How Ultra-Processed Foods Affect Gut Microbiome and Health

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Several studies have demonstrated a potential link between ultra-processed foods (UPF) and chronic inflammation. A recent review published in The Lancet Gastroenterology and Hepatology describes the mechanistic association between UPF consumption and chronic medical conditions, particularly those involving the gut microbiome.

Study: Ultra-processed foods and human health: from epidemiological evidence to mechanistic knowledge. Image Credit: Dawid Rojek/Shutterstock.com

Introduction

Many techniques have been developed to process food over the past centuries in order to preserve food and improve its taste and digestibility. Modern industrially processed foods exploit the availability of salt, sugar, vegetable oils, animal fats and flour.

Typically, the production of these products uses mechanical and physical techniques such as roller milling, extrusion and pressure rendering, as well as chemical methods such as hydrogenation. Artificial flavoring and preservative agents, anti-caking agents and other additives are also used to achieve the desired final texture, color and taste of these food products.

These techniques have enabled the large-scale production and manufacturing of mass-produced processed foods, making them available year-round..”

These highly processed foods are generally hygienic, convenient, affordable, and accessible, making them ideal products for many high-income countries (HICs). More recently, low- and middle-income countries (LMICs) have also become increasingly dependent on these food products.

Coinciding with this trend, there has been an increase in the number of chronic inflammatory cases, including metabolic syndrome and inflammatory bowel disease (IBD). The current article explores evidence for a correlation between modern UPFs and gut microbiota-mediated chronic diseases.

Types of processed foods

There are several classification systems used to describe foods based on their processing. The most commonly used is NOVA, which classifies foods into groups 1 to 4.

Group 1 includes unprocessed or minimally processed foods, such as fresh, chilled, dried, frozen, fermented or pasteurized. Group 2 consists of processed ingredients like vegetable oils, sugar, salt, butter, or other food extracts added to Group 1 foods.

Group 3 includes all typical processed foods, such as salted preserves, candied dried fruits, salted meats, cheeses and fresh bread. Briefly, Group 3 describes Group 2 products added to Group 1 foods.

Group 4 includes UPFs that have undergone one or more of the above industrial processes. These may contain non-domestic ingredients, including those used to flavor, color, sweeten or emulsify.

UPF intake increased HICs, where they account for up to 30%, 50%, and nearly 60% of caloric intake in France, the UK, and the US, respectively.

Study results

Nearly 50% of the 100 prospective studies analyzed in this review examined the association between FPU and various health or mortality outcomes.

Mortality

Seven studies indicated a link between UPF and death from all causes, with a 20% to 60% increased risk in the highest category of UPF intake compared to the lowest. Five studies showed an increased risk of illness or death from cardiovascular disease or stroke. Four studies showed a higher risk of type 2 diabetes, while one reported an increased risk of gestational diabetes.

Hypertension

Four studies reported an increased risk of hypertension of up to 30%, one with cancer risk and several with overweight and obesity. Many of these studies also reported an association with increased weight, waist circumference, and increased serum lipid levels in children.

IBD

In the 2021 Prospective Urban Epidemiology (PURE) study, UPF intake was associated with a higher risk of IBD, particularly for Crohn’s disease, but not for ulcerative colitis. Other studies have linked UPF consumption to an increased risk of depression, abnormal lipid levels, declining kidney function, and fatty liver degeneration.

Weight gain

Short-term randomized intervention trials are currently underway, in which FPUs and unprocessed foods are assigned to different cohorts for short periods of time. Following this, the researchers observed an increase in energy intake on average of more than 500 kcal per day and an average weight gain of 0.8 kg in the UPF group. Conversely, an average weight loss of more than 1 kg was reported in the unprocessed food cohort.

Mechanisms behind chronic inflammation with UPFs

Many mechanisms can be attributed to the weight gain and chronic inflammation seen with high UPF consumption. An example includes the poor nutritional quality of many UPFs.

