For decades, fatty liver disease was considered a problem of people who were overweight or obese. Physicians often reassured patients with a normal body weight that they were at low risk of developing fatty liver.
Modern research has completely changed this understanding.
Across India, an increasing number of adults with a normal Body Mass Index (BMI) are being diagnosed with Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)—formerly known as Non-Alcoholic Fatty Liver Disease (NAFLD). This condition is now recognized as Lean MASLD, a distinct clinical entity that is especially common among South Asians. Recent evidence suggests that many Indians who appear lean externally may still carry excess visceral fat, insulin resistance, and a unique pattern of gut microbial imbalance that predisposes them to liver disease.
This phenomenon has led researchers to describe many affected individuals as “Metabolically Obese, Normal Weight (MONW)”—people whose BMI appears healthy but whose metabolism resembles that of someone with obesity.
A recent review published in Frontiers in Nutrition highlights that Indian patients with Lean MASLD exhibit a distinctive gut microbiome characterized by depletion of beneficial butyrate-producing bacteria such as Faecalibacterium prausnitzii, Lachnospira, and Subdoligranulum, together with enrichment of pro-inflammatory Escherichia-Shigella. These changes may impair the intestinal barrier, promote chronic inflammation, and contribute directly to fat accumulation in the liver.
In this article, we examine the science behind Lean MASLD, why it is particularly relevant for Indians, how the gut microbiome influences liver health, and practical lifestyle strategies that may help reduce risk.
What Is MASLD?
MASLD (Metabolic Dysfunction-Associated Steatotic Liver Disease) is the modern term used to describe excessive fat accumulation in the liver associated with metabolic dysfunction. The diagnosis requires evidence of liver fat together with at least one cardiometabolic risk factor, such as impaired glucose regulation, elevated triglycerides, excess body fat, or reduced HDL cholesterol. The terminology replaces NAFLD to better reflect the metabolic basis of the disease rather than focusing on alcohol consumption.
Lean MASLD: An Emerging Indian Health Challenge
Although obesity remains an important risk factor for fatty liver disease, a substantial proportion of Indian patients develop MASLD despite having a BMI below the conventional threshold for overweight. Several studies cited in the Frontiers in Nutrition review indicate:
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Lean MASLD accounts for a meaningful proportion of MASLD cases worldwide
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South Asian populations show a particularly high prevalence
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A biopsy-based Indian study found fatty liver in approximately one-third of lean liver donors
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Many patients have significant metabolic abnormalities despite appearing healthy by BMI criteria
BMI alone therefore fails to identify many at-risk Indians.
Why Are Indians Different?
Researchers have long recognized the “Asian Indian phenotype.” Compared with many Western populations, Indians tend to have:
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More visceral abdominal fat – thanks to excessive carbs intake
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Lower skeletal muscle mass – thanks to excessive carbs and low protein intake
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Higher insulin resistance – thanks to excessive and continued carbs consumption
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Greater tendency toward central obesity – thanks to excessive and continued carbs consumption
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Earlier onset of type 2 diabetes – thanks to excessive and continued carbs consumption
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Increased fatty liver risk at lower BMI – also thanks to excessive and continued carbs consumption
Consequently, a person with a BMI of 23–24 kg/m² may already have significant metabolic risk.
The Gut–Liver Axis
The liver and intestine are directly connected through the portal circulation. This communication network, known as the gut–liver axis, allows nutrients—but also bacterial products and inflammatory molecules—to travel directly from the intestine to the liver.
A healthy intestinal barrier prevents harmful bacterial toxins from entering the bloodstream. When gut microbial balance is disturbed (dysbiosis):
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intestinal permeability increases,
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bacterial endotoxins enter the circulation,
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immune activation increases,
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liver inflammation develops,
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fat accumulation accelerates.
This process is increasingly considered one of the central mechanisms driving Lean MASLD.
