Is there an association between the consumption of ultra-processed food and adverse microbiota-gut-brain axis implications?

In a recent study published in the Food Research International Journal, researchers reviewed the impact of ultra-processed foods (UPFs) on the microbiota-gut-brain axis.

Study: Effects of ultra-processed foods on the microbiota-gut-brain axis: The bread-and-butter issue. Image Credit: Phairohchimmi/Shutterstock.com

Background

Focus on nutrient recommendations and dietary patterns has increased due to the rise of non-communicable chronic diseases in recent years. Identifying the dietary approaches that are advantageous or disadvantageous to personal well-being is, therefore, key.

The composition and function of the gut can be influenced by diet. The gut microbiota produces metabolites that can affect brain functions, either directly or indirectly, by digesting and fermenting food.

Exposure to UPF may impact gut microbiota, potentially causing metabolic imbalances and inflammation, increasing the likelihood of disrupting the neural network.

The impact of ultra-processed food ingredients on the gut-brain axis

High sugar

Sugar affects the brain regions responsible for controlling appetite and eating habits. The hypothalamic neurons receive signals from the gastrointestinal tract and peripheral systems to monitor energy balance, while eating behaviors are driven by the motivation system/dopamine reward.

Sugar consumption triggers the mesolimbic dopamine reward system, leading to the release of opioids and dopamine, which induces pleasure feelings.

High consumption of sugary foods can cause functional changes that may lead to metabolic disorders and overeating. This can result in an increased desire for high-sugar foods and consuming more energy than necessary. Sugar cravings can also originate from the gut.

A recent study found that sugar triggers neurons in the brainstem and the vagal ganglia through the gut-brain axis, leading to an affinity for sugar and highlighting the gut's importance in sugar signaling.

High- and low-fat

Ultra-processed food is typically high in energy density and contains saturated and trans fats, which can negatively impact the gut and the brain. Research has shown that a high-fat diet (HFD) consumed over a long period can negatively affect both brain and gut function.

Lipid oxidation products are present in foods that undergo extensive thermal processing or contain high pro-oxidant levels. Lipid oxidation products can pass through the gut barrier and cause gut inflammation and neuronal membrane damage, even if the plasma does not absorb them.

Long-term high-fat diet intake leads to inflammation in both the gut and brain, resulting in memory impairment and behaviors resembling anxiety and depression. Altered gut microbiota, specifically the depletion of Akkermansia muciniphila, is associated with cognitive function impairment.

The HFD microbiota transplantation results in memory and learning deficits dependent on the hippocampus. However, treating Akkermansia muciniphila orally can reduce neuroinflammation in the hippocampus and improve memory and learning.

High salt

Dityrosine, an oxidized protein product found in high salt, can cause intestinal oxidative damage and inflammation leading to tissue damage. Dityrosine increases oxidative stress in the brain, resulting in neurotransmitter disorders and impaired learning and memory abilities.

High-salt diet-induced memory impairment is linked to oxidative stress or synaptic protein disorder. The study found that mice fed a high-salt diet for eight weeks experienced impaired memory abilities and learning.

Additionally, the abundance of certain bacteria increased while others decreased in these mice.

Food additives

Emulsifiers

Studies have shown that, aside from lecithin, the most commonly utilized dietary emulsifiers negatively affect the gut microbiota.

Several substances, including P80, glycerol monolaurate, and carrageenan, have been found to impact the composition and diversity of the microbiota and harm epithelial functions.

This can lead to the onset of obesity/metabolic syndrome and intestinal inflammation. The human body's critical micelle concentration (CMC) improved postprandial abdominal discomfort and a change in the fecal metabolome's free amino acids and short-chain fatty acids (SCFAs).

Sweeteners

Sweeteners are sugar alternatives with a sweet flavor and are typically poorly absorbed by the body. The popularity of non-nutritive sweeteners (NNS) or non-calorie artificial sweeteners (NAS) is increasing due to their low-calorie content, cost-effectiveness, and ability to regulate blood sugar levels.

Consuming sweeteners can impact how humans perceive sweetness and affect the decision to choose healthy whole foods. NAS may cause glucose intolerance by altering the composition and function of the gut microbiota.

Studies in humans have found that consuming NAS over a long period may lead to an increased risk of type 2 diabetes and weight gain.

Food preservatives

Bacteriostatic antiseptic agents have been found to impact gut microbiota composition in both in vitro and in vivo studies. This sheds light on the safety of food preservatives. The immune system of zebrafish is impacted by potassium sorbate (PS) exposure, which changes the microbiota content and metabolism.

Sulfites have been found to hinder the growth of four beneficial bacteria strains, including Streptococcus thermophilus, Lactobacillus rhamnosus, Lactobacillus casei, and Lactobacillus plantarum.

Conclusion

The study findings highlighted how UPF could disturb the gut microbiota, leading to metabolism dysbiosis, inflammation, and impaired brain function through the MGB axis.

Future studies could focus on observing intestinal health to understand the underlying mechanism better. Future research should focus on species-level changes and their corresponding metabolic functions.

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.