Improving Diet and Physical Activity Together Helps Prevent Harmful Fat Gain in Adults

A long-term study from the University of Cambridge offers clear evidence that improving both diet quality and physical activity levels at the same time is more effective at preventing weight gain—especially the build-up of visceral fat, the harmful fat stored deep in the abdomen—than focusing on either behavior alone. The research comes from the Medical Research Council (MRC) Epidemiology Unit and was published in JAMA Network Open.

The study followed 7,256 adults from the Fenland Study over an average of seven years, making it one of the more detailed longitudinal investigations into lifestyle behavior, body fat distribution, and long-term metabolic health. Participants were, on average, 49 years old at the start and 56 years old at follow-up.

To understand how everyday lifestyle changes influence health over time, researchers measured three major areas at the beginning and end of the study period:

Physical activity energy expenditure using wearable heart-rate and movement sensors for at least 72 hours.
Diet quality, assessed through a food frequency questionnaire focused on adherence to the Mediterranean diet, a well-researched eating pattern rich in fruits, vegetables, whole grains, legumes, nuts, and olive oil.
Body fat levels and distribution, tracked using DEXA scans, which differentiate between total body fat, subcutaneous fat, visceral fat, bone, and lean mass. Fatty liver presence was also checked using ultrasound.

What the Researchers Found

The study revealed that improvements in diet quality and improvements in physical activity were each independently linked to lower increases in body fat and better fat distribution. However, the strongest benefits occurred when individuals improved both behaviors simultaneously.

Participants who enhanced both diet and physical activity gained, on average:

1.9 kg less total body fat, and
150 g less visceral fat

compared with those who did not improve either behavior. These differences represent about 7% of baseline total body fat and a striking 16% of baseline visceral fat, underscoring how responsive visceral fat is to lifestyle improvements.

Even after adjusting for BMI, the changes in visceral fat remained statistically significant. Meanwhile, changes in subcutaneous fat became less pronounced after adjusting for BMI, indicating that visceral fat is particularly sensitive to lifestyle shifts.

Visceral fat matters because it surrounds vital organs such as the liver, pancreas, and intestines. Higher levels of this fat are strongly linked to type 2 diabetes, fatty liver disease, and heart disease. Subcutaneous fat—fat stored under the skin—is considered less harmful. This study reinforces the idea that where fat is stored matters just as much as how much fat a person carries.

Why Diet and Activity Together Matter

The Mediterranean diet used as the measure of diet quality emphasizes nutrient-dense foods and minimizes red meat and sugary foods. It has a long track record of being associated with better metabolic health, reduced inflammation, and lower risk of chronic disease. Meanwhile, higher physical activity energy expenditure—regardless of the specific form of exercise—boosts caloric burn, improves cardiovascular health, and supports healthier fat distribution.

The new study adds an important layer: improving both at the same time appears to compound the benefits. Although each behavior works independently, the combined effect produces the greatest impact on long-term fat accumulation and placement.

Additional Context on Visceral Fat

To give readers more clarity, here’s a deeper look at why visceral fat is especially concerning:

Metabolic Activity: Visceral fat is more metabolically active than subcutaneous fat. It releases inflammatory markers and hormones that contribute to insulin resistance and chronic inflammation.
Fatty Liver Risk: Excess visceral fat often accompanies fat buildup in the liver, which can progress to nonalcoholic fatty liver disease (NAFLD).
Cardiovascular Impact: Higher visceral fat levels correlate strongly with increased risk of hypertension, high triglycerides, and atherosclerosis.

Even relatively minor reductions in visceral fat—like the 150 g difference seen in participants who improved both lifestyle behaviors—lead to meaningful improvements in metabolic markers.

How the Measurements Worked

The study’s use of DEXA scans is a key strength. Many studies rely simply on weight or BMI, but these do not tell the full story. Two individuals with the same BMI can have very different fat distributions. DEXA offers a precise view of fat location, making this a robust method for tracking visceral and subcutaneous fat separately.

The use of wearable sensors is also notable. Rather than relying on self-reported physical activity—which is often unreliable—the study tracked real-world daily movement and heart-rate patterns, producing high-quality data.

What This Means for Public Health

The researchers argue that small, sustained improvements in diet and physical activity can support healthier aging, especially for adults in middle age—when metabolic slowdowns and fat gain often begin to accelerate.

They emphasize that environments promoting easy access to unhealthy food and reduced physical activity make lifestyle change challenging at a population level. Therefore, policy efforts should focus on creating conditions where healthy behaviors are the default, not the exception.

Examples include:

Expanding access to safe walking and cycling routes
Improving availability and affordability of nutritious foods
Designing workplaces and public spaces that encourage movement

Expanding the Topic: The Importance of Long-Term Behavior Change

This study also highlights an often-overlooked truth: lifestyle change does not need to be extreme to be effective. The participants in this study didn’t undergo strict diets or intense training programs. Instead, they made gradual improvements that added up over years.

Research in behavioral science shows that small, consistent habits—such as adding one or two servings of vegetables per day or incorporating brisk walking—are far more sustainable than drastic short-term interventions.

Long-term consistency appears to be the real driver behind the reduced visceral fat seen in this population.

A Quick Overview of the Mediterranean Diet

Since diet quality was central to the study, here are the core components of the Mediterranean diet, which readers may find helpful:

Emphasized Foods: Vegetables, fruits, whole grains, legumes, nuts, seeds, and olive oil
Moderate Foods: Fish, poultry, eggs, and dairy
Limited Foods: Red meat, processed foods, and sweets
Typical Benefits: Improved heart health, reduced inflammation, and lower risk of metabolic disease

The diet is flexible and focuses more on food quality than strict calorie counting, which may help explain its sustainability among study participants.

Final Thoughts

The Cambridge study offers strong, evidence-based support for a simple message: improving both diet quality and physical activity is the most effective long-term strategy for reducing harmful fat and promoting healthier aging. The measurable impact on visceral fat, in particular, highlights how lifestyle changes can meaningfully alter disease risk even without major weight loss.

As health challenges related to obesity continue to grow globally, studies like this provide valuable guidance for individuals, clinicians, and policymakers alike.

Research Source:
Concurrent Changes in Diet Quality and Physical Activity and Association With Adiposity in Adults – JAMA Network Open
https://doi.org/10.1001/jamanetworkopen.2025.45232