Ultra-processed foods (UPFs) contribute to obesity due to several factors, many of which relate to their composition, effects on metabolism, and the way they influence eating behaviour. 

High in Calories and Low in Nutrients

UPFs are often calorie-dense but nutritionally poor. They tend to be packed with sugars, unhealthy fats, and refined carbohydrates but are low in fibre, vitamins, and minerals. This imbalance can lead to an overconsumption of calories without providing the nutrients the body needs, which can result in weight gain.

Increased Appetite

Many ultra-processed foods contain additives like artificial sweeteners, flavour enhancers (e.g., monosodium glutamate), and emulsifiers that can increase appetite and make it harder for the body to signal when it’s full. This can lead to overeating.

Disturbed Satiety Signals 

UPFs often lack the components of whole foods, like fibre and protein, which help regulate satiety (the feeling of fullness). As a result, people may feel hungry again soon after consuming them, leading to overeating.

Addictive Properties 

Some ultra-processed foods are designed to be highly palatable with a combination of fat, sugar, and salt that can trigger the brain’s reward system, making people crave these foods more often. This can lead to habitual consumption and overeating.

Convenience and Portion Sizes 

Many ultra-processed foods are packaged in convenient, ready-to-eat formats that encourage frequent consumption, and they often come in large portion sizes. This can make it easy to consume excess calories without realising it.

Altered Gut Microbiota 

Studies suggest that diets rich in ultra-processed foods may negatively affect gut microbiota (the community of bacteria in the digestive system), which can influence metabolism and fat storage, potentially contributing to weight gain.

Insulin Resistance

Frequent consumption of refined sugars and processed carbohydrates found in UPFs can lead to spikes in blood sugar and insulin levels. Over time, this can contribute to insulin resistance, a condition where the body doesn’t respond effectively to insulin, leading to fat storage and weight gain.

In essence, ultra-processed foods often disrupt the body’s natural mechanisms for regulating hunger, fullness, and metabolism while also providing excess calories and little nutritional benefit, making it easier to gain weight and harder to maintain a healthy weight.


Felciya, is a Specialist Dietitian at The London Obesity & Endocrine Clinic. She has helped many patients overcome weight management barriers. ©Simplyweight