According to the French Open Food Facts database, only one in five FPUs has a high nutritional score. Even when energy intake from FPUs is standardized for comparison with unprocessed foods, adverse health effects continue to show a strong association, indicating that “factors beyond nutritional aspects have a role.”

Another issue is the presence of potentially toxic substances in UPFs, such as polycyclic aromatic hydrocarbons, furans, advanced glycation end products, trans fatty acids from the hydrogenation of fats, and acrylamide from cooking. high temperature starches. This last chemical can be found in common foods such as French fries, crisps and biscuits, whether produced at home or industrially; however, acrylamide levels are often higher in these industrial products.

Other contaminants such as phthalates, bisphenols, mineral oils and microplastics can leach into food from packaging, especially when food is left in contact for long periods of time. This probably occurs in food products that are shelf stable.

Prepared meals are typically UPFs and require microwave heating, which can enhance leaching of bisphenols from polycarbonate packaging or increase acrylamide formation.

The outcome of such exposures is unknown; however, previous research suggests a link to cancer, cardiovascular disease, insulin resistance, type 2 diabetes, obesity, and endocrine aberrations.

Another issue is the structural change that occurs in the various components of a food product due to processing, which could impact its bioavailability through altered digestibility, satiety, consumption rate and chewing, all of which can contribute to increased energy intake with UPFs. . This area is very little studied.

Over 300 food additives are authorized in Europe, several of which may be involved in chronic inflammation, possibly through their effects on the gut microbiome. Landmark studies have established that diets influence gut microbiota profiles, which can then alter host metabolism and promote obesity.

Gut bacteria are often able to ingest and process simple sugars when exposed to high dietary fat content. Gut stressors include certain food colorings, emulsifiers, artificial sweeteners, and nanoparticles like E171 (titanium dioxide).

These additives alter the ratio of key bacterial genera in the gut, where they affect the protective mucosal layer and the expression of important defensive molecules like β-defensins, and allow microbes to reach the sterile area of ​​the mucosa. This triggers a buildup of endotoxins which then leads to metainflammation and IBD.

Simultaneously, the changes in the molecular profile favor the extraction of increased energy from ingested food, thus causing metabolic dysregulation and obesity.

This links the calorie extraction from food consumed to diet-induced metabolic aberrations. This dysregulated metabolism is marked by low-grade inflammation and changes in the gut microbiome. The result is leakage of bacterial products like lipopolysaccharides (LPS) from the gut into the host system.

Gram-negative bacterial cell wall LPS contain lipid A, which is a molecule that crosses the intestinal mucosa. Once lipid A reaches the blood, it can trigger inflammation in various target tissues like the liver and fatty deposits in the body.

This cycle has been called “metainflammation”. Metainflammation can be defined as a metabolic inflammatory state defined by chronic low-grade inflammation created by metabolic cells and stress sensors.

This suggests the need for interventions in FPU intake to produce a beneficial change in the gut microbiome that will promote the production of “good” bacterial metabolites through appropriate gene expression by gut mucosal cells. These include anti-inflammatory short chain fatty acids (SCFAs).

conclusion

The results of the study underscore the need to improve current understanding of how food processing affects human health. Large-scale studies will be needed to identify components causally linked to metainflammation and obesity.

Public education is also crucial to support the consumption of healthier foods, preferably those that are minimally processed and free of additives. These food choices are underlined by recommendations from the Food and Agriculture Organization of the United Nations (FAO), as well as several national dietary guidelines.

Using measures such as financial incentives, laws, and mobile phone apps that provide evidence of food choices, federal policies should be directed toward promoting the production and distribution of healthy, good food products. quality.

Governments and the food industry should work together to establish policies that promote a healthier food environment for consumers to effectively combat the growing incidence of chronic inflammatory diseases.”

Journal reference:

  • Srour, B., Kordahi, MC, Bonazzi, E., et al. (2022). Ultra-processed foods and human health: from epidemiological evidence to mechanistic knowledge. The Lancet Gastroenterology and Hepatology. doi:10.1016/S2468-1253(22)00169-8.
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