Do Processed Foods Ruin Your Gut Health?

This article was written by Associate Registered Nutritionist (ANutr) Sophie Gastman, and reviewed by Registered Dietitian Maeve Hanan.

As the focus shifts from demonising carbohydrates and fats, processed foods have emerged as the new nutritional pariah. While the media has highlighted the potential downsides of these foods, the true extent of their impact on gut health remains a question. 

This article explores the current research on the link between processed foods and gut health. 

Understanding Processed Foods

‘Processed food’ is a very broad term. It includes any food that has been altered in some way during preparation. The processing can be as simple as freezing green peas or as complicated as adding a concoction of preservatives and additives to sliced bread to make it last longer on the shelf. So how do we differentiate between these very different foods? 

There is no universal agreement on the definition of processed foods but the main classification system that exists for defining the level of processed foods is the NOVA system. It places foods into four categories: 

1. Unprocessed/minimally processed foods 
2. Processed culinary ingredients 
3. Processed foods 
4. Ultra-processed foods (UPF)

However, a recent statement from the SACN (Scientifc Advisory Committee on Nutrition) acknowledges that while the NOVA classification was the only system that met the criteria for use in the UK, it also has its limitations.

The reason we process food isn’t with the goal to make it unhealthy, it’s to make it either last longer, remove harmful substances, make it easier to digest or to improve flavour and appearance.

For example, grains like rice need to be cooked in order to be digested and milk needs to be pasteurised to remove harmful bacteria. 

Therefore, even though it makes for a much more dramatic headline, we can’t paint all processed foods with the same brush. Instead, we should focus on the overall quality and composition of our diets rather than blaming or cutting out processed foods entirely.

The Role of Gut Health

Gut health is another hot topic that’s been spoken about in the media a lot over the last few years, and for good reason. The tiny microbes that coexist in our guts might seem insignificant in the grand scheme of things, but we shouldn’t underestimate them. Not only can they produce a variety of essential hormones and vitamins we need to function, but they can also contribute to our immune health, mental health and brain health.

The makeup of our gut microbiome is largely influenced by what we eat. Therefore, the best way to support a healthy gut is to eat a diverse range of foods, particularly foods high in fibre like beans, whole grains and fruits and vegetables. This will translate to a diverse gut microbiome and the more variety of microbes we have, the more capable and resilient our gut is. 

Impact of Processed Foods on Gut Health 

There’s no doubt that a diet dominated by highly processed foods isn’t great for our guts, or overall health. Certain processed foods, particularly ultra processed foods can be high in sugar, fat, salt and artificial additives, which may negatively impact gut health when consumed in excess (1).

For example, a study looking at the association between ultra-processed food consumption and gut microbiota in those aged between 55-75 years found ultra-processed food consumption was associated with certain microbes that are linked to inflammatory gastrointestinal diseases (2). 

However, while it may be tempting to try to eliminate processed foods to preserve your gut health, the research is still in its early stages, so such broad conclusions are premature.

A lot of the existing research also has many limitations. The majority of them, for example, use the NOVA classification system for processed foods, which is itself limited, and much of the data is entirely observational and relies on self-reporting dietary choices, which rarely provide an accurate picture. Other limitations of this research include: a lack of diversity in study groups, reporting methods and validation vary, and important confounding factors like smoking and finances aren’t always taken into account in this research.

Overall SACN state that “the evidence to date (based on the NOVA classification system) needs to be treated with caution” (3)

Before making sweeping statements about entire categories of food, keep in mind that individual circumstances differ.

For some people, processed foods may benefit gut health as they help to make a varied diet more accessible.

For example, tinned or frozen fruits and vegetables might be your only option if you live in a food desert, or you know they will spoil if you buy them fresh, or simply because they are less expensive. Tinned and frozen fruit and vegetables are also just as nutritious as fresh versions, and can sometimes be more nutritious as certain nutrients are protected by these processes. Equally, fish fingers, which are classed as an ultra-processed food, may be the only way you can get your children to eat a portion of fish. 

Baked beans are also classed as ultra-processed because they contain modified cornflour, which acts as a stabiliser and thickens the sauce. But, despite some versions having a high sugar and salt content, they are still a good source of fibre and should not be overlooked when 3 heaped tablespoons contribute to one of your five-a-day portions of vegetables. 

The key is to find a happy medium. Rather than condemning entire categories of food because the latest news article claims they’re destroying our guts, a more balanced approach would be to incorporate them alongside foods known to support gut health. For instance, pairing a frozen ready meal with a generous portion of vegetables, or having a handful of nuts alongside a a chocolate bar (etc.). 

Conclusion 

Overall, the relationship between processed foods and gut health is complex and nuanced. While some studies may show a connection between highly processed foods and undesirable changes to our gut microbiome, the current research is preliminary and often limited. 

Rather than occupying your headspace with how you can cut out processed foods entirely, consider how they can complement and be part of a balanced diet, which allows for convenience, enjoyment and pleasure as much as nutrition and health. 

For more information about processed foods check out our previous article Should Processed Foods Be Feared.

References 

1. Song, Z. et al. (2023) ‘Effects of ultra-processed foods on the microbiota-gut-brain axis: The bread-and-butter issue’, Food Research International, 167, p. 112730. doi:10.1016/j.foodres.2023.112730. 
2. Atzeni, A. et al. (2022) ‘Association between ultra-processed food consumption and gut microbiota in senior subjects with overweight/obesity and metabolic syndrome’, Frontiers in Nutrition, 9. doi:10.3389/fnut.2022.976547. 
3. SACN statement on processed foods and health (2023). https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1168948/SACN-position-statement-Processed-Foods-and-Health.pdf