Heart health and digestive disease have been shown to be stemmed by diets plentiful in foods containing long-chain fatty acids such as Omega-3, Omega-6, or Alpha-Linolenic Acids. These compounds are common among foods such as flax seeds and tree nuts. Recently published research has shown a connection between diets containing walnuts and gastrointestinal health—specifically through their impact on the microbiome [5].

Digestive Support & Lowered Ldl Cholesterol

This study was a follow up to a primary study which analyzed the total metabolic energy of walnuts. The secondary outcomes, reported by this most recent study, described the impacts of a small serving of walnuts on digestive bacteria, bile production, and cholesterol levels. Participants of this study were given 42 grams (1.5 servings) of walnuts to supplement their diet over two 3-week periods. Researchers describe this amount being chosen to adhere to recommendations put forth by the FDA which describe 1.5 grams of certain types of nuts being able to reduce the incidence of heart disease [3].

Lowers Secondary Bile Production

Bile is a compound produced by the liver, stored in the gallbladder, which is used to help dissolve foods to assist with digestion. Primary bile is produced directly by our bodies while secondary bile is often a by-product of bacteria. Conditions such as Small Intestinal Bacterial Overgrowth (SIBO) are often characterized by lowered levels of bile and stomach acid—making overall digestion more difficult. Health professionals often recommend taking supplements such as Betaine-HCL or Pepsin to help account for this deficiency. This latest research found that 1.5 grams of walnuts per day accounted for a significant decrease in secondary bile. Specifically, researchers found significant (P<0.01) reductions in both deoxycholic acid and lithocholic acids. While such reduction may be attributed to the reduction in certain types of bacteria, it should be noted that these acids are often attributed to positive health impacts such as modulating Vitamin D receptor sites [4].

Lowers Ldl Cholesterol

When it comes to cholesterol, there are many varying opinions on the subject. For years we were bombarded by the thought that eggs would kill us and imitation butter would be our salvation. Modern research has helped dissuade much of the alarmist opinions on total cholesterol levels and has elucidated that certain cholesterols have greater potential in wreaking havoc in our bodies. High-Density Lipoprotein (HDL) is the type of cholesterol that is considered “good.” HDL cholesterol is eliminated by the liver and has little chance of clogging up arteries. Low-Density Lipoprotein (LDL) cholesterol is the type commonly attributed to increased risk of such diseases as coronary artery disease.

The general opinion in the medical community is that higher total cholesterol levels are much less worrisome when there is a strong favor towards HDL cholesterol. This study described walnuts as lowering the total cholesterol (P=0.03) and the LDL cholesterol levels (P<0.01) significantly while also notably increasing HDL levels (P=0.51). Simply put; it seems that walnuts may be able to improve your overall cholesterol levels by lowering the bad (LDL) cholesterol and slightly increasing the good (HDL) cholesterol—overall providing a shift towards a healthier balance.

Strengthening Good Digestive Bacteria

The bacteria found in our digestive tracts number in the hundreds of trillions and are thought to be at the center of many of our bodies’ most vital processes. That’s to say; a poor bacterial balance is likely to drive poor overall health. That’s still personal opinion at the moment, but the Scientific community has been reinforcing this perspective with great vigor in recent years. This most recent study found that walnuts were able to increase the counts of certain types of bacteria commonly-regarded as being beneficial to human health. Two such bacteria are Faecalibacterium and Roseburia which are attributed to increased production of butyrate—later converted into such useful compounds as Gama Aminobutyric Acid (GABA). Researchers also noted a significant (P<0.03) reduction in Bifidobacterium species which are generally regarded as being beneficial to human health.

The Importance Of Balance

These many trillion bacteria help us digest food, act as the first line of defense against potentially dangerous compounds like Salmonella. These bacteria come in many varieties and are thought to be at the root of many chronic health issues when they shift towards a balance in favor of pathogenic bacteria. One simple example is illustrated by the genus of bacteria Streptococcus, which can be found in the digestive tracts of normal healthy people [1]. However, when this bacteria grows out of balance, it can be found in areas of our body such as the throat—diagnosed as Strep Throat (Streptococcus Throat.)

There are many more such cases where bacteria that are part of the natural human microbiota can become harmful when the overall balance of the microbiota sways in their direction. Before you go out and gorge yourself on fiber consider this; if dietary fiber supports the bacterial balance of one’s digestive tract what happens when one eats fiber in the presence of a bad bacterial balance? My personal experience has been that disaster ensues. In fact, diets low in fiber are often heralded by those with food-sensitivities of other conditions thought to be bacterial such as Chronic Fatigue Syndrome. The most popular of such diets is the Low FODMAP diet.

Fiber Makes The World Go ‘Round

Amidst the many healthy fatty acids in walnuts (and many other foods for that matter) there are also large percentages of fiber. Consuming fiber on a regular basis helps support the bacterial communities, known collectively as the microbiome, that is present in each of our digestive systems. Dietary fiber acts as a food source for the many bacteria in our digestive tract. When adequate amounts of dietary fiber are consumed, the diversity of the existing microbiota is preserved. Research has demonstrated that diets high in fiber account for a significant reduction in chances of nearly all major disease [2]. Ensuring adequate nutrition can be difficult for those with diet-related issues that restrict total fiber intake. One way to “hack” one’s way around this restriction is by juicing fruits and vegetables to extract the nutrients without all the fiber. Of course, you need an actual juicer to do this—not just a blender!

Final Thoughts

This study adds to the growing body of evidence that human well-being may largely be dictated by the balance of the bacteria found in our bodies. Personal experience has taught me to recognize the importance of balance rather than focusing on specific numbers or species. That’s to say; it’s a good thing to have a little Streptococcus, but if you get too much you’ll wind up feeling pretty crappy. Dietary habits that support a positive balance of bacteria are a great way to ensure you hang on to those times in life where you just “feel great.” For those of us that suffer from bacterial imbalance, however, things can often be much more complicated.

This research, small as it was, helps uncover some useful tools for those seeking to sway their bacterial balance. Namely, it suggests the addition of walnuts to one’s diet may lower secondary bile production (from bacteria), improve butyrate-producing bacteria, but may also lower Bifidobacterium counts. As an added bonus, this study also reinforced the understanding of how walnuts may lower the risk of heart disease by improving the balance between LDL cholesterol and HDL cholesterol. I say it often, but still can’t say it enough; everyone is different and what may be heralded as a miracle by one may be scorned by another. This research describes how adding 1.5 grams of walnuts to one’s daily diet may serve as a tool for maintaining a healthy balance.


  1. Patterson, Maria Jevitz. “Streptococcus.” Medical Microbiology. 4th Edition., U.S. National Library of Medicine, 1 Jan. 1996,
  2. Park, Yikyung, et al. “Dietary Fiber Intake and Mortality in the NIH-AARP Diet and Health Study.” Archives of Internal Medicine, U.S. National Library of Medicine, 27 June 2011,
  3. FDA. “Labeling & Nutrition – Summary of Qualified Health Claims Subject to Enforcement Discretion.” U S Food and Drug Administration Home Page, Center for Biologics Evaluation and Research, 14 July 2003,
  4. Eaton, John E. “Lithocholic Acid.” Egyptian Journal of Medical Human Genetics, Elsevier, 2014,
  5. Holscher Hannah, et al; Walnut Consumption Alters the Gastrointestinal Microbiota, Microbially Derived Secondary Bile Acids, and Health Markers in Healthy Adults: A Randomized Controlled Trial, The Journal of Nutrition, , nxy004,
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