By Dr. Mercola

The importance of fiber to your diet is nothing new. The dietary fiber you get from foods such as nuts and seaweed, for example, acts as a food source for your gut microbiota, helping your beneficial bacteria do their jobs. This involves breaking down complex foods, providing your body with nutrients and helping you feel full.

Most people eat nuts because they are a convenient snack. While almonds and cashews are popular choices, you now have a new reason to choose walnuts. A study at the University of Illinois underscores the value of walnuts not only because they are a healthy fat and good source of fiber, but also because of the specific ways they may benefit your gut microbiome.

Similarly, research out of Stanford University involving seaweed takes gut bacteria to the next level in that scientists have identified a means of manipulating bacterial strains for potential therapeutic use. Both bodies of research underscore the need for optimizing your gut, which I consider to be one of the most important factors in your overall health and well-being. I say that because 70 to 80 percent of your immune system resides within your digestive tract.

If you routinely eat nuts but overlook walnuts, you may be missing out. According to PreventDisease.com walnuts have some impressive health benefits:1

“Walnuts have been called a ‘superfood’ because they are rich inomega-3 fatty acid, alpha-linolenic acid and fiber and they contain one of the highest concentrations of antioxidants,” states registered dietitian Lauri Byerley, Ph.D., research associate professor of physiology at Louisiana State University Health New Orleans School of Medicine. “Now, an additional superfood benefit of walnuts may be their beneficial changes to your gut microbiota.”8

A study published in The Journal of Nutrition9 suggests walnuts affect your gut microbiota — the trillions of mostly beneficial microorganisms inhabiting your gut — in beneficial ways.10 Researchers at the University of Illinois at Urbana-Champaign, led by Hannah Holscher, Ph.D., assistant professor of food science and human nutrition, fed 18 participants either 42 grams (about one-third cup) ofwalnutsor no walnuts during two three-week periods that were separated by a one-week “washout” period.

Blood and fecal samples were collected and analyzed at the beginning and end of each study time frame to evaluate the effects of walnuts on fecal microbiota, bile acids and metabolic markers of health. Walnut intake was shown to increase levels of three bacteria: Clostridium, Faecalibacterium and Roseburia, which produce a metabolic byproduct called butyrate that is believed to improve colon health.

It’s important to note, however, Holscher and her team did not measure butyrate levels. She says, “[W]e can't say that just because these microbes increased that butyrate also increased. We still need to answer that question."11 Other interesting highlights from the research include:12

The work Holscher and her team completed builds on earlier research14 conducted at Louisiana State University in 2017. Working with lab rats for up to 10 weeks, Byerly and her colleagues discovered the walnut-eating group had different bacteria in its descending colon than rats eating a replacement diet containing comparable amounts of fat, protein and fiber.

In my opinion, the replacement diet of corn oil, protein casein and a cellulose fiber source was horrible and not an effective basis of comparison to walnuts. With the walnut diet, researchers noted the presence of increased amounts of beneficial bacterial. They also observed the numbers and types of bacteria changed, as did the bacteria's functional capacity. Said Byerly:15

In a study published in the journal Nature,16,17,18 researchers at Stanford University School of Medicine have shown it’s possible to manipulate animal diets as a means of influencing their gut bacteria. In fact, the team, led by Justin Sonnenburg, Ph.D., associate professor of microbiology and immunology at Stanford, was able to control the amount of bacterium growing in mice intestines simply by adjusting the amount of a specific carbohydrate in their food and water.

Previously, a 2010 study19,20 published in Nature investigated the transfer of carbohydrate-active enzymes from marine bacteria to the human gut, particularly among Japanese people due to seaweed comprising a large portion of their diet. About the current body of work Sonnenburg said:21

Despite the increased attention on the importance of gut health and probiotics, regardless of the source, little is known about why certain strains are more successful than others. As such, Sonnenburg and his colleagues speculated that a “dietary boost” would give specific bacterial strains an advantage inside the gut microbiome.

