Improving diet and increasing physical activity levels together may be more effective at preventing weight gain – particularly harmful fat inside the abdomen – than just changing one of these behaviours, new research from the University of Cambridge suggests.
An analysis of changes in physical activity and diet quality in UK adults found that while improved diet quality and increased physical activity were each independently associated with lower increases in body fat, the greatest benefits were achieved by combining both.
Body fat is stored in different locations, some of which are more harmful than others. Subcutaneous fat is stored under the skin and can be considered relatively healthy. In contrast, visceral fat stored around the organs in the abdomen is linked to a higher risk of diseases such as type 2 diabetes, fatty liver disease, and heart disease.
In a study published today in JAMA Network Open, researchers from the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge followed 7,256 adults from the Fenland Study over seven years.
The mean age of the study participants was 49 years at baseline, and 56 years at follow-up. At baseline, and again after an average of around seven years, the researchers measured Fenland study participants' physical activity energy expenditure for at least 72 hours using wearable heart rate and movement sensors.
The researchers also assessed participants' diet quality by the degree of adherence to the Mediterranean diet pattern using a food frequency questionnaire. The Mediterranean diet focuses on eating fruits, vegetables, whole grains, legumes, nuts, and olive oil, with moderate amounts of fish, poultry, eggs, and dairy, while limiting consumption of red meat and sweets.
On both occasions, the researchers also measured the quantity and distribution of body fat using DEXA, a low-intensity X-ray scan that can distinguish body fat, bone composition, muscle and lean mass across the whole body, and used ultrasound to identify the occurrence of fatty liver disease.
The researchers found that improvements in diet quality and physical activity energy expenditure over time were independently associated with reductions or less gain in weight, overall body fat, and subcutaneous and visceral fat, and a lower incidence of fatty liver disease.
Simultaneous improvements in both diet and physical activity were associated with the greatest reduction in body fat, while improvement in only one of the two behaviours was associated with relatively modest changes.
For example, Fenland Study participants who improved both their diet and activity gained on average about 1.9 kg less total body fat and 150g less visceral fat over the follow-up period compared with those who did not improve their behaviours. This difference is equivalent to approximately 7% of the baseline total body fat and 16% of the baseline visceral fat in the population.
The researchers found that after adjusting for body mass index, the association of changes in diet and physical activity with changes in visceral fat remained significant, while the association with subcutaneous fat did not, indicating that visceral fat was particularly responsive to the changes in health behaviours.
First author Dr Shayan Aryannezhad from the MRC Epidemiology Unit, said: "When people talk about changes in body weight, they often refer to a single number on the scale. But not all weight loss or gain is the same. First of all, we need to focus on fat mass when considering the risk of metabolic diseases like diabetes and heart disease. Second, body fat is stored in different places, and some types are more harmful than others. So, when we gain or lose weight, it matters where these changes happen.
"We found that combining a better diet with more physical activity is an effective way to improve not just weight, but how much and where fat is stored in the body. It's particularly effective at reducing the build-up of harmful fat around organs."
Senior author Professor Nita Forouhi, also from the MRC Epidemiology, said: "Our research shows that improvements in diet with more physical activity in middle-age don't just result in weight loss, but can potentially help prevent disease and support healthier ageing.
"Despite the challenges of living in environments that promote unhealthy eating and inactivity, there is benefit from making small, sustained changes that lead to both healthier diets and increased energy expenditure.
"To address the epidemic of obesity and its huge social, psychological and health service costs, policy makers should seek to alter the food and physical activity environments to make healthier choices more accessible for all."
The research was funded by the Medical Research Council and the Wellcome Trust, with support from the NIHR Cambridge Biomedical Research Centre.
Reference
Aryannezhad, S et al. Concurrent Changes in Diet Quality and Physical Activity and Association With Adiposity in Adults. JAMA Network Open; 21 Nov 2025; DOI: 10.1001/jamanetworkopen.2025.45232
