Heyo,

It's time for another instalment of the Vitamin––the weekly fitness newsletter that helps you be healthier, stronger, and leaner while navigating fitness bullshit.

Are ultra-processed foods bad for you?

Ultra-processed foods (UPFs) have become an ultra-hot research topic in recent years, and for good reason–they now make up more than half of the calories consumed in places like the UK, USA, and the rest of Europe [1, 2].

But let's back up a second. What exactly are 'ultra-processed foods'?

According to the NOVA classification system [3], foods are grouped by the extent of processing they've undergone. UPFs sit on one end of the spectrum while unprocessed foods sit on the other end.

• Group 1 – Unprocessed or Minimally Processed Foods: Whole or lightly altered foods like fruits, vegetables, grains, meat, fish, eggs, and milk—washed, frozen, or cooked, but with no added ingredients.
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• Group 2 – Processed Culinary Ingredients: Substances extracted from whole foods used in cooking, like oils, butter, sugar, honey, and salt.
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• Group 3 – Processed Foods: Foods made by adding salt, sugar, or oil to Group 1 foods for preservation or flavour—examples include cheese, canned beans, pickles, and fresh bread.
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• Group 4 – Ultra-Processed Foods: Industrial formulations packed with additives, flavourings, and refined ingredients—think soft drinks, sweets, packaged snacks, instant meals, and fast food.

The fuss around UPFs isn't entirely unwarranted. Observational research consistently links higher UPF consumption with poorer health outcomes, including greater risk of obesity [4], heart disease, type 2 diabetes, and even earlier mortality [5, 6].

But here's the catch: most dietary guidelines – like the UK's Eatwell Guide – don't actually care about processing. They care about nutrients and food groups. Eat your five-a-day, get enough fiber, don't mainline butter, etc.

So this raises an interesting question - what would happen if you follow all the official guidelines but make one diet from mostly whole foods and another from mainly processed stuff?

Well, a recent study investigated just that. [7]

The setup:

• 55 adults in England (BMI 25-40, already eating lots of UPFs - 67% of their total daily calories)
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• 50 made it to the final analysis
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• Both diets followed the UK Eatwell Guide (balanced macros, lots of fruit and veg, etc), and the only difference was the processing:
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  • Minimally processed foods (MPF): meals built from basic ingredients you’d cook at home.
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  • UPF: nutritionally “healthy” supermarket products (cereals, ready meals, plant-based alternatives) that still hit guideline targets.
• The study used a crossover design where everyone did both diets in random order - either UPF first then MPF, or MPF first then UPF - with each diet lasting 8 weeks and a 4-week break in between. This design meant each person served as their own comparison, making the results more reliable.
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• Participants were given all meals, snacks and drinks for both diets, which were delivered to participants’ homes twice per week.
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• Intake was ad libitum–i.e. participants were asked to consume as much or as little of the provided diets as they wanted.
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• The primary outcome was the percentage weight change over each 8-week period.
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• Secondary outcomes included changes in body composition, blood pressure, blood lipids and glucose, as well as subjective appetite measures, dietary intake, physical activity, and adverse events.

What happened?

Both diets led to weight loss, but:

• MPF diet: -2.06% body weight
• UPF diet: −1.05% body weight

As for the secondary outcomes, the minimally processed diet led to slightly greater improvements across most measures: participants lost about 1 kg more body fat, reduced their body fat % by ~0.8%, and saw a modest reduction in triglycerides. Visceral fat also declined a bit more with the MPF diet, while lean mass and muscle were maintained on both. Overall, the changes were small in magnitude but consistently favoured the minimally processed diet.

Additionally, people on the MPF diet reported better craving control and lower desire for sweet and savoury foods, and consumed 327 fewer calories per day.

So, what?

The results of this study suggest that while weight loss can occur on diets with higher or lower amounts of processed foods, the loss is greater when eating minimally processed foods.

Even though both diets followed healthy eating guidelines and were matched for nutrients, participants ate more calories on the UPF diet, likely because those foods were more energy-dense, faster to eat, and more palatable. In other words, food processing matters mostly because it influences how much you eat. On the other hand, the MPF diet promoted better appetite regulation and meal satisfaction.

These results align with earlier research showing UPFs tend to increase how much people eat.

For example, Hall and colleagues showed that people lost weight on an MPF diet but gained weight on the UPF diet due to an increase in caloric intake. [8] Another study found weight gain on both diets, but more gain on the UPF diet. [9]

Taking all of this together, UPFs aren't necessarily 'bad' for your health or fat loss goal.

But if you're trying to lose fat or maintain weight loss, prioritising minimally processed foods is still the smart thing to do. They'll help you manage hunger better, improve diet adherence, and ensure you're eating enough micronutrients to support overall health. In contrast, if you're trying to gain weight and you struggle with low appetite, incorporating more UPFs is an easy way to increase caloric intake.

Lastly, it's worth remembering that "ultra-processed" is a very broad term, and context matters. For instance, zero-calorie drinks would be considered ultra-processed. However, if someone is trying to lose weight, they can be a net positive for weight loss. Meanwhile, freshly squeezed orange juice is classed as minimally processed under NOVA, but if it consistently pushes you into a calorie surplus, it can still contribute to weight gain.

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​Related article:

• What everyone gets wrong about calories

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