It is hardly news that diet is the most powerful way to keep your gut microbiota in good shape. People with gastrointestinal conditions will sometimes try extreme diets, often with the aim of improving health or weight management. Caution is required, however, as not all current fad diets improve the good bacteria in your gut.

Ensuring you provide the right amount of fuel for your gut microbes is the best recipe for improving your gut health

The plant-based Mediterranean diet, characterized by greater intake of vegetable over animal protein, has been acknowledged as the best science-backed diet for boosting gut health. Why? Because the variety of plant-based foods—rather than caloric intake—provides fiber, certain vitamins, minerals and other nutrients (e.g., polyphenols) that our cells cannot digest but which increase the levels of both fecal short-chain fatty acids and beneficial bacteria, including Lactobacillus and Bifidobacterium.

In contrast, unbalanced and extreme diets can affect the intake of microbiota accessible carbohydrates (MACs)1. This is the case with the Western diet (high in animal protein and fat, low in MACs), which has been linked to a drop in the number of gut microbial genes (considered a marker of an altered gut microbiota) and compromised gut barrier integrity due to MAC restriction.

Similarly, a high intake of proteins increases protein fermentation in the large intestine and has an impact beyond the gut. While plant protein increases beneficial gut bacteria, strengthens the gut barrier and decreases inflammation, dietary patterns that are high in proteins and low in carbohydrates—such as the Paleo diet—have been associated with unfavorable changes in the gut microbiota and higher cardiovascular risk over the long term.

The keto diet might also provide cause for concern. This high-fat diet restricts carbohydrate intake and has been associated with gut-related side effects such as abdominal pain. It also poses a challenge in terms of obtaining all required nutrients (particularly fiber and B vitamins), a negative effect on microbial diversity, and a reduction in the levels of beneficial bacteria.

Beyond affecting your gut health, the elimination of certain foods and nutrients may also affect the proper functioning of your immune system, lead to poor metabolic health, and make your brain more susceptible to stress.

Even if you struggle with digestive symptoms, it is not a good idea to cut out your gut microbiota’s fuel of choice!

 Low-FODMAP, gluten-free and lactose-free diets are usually chosen as a means of reducing digestive symptoms (such as those associated with irritable bowel syndrome). However, extreme dietary choices are not necessarily a good fit for everyone. For example, it is not always a good idea to completely rule out lactose, as undigested lactose could act as a potentially beneficial prebiotic.

As exclusion diets eliminate some staple foods (e.g., whole grains, vegetables, pulses, fruits and fermented dairy products), which include carbohydrates that nourish your gut microbiota, they should always be seen as a temporary treatment in those with functional digestive complaints. As such, a subject’s regular diet should be slowly reintroduced according to individual tolerance, so as to avoid nutritional deficiencies.

In summary, a well-balanced diet, tailored to an individual’s needs and situation, is the best option for both healthy people and people with gastrointestinal conditions. While a Mediterranean diet is highly regarded as a healthy gut balanced diet, popular exclusion diets such as the low-FODMAP diet, the gluten-free diet and the lactose-free diet can leave the gut microbiota without its fuel of choice in the long term. So before completely eliminating a food group you love, it is worth contacting a registered dietitian with any doubts or questions you may have.

1Microbiota-accesible carbohydrates (MACs): certain types of fiber that come from plants, fungi or animal tissues that can be used by the gut microbiota. In contrast, other fibers such as wheat bran are not fermented by the gut microbiota.



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