Do ultra-processed foods alter the gut microbiome?

A recent review published in the journal Nutrients summarized the existing knowledge on the impact of ultra-processed foods on the gut microbiome. The researchers also discussed the NOVA system of food classification and how variations in the implementation of food classification impact the research on ultra-processed foods.

Review: Ultra-Processed Foods: A Narrative Review of the Impact on the Human Gut Microbiome and Variations in Classification Methods. Image Credit: Lightspring / Shutterstock

Background

Processed meats and other processed and refined foods form a major part of the Western diet resulting from large-scale, industrialized food production. Along with processed foods, the Western diet also consists of large amounts of added sugars, saturated fats, red meat, and trans fats. Pre-packaged, ready-to-eat foods that are low in nutrients and high in calorific content constitute a large part of processed foods.

However, the convenience, affordability, and added flavors in processed foods have resulted in an increase in unhealthy food choices. Coupled with a lack of adequate physical activity, the Western diet contributes significantly to the increased risk of non-communicable diseases such as diabetes, obesity, cancer, and cardiovascular disease.

Some of the mechanisms through which the consumption of processed foods elevates the risk of non-communicable diseases include an increase in glycemic response, oxidative stress, insulin resistance, intestinal inflammation, and the impact of excess sugars and salt. There is also growing evidence that processed foods alter the gut microbiome’s composition and function, contributing to increased morbidity.

About the study

In the present study, the researcher reviewed studies that provided clinical evidence on the role of ultra-processed foods in altering the gut microbiome. They also examined the association between the gut microbiome and fast foods, plant-based diets, and ultra-processed meals or supplements with high nutritional value. Furthermore, the review also addressed the abundance of food additives in ultra-processed foods.

Additionally, the reviewers discussed the usage of the NOVA food classification system in observational studies and randomized control trials, the variations in the application of this classification system, and the data collection methods used to conduct dietary studies.

To examine the association between ultra-processed foods and the gut microbiome, the review included relevant publications on processed diets, the Western diet, fast foods, additives, and the gut microbiome.

To determine variations across studies in the application of the NOVA food classification method, the researchers reviewed randomized controlled trials published in the last decade and observational studies that addressed ultra-processed foods or food processing. Only those studies that classified foods using the NOVA classification system into groups based on the degree to which the foods were processed were included in the review.

The articles included also used measures of health, such as cardiovascular disease risk and body composition. Some of the included articles were considered as having highly detailed methods if the NOVA system rules were used to address discrepancies in food classification. The study included a method to categorize foods with inadequate information, specific ingredients were considered while classifying foods as ultra-processed, and a detailed menu was provided to ensure the study could be replicated.

Results

The review identified four studies examining ultra-processed foods’ impact on the gut microbiome. Of these, two studies reported that greater consumption of ultra-processed foods was associated with an increase in the abundance of Prevotella species and a decrease in the abundance of Ruminococcus and Lachnospira species.

One of the studies also reported an association between Prevotella species and the consumption of animal-based foods, while Ruminococcus and Lachnospira species were reported to be associated with an increased intake of plant-based foods. Three out of the four studies did not report any correlation between the intake of ultra-processed foods and the Firmicutes/Bacteroidetes ratio, which is believed to be linked to dietary patterns, as well as diabetes and obesity.

Studies examining the effect of fast foods on gut bacteria reported an increase in bile-tolerant bacteria such as Bilophila wadsworthia and those from the genera Collinsella and Parabacteroides, and a lower abundance of fiber-fermenting bacteria such as Butyricicoccus and Lachnospiraceae species.

The researchers found that very few observational studies or randomized controlled trials provided a comprehensive explanation of the methods or the level of detail necessary to determine the impacts of ultra-processed foods reliably. They believe that finding methods to overcome the challenges in accurately categorizing foods is essential for assessing the impact of ultra-processed foods on gut microbiota and overall health.

Conclusions

To summarize, the review found that despite the challenges and limitations in accurately categorizing foods and the inadequacy of details in the method descriptions provided by studies on ultra-processed foods, there is growing evidence of their detrimental impacts on health. However, more detailed studies are required to obtain a reliable understanding of the association between ultra-processed foods and human health.