lead to cause insufficient activation of PPAR-γ by oleic acid, a common MUFA, simultaneously promoting a more effective increase in SREBP-1 expression than SFAs. This mechanism allows hepatocytes to accumulate large amounts of fat, resulting in progressive steatosis without the cellular apoptosis that would otherwise limit the process. This finding raises questions about the established benefits of the mediterranean diet in the nutritional treatment of MASLD[9].

MYTH 3

The belief that only the number of calories matters, not the quality of food: False. Research shows that isocaloric diets with different nutritional compositions have distinct effects on liver health[10]. For instance, diets high in saturated fat and fructose are associated with increased steatosis, regardless of caloric intake. Conversely, the Mediterranean diet, which is rich in fiber, unsaturated fats, and antioxidant compounds, has been shown to reduce liver fat content, even independent of weight loss[11]. For populations where this diet may be inaccessible due to cost or cultural differences, such as in Brazil, adapting the dietary approach is crucial. A viable strategy is a low-carbohydrate diet with a meal plan tailored to the individual's socioeconomic and cultural context[12].

MYTH 4

The claim that any amount of weight loss improves MASLD is only partially: Fact. While even modest weight loss (3%-5%) can reduce hepatic steatosis, a more significant reduction of at least ≥ 7%-10% is typically necessary to resolve inflammation and fibrosis[12,13]. Therefore, the therapeutic goal should be ambitious yet realistic, focusing on long-term sustainability. Furthermore, the quality of the weight loss is also crucial. The process should be gradual, aiming to maximize fat loss while minimizing the loss of muscle mass. This is best achieved by combining a suitable diet with resistance training[14,15].

MYTH 5

People with normal weight don’t need to worry about their diet: False. Although MASLD is frequently associated with obesity, it can also affect individuals with a normal body mass index - a phenomenon known as “lean MASLD”. This group represent up to 20% of all cases and are equally susceptible to disease progression[16,17]. In these patients, the disease develops through distinct and complex mechanisms. A primary factor is body fat distribution, as lean individuals with MASLD often exhibit greater visceral fat accumulation compared to subcutaneous fat. Studies show that visceral fat, even in smaller amounts, has greater inflammatory and lipolytic activity, which promotes an increased release of free fatty acids into the liver[18,19]. Furthermore, these individuals typically present metabolic alterations such as insulin resistance, diabetes mellitus and dyslipidemia. A genetic predisposition, like single nucleotide polymorphism rs738409 in the Patatin-like phospholipase domain containing 3 (PNPLA3), can also be a key factor. Each of these elements, even in isolation, significantly contribute to the progression of steatotic liver disease[20].

Another mechanism that explains the “lean MASLD” phenomenon is mitochondrial dysfunction. In these individuals, mitochondria, which are responsible for fatty acid oxidation in hepatocytes, can show structural and functional. This dysfunction reduces capacity to metabolize fatty acids, leading to lipid accumulation and lipoperoxidation. Consequently, this increases the production of reactive oxygen species and greater oxidative damage to liver cells. Mitochondrial dysfunction also amplifies inflammatory and fibrogenic processes, accelerating disease progression to more severe forms, such as cirrhosis[21]. Additionally, genetic factors, alterations in the gut microbiome, and hormonal disturbances, especially in Asian populations and in contexts of low body mass index, also play a relevant role in lean MASLD[22].

Therefore, nutritional management for this population should follow the same principles applied to overweight or obese patients. The primary focus on diet quality, a strategy that has proven to be effective in both groups.

MYTH 6

Intermittent fasting (IF) is contraindicated: False. Recent studies have shown that IF protocols, such as the 16:8 method, can promote weight loss, improve insulin sensitivity, and reduce liver fat when properly guided and monitored[23]. However, these strategies are not superior to other forms of caloric restriction and should be individualized. IF can serve as a useful too within the nutritionist-guided plan to reduce body fat, rather than being a required long-term lifestyle.

MYTH 7

Supplements and “superfoods” can cure MASLD: False. There is no dietary supplement or isolated food with robust evidence of efficacy in reversing MASLD[24]. Despite this, many individuals, including some healthcare professionals, promote the idea that various vitamins and minerals have the “power” to treat steatotic liver disease. While certain compounds such as vitamin E, omega-3 fatty acids, and brewed coffee have shown modest benefits in specific subgroups, none can replace a comprehensive dietary and behavioral approach[25,26].

MYTH 8

Herbal teas and supplements are always safe and help “cleanse” the liver: False and dangerous. The indiscriminate use of teas and herbal products is common among patients with MASLD, often driven by promises of “liver detoxification”. However, most of these substances lack scientific evidence of efficacy and, more concerningly, may cause liver toxicity[27-29].

Cases of hepatotoxicity induced by medicinal plants such as Camellia sinensis (high-doses of green tea supplements), Teucrium polium (germander), kava-kava (Piper methysticum), valerian, turmeric (Curcuma longa), have been well documented. The lack of proper regulation and variability in the composition of these products significantly increase the risk[27].

