Your Future: It's in Your Gut

author : Nancy Clark

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Gut health and triathlon nutrition

When I think about eating, I think about the yummy taste of food and the pleasure of feeling satiated. But after attending a Harvard Medical School conference on Gut Health, Microbiota and Probiotics Throughout the Lifespan, I now realize I am not feeding my body but rather the 100 trillion bacteria that live in my gut – my microbiome. We have about 3 to 4.5 pounds of microbes that outnumber human cells by a factor of 10 to 1.

The microbiome is a signaling hub. Gut microbes produce neurotransmitters that talk to the brain. This ultimately impacts our immune system, brain, weight, and mood. Genetics, diet, and environment influence these microbes.

Gut microbes can be our best friends or our worst enemies. Thanks to antibiotics, we no longer suffer from infections and illnesses such as pneumonia. But, the antibiotics that kill the bad bacteria also kill the good guys. Animal studies suggest antibiotics can kill off 80% to 90% of the total microbiome. Does this have a lingering effect? For example, in humans, is the overuse of antibiotics related to the dramatic rise in autism, anxiety, diabetes, asthma, Crohn’s disease, MS, and yes, obesity? (The highest rates of obesity are seen in the states with the highest use of antibiotics.)

We have much to learn about the microbiome. Perhaps these conference highlights will encourage you to eat well to invest in having the healthiest possible gut. That, ultimately, will help you be the healthiest runner you can be.

• Babies born via cesarean section are not exposed to the microbes living in the mother’s birth canal. As a result, their microbiome differs from babies born vaginally. Will this have an impact on their immune system (more allergies, asthma) and future health?


• Research with mice indicates a maternal diet high in saturated fat (think “junk food”) affects the microbes that will live in her infant’s intestinal tract. These microbes affect behavior, particularly the behavior of the males (both male baby mice and humans). They become more anxious, and less social. Tips for pregnant women: Eat less junk food—and breast-feed your babies—to help create a healthy gut for a happier babe!


• Gut microbes seem to affect genders differently. Do these bugs explain why five times more males than females have autism? And why, when a male mouse’s microbiome is transplanted into a female mouse, does the female generate more testosterone? 


• When microbes from a fat mouse are transplant into a lean mouse, the lean mouse gets fat – and vice versa. Lean microbes transplanted into a fat mouse help the fat mouse lose weight.


• Firmicutesand Bacteriodes are two prevalent types of microbes. Having a high amount of Firmicutes is associated with obesity. Obese women who altered their gut microbiota, lost fat, improved their blood sugars, and reported less hunger. Questions arise: Does this imbalance explain why some people gain weight easily more easily than others, and why others stay lean? Does the microbiome contribute to obesity? Or does obesity change the microbiome? Stay tuned.


• Intestinal motility (think constipation, diarrhea) is controlled by the brain via microbes that send signals to the brain. While many intestinal issues start in the gut, others start in the brain. For example, the mental stress that occurs pre-event (more so than microbes) explains to the long lines at the porta-toilets before a competition. Mice fed Bifidobacteria became less anxious and were better able to solve problems (such as get out of a maze) compared to the control group. Humans fed Bifidobacteria had lower levels of morning cortisol (a stress-related hormone) and perceived themselves as being less stressed. Does this mean, in the future, we might be taking psychobiotics instead of drugs?


• Processed foods tend to be low in fiber. This results in less diversity in the microbiome and can lead to inflammation and pre-diabetes. Emulsifiers such as Polysorbate 60 are found in some processed foods (such as coffee creamers). They can change the microbiota and create a low-grade inflammation that can be associated with colitis and other inflammatory bowel diseases.

What to do 

Much more research is needed to determine if the results of microbiome studies with animals hold true for runners. We also need to learn about proper use of probiotic supplements. In the meanwhile, the probiotic industry is booming—and it is unregulated by the FDA. Hence, a note of caution: The quality of a probiotic is not guaranteed.

Your best bet is to feed your gut microbes (and your muscles) generous portions of fiber-rich carbohydrates from fruits, vegetables, legumes, beans and whole grains. You’ll naturally do this when you eat, for example, fewer cookies and instead snack on dried fruit. Yogurt, kefir, blue cheese and miso are also smart choices.

In the future, sports dietitians will be able to offer personalized nutrition based on each athlete’s microbiome. Until then, stay tuned, and know that a high-quality sports diet is the same diet that will support good gut health as well as top performance.

Nancy Clark, MS, RD counsels both casual and competitive athletes in the Boston-area (Newton; 617-795-1875). Her Sports Nutrition Guidebook and food guides for runners, marathoners, and cyclists are available at www.nancyclarkrd.com. See www.NutritionSportsExerciseCEUs.com for information about online and live workshops.

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date: October 31, 2016