Ultra-processed food and body fat: what a study of 8,783 adults found

A new Canadian study adds to the debate about ultra-processed food. Researchers at the Population Health Research Institute (PHRI) at McMaster University looked at the diets, body fat and brain scans of 8,783 middle-aged adults. Their paper in JAMA Network Open came out on 16 October.

The short version: people who ate the most ultra-processed food carried more body fat, including more of the deep fat stored around the organs, than people who ate the least. They were also more likely to show small changes on brain scans. Here's what that does and doesn't mean.

What the researchers did

The volunteers were aged 35 to 69 and had no history of heart disease. They came from two existing Canadian studies and filled in detailed food questionnaires. The team worked out how many servings of ultra-processed food each person ate for every 2,000 calories, then split everyone into four groups from lowest to highest intake.

Body fat percentage was measured with bioelectrical impedance, the technology behind many body composition scales. The team also measured visceral fat (the deep belly fat around the organs) and liver fat, and used MRI to look for small areas of damage linked to the brain's blood vessels.

According to PHRI's announcement, ultra-processed foods made up about 25% of daily food servings on average. In the highest group that rose to 45%, against 16% in the lowest. The examples will sound familiar: packaged snacks, sugary breakfast cereals, soft drinks, instant noodles and ready-to-eat frozen meals.

What they found

Compared with the lowest group, people in the highest group had:

• a body fat percentage 1.7 percentage points higher
• 5.7 mL more visceral fat
• no meaningful difference in liver fat
• 40% higher odds of small signs of damage to the brain's blood vessels on MRI, changes that usually cause no obvious symptoms

There was no link between ultra-processed food and scores on two thinking and memory tests. PHRI also reported that the brain finding looked stronger in women.

The people eating the most ultra-processed food weren't simply eating it on top of an otherwise similar diet. Fruit, vegetables, grains and other minimally processed foods made up 41% of daily servings in the highest group, compared with 68% in the lowest. As first author Russell de Souza put it, "These foods appeared to crowd out healthier whole foods."

What it doesn't show

This was a cross-sectional study, which means each person was measured once. It can show that two things tend to go together, not that one causes the other. The authors say longer studies are needed to sort out which came first, and PHRI says follow-up with repeat scans is under way. The paper also notes that the brain result shifted depending on how ultra-processed food was defined.

UK experts made similar points to the Science Media Centre. Professor Derek Hill of UCL said the study shows an association, not that ultra-processed food is a risk factor for blood vessel damage in the brain. Professor Jules Griffin of the Rowett Institute at the University of Aberdeen pointed out that the highest group also ate more calories. The researchers adjusted for calories, age, sex, city, education and income, but not for the extra salt, sugar and saturated fat in those diets, which we already know matter for health.

Food questionnaires also rely on memory, and everyone lived in Canada, so the results may not map neatly onto UK diets.

What it means for your plate

None of this means you need to clear out your cupboards or feel guilty about a packet of crisps. The NHS points out that most food is processed in some way, and that some ultra-processed foods, such as wholemeal sliced bread, higher fibre breakfast cereals and baked beans, can be part of a healthy diet. It also says it isn't known whether the problem is the processing itself or the calories, fat, salt and sugar many of these foods contain.

What the study does back up is something most of us already know. When snacks and ready meals make up a big chunk of the day, there's less room for the foods that fill you up and fuel your training. A few small changes add up over a week:

• Build meals around a protein and a veg. Eggs, tinned fish, chicken, beans or lentils with whatever vegetables you've got is often quicker than a ready meal.
• Cook once, eat twice. A big pot of chilli, dal or soup on Sunday sorts out a few lunches.
• Keep easy snacks in. Fruit, yoghurt, a handful of nuts, or carrots and hummus are as quick to grab as a biscuit.
• Check the label. Some packs use colour-coding, which makes it quick to compare fat, saturated fat, salt and sugar.
• Aim for better, not perfect. Shifting the balance a little at a time is far easier to stick to than cutting everything out.

For cheap, filling meals built from simple ingredients, try our high-protein meals on a budget guide.

If you have a health condition or you're worried about your diet, have a chat with your GP or a registered dietitian before making big changes.