After choosing members of Bacteroides, the most prominent genus in human guts, the researchers sought to determine if the bacteria could use a carbohydrate called porphyrin, found in the sea vegetable nori. As to the choice of nori and that particular carbohydrate, Sonnenburg stated:22

After identifying a nori-eating strain of Bacteroides, the Stanford scientists attempted to introduce it to three groups of lab mice:23

When all three groups were fed a standard mouse diet, researchers were successful in engrafting the porphyrin-digesting strain in only two groups, and only to varied and limited degrees. However, when the three groups were fed a porphyrin-rich diet, the bacteria engrafted at similar levels in all mice.

Notably, the team discovered they could precisely calibrate the size of the engrafted bacteria population simply by increasing or decreasing the amount of the isolated nori compound. About the results, which stunned researchers, Sonnenburg said:24

Besides eating a few more walnuts and adding sea vegetables to your diet, below are other ways you can intentionally nourish your gut microbiome.

• Fermented foods: I often highlight the importance of eatingfermented foods to help "heal and seal" your gut. Culturing vegetables is easy and inexpensive and you also can make your own homemade yogurt, kefir or kimchi. These foods are not only packed with good bacteria, but also are detoxifying, immune-boosting and nutrient-rich. Fermented foods provide a wider variety of beneficial bacteria than you could ever receive in supplement form.

• Prebiotic foods: A great way to support your friendly gut bacteria is by providing them with prebiotics, which are found primarily in fiber-rich foods. Lab research25 involving young rats found that dietary prebiotics have a significant effect on your rapid eye movement (REM) and non-rapid eye movement (NREM) sleep cycles. The following whole foods help add prebiotic fiber to your diet and improve the health of your microbiome, thus improving your overall health:26,27

• Probiotics: While I highly recommend you obtain most of your nutrients from real food, probiotic supplements can be helpful if you are unable to eat fermented foods. For probiotics to do their job, you must nourish your microbiome with real food. That’s true because pathogenic, disease-causing bacteria thrive on sugar and processed food.

By eating whole, natural foods — plenty of healthy fats and organic vegetables, as well as moderate amounts of grass fed meat — you’re supporting the growth of your beneficial gut bacteria. Research suggests the benefits of probiotics aren’t limited to your gut, but also affect your immune system, mental health, mood and even your brain function. Probiotics have been shown to help reduce the symptoms of depression.

• Sporebiotics: Spore-based probiotics, or sporebiotics, which are part of a group of derivatives of the microbe called bacillus, are a great complement to probiotics. Sporebiotics consist of the cell wall of bacillus spores, and they help boost your immune tolerance, especially when it comes to antibiotics.

Chronic low-dose exposure to antibiotics through your food, particularly with respect to meat sourced from concentrated animal feeding operations (CAFOs), takes a toll on your gut microbiome. This can result in chronic ill health and an increased risk of drug resistance.

Whatever steps you take — eating walnuts and sea vegetables, eliminating sugar and processed foods, adding prebiotic foods, incorporating fermented foods, taking probiotics or sporebiotics, or all of the above — I encourage you to begin optimizing your gut. A healthy gut will boost your immunity, help your body resist disease and positively affect your health and well-being in ways that may surprise you.

Sources and References

1 PreventDisease.com May 6, 2018

2 The Journal of Nutrition April 2014; 144(4 Suppl): 547S-554S

3 WebMD March 28, 2011

4, 8 Louisiana State University Health New Orleans School of Medicine,

LSUHealthNO Research Finds Walnuts May Promote Health by Changing Gut Bacteria

5 The Journal of Nutrition April 2014; 144(4): 555S-560S

6 Heliyon February 2017; 3(2): e00250

7 The Journal of Nutrition Health and Aging May 2014; 18(5): 496–502

9, 13 The Journal of Nutrition May 3, 2018 [e-Pub ahead of print]

10, 11, 12 Medical News Today May 8, 2018

14 The Journal of Nutritional Biochemistry October 2017; 48: 94-102

15 Science Daily July 28, 2017

16 Nature May 9, 2018 [e-Pub ahead of print]

17 Science Newsline May 9, 2018

18, 21, 22, 23, 24 Science Daily May 9, 2018

19 Nature April 8, 2010; 464: 908-912

20 Wired April 7, 2010

25 Frontiers of Behavioral Neuroscience, January 10, 2017

26 DrJockers.com, The Top 33 Prebiotic Foods for Your Digestive System

27 Monash University, FAQs for the High Fiber, High Prebiotic Diet