There’s a reason why proverbs like “All that glitters is not gold”, “Don’t judge a book by its cover” have stayed relevant throughout the ages. It is to reiterate the fact that oftentimes, what meets the eyes isn’t the truth – but that truth lies deep within.

In the periphery of health, too, you can look absolutely healthy while worrisome diseases might be festering inside.

Fatty liver is one of those diseases.

One can be lean and have a visibly fit physique and still have fatty liver – also known as – non‑alcoholic fatty liver disease (NAFLD). In fact, what’s often overlooked is the growing recognition of lean NAFLD – a condition where apparently healthy individuals develop fat accumulation in the liver.

Let’s unpack.

What is NAFLD – and what about "lean" cases?NAFLD, now often referred to as metabolic dysfunction–associated steatotic liver disease (MASLD), is defined by excess fat in liver tissue without alcohol as the cause.

Initially, it was linked closely to obesity and metabolic syndrome – conditions with high BMI, insulin resistance, and dyslipidemia. Yet over 10–20% of individuals with NAFLD are  – with normal BMI (<25 kg/m² for Caucasians, <23 kg/m² for Asians).

This “thin outside, fat inside” phenotype is increasingly recognized in clinical studies: lean-NAFLD prevalence is reported at 5–26% worldwide, with even higher rates (~25%) in some Asian regions.

Through thick and thin: Why can lean people get NAFLD?

Lean or athletic people can and do develop NAFLD.

Here’s why.

Visceral fat and insulin resistance: Thin individuals may still carry a high proportion of – deep fat around internal organs, which is more harmful than subcutaneous fat. Even with normal glucose and lipid levels, they can exhibit  – a core driver of fat build‑up in the liver.

Sarcopenia and fat repartitioning: According to , many lean NAFLD patients have lower muscle mass (sarcopenia) alongside more visceral fat. This imbalance disrupts metabolism and encourages liver steatosis.

Genetics and environment: Variants in genes like PNPLA3 and TM6SF2 increase NAFLD risk irrespective of weight. Diets high in fructose, cholesterol, low activity levels, pollutant exposure, and microbiome shifts also contribute.

What symptoms to watch out for?

Unfortunately, many lean NAFLD cases are asymptomatic and discovered incidentally through imaging or elevated liver enzymes. When symptoms occur, they’re often subtle. They include fatigue and low energy, mild discomfort or dull pain in the upper right abdomen (under the ribs), or abnormal liver enzymes in routine bloodwork: ALT/AST or GGT.

Some physical clues like dark skin patches around the neck or armpits, or cholesterol deposits on eyelids (xanthelasmas) – although they are rare.

Red flag symptoms indicating more progressed forms (steatohepatitis or early fibrosis/MASH) include persistent abdominal pain, worsening fatigue, and possible inflammation signs (though these are often silent).

How does the disease severity vary?

Despite a normal exterior, lean NAFLD can be just as serious.

Liver inflammation and fibrosis can be comparable to those in obese counterparts. In some cases, lean individuals show higher liver enzyme levels, possibly because lean patients are diagnosed later. They often face an increased risk of type 2 diabetes, cardiovascular disease, and even higher all‑cause mortality compared to healthy individuals.

What should the lean and apparently healthy individuals do?

Be vigilant: If you’re fit but have symptoms like fatigue, mild abdominal discomfort, or abnormal liver panels, ask your doctor about NAFLD. Standard BMI-based assessments may miss lean cases.

Diagnostic tools: Consult a professional healthcare provider. They might be using blood markers and liver enzymes, ultrasound, or elastography (FibroScan) for an accurate diagnosis. Non-invasive panels or calculators might come in handy to determine liver fat or fibrosis risk.