Explainer: Why Genetics Matters in Obesity – and Why Lifestyle Still Counts

A new study published in PLOS Medicine has identified more than 3,000 genetic variations linked to obesity, providing new evidence that inherited biology plays a major role in how people gain weight and regulate appetite and metabolism.

The research found that genetic factors explain a large share of the relationship between parents' and their children's body mass index (BMI). Rather than identifying a single "obesity gene", the study shows that thousands of small genetic differences combine to influence a person's risk of developing obesity. 

Researchers estimate that genetics account for between 40 and 70 percent of obesity risk, although they emphasise that genes alone do not determine a person's future. Lifestyle, environment and access to healthy food remain important influences.

The findings suggest that obesity cannot be explained by diet, exercise or willpower alone. Some people inherit traits that increase hunger, reduce energy use or encourage the body to store more fat.

However, environmental factors determine how common obesity becomes. As the researchers note, the environment influences the overall level of obesity in a population, while genetics helps explain why some people are more affected than others. The study also found that genetic differences may influence how patients respond to weight-loss medicines, supporting the development of more personalised treatments.

The findings are particularly relevant for Kenya, where obesity is increasing, especially in urban areas. Estimates suggest that about 70 percent of adults in cities are living with overweight or obesity. The country is facing a double burden of malnutrition, with undernutrition continuing in some communities while others experience rising rates of obesity and related conditions such as type 2 diabetes, hypertension and cardiovascular disease. 

Urban lifestyles, including greater consumption of processed foods and sugary drinks, more sedentary work and limited access to affordable healthy food, have contributed to this trend. Improving access to nutritious food, encouraging regular physical activity and supporting healthy sleep and stress management could help reduce obesity rates. 

Greater understanding of genetic risk may also help reduce stigma by showing that obesity is influenced by factors beyond individual choice. The researchers conclude that obesity is not a single condition but a group of disorders shaped by different combinations of genetic and environmental factors. 

People with similar body weight may have different health risks and may respond differently to treatment. They say future strategies should reflect these differences while continuing to promote healthy lifestyles and supportive environments.