Low-Fiber Diets Harm the Good Bacteria in Your Gut

A lack of fiber is one of the main flaws of the modern diet.

Whole plant foods have largely given way to heavily processed products that have lost most of their fiber.

Growing evidence suggests that low-fiber diets may adversely affect the gut microbiota, contributing to the development of many chronic lifestyle diseases.

A recent review discussed the importance of dietary fiber for the beneficial bacteria living in your gut, and how you can preserve a healthy gut microbiota.

Article Reviewed

This review discussed the importance of maintaining a healthy gut microbiota by eating enough fiber and probiotic for weight loss.

The Fiber Gap and the Disappearing Gut Microbiome: Implications for Human Nutrition.

What is the Gut Microbiota?

The microbes — bacteria and yeasts — living in your digestive system are collectively known as the gut microbiota or gut flora.

Most of these microbes rely on the things you eat. For example, some thrive on fiber, whereas others multiply when your diet is high in fat and sugar.

Simply put, your dietary choices determine what types of bacteria live in your digestive system. This can have important health implications and weight loss efforts
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Generally, a diet based on whole, fiber-rich foods promotes the growth of beneficial bacteria, whereas other diets may favor bacteria you would do better without.

Bottom Line: The bacteria in your digestive system are collectively known as the gut microbiota. Their numbers and diversity depend on your diet.

The Importance of a Healthy Gut Microbiota

A healthy gut contains trillions of bacteria. The types of bacteria that are dominant, as well as their quantities, are also important.

For optimal health, your gut should host a variety of beneficial bacteria. Some of their health benefits include:

  • Colon nutrition: The bacteria produce short-chain fatty acids in your colon, providing nutrition for the cells lining the colon, improving colon health and reducing inflammation (1).
  • Stronger gut wall: The bacteria may protect and strengthen the gut wall, preventing harmful substances from entering the blood (234).
  • Vitamin K: The bacteria also produce vitamins, such as vitamin K (5).
  • Immune system regulation: Animal studies indicate that the gut microbiota provides the immune system with important signals, regulating its function (6).

An imbalance in the gut microbiota, often referred to as dysbiosis, is when beneficial bacteria are lacking and undesirable bacteria overpopulate the gut.

As discussed in a previous research review, dysbiosis is associated with inflammation, obesity and metabolic diseases.

Bottom Line: Your health may depend on the dominant bacteria in your gut. Some may harm your body, whereas others provide health benefits.

Is the Gut Microbiota Disappearing?

Evidence indicates the modern diet may have led to the loss of beneficial microbes.

The consumption of processed foods has increased, and diets may have become deficient in fiber, at least compared to pre-industrial levels (7).

This is supported by observational studies comparing the gut microbiota of people living in primitive societies with that of people living in Western countries.

For example, gut microbial diversity is significantly greater in people living in rural communities in Papua New Guinea, South America and Africa, compared to people in the US and Europe (8).

Furthermore, the average diet of people in Western society is low in fiber. In fact, it’s only half of what is recommended in official guidelines (9).

Bottom Line: The Western diet contains low amounts of fiber. This may have led to a reduction in the diversity of microbes living in people’s guts.

A Low-Fiber Diet Harms the Gut Microbiota

Multiple factors may affect the gut microbiota. However, the strongest determinant of gut microbial health and diversity is your diet, especially your fiber intake.

Not all fiber is equal. The types of fiber that promote the growth of beneficial bacteria are known as prebiotics or microbiota-accessible carbohydrates (MACs) (10).

Prebiotics are indigestible carbs that pass down into the lower parts of the digestive tract, where they are fermented by the resident bacteria.

A diet deficient in prebiotic fiber reduces the numbers of bacteria that rely on them. Foods like applesauce might seem healthy but are have no fiber.

As a result, levels of short-chain fatty acids in the colon decrease, potentially leading to poor colon health and inflammation (11).

Bottom Line: Fiber intake is very important to gut microbial health. A prolonged low-fiber diet may reduce the numbers of beneficial bacteria.

How to Preserve the Gut Microbiota

The single most important thing you can do to preserve your gut microbiota is to eat enough prebiotic fiber.

Human studies have shown that eating fiber and whole grains increases the diversity of fecal bacteria, which is an indicator of bacterial diversity in the colon (1213).

Although fiber can be obtained from a variety of whole foods, supplements may be convenient for those who find it hard to get enough from their diet.

Here is a list of a few types of prebiotic fiber:

  • Beta-glucan: Found in cereals, especially oats and barley (14).
  • Galacto-oligosaccharides: A food additive also sold as a supplement (15).
  • Guar gum: A food additive widely used in a variety of products (16).
  • Inulin: Found in chicory root, Jerusalem artichokes, garlic, onions and asparagus (17).
  • Pectin: Found in fruits, such as apples, oranges, plums and bananas (18).
  • Resistant starch: Found in whole grains, legumes, green bananas and potatoes (19).

Bottom Line: Eating enough prebiotic fiber may be a good way to preserve or even restore the gut microbiota.

Summary and Real-Life Application

Evidence indicates the modern lifestyle may have reduced the number of beneficial gut bacteria, potentially contributing to chronic disease such as high blood sugar.

The low fiber content of the Western diet is partly to blame.

So if you value your health, getting enough prebiotic fiber from whole foods or supplements should be a high priority for natural weight control without resorting to pills like garcinia cambogia or alli.