Explainer: How genetics shapes obesity and why environment still matters

For many years, obesity was often viewed as a simple result of poor diet or lack of exercise. However, a recent study published in the scientific journal PLOS Medicine shows that the causes of obesity are far more complex. A person’s genes can influence how easily they gain weight, how their body stores fat, how hungry they feel, and how their metabolism works. Researchers identified more than 3,000 genetic variations linked to obesity risk and estimated that inherited factors explain a large proportion of the relationship between parents’ and children’s body mass index (BMI). These variations do not act like a single “obesity gene”. Instead, thousands of small genetic differences work together to influence a person’s chances of gaining excess weight. The researchers emphasised that genes do not determine a person’s future on their own. Environmental factors, including diet, physical activity, sleep, and access to healthy foods, interact with genetic risk to shape body weight. They estimated that genetic factors may explain between 40 and 70 per cent of obesity risk in individuals. These figures do not mean people are controlled by their DNA. Rather, they show that some people may have biological factors that make maintaining a healthy weight more difficult. “Genes influence our risk, but they do not determine our destiny,” researchers often emphasise when explaining obesity. A person may inherit genes that make weight gain easier, but environmental conditions can either increase or reduce that risk. “The environment determines how common obesity becomes, while genetics helps explain why some individuals are more affected than others,” scientists say. Additionally, genetics can affect several biological processes connected to weight. Some people may experience stronger hunger signals, slower energy use, or a tendency to store more fat. These differences can make weight management more challenging. According to the scientists, obesity is not one single disease; two people with the same body weight may have different genetic backgrounds and health risks. Some individuals with obesity develop conditions such as diabetes and heart disease, while others may remain healthier for longer. New research is also exploring why weight-loss treatments do not work equally for everyone. Genetic differences may influence how people respond to certain medications, helping doctors develop more personalised approaches in the future. Understanding the role of genetics changes the way society views obesity. It challenges the idea that body weight is only a matter of personal discipline or willpower. However, genetics does not mean obesity cannot be prevented or treated. Healthy eating, regular physical activity, good sleep, stress management, and supportive environments remain important. Kenya, like many other African countries, is facing a changing nutrition landscape. While undernutrition remains a challenge in some communities, overweight and obesity are increasing, creating what experts describe as a “double burden” of malnutrition. Estimates indicate that about 70 per cent of Kenyan adults are living with obesity, with higher levels reported in urban areas. Rising obesity levels are also linked to increasing cases of non-communicable diseases such as type 2 diabetes, high blood pressure, and heart disease. Urban lifestyles have contributed to these changes. Many people now consume more processed foods, sugary drinks, and high-calorie meals while spending less time being physically active. Busy work schedules, increased transport use, and limited access to affordable, healthy foods can make maintaining a healthy weight more difficult.