Probiotics (good bacteria) and prebiotics (fibers that bacteria eat) impact gut health. Bacteria are able to both break down dietary fiber that our bodies cannot and make products that are linked to gut health and prevention of diseases like diabetes, cardiovascular disease, obesity, and colon cancer. But what about all of the other foods we eat every day? They come in contact with these bacteria too as they pass through our gut. Foods do not have to be classified as “probiotics” or “prebiotics” to affect the gut microbiome—everything we eat can impact the microbes in our gut.
Let’s take nuts, for example. They have a Qualified Health Claim by the FDA stating that eating 1.5 daily ounces per day of most nuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart diesase.1 Interestingly, a few studies found that eating nuts lowered blood cholesterol more than what the researchers predicted, leading them to suspect that something else was going on.2,3 This something else may be related to nuts impacting the bacteria that make up the gut microbiome.
So, what’s so great about nuts? In addition to being delicious, nuts are nutrient dense plant foods rich in monounsaturated and polyunsaturated fatty acids. Some of the heart-protecting health effects of nuts are linked to their relatively high monounsaturated and polyunsaturated fat content. Nuts also contain dietary fiber, vitamin E, phytosterols, and other compounds with known health benefits. Bacteria can use dietary fiber for energy and produce byproducts such as butyrate. Butyrate provides energy for cells in the gut and is linked to reduced inflammation.4 Systemic inflammation, or inflammation present throughout the body, is a precursor to metabolic diseases such as obesity and heart disease, and researchers think that these anti-inflammatory bacterial byproducts, including butyrate, may help to partially explain why nuts improve heart health.5
|Table 1. Quantity per serving and selected nutrient concentration per ½ oz USDA ounce equivalent serving of nuts1|
|Quantity per serving||Energy (kcal)||SFA
|Total Fiber (g)|
1Data were obtained from the USDA National Nutrient Database for Standard Reference.
Abbreviations: SFA=saturated fatty acids, MUFA=monounsaturated fatty acids, PUFA=polyunsaturated fatty acids
Cardiovascular Benefits of Nut Consumption
A lot of research demonstrates that nuts are heart healthy, with many studies finding that eating nuts can lower total and LDL cholesterol.
- An analysis of 4 large studies found a 35% lower risk of death related to heart disease in individuals that ate nuts 5 or more times per week.6
- Eating nuts 5 or more times per week was associated with healthy cholesterol levels in a study involving 6000 women with type 2 diabetes.7
- A systematic review of 23 nut-focused research studies found that 1.5 to 3.5 ounce servings 5 or more times per week of almonds, peanuts, pecans, and walnuts reduce total cholesterol and LDL cholesterol.3
- Another review specific to walnuts found that this tree nut lowered LDL and total cholesterol in 13 randomized controlled trials.8
Nut Consumption and the Gut Microbiome
Connections between heart health and the gut microbiome have become more evident in recent years. Certain heart disease risk factors, such as blood cholesterol levels and markers of blood vessel health, have been associated with abundances of specific bacteria in the gut. One study of 893 adults found that certain gut microbes were associated with body weight, triglycerides, and HDL cholesterol.9 Another study found differences in the bacteria that were present in the guts of patients with heart disease compared to a group of healthy adults. Healthy adults had greater abundances of certain bacteria, Roseburia and Eubacterium, than those with heart disease.10 These bacteria produce byproducts such as butyrate that have anti-inflammatory properties.
These studies prompted scientists to work to try to better understand if there is a cause and effect relationship between eating nuts and gut health. A study of 1.5 or 3 servings per day of almonds and pistachios (tree nuts) found that both nuts increased abundances of known butyrate-producing bacteria.11 Recent work from our laboratory, the Nutrition and Human Microbiome Laboratory, found that 1.5 daily ounces of walnuts increased abundances of butyrate-producing bacteria.12 We also found that 1.5 servings per day of almonds resulted in increases of butyrate-producing gut bacteria.13 More work is needed to understand whether and how certain bacteria that produce butyrate, a beneficial by-product, may also be helping improve heart health.
