Researcher Explores the Role of Gut Microbiome and Diet to Potentially Improve Cancer Patients’ Response to Treatment

Cancer, diabetes, heart disease, and other chronic diseases affect quality of life for millions of Americans. According to the Centers for Disease Control and Prevention, six in 10 adults live with a chronic disease, and it is a leading driver of the United States’ $4.1 trillion in annual health care costs.

Leigh Greathouse, PhD, MPH, MS, RD, Associate Professor of Nutrition Sciences in the Department of Human Sciences and Design, is focused on cancer research. Specifically, she is studying the relationship between our gut microbiome, nutrition, and chronic disease.

The gut microbiome plays a significant role in one’s health and resides in the intestines. It is made up of trillions of bacteria, viruses, fungi, and other microbes—a combination of healthy and unhealthy ones—which help to control digestion and can greatly influence a person’s immune system. An imbalance in healthy and unhealthy microbes can contribute to chronic disease.

For Greathouse, research is personal. When she was 24 years old, and working toward a master’s in exercise and sports nutrition, she was diagnosed with stage IV uterine leiomyosarcoma, a rare form of cancer. Ultimately, the cancer treatments saved her life. But throughout the treatments, she experienced horrible side effects, