Research by the UK’s University of Cambridge has concluded that obesity is a result of our genes and individuals have less power over their weight than we like to believe.

The Study Into Lean and Thin Subjects (STILTS) involved 2,000 healthy, thin people (defined as having a BMI of less than 18 kg/m2) with no medical conditions or eating disorders, who were questioned about their health and lifestyles. Saliva samples were also used for DNA analysis and compared with samples from 1,985 severely obese people and 10,433 normal weight controls.

Funded by Wellcome and the European Research Council, the study was led by Professor Sadaf Farooqi at the Wellcome-MRC Institute of Metabolic Science, University of Cambridge, collaborating with a team from Wellcome Sanger Institute, led by Dr Inês Barroso.

Several known genetic variants that play a role in obesity were discovered, as well as new genetic regions involved in severe obesity and some involved in healthy thinness. The researchers added up the contribution of the different genetic variants to calculate a genetic risk score. The thin people had fewer of the genetic variants that are known to increase a person’s chances of being overweight.

Dr Barroso concluded the genetic dice are loaded against obese people: “As anticipated, we found that obese people had a higher genetic risk score than normal weight people, which contributes to their risk of being overweight.”

Seventy four per cent of those in the STILTS cohort had a family history of being thin and healthy and the team found some genetic changes that were significantly more common in thin people, which may allow them to pinpoint new genes and biological mechanisms that help people stay thin.

“This research shows for the first time that healthy thin people are generally thin because they have a lower burden of genes that increase a person’s chances of being overweight,” says Professor Farooqi.

“We have far less control over our weight than we might wish to think. Some people can eat what they like, but never put on weight. If we can find the genes that prevent them from putting on weight, we may be able to target those genes to find new weight loss strategies and help people who do not have this advantage.”

Sarah LeBrocq, founder and director of All About Obesity, says for individuals living in larger bodies, this research is both validating and frustrating: “On one hand, it acknowledges that weight is not simply a matter of willpower, or personal responsibility, but is heavily influenced by genetics. This can help combat the stigma that people living in larger bodies often face, challenging the narrative that obesity is solely due to lifestyle choices like diet and exercise.

“However, it might also be disheartening for those who have struggled with their weight, as it suggests that their efforts may be limited by genetic factors beyond their control.

"It may also raise concerns about how society and the medical community will interpret this – whether it will lead to more compassion and support, or reinforce a fatalistic attitude toward obesity that could hinder access to effective interventions.”

LeBrocq advises fitness professionals to use this research as a reminder to shift away from weight-centric approaches and focus on overall health, strength, mobility and wellbeing. This involves promoting inclusive fitness, working to reduce stigma, personalising approaches and encouraging realistic goals.

While this research has found that obesity is the result of genes, the environment is also playing a role in the rising numbers of people living with obesity. Ultra-processed food which makes it easier to consume more calories without feeling full, while sedentary lifestyles, economic disparities, stress and insomnia all lead to weight gain.

“Recognising both genetic and environmental influences allows for a more nuanced, compassionate, and effective approach to supporting people in their health journeys,” says LeBrocq.

LeBrocq is collaborating with psychologist and educator, Dr Glenda Rivoallan and fitness industry veteran, Fiona Cresswell, to launch a company aimed at empowering the health and fitness industry to create inclusive and supportive spaces for individuals in larger bodies. Due for launch next month, My Healthy Shift will offer operators an end-to-end solution to welcome this cohort, including the design of environments, marketing, messaging and programming.