Why two people with same BMI can have different risks of diabetes, heart disease and fatty liver

Two individuals with identical body weight and body mass index (BMI) can still exhibit vastly different risks for diabetes, cardiovascular disease, and fatty liver. The key factor lies in their body composition, specifically the amount and location of body fat.

Dr. Saurabh Juneja, a cardiac specialist, explains that BMI only considers weight in relation to height and does not account for how much fat a person has, where that fat is stored, or the amount of muscle they possess. Consequently, two people with matching BMI readings may have distinct body compositions, such as one person being leaner with more muscle and less harmful fat, while another may have excessive internal fat.

The type of fat known as visceral fat, which accumulates inside the abdominal cavity, is particularly concerning. Unlike subcutaneous fat just beneath the skin, visceral fat is metabolically active and can release fatty acids and inflammatory substances that impair the body's ability to regulate blood sugar and fat metabolism.

This internal fat has significant implications for various organs. It contributes to insulin resistance, elevates blood sugar levels, and raises the risk of type 2 diabetes. Additionally, visceral fat is linked to high blood pressure, unhealthy cholesterol levels, chronic inflammation, and increased cardiovascular risks—potentially manifesting even in individuals with normal BMI readings.

Fatty liver disease can also develop due to excess fat accumulation around abdominal organs. While not everyone with fatty liver experiences inflammation or liver damage, some cases may progress over time.

However, having a normal BMI does not guarantee safety. Some individuals, often referred to as "normal-weight obesity," may appear healthy on the outside but still harbor excess visceral fat or have low muscle mass. This condition can still lead to insulin resistance, abnormal cholesterol levels, and heart disease.

Dr. Juneja emphasizes that various other factors, including genetics, age, gender, physical activity, diet, sleep patterns, stress, smoking, alcohol consumption, and family history, also influence disease risk. Muscle mass plays a crucial role as well, as it aids in regulating blood sugar. Genetic predispositions can further impact where the body stores fat, making some people more susceptible to metabolic conditions even with a seemingly healthy weight.

To assess metabolic health beyond BMI, Dr. Juneja recommends checking waist circumference, waist-to-height ratio, and conducting blood tests like fasting blood sugar, HbA1c, lipid profile, and liver function tests. Blood pressure monitoring is also essential for evaluating cardiovascular risks. In some cases, body composition analysis, ultrasound scans, or advanced imaging tests may reveal visceral fat and liver fat that BMI fails to detect.