In summary, nuts are nutrient dense foods linked to many health benefits. They reduce the risk of heart disease, and emerging research indicates that nuts also impact the human gut microbiome. More research is needed to understand the full picture and to identify long-term effects of nut consumption on the gut microbiome. As the scientific community learns more about these plant foods, however, one can infer that nut consumption can benefit one’s heart – and potentially one’s gut.
- Administration UF and D. Summary of qualified health claims subject to enforcement discretion: Nuts & heart disease. http://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm073992.htm#nuts. Accessed May 16, 2016.
- Kris-Etherton PM, Zhao G, Binkoski AE, Coval SM, Etherton TD. The effects of nuts on coronary heart disease risk. Nutr Rev. 2001;59(4):103-111. http://www.ncbi.nlm.nih.gov/pubmed/11368503. Accessed May 20, 2016.
- Mukuddem-Petersen J, Oosthuizen W, Jerling JC. A systematic review of the effects of nuts on blood lipid profiles in humans. J Nutr. 2005;135(9):2082-2089.
- Brahe LK, Astrup A, Larsen LH. Is butyrate the link between diet, intestinal microbiota and obesity-related metabolic diseases? Obes Rev. 2013;14(12):950-959. doi:10.1111/obr.12068.
- Souza RGM, Gomes AC, Naves MM V, Mota JF. Nuts and legume seeds for cardiovascular risk reduction: scientific evidence and mechanisms of action. Nutr Rev. 2015;73(6):335-347. doi:10.1093/nutrit/nuu008.
- Kris-Etherton PM, Hu FB, Ros E, Sabate J. The Role of Tree Nuts and Peanuts in the Prevention of Coronary Heart Disease: Multiple Potential Mechanisms. J Nutr. 2008;138(9):1746S – 1751. http://jn.nutrition.org/content/138/9/1746S.full. Accessed May 19, 2016.
- Li TY, Brennan AM, Wedick NM, Mantzoros C, Rifai N, Hu FB. Regular consumption of nuts is associated with a lower risk of cardiovascular disease in women with type 2 diabetes. J Nutr. 2009;139:1333-1338. doi:10.3945/jn.108.103622.there.
- Banel DK, Hu FB. Effects of walnut consumption on blood lipids and other cardiovascular risk factors : a meta-analysis and systematic review 1 – 3. Ajcn. 2009:56-63.
- Fu J, Bonder MJ, Cenit MC, et al. The Gut Microbiome Contributes to a Substantial Proportion of the Variation in Blood LipidsNovelty and Significance. Circ Res. 2015;117(9):817-824. doi:10.1161/CIRCRESAHA.115.306807.
- Karlsson FH, Fåk F, Nookaew I, et al. Symptomatic atherosclerosis is associated with an altered gut metagenome. Nat Commun. 2012;3:1245. doi:10.1038/ncomms2266.
- Ukhanova M, Wang X, Baer DJ, Novotny JA, Fredborg M, Mai V. Effects of almond and pistachio consumption on gut microbiota composition in a randomised cross-over human feeding study. Br J Nutr. 2014;111(12):2146-2152. doi:10.1017/S0007114514000385.
- Guetterman HM, Swanson KS, Novotny JA, Baer DJ, Holscher HD. Walnut Consumption Influences the Human Gut Microbiome. FASEB J. 2016;30(1_Supplement):406.2 – . http://www.fasebj.org/content/30/1_Supplement/406.2.short. Accessed May 19, 2016.
- Taylor AM, Swanson KS, Novotny JA, Baer DJ, Holscher HD. Impact of Almond Consumption on the Composition of the Gastrointestinal Microbiota of Healthy Adult Men and Women. FASEB J. 2016;30(1_Supplement):406.5 – . http://www.fasebj.org/content/30/1_Supplement/406.5.short. Accessed May 19, 2016.
Sharon Thompson, Graduate Research Fellow, and Heather Guetterman, Research Assistant, work in the Nutrition and Human Microbiome Laboratory directed by Dr. Hannah Holscher at the University of Illinois at Urbana-Champaign. Research in our laboratory focuses on understanding the impact of diet on the human gastrointestinal microbiome with an overarching goal of improving human health through dietary modulation of the gastrointestinal microbiome.