You are what you eat. And people who eat a diet rich in seafood have healthier collections of gut microbes. 05/05/2020
Inside your stomach, some 100 trillion living things are working on your behalf. It’s a vast community that includes single-celled organisms, bacteria, fungi and even viruses. Together, these tiny inhabitants are known as the microbiome. They help draw energy from the food you eat, maintain your immune system and create micronutrients.
In recent years, scientists have devoted enormous effort to understanding the human gut microbiome, as study after study has linked common ailments to the health of these organisms. There’s evidence for the microbiome’s role in everything from diabetes and allergies to obesity. It suggests that when they’re out of balance, we’re out of balance.
Meanwhile, researchers have also been finding ways of keeping our gut flora happy. Unsurprisingly, eating a healthy diet is at the top of the list. Regular seafood consumption in particular has proven to have a large role in shaping our microbiome (ISSFAL 2014). Frequently eating omega-3s fatty acids has been shown to improve the overall diversity of our microbiomes (Watson et al. 2018). These healthful fats can also cut down on inflammatory bowel disease (Hudert et al. 2006). Omega-3s even influence the connection between the gut and the brain, an important driver of mood and overall health (Costantini et al. 2017).
Recently, researchers also added another important link between seafood and gut health. Eating seafood can promote certain markers of heart health found in the gut.
Seafood for Gut Health
Heart disease has been the leading cause of death in the United States for years, and it’s generally linked with unhealthy food choices. But scientists have shown that, over time, it’s possible to reduce some risk factors from heart disease by changing your diet. This might have something to do with the way our microbiomes interact with our overall health. And eating a healthy diet, especially one rich in seafood, might be one way to keep our microbiomes happy.
In one recent study, scientists from Norway and Denmark showed this by feeding people a seafood-rich diet for a month that included a variety of fish and shellfish. At the end, the participants had more beneficial organisms and fewer harmful ones in their gut microbiomes than when those same people were fed a diet without seafood (Schmedes et al. 2018). And it wasn’t just their microbiomes that benefitted. The researchers also found that eating seafood helped people’s cholesterol levels, and led to better heart health overall.
The researchers recruited 20 people for the study and broke them into two groups. Half were given lunches and dinners that featured cod, pollock and scallops. The other half stuck to a non-seafood diet heavy on chicken, turkey, lean beef, pork, egg and milk products. Once they’d eaten their assigned diets for a month, both groups took three weeks off and switched to the other diet.
Then, the team analyzed patients’ stool to get a rough census of their microbiome as well as look for chemical markers of their health. After eating a diet rich in lean seafood, they found the participants had reduced their markers of certain risk factors for cardiovascular disease. People on the seafood diet saw populations of several species of helpful bacteria increase, while levels of harmful bacteria decreased. For example, eating seafood raised the populations of a microbe called Roseburia, which lives in the colon and has been connected with weight loss in studies done on mice.
While they were eating seafood, participants also had increased levels of high-density lipoproteins, or HDL, the so-called “good” cholesterol. HDL works like a vacuum cleaner that sucks cholesterol into the liver so it can be flushed out. It can also help remove plaque from your arteries.
“The lean-seafood diet signiﬁcantly reduced [cardiovascular disease] risk factors compared to the non-seafood diet,” the authors wrote.
Omega-3s and the Microbiome
This isn’t the first time seafood has been tied to better gut health.
Many studies have shown that eating fish is good for our microbiomes overall, which boosts our health in a variety of ways. But the link to heart health adds to a growing body of evidence that keeping our microbiomes happy carries benefits far beyond the stomach.
In the past, studies have shown that seafood’s biggest benefits for the gut microbiome come from omega-3s. These fatty acids are commonly found in high amounts in foods like wild salmon, mackerel and cod liver oil. Omega-3s appear to play a role in everything from brain health to emotional stability, and they’ve been studied for decades.
So, it should come as no surprise that omega-3s play a role in our microbiomes, too.
While there are many different microbial species living in our guts, a few in particular appear to have an outsized role in human health. For example, Lactobacillus is one of the most common bacteria in probiotics, living organisms that can improve gut health. And studies show that eating omega-3s can increase the abundance of Lactobacillus in your microbiome (Bomba et al. 2003). You’ll find Lactobacillus in everything from yogurt to fermented foods like kimchi. In the gut, these bacteria seem to play a role in reducing cholesterol levels, which in turn reduces the risk of heart disease.
And omega-3s help with a range of other things, too. They can give a boost to another helpful bacteria called Bifidobacterium, which are vital for digestion and fighting off harmful bacteria (Watson et al. 2018). The fatty acids can also reduce inflammation and help make our guts less permeable, which some scientists think is a factor in certain autoimmune diseases. (Arrieta et al. 2007)
So, if you’re worried about heart health, consider mixing more seafood into your diet. Your gut will send you trillions of thanks.
Arrieta MC, Bistritz L, Meddings JB. Alterations in intestinal permeability. Gut. 2006;55(10):1512-20.
Bomba A, Nemcová R, Gancarcíková S, et al. The influence of omega-3 polyunsaturated fatty acids (omega-3 pufa) on lactobacilli adhesion to the intestinal mucosa and on immunity in gnotobiotic piglets. Berl Munch Tierarztl Wochenschr. 2003;116(7-8):312-6.
Centers for Disease Control and Prevention: National Center for Health Statistics. “Leading Causes of Death.” 2017 https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm
Holm JB, Rønnevik A, Tastesen HS, et al. Diet-induced obesity, energy metabolism and gut microbiota in C57BL/6J mice fed Western diets based on lean seafood or lean meat mixtures. J Nutr Biochem. 2016;31:127-36.
Hudert CA, Weylandt KH, Lu Y, Wang J, Hong S, Dignass A, Serhan CN, Kang JX. Transgenic mice rich in endogenous omega-3 fatty acids are protected from colitis. Proc Natl Acad Sci U S A. 2006 Jul 25;103(30):11276-81. Epub 2006 Jul 17.
International Society for the Study of Fatty Acids and Lipids (ISSFAL). Omega-3 Fats May Reduce Risk of Gastrointestinal Diseases. July 2, 2014. http://www.issfal.org/news/articles/2014/07/02/omega-3-fats-may-reduce-risk-of-gastrointestinal-diseases
Schmedes M, Brejnrod AD, Aadland EK, et al. The Effect of Lean-Seafood and Non-Seafood Diets on Fecal Metabolites and Gut Microbiome: Results from a Randomized Crossover Intervention Study. Molecular Nutrition & Food Research. 2019 Jan;63(1):e1700976. DOI: 10.1002/mnfr.201700976.
Watson H, Mitra S, Croden FC, et alA randomised trial of the effect of omega-3 polyunsaturated fatty acid supplements on the human intestinal microbiota. Gut 2018;67:1974-1983.