Weight gain as an adult increases the risk of cancer by up to five times, according to new research involving more than 600,000 patients. The study, presented at the European Congress on Obesity in Istanbul, analyzed weight and cancer incidence data from over 250,000 men and nearly 380,000 women in Sweden, measuring their weight an average of four times between the ages of 17 and 60. Cancer diagnoses were tracked until 2023.
Key Findings on Weight and Cancer Risk
The researchers found that increased cancer risk, both overall and for many specific cancer types, was associated with heavier initial weight in early adulthood as well as weight gained during adulthood. Anton Nilsson, lead author and an associate professor at Lund University, stated: “The higher the starting weight and the greater the weight gain, the higher the cancer risk tended to be.”
Men who became obese before age 30 had a five times higher risk of liver cancer, double the risk of pancreatic and kidney cancer, and a 58% increased risk of colon cancer compared to those who remained slim. Women who developed obesity before age 30 faced a four-and-a-half times increased risk of endometrial cancer, a 67% higher risk of pancreatic cancer, double the risk of kidney cancer, and a 76% increased risk of meningioma.
Gender Differences in Later Weight Gain
For those who gained weight later in life, gender differences emerged. In women, weight gain after age 30 was strongly associated with increased risks of endometrial cancer, postmenopausal breast cancer, and meningioma—cancers for which sex hormones are considered a primary causative factor. Colon cancer was also strongly linked to female weight changes. Among men, associations with obesity-related cancers were stronger for weight gains below age 45, particularly for oesophageal and liver cancer. Nilsson explained this may be because “earlier weight gain allows more time for biological processes such as inflammation and raised insulin levels to act on susceptible tissues.”
Impact of Weight Gain Magnitude
Those who gained the most weight (an average of 32kg, or 5 stone) were 7% more likely to develop cancer than those who gained the least (average 8kg). Men who gained the most weight were nearly three times more likely to develop liver cancer and more than twice as likely to develop oesophageal cancer. They also had three times the risk of pituitary tumours and a more than 50% increased risk of renal cell carcinoma, gastric cardia, and colon cancers. Women who gained the most weight had nearly four times the risk of endometrial cancer, double the risk of pituitary tumours, and significantly higher risks of renal cell carcinoma (91%), postmenopausal breast cancer (42%), meningioma (32%), and colon cancers (31%).
No Safe Level of Weight Gain
Even those who gained lower amounts of weight still had a higher risk of developing cancer, underscoring the need to avoid excess weight. Nilsson added: “While our results do not speak to any specific interventions or behaviours, they highlight the importance of maintaining a stable, healthy weight throughout adult life.”
Response from Cancer Research UK
Megan Winter of Cancer Research UK responded: “Overweight and obesity is the second biggest cause of cancer in the UK. The government should do more to help people find it easier to keep slimmer. Further measures to restrict the advertising and promotion of junk food, introduce mandatory reporting on healthy food sales, and make nutritious food more accessible to everyone could all help reduce obesity rates and improve health across the country.”
