Why ultra-processed foods are making us gain weight: What Science says

Ultra-processed foods (UPFs) are products made mostly in factories. They have many added ingredients like sugar, fats, salt, colors, and flavors. Examples include sugary cereals, packaged snacks, ready meals, and soft drinks. These foods are very common in modern diets.

What are Ultra‑Processed Foods?

Ultra‑processed foods are defined by the NOVA classification, a system created by scientist Carlos Monteiro. The NOVA system shows that UPFs are very different from natural foods because of how much factories change them. UPFs aim to taste good, last long, and be easy to eat. They are usually soft, sweet, salty, or fatty—making them attractive to eat quickly. Many people eat fast or while doing other things, which makes it easier to eat too much .

How UPFs cause weight gain

1. Calories and Nutrients
   UPFs often have high calories from fats, sugars, and refined carbs, but they lack fiber and protein. This means people eat more calories without feeling full .

2. Overeating by Design
   These foods are made to be eaten quickly and in large amounts. Studies show people eating UPFs tend to eat about 500 extra calories per day—and gain weight even when the foods have similar nutrients as less processed foods.

3. Changes in the Body
   UPFs change how our brain and gut work. They affect important hormones that tell us when we are hungry or full. They may also change gut bacteria and cause inflammation—both related to weight gain.

4. Harmful Additives
   Some additives in UPFs—like artificial sweeteners, emulsifiers, and packaging chemicals—can affect metabolism and fat-building processes in the body.

Evidence from studies

• A major European study (EPIC) followed nearly 350,000 adults for 5 years and found that those eating the most UPFs had a 15–16% higher risk of becoming overweight or obese.

• A UK Biobank study showed almost a 79% increased risk of obesity and 30% higher risk of belly fat among high UPF eaters over five years .

• Similar links appear in Australia and China—where high UPF intake raises obesity risks between 10–60% .

• A meta-analysis of multiple studies confirmed a clear association: people who eat more UPFs are more likely to be overweight or obese .

Obesity greatly increases the risk of diabetes, heart disease, and some cancers. With UPFs making up more than half of many people’s calorie intake—61% in the US, 62% in Canada, and 63% in the UK—the health impact is large . UPFs are also linked to other health issues like high blood pressure, type 2 diabetes, dementia, and early death 

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What you can do

• Choose whole foods like fruits, vegetables, beans, eggs, nuts, and grains instead of UPFs 

• Cook at home using fresh ingredients. Try healthy eating habits like the Mediterranean diet.

• When buying packaged foods, read ingredient labels. Avoid items with many chemical-sounding ingredients 

• Eat slowly and mindfully. Chew slowly and stop when you feel full.

Eating a lot of ultra-processed foods is strongly linked to weight gain and obesity—even when they have similar calories as healthier foods. Making small changes—like eating more whole foods—can help maintain a healthy weight and reduce health risks.