Studies show that many cases of acute hepatitis and acute liver failure requiring transplantation are associated with the use of so-called “natural” supplements or herbal products. This risk is particularly pronounced in patients with pre-existing liver conditions, such as MASLD[27-29].

Therefore, the recommendation must be unequivocal: Avoid using any herbal product or “medicinal” tea without guidance from a qualified professional. The belief that “if it’s natural, it’s safe” is a dangerous misconception that can worsen liver disease.

MYTH 9

Coffee is harmful for people with fatty liver: False. Black coffee has hepatoprotective effects and may slow the progression of MASLD. These benefits are most pronounced when consuming of filtered black coffee without added sugar, milk, or plant-based creamers.

Most studies suggest that an intake of two to three cups per day is a safe and potentially beneficial amount for the majority of patients, including those with MASLD[30-32]. Higher intakes, such as four or more cups daily, should be evaluated on a case-by-case basis, considering individual tolerance, comorbidities, and any concomitant medications.

While coffee has established hepatoprotective properties, it is crucial to acknowledge the effects of caffeine. As a central nervous system stimulant, caffeine in high doses can lead to adverse effects, including an increased heart rate, anxiety, nervousness, tremors, and sleep disturbances like insomnia. Furthermore, excessive consumption can cause irritation to the gastrointestinal tract, leading to heartburn or gastritis. Individuals with certain pre-existing conditions, such as hypertension or anxiety disorders, may be particularly sensitive to these effects, which can exacerbate their symptoms[33].

MYTH 10

Iron-rich foods should be avoided when ferritin is elevated in MASLD: False. In most cases, elevated ferritin levels in these patients reflect a state of inflammation and insulin resistance rather than true iron overload. Therefore, studies show that dietary iron restriction is rarely indicated, except in some confirmed cases of iron overload or hereditary hemochromatosis[34,35].

MYTH 11

Red meat can be consumed freely in MASLD: False. Excessive consumption of red meat, particularly when processed or prepared at high temperatures (e.g., grilled, fried, or smoked), has been associated with worsening hepatic steatosis and inflammation[36]. Furthermore, studies indicate that individuals with the I148M variant of the PNPLA3 gene-which is linked to a greater susceptibility to liver fat accumulation-exhibit a worsening liver markers with frequent red meat intake[37].

Moreover, preparation method is a significant factor. Cooking techniques that produce compounds like heterocyclic amines and polycyclic aromatic hydrocarbons, founds in heavily grilled or smoked meats, may increase oxidative stress and liver inflammation.

The general recommendation is to limit red meat consumption to a maximum of twice a week, prioritize lean cuts, and opt for cooking methods such as boiling or baking that avoid excessive charring.

Replacing red meat other protein sources, such as plant-based proteins or omega-3- rich fish, may be particularly beneficial, especially for individuals carrying the PNPLA3 risk variant.

MYTH 12

Gluten and lactose must be eliminated from the diet in MASLD: False. The exclusion of gluten and lactose is not routinely recommended in the management of MASLD unless the patient has a confirmed diagnosis of celiac disease, lactose intolerance, or non-celiac gluten sensitivity[38-40].

While gluten- and lactose-free diets have become popular, there is no robust scientific evidence to suggest that their removal provides direct benefits to liver health in individuals without these specific conditions. Moreover, such restrictive diets, when adopted without clinical indication, may lead to nutritional imbalances and an unnecessary reduction in dietary diversity.

Therefore, nutritional guidance should be individualized and focus on establishing healthy eating patterns, rather than on the generalized exclusion of entire food groups.

MYTH 13

There is a “safe” dose of alcoholic beverage: False. Even small amounts of alcohol can have harmful effects on the liver in patients already diagnosed with hepatic steatosis. Robust evidence indicates that moderate or occasional alcohol consumption may accelerate the progression of the disease to more severe stages, such as cirrhosis[41]. The broad consensus among experts is total abstinence from alcohol for individuals with hepatic steatosis, regardless of etiology, since it is difficult to establish safe intake thresholds for patients predisposed to liver injury[41].

DISCUSSION

Misunderstanding the severity of fatty liver disease and the misinterpreting of the role of diet in MASLD can compromise treatment adherence and lead to frustration. Therefore, an evidence-based, individualized, and sustainable eating plan must be the cornerstone of the dietary approach. Healthcare professionals have a crucial role in staying updated on the latest evidence to effectively dispel myths and provide practical, realistic guidance.

CONCLUSION

Diet remains the cornerstone of MASLD management. To optimize therapeutic outcomes, it is essential to distinguish myths from scientifically-backed facts. A high-quality diet-combined with gradual weight loss, healthy lifestyle behaviors, and the avoidance of potentially harmful practices such as unsupervised use of herbal supplementsis key to controlling the disease and preventing its progression.