Diet & Gut microbiota

The influence of diet on gut microbiota

Environmental factors—mainly lifestyle, diet and medication—outweigh the body’s genetics in determining the composition and proper functioning of the gut microbiota.

A diverse diet is considered a major factor in influencing your gut and the composition and function of the bacteria that live within it.

The idea that what you eat affects your health and that health starts in the gut isn’t new. Hippocrates, the father of medicine, suggested that “All disease begins in the gut”. Later, in 1907, Elie Metchnikoff was the first to hypothesize that replacing or diminishing harmful bacteria in the gut with lactic acid bacteria found in fermented foods could prolong life through a healthy gut.

Fast forward to the 21st century and scientists have learned that, although there’s a heritable component associated with the gut microbiota, environmental factors related to diet and drugs also have a major influence.

Recent studies have shown that a diet high in fat and sugar leads to changes in the gut microbiota that may explain the coincident increase in conditions such as type 2 diabetes, obesity, and inflammatory bowel diseases.

That’s why scientists recommend that a diet rich in microbiota-accessible carbohydrates (MACs)—abundant in whole grains, vegetables, legumes and nuts but lacking in processed foods—and exposure to fermented foods may be beneficial for preserving gut bacteria that are beneficial to human health. Beyond the well known effects of dietary fiber on gut health, other nutrients including carbohydrates, proteins, fats, vitamins, minerals and small compounds such as dietary polyphenols (with their antioxidant properties) can also act on the gut microbiota. In other words, the food you eat is the main fuel for your gut microbes.

With this in mind, the principle of “You are what you eat” is further clarified by science, which presents the alternative mantra of “You are what your gut microbes do with what you eat”.

Targeting the gut microbiota through diet not only matters in healthy people, but can also be added to medical treatment for conditions linked to lower bacterial diversity. In other words, maintaining a species-rich gut ecosystem through diet is a science-backed way to achieve a healthier lifestyle.

Another thing to consider is that not everyone responds to diet in the same way. And as gut microbiome responses to nutrition are specific to each individual, a “one-size-fits-all” dietary approach is being replaced by the idea of harnessing the potential of gut microbiome-informed personalized nutrition for better health.

  • Within diet, prebiotics, fibers, probiotics and fermented foods have largely been studied as ways of keeping the gut microbiota in good shape and maintaining its capacity for resilience.

A prebiotic is food for the beneficial gut bacteria that are hosted by the human body. Prebiotics are naturally present at low levels in vegetables (onions, garlic, bananas, cabbage, kale, chicory root and Jerusalem artichokes) and whole grains. Prebiotics may be also added to some foods, including yogurts, infant formula, cereals, bread or even drinks.

Most prebiotics are fibers fermented by the gut microbiota, but not all dietary fibers are prebiotics. That’s why some scientists prefer the term ‘microbiota-accessible carbohydrates’ or MACs to refer to carbohydrates that cannot be digested by humans but which are available to bacteria in the colon.

So what  contributions do these prebiotics make to your health? Prebiotics can help improve bowel habits, including reducing constipation and diarrhea, and improve the symptoms of irritable bowel syndrome.

Furthermore, the metabolites produced during the fermentation of prebiotics by gut bacteria, known as short-chain fatty acids, beyond a local effect, may also act on regulating satiety. When consumed in excess, however, prebiotics can cause gas, bloating and/or diarrhea.

Probiotics are live microorganisms that are beneficial to health. They are usually present in yogurts and certain fermented foods and also exist as food supplements.

It is important to know that probiotics can affect health in many possible ways, regardless of whether they establish in the gut and change the resident gut microbiota

For example, probiotics may act by: 

  • interacting with immune cells lining the digestive tract; 
  • helping the gut microbiota resist growth of harmful bacteria; and 
  • producing short-chain fatty acids that have health effects that can be either local or systemic (within the human body).

As a result, probiotics may help you stay healthy by:

  • relieving certain gut symptoms (diarrhea, constipation and bloating);
  • reducing associated symptoms of lactose maldigestion;
  • decreasing symptoms of irritable bowel syndrome;
  • reducing side effects of treatment for Helicobacter pylori eradication;
  • decreasing respiratory, gut, vaginal and urinary tract infections;
  • balancing the gut microbiota after taking antibiotics, acid suppressants, anti-diabetic drugs, nonsteroidal anti-inflammatory drugs and antipsychotic medication;
  • relieving colic in breastfed babies;
  • supporting the immune system; and
  • helping with some psychological symptoms (e.g., anxiety and depression), although the research suggesting this has yet to be confirmed.

The efficacy of probiotics with regards to digestive health and the immune system is recognized by consensus. In addition, it should be noted that probiotics are not all the same, they do not all act in the same way, and do not all offer the same benefits. Instead, these benefits are specific to probiotic strains, even if these strains may have common characteristics.

More recently, the term ‘paraprobiotics’ has been coined for inactivated probiotics (i.e. dead bacteria such as cell-wall components) that may confer health benefits on the host.

Synbiotics combine probiotics and prebiotics in food or dietary supplements, with conferred health benefits.

Conditions in which synbiotic treatments have been explored include inflammatory bowel diseases, diarrhea, irritable bowel syndrome, metabolic syndrome, colon cancer, and kidney and liver diseases.

Fermented foods result from the transformation of a food by living microorganisms (bacteria, yeasts). The transformation brings to this new food a different texture and taste. However, not all fermented foods are probiotics, as not all contain live organisms that are well characterized and confer a health benefit.

Yogurt is a good example of fermented food that contains probiotics. The transformation of milk by lactic acid bacteria, for instance, will produce a yogurt with improved nutritional properties (higher vitamin and mineral content) and increased digestibility compared with milk. Thanks to the bacteria it contains (Lactobacillus acidophilus and Streptococcus thermophilus), yogurt allows better digestibility of lactose, and its consumption has also been associated with a healthier lifestyle.