written by Marsha Seidelman, M.D. on Friday, August 14, 2020
Last week, I attended – virtually, of course – the annual International Conference on Nutrition in Medicine cosponsored by the GW University School of Medicine and the Physician’s Committee for Responsible Medicine. Dr. Wilson Tang is the Research Director of Heart Failure and Transplant at Cleveland Clinic. His talk about how our bodies differ from each other based on the composition of the gut microbiome was fascinating.
People have different nutritional responses when eating the same foods. The extent to which their sugar, insulin and triglyceride levels change after a meal vary from one person to the next. 30-50% of this difference can be explained by genetic factors (i.e. those in the general population versus identical twins).
Macronutrient content in the labels only explain about 40% of the response. Something in our bodies, beyond our genes has a role in how our body processes a particular food. It turns out that it’s the microbes that live inside us. If we characterized our biological self, we’d be 1/10 human and 9/10 microbes!
Our microbiome changes from birth until weaning, then stabilizes for decades. At 50-60 years old, there seems to be another shift. Across the human race, we know there is only 3% variation in our genes from one person to another, but probably 50% variation in our microbiome. In certain illnesses, like congestive heart failure, the quantity and variety of microbes is reduced. Is that cause or effect?
Research is now ongoing about how certain microbes might mimic cells in our bodies, like heart cells. Antibodies can then be produced in response to the microbes, which then attack our own body organs and cause damage or exaggerate prior damage, as in rheumatic heart disease, which fortunately is not common now. The combination of certain microbes and specific genetics for immune responses can make the body susceptible to harm.
We are starting to understand that the host and microbe metabolism interact all the time.
Much of the recent research has revolved around TMAO (trimethylamine N-Oxide), since high levels in our blood predict a high risk of death, heart attack and stroke in those with cardiac disease. Animal products, including eggs, have carnitine and choline, which contain TMA. Certain microbes can extract the TMA, the body absorbs and oxidizes it to TMAO, and excretes it through the kidney. Interestingly, the higher the TMAO level in the blood, the lower the fraction of it is excreted by the kidney. So the level spirals upward with more and more animal products.
Research is ongoing to see if bacteria can be inhibited from extracting the TMA. They would still be able to survive, but would use other fuel sources. Some extra-virgin olive oils have molecules that mimic TMAO and may be able to reduce TMA reactions. As such, they can decrease the risks of TMAO: clotting, kidney damage and heart remodeling. Since human cells do not use the same enzymes, this kind of strategy should be safe because they would only affect the microbes. Of course more study is needed. The source of the majority of our plasma and urine levels of TMAO are not understood, but perhaps impacting the additional supply from our microbes can help human health.
When we take antibiotics for infections, we intend to kill unwanted bacteria, but we unintentionally decrease the number of microbes in our gut at the same time. As we wipe them out, we see the blood levels of TMAO go down. Three weeks later, they rise again. Our microbes are very resilient, so after antibiotics, our own microbes return in the same distribution as before. Along the same lines, probiotics do not have any clear benefit in that it is difficult for any additional bacteria to take root; most are eliminated. Dr. Tang noted that, in fact, there are potential downsides to using probiotics. They may have some components that produce TMAO; even yogurt as a probiotic can have sugar which has calories and adds to other medical issues. So far the data is mixed and the best way to avert GI side effects from antibiotics is unclear at the moment.
A key point that he wanted to make is that the TMAO levels in vegans and vegetarians are lower than in others. If they are given carnitine pills, to mimic what happens when you eat animal products, over the course of months, bacteria can be induced to produce TMAO. Regardless of diet, those with the highest TMAO levels seem to respond most to a more plant-based diet by lowering their TMAO levels. With this, they also have a reduced risk of heart attacks and strokes. The speaker related that changing to a more plant-based diet can have the equivalent beneficial health effect as stopping smoking and has great potential for improved health on a population level.
Studies over the past 5 years have shown that TMAO decreases with caloric restriction, intermittent fasting, and the use of aspirin and statins. It increases with high animal protein diets, especially Paleo and Atkins type diets. There are indeterminate effects on the TMAO level related to the use of B12, probiotics, fermented dairy, Mediterranean diet and fecal microbial transplant.
TMAO is only one of the pathways being studied. There is an additional pathway being examined related to phenylalanine that increases our platelet activity and can cause clotting.
Dr. Tang’s message was that our bodies – 10% human, 90% microbes – do a balancing act on a daily basis. Whatever we choose for our nutrition then creates a complex interface between our living components. As a cardiologist, he sees tremendous promise in PREVENTION related to more plant-based nutrition- not only regarding cardiovascular and kidney disease, but also for obesity, diabetes, cancer and inflammatory illnesses.
In other talks at this conference, speakers discussed how a plant-based diet can impact a genetic tendency for early heart attacks and strokes. Exercise, while very important for good health, does not reverse the effects of an unhealthy diet that includes many animal products and highly processed foods. If you have animal products on a daily basis, consider setting aside one day a week, or one meal every day, when you avoid animal products. Each serving of fruits and vegetables that you add on a daily basis decreases your risk of heart disease and death. Prevention and reversal of chronic disease through diet is the GOAL!