Unique Gut Microbial Signature of Indian Lean MASLD
One of the most important contributions of the recent Frontiers in Nutrition review is the identification of a characteristic microbial pattern in Indian Lean MASLD. Researchers consistently observed:
Reduced beneficial bacteria
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Faecalibacterium prausnitzii
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Lactobacillus
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Ruminococcus
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Lachnospira
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Subdoligranulum
Increased inflammatory bacteria
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Escherichia-Shigella
The combination of increased Escherichia-Shigella with decreased Lachnospira and Subdoligranulum demonstrated promising diagnostic performance for identifying Lean MASLD in Indian patients.
Why Does Losing Faecalibacterium prausnitzii Matter?
Among all the bacterial changes reported, depletion of Faecalibacterium prausnitzii may be particularly important. This organism:
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produces butyrates,
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strengthens the intestinal barrier,
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reduces inflammation,
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supports immune regulation,
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improves insulin sensitivity.
Experimental studies suggest that restoration of F. prausnitzii can reduce hepatic fat accumulation, improve glucose metabolism, and preserve gut barrier integrity.
Diet and the Indian Microbiome
The review proposes that several dietary patterns common in urban India may contribute to dysbiosis:
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low fibre intake,
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refined carbohydrates,
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highly processed foods,
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inadequate whole grains,
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low intake of fermented foods,
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sedentary lifestyles
These dietary patterns reduce production of beneficial short-chain fatty acids such as butyrate while favouring growth of inflammatory bacterial species.
Genetics Also Play a Role
Diet alone does not explain why some lean individuals develop MASLD while others remain healthy.
One important genetic factor is the PNPLA3 rs738409 variant, which has been associated with altered liver fat metabolism and may also influence gut microbial composition. The interaction between genetics, diet, body fat distribution, and the microbiome is believed to contribute to the distinctive Indian Lean MASLD phenotype.
Can the Gut Microbiome Become a Treatment Target?
The review highlights several promising strategies under investigation:
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increased dietary fibre,
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prebiotics,
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selected probiotic strains,
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synbiotics,
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microbiome-directed nutrition,
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faecal microbiota transplantation (currently investigational).
While these approaches are promising, routine clinical management still focuses on improving diet quality, increasing physical activity, reducing visceral fat, and controlling metabolic risk factors.
Practical Take-Home Messages
For Indian adults, maintaining liver health involves much more than keeping weight within the normal range. Practical steps include:
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Eat a fibre-rich diet with vegetables, legumes, fruits, and whole grains
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Reduce ultra-processed foods and refined carbohydrates and replace with high quality, highly bioavailable animal meats, NOT CHICKEN
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Maintain regular physical activity and preserve muscle mass – through increased animal origin protein consumption
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Screen for diabetes, dyslipidaemia, and fatty liver even if BMI is normal.
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Seek medical evaluation if there are additional metabolic risk factors or a family history of diabetes
Conclusion
Lean MASLD challenges the traditional assumption that only obesity leads to fatty liver disease. For many Indians, normal body weight does not necessarily mean normal metabolic health. Emerging evidence suggests that alterations in the gut microbiome—particularly the loss of beneficial butyrate-producing bacteria and enrichment of inflammatory microbes—may contribute to the development of fatty liver in otherwise lean individuals.
As research advances, microbiome-based diagnostics and therapies may become valuable additions to current prevention strategies. Until then, maintaining a healthy diet rich in fibre, animal proteins, engaging in regular physical activity and addressing metabolic risk factors via low carb consumption remain the most evidence-supported approaches for protecting liver health.
References (selected)
- Dey P. Gut microbial signatures associated with the Indian lean MASLD phenotype. Frontiers in Nutrition. 2025
- Frontiers in Nutrition PDF version of the review –Frontiers in Nutrition PDF version of the review
- Multi-omics analysis of gut microbial and metabolic signatures in MASLD. Frontiers in Microbiology. 2025