Studies show significant short-term changes to the microbiome when eating fruits, vegetables and plant fiber
By David Dunaief, M.D.
Considering our recent focus on cleansing germs from every surface, it’s a leap to acknowledge that we harbor a multitude of microorganisms, or microbes, in our bodies. We have so many, over one trillion microorganisms, that they outnumber our cells by a 10-to-1 ratio, even in healthy individuals.
These make up what we call the microbiome. It includes bacteria, viruses and single-cell eukaryotes. Our relationship to these organisms is complex, spanning from parasitic to commensalistic (one benefits and the other is not affected) to mutualistic (both benefit). While the microbiome is found throughout our bodies, including the skin, the eyes and the gut, we’re going to focus on the gut, where the majority of the microbiome resides.
Why do we care about the gut microbiome?
The short answer is it may have a role in diseases — preventing and promoting them. These include obesity, diabetes, irritable bowel syndrome, autoimmune diseases, such as rheumatoid arthritis and Crohn’s, and infectious diseases, such as colitis. Like the Human Genome Project, which mapped our genes, there is a Human Microbiome Project, launched by the National Institutes of Health in 2007, to map out the composition and diversity of these gut organisms. We are still in the early stages of understanding this vast universe of microbes, yet there have been some preliminary studies.
What affects the microbiome?
Drugs, such as antibiotics, can wipe out the diversity in the microbes, at least in the short term. Also, lifestyle modifications, such as diet, can have an impact. Microbiome diversity also may be significantly different in distinct geographic locations throughout the world. Let’s look at the evidence.
Using twins to study obesity
Obesity can be one of the most frustrating disorders; most obese patients continually struggle to lose weight. Obese and overweight patients now outnumber malnourished individuals worldwide (1).
I know this will not come as a surprise, but we are a nation with a weight problem; about 70% of Americans are overweight or obese (2) (3). For the longest time, the paradigm for weight loss had been that if you ate fewer calories, you would lose weight. However, extreme low-caloric diets did not seem to have a long-term impact. It turns out that our guts, dominated by bacteria, may play important roles in obesity and weight loss, determining whether we gain or lose weight. Let’s look at the data on obesity.
The results from a study involving human twins and mice are fascinating (4). In each pair of human twins, one was obese and the other was lean. Gut bacteria from obese twins was transplanted into thin mice. The result: the thin mice became obese. However, when the lean human twins’ gut bacteria were transplanted to thin mice, the mice remained thin.
By pairing sets of human twins, one obese and one thin in each set, with mice that were identical to each other and raised in a sterile setting, researchers limited the confounding effects of environment and genetics on weight.
The most intriguing part of the study compared the effects of diet and gut bacteria. When the mice who had received gut transplants from obese twins were provided gut bacteria from thin twins and given fruit- and vegetable-rich, low-fat diet tablets, they lost significant weight. But they only lost weight when on a good diet; there was no impact if the diet was not low in fat. The authors believe this suggests that an effective diet may alter the microbiome of obese patients, helping them lose weight. These are exciting, but preliminary, results. It is not clear yet which bacteria may be contributing these effects.
This definitely suggests that the diversity of gut bacteria may be a crucial piece of the weight-loss puzzle.
Do gut bacteria influence rheumatoid arthritis development?
Rheumatoid arthritis (RA) is an autoimmune disease that can be disabling, with patients typically suffering from significant morning stiffness, joint soreness and joint breakdown. What if gut bacteria influenced RA risk? In a study, the gut bacteria in mice that were made susceptible to RA by deletion of certain genes (HLA-DR genes) were compared to those who were more resistant to developing RA (5). Researchers found that the RA-susceptible mice had a predominance of Clostridium bacteria and that those resistant to RA were dominated by bacteria such as bifidobacteria and Porphyromonadaceae species. The significance is that the bacteria in the RA-resistant mice are known for their anti-inflammatory effects.
Although nobody can say what the ideal gut bacteria should consist of, and the research is still evolving when it comes to the microbiome, there are potential ways of influencing this milieu, especially in our gut. Diet and other lifestyle considerations, such as eating and sleeping patterns or their disruptions, seem to be important to the composition and diversity of gut bacteria (6). Studies have already demonstrated prebiotic effects of fiber and significant short-term changes to the microbiome when eating fruits, vegetables and plant fiber. The research is continuing, but we’ve learned a lot already that may help us tackle obesity, inflammatory bowel syndrome and autoimmune disorders.
(1) “The Evolution of Obesity”; Johns Hopkins University Press; 2009. (2) cdc.gov (3) nih.gov (4) Science. 2013;341:1241214. (5) PLoS One. 2012;7:e36095. (6) Nutrients. 2019 Dec;11(12):2862.
Dr. David Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, visit www.medicalcompassmd.com.