Cutting ultra-processed food: what two trials in people showed

Key points

Good news: eating "right" can be simple. Cooking from simple ingredients more often is enough. When researchers matched meals for calories, sugar, salt and fibre, people on simple food ate more moderately and lost weight, while on factory food they ate more and gained. You do not need to count calories: simple food helps you avoid overeating by itself.

What was compared in the ward

At the US National Institutes of Health Clinical Center, 20 adults (average age 31, body mass index 27 kg/m²) lived under observation for 4 weeks. For two weeks they received ultra-processed food and for two weeks simple food, in random order, one after the other. Meals were matched for offered calories, energy density, nutrients, sugar, salt and fibre. People could eat as much as they wanted (Hall K D Cell Metab 2019. PMID 31105044^[1]).

On ultra-processed food people ate on average 508 kcal a day more (standard error 106 kcal). Most of the increase came from carbohydrate (about 280 kcal) and fat (about 230 kcal); protein stayed the same. Weight followed calories: plus 0.9 kg in two weeks on factory food and minus 0.9 kg on simple food (Hall K D Cell Metab 2019. PMID 31105044^[1]). The participants were adults living in a ward and the trial was small, so the figures show a direction, not an exact result for your kitchen.

A newer trial: also within healthy-eating guidance

Critics said factory food is bad only because it lacks "healthy" content. So in an English trial, 55 adults with a body mass index of 25 to 40 kg/m², who usually got at least half of their calories from ultra-processed food, received two 8-week diets, both following the Eatwell Guide, and ate as much as they wanted. The intention-to-treat analysis included 50 people (Dicken S J Nat Med 2025. PMID 40760353^[2]).

On minimally processed food weight fell by 2.06% (confidence interval 1.13% to 2.99%), on ultra-processed food by 1.05% (0.13% to 1.98%). The difference of 1.01 percentage points was significant (P = 0.024). So on simple food people lost roughly twice as much, but they also lost weight on "healthy" factory food (Dicken S J Nat Med 2025. PMID 40760353^[2]). Mild gastrointestinal events occurred on both diets.

How to apply this

• Start with one meal. For example breakfast: an omelette or porridge from flakes instead of sweetened ready-to-eat cereal.
• Replace the most obvious items: sausages with baked meat or fish, sweet drinks with water, snacks with nuts or fruit.
• Read the label: the shorter the list and the more familiar words in it, the simpler the product.
• One pot for two days: soup, stew, roasted vegetables. Cooking at home does not mean spending the evening.
• Do not give up convenience: canned beans, frozen vegetables and plain yogurt remain a good choice.

Who should see a doctor first

If you are losing weight because of illness, take medicines for diabetes or blood pressure, are pregnant, breastfeeding, have an eating disorder or chronic kidney disease, change your diet together with a doctor. Rapid unexplained weight loss needs investigation, not celebration.

If you monitor sugar: a repeat glucose result below 3.0 mmol/L (54 mg/dL) or above 8.9 mmol/L (160 mg/dL) is a reason to see a doctor. In diabetes targets are individual, and below 3.0 mmol/L (54 mg/dL) always means a doctor. Do not change prescribed treatment on your own.

Bottom line

Simple food helps you eat less without counting calories and gave a larger weight loss than factory food, even when both followed healthy-eating guidance. Start with one meal a day and replace the most "factory" products gradually.

A real-life example: a person is used to sweet cereal for breakfast, sausage on a sandwich and a sweet drink in the afternoon. They swap breakfast for an omelette with vegetables, the sausage for baked chicken, the drink for water, and leave the rest alone. After two or three weeks they notice they snack less often and do not feel on a diet.