The link between ultra-processed foods and obesity

You may have noticed the increase in discussion about the consumption of ultra-processed foods: What are they? Are they all bad for you? And, do they lead to obesity and poor health? 

With 57% of daily energy intake coming from these foods^[1], it’s essential to know exactly what the effects of the food you’re eating are and whether you should avoid ultra-processed foods.

What does ultra-processed food (UPF) mean, and how is it different from processed food?

While there isn’t one definition of ultra-processed foods, the NOVA classification system refers to food that contains “formulations of ingredients, mostly of exclusive industrial use, typically created by a series of industrial techniques and processes^[2]

They classify food into four different groups:

Group 1: Unprocessed and minimally processed foods

Group 2: Processed culinary ingredients

Group 3: Processed foods

Group 4: Ultra-processed foods

Spotting the difference between processed foods and ultra-processed foods is not always clear—a good way is to look at the ingredients. Different types of sugars (fructose, dextrose), modified oils (hydrogenated), and protein sources (soya protein, whey protein, “mechanically separated meat”) are all very common in UPFs.

Another way to distinguish between these and processed foods is that processed foods are made by combining foods from groups 1 and 2. These are altered in ways you can do yourself, e.g., jam, tinned fruit, homemade breads, and cheeses^[3], while ultra-processed foods would be too industrial.

Examples of UPFs and how they’re processed

Different processed foods undergo different levels of processing. From simple preservation techniques to complex manufacturing processes. Common processed foods include:

Is there any nutrition in processed food?

Processed foods can contain nutrition, though the nutritional value varies widely depending on the extent of the processing. Frozen fruit and vegetables can sometimes retain more vitamins than fresh produce that’s been sitting on a shelf. However, heavily processed foods will often have less nutritional density as they’ve got fewer vitamins, minerals, and fibre.

Is all processed food bad?

It’s a misconception that because a food is processed, it’s unhealthy for you. Items like frozen vegetables, tinned beans, wholemeal bread, and pasteurised milk are processed foods that retain nutritional value while offering convenience^[4]. These can be valuable parts of a balanced diet.

Health concerns relate specifically to ultra-processed foods (UPFs) like ready meals, sugary breakfast cereals, and packaged snacks containing industrial additives. Research published in The BMJ in 2024 found associations between UPF consumption and obesity^[5]. For weight management, choose minimally processed options whilst limiting ultra-processed products.

Why do people opt for processed foods?

There are three big reasons people will choose processed foods: convenience, cost and taste.

Convenience

Reducing cooking times from 30 to 60 minutes to under 10 minutes means that people trying to have a substantial amount of food in a short period, e.g., a lunch break at work, will be able to eat without any of the preparation or cooking time.

Frozen pizzas, ready meals, and jarred sauces are all UPFs that can help reduce cooking time at home, which may make them more attractive to those working long hours or with young children.

Cost

For some, relatively inexpensive ready meals and frozen alternatives drive their consumption of more processed food. With some recipes requiring a long list of ingredients that might not be pantry staples in some homes, UPFs can become an easy alternative.

Adolescents from lower-income families are more likely to eat more ultra-processed foods, especially less healthy foods^[6][7].

Taste

Because processed food has become so industrialised, manufacturers can make it the most appetising. For example, the ‘bliss point’^[8] is a precise combination of fats, salt and sugar designed to trigger the feeling of reward in the brain, leading you to eat more.

Additionally, processed food tends to have specific combinations of textures (crispy, creamy, chewy) that reduce how full you feel, but increase how much you want to eat compared to unprocessed or minimally processed foods.

How ultra-processed foods can cause obesity

Low satiety (fullness)

Recently, UPFs have been linked to low satiety (not feeling full after a meal) due to decreased meal eating times. They are eaten quickly and are designed to be ‘hyper-palatable’. These three factors can soon lead to overconsumption and a higher amount of calories consumed daily, which is a driving factor for weight gain and obesity.

Calorie intake

Adults' daily recommended calorie intake is roughly 2500kcal for men and 2000kcal for women. Those with a diet high in ultra-processed food could consume an additional 500 calories daily and gain an average of about 2 pounds in two weeks^[9]. The study showed that the extra calories were mainly from additional carbohydrates and fats, whilst their protein intake remained the same.

It’s the high amount of calories that are hidden in processed foods that, over time, can contribute towards obesity and ultimately lead to an increased risk of heart disease. Additionally, these foods tend to offer little nutritional value. 

Why are ultra-processed foods so bad for you?

Modified ingredients

If you’ve ever looked at the ingredients on any ultra-processed food packet, then you’ll likely see a long list of different additives like^[10]:

• Flavours
• Colouring
• Emulsifiers
• Sweeteners
• Thickeners

These additional ingredients in UPFs have been referenced in an extensive study by Imperial College London, which has shown that for every 10 per cent increase in ultra-processed food in a person’s diet, there was a 2% increase in the overall frequency of cancer.

High in fat, sugar and salt

There is good evidence that foods high in saturated fat, sugars, or salt (also known as HFSS) are detrimental to health^[11] and are even subject to regulation within the UK^[12]. There is a significant crossover between these and ultra-processed foods, with two-thirds of calories in UPFs coming from HFSS products.

Gut microbiome

Modern ultra-processed foods contain large quantities of saturated and trans fat, added sugar, salt, and food additives that seriously affect the gut and physical health^[13]. These components directly alter your gut's microbiome, potentially causing metabolic issues and influencing your behaviour.

Additionally, there is now an increasing association between UPFs and gut disease, such as:

• Inflammatory bowel disease
• Colorectal cancer
• Irritable bowel syndrome

Although the government’s scientific committee (the Scientific Advisory Committee on Nutrition or SACN) said in 2023 that more research is needed before any conclusions can be drawn about whether ultra-processed foods cause poor health^[14], it can be suggested that foods made with highly processed ingredients are more likely to cause obesity and the co-morbidities that come with it (e.g., obstructive sleep apnoea, type 2 diabetes, etc.).