What are ultra-processed foods and how do they impact the gut microbiome?

Many of the foods that we eat are processed in some way in order to make them tasty, digestible, and safe to eat. Processed doesn’t always mean bad! However, there has been a rise in the amount of ultra-processed foods we eat which has been linked to poorer health outcomes. 

Firstly, what are what are ultra-processed foods? 

The NOVA classification is used to group foods according to the extent and purpose of processing they undergo and consists of four groups. 

Group 1 – Unprocessed or minimally processed foods  

The first NOVA group is of unprocessed or minimally processed foods. Unprocessed (or natural) foods are edible parts of plants (seeds, fruits, leaves, stems, roots) or of animals (muscle, offal, eggs, milk), and also fungi, algae and water, after separation from nature. 

Minimally processed foods are natural foods altered by processes such as removal of inedible or unwanted parts, drying, crushing, grinding, fractioning, filtering, roasting, boiling, pasteurisation, refrigeration, freezing, placing in containers, vacuum packaging, or non-alcoholic fermentation. None of these processes adds substances such as salt, sugar, oils or fats to the original food. 

Group 2 – Processed culinary ingredients  

The second NOVA group is of processed culinary ingredients. These are substances obtained directly from group 1 foods or from nature by processes such as pressing, refining, grinding, milling, and spray drying. The purpose of processing here is to make products used in home and restaurant kitchens to prepare, season and cook group 1 foods and to make with them varied and enjoyable hand-made dishes, soups and broths, breads, preserves, salads, drinks, desserts and other culinary preparations. 

Group 3 – Processed foods 

The third NOVA group is of processed foods. These are relatively simple products made by adding sugar, oil, salt or other group 2 substances to group 1 foods. Most processed foods have two or three ingredients. Processes include various preservation or cooking methods, and, in the case of breads and cheese, non-alcoholic fermentation. 

The main purpose of the manufacture of processed foods is to increase the durability of group 1 foods, or to modify or enhance their sensory quality. 

Group 4 - Ultra-processed food and drink products 

The fourth NOVA group is of ultra-processed food and drink products. These are industrial formulations typically with five or more and usually many ingredients. Such ingredients often include those also used in processed foods. Ingredients only found in ultra-processed products include substances not commonly used in culinary preparations, and additives whose purpose is to imitate sensory qualities of group 1 foods or of culinary preparations of these foods, or to disguise undesirable sensory qualities of the final product.  

Group 1 foods are a small proportion of or are even absent from ultra-processed products. 

What foods count as ultra-processed? 

Group 1  

  • Fruit (fresh, squeezed, chilled, frozen, or dried) 
  • Leafy and root vegetables  
  • Grains  
  • Legumes 
  • Starchy roots and tubers (such as potatoes)  
  • Meat, poultry, fish and seafood  
  • Eggs  
  • Milk  

Group 2  

  • Salt  
  • Sugar  
  • Honey  
  • Vegetable  
  • Butter and lard  

Group 3  

  • Canned or bottled vegetables, fruits and legumes 
  • Salted or sugared nuts and seeds 
  • Salted, cured, or smoked meats 
  • Canned fish 
  • Fruits in syrup 
  • Cheeses 
  • Beer, cider and wine 

Group 4  

  • Carbonated drinks 
  • Sweet or savoury packaged snacks  
  • Ice-cream 
  • Chocolate,  
  • Confectionery) 
  • Mass-produced packaged breads and buns 
  • Margarines and spreads 
  • Cookies (biscuits), pastries, cakes, and cake mixes 
  • Breakfast cereals and energy bars 
  • Fruit yoghurts and fruit drinks;  
  • Instant sauces 
  • Poultry and fish ‘nuggets’ and ‘sticks’, sausages, burgers, hot dogs, and other reconstituted meat products 
  • Powdered and packaged ‘instant’ soups, noodles and desserts 
  • Whisky, gin, rum, vodka 

Effect of ultra-processed foods  

Ultra-processed foods and drinks can contain high levels of refined carbohydrates, saturated fats, salt, and chemical additives. They often lack dietary fibre, good sources of protein, and healthy fats.  

We are eating an increasing amount of ultra-processed foods, with more than half of our daily calories now coming from those types of foods.  

A diet high in ultra-processed food is associated with being overweight and having worse health outcomes, including conditions like heart disease, type 2 diabetes, irritable bowel syndrome, depression, asthma, and cancer. Additionally, research suggests that ultra-processed foods might also be having an impact on our gut health.  

How do ultra-processed foods affect our gut microbiome? 

The PREDICT study* showed that eating a diet rich in minimally processed plant-based foods is associated with having more “good” gut microbes linked to better heart and metabolic health. Research has shown that we should be aiming for at least 30 different types of plant-based foods per week for a diverse gut microbiome. It is also important to highlight that the results were the same from both animal and plant foods therefore, it is important that these plant foods are coming from minimally processed foods. 

A diet rich in highly processed foods, whether from animals or plants, are associated with “bad” gut microbes linked with poorer health markers. This may be due to the specific ingredients in UPFs affecting your gut microbiome or due to the low fibre content of UPFs. 

We believe that life should be about balance, and you don’t need to cut these foods out of your diet completely for good gut health however, it is important to try and base the majority of your diet around minimally processed foods. Check out our top tips for feeding your gut microbiome here. 

To learn how to get the most of what you’re eating to feed your gut microbes,  book a free 1:1 consultation with our in-house nutrition team. 

*The PREDICT study is a large, nutritional research programme with 1,102 healthy individuals to examining how genetics, metabolic differences, the gut microbiome, meal context (e.g. exercise, sleep, meal ordering, time of day), meal composition, and individual characteristics (e.g. age, sex, BMI) affect postprandial responses to meals.  

Monteiro, C., 2016. NOVA. The star shines bright.World Nutrition V, 7(1-3).

Rauber, F., da Costa Louzada, M., Steele, E., Millett, C., Monteiro, C. and Levy, R., 2018. Ultra-Processed Food Consumption and Chronic Non-Communicable Diseases-Related Dietary Nutrient Profile in the UK (2008–2014). Nutrients, 10(5), p.587. 

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