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Beans Keep it Healthy

Your Gut Microbiome Influences Immune Function

written by Joel Fuhrman, M.D. April 30, 2021
Beans Keep it Healthy

Why beans?

Beans, lentils, and split peas are rich in fiber, resistant starch, and plant protein, and they are a low-glycemic carbohydrate source. The health benefits of these legumes sometimes get overlooked, but adding beans to your diet promotes weight loss, cardiovascular health, and insulin sensitivity.

Related post: Clinical study confirms that beans are the preferred starch source for diabetics

What is the microbiome?

The human microbiome is a complex collection of bacteria, viruses, fungi, and other microorganisms that inhabit body surfaces, including the skin and digestive tract. The majority of the microbiome lives in the gut, where there are more than 1000 different species of bacteria.

The gut microbiome in action

The trillions of organisms in the gut microbiome are busy: They produce vitamins, such as K2 and B12, help develop immunity, enhance the benefits of some phytochemicals, and protect against pathogens. The bacteria of the microbiome converts dietary fiber and resistant starch from plant foods into short-chain fatty acids (SCFAs) that protect intestinal cells and regulate metabolism.1-4 The gut microbiome can even be considered an organ of the human body; without it, the body would not function properly.


Intestinal immune function is largely shaped by the microbiome

The intestinal mucosal immune system is a large and important part of the whole human immune system, and the microbiome is closely connected with intestinal immunity. The microbiome modulates the activity of immune cells, counteracts inflammation, and maintains the integrity of the intestinal barrier.5-7 This means we count on a healthy gut for a powerful immune response.


What makes beans special?

Beans, lentils, split peas, and other legumes are rich in fiber and resistant starch, carbohydrates that cannot be broken down by human digestive enzymes.

The bacteria that reside in the large intestine depend on “microbiota-accessible carbohydrates,” also known as prebiotics, to survive; prebiotics are food for gut bacteria. Without enough prebiotics in our diet, gut bacteria begin to consume an alternative energy source: the first line of our immune defense on the surface of the intestinal lining. This intestinal lining is made up of molecules called mucins.3

All plant foods contain some prebiotics, but beans are special because they are very high in resistant starch, making them especially rich in prebiotics. Not all indigestible plant carbohydrates act as prebiotics, but resistant starch from beans provides large amounts of prebiotics. Prebiotics nourish the microbiome and allow for production of SCFAs.3

So the fiber and resistant starches from beans are waiting in our digestive tract and full of microbiota-accessible carbohydrates. To sum it up, we eat beans because they nourish our microbiome and  promote production of short chain fatty acids. SCFAs help kick our immune system into gear.

What’s a SCFA?

Diet plays a large role in determining what kinds of microbiota live in the colon. Prebiotic fiber and resistant starch can only be broken down and fermented by enzymes from microbiota living in the colon. Short chain fatty acids (SCFA) are released as a result of this fermentation.

Growing research on SCFAs explores their wide-ranging effects on health, including stimulating immune cell activity and maintaining normal blood levels of glucose and cholesterol.

The production of SCFAs is an essential part of the microbiome’s effects on immune function. SCFAs both have anti-inflammatory effects and promote integrity of the intestinal epithelial barrier. This barrier helps to prevent pathogenic bacteria in the gastrointestinal tract from causing an infection.7

When we eat fiber- and resistant starch-rich foods, we support the growth and development of a healthy microbiome.4


Action items

Beans to try:

Adzuki beans, black beans, cannellini, chickpeas, edamame, green split peas, lentils, kidney beans, Navy beans, pinto beans


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Beans, Beans the Wonderful Fruit

Learn more about the microbiome:


  1. Rowland I, Gibson G, Heinken A, et al. Gut microbiota functions: metabolism of nutrients and other food components. Eur J Nutr 2018, 57:1-24.
  2. Duda-Chodak A, Tarko T, Satora P, Sroka P. Interaction of dietary compounds, especially polyphenols, with the intestinal microbiota: a review. Eur J Nutr 2015, 54:325-341.
  3. Sonnenburg ED, Sonnenburg JL. Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell Metab 2014, 20:779-786.
  4. Sonnenburg JL, Backhed F. Diet-microbiota interactions as moderators of human metabolism. Nature 2016, 535:56-64.
  5. Shi N, Li N, Duan X, Niu H. Interaction between the gut microbiome and mucosal immune system. Mil Med Res 2017, 4:14.
  6. McDermott AJ, Huffnagle GB. The microbiome and regulation of mucosal immunity. Immunology 2014, 142:24-31.
  7. Kau AL, Ahern PP, Griffin NW, et al. Human nutrition, the gut microbiome and the immune system. Nature 2011, 474:327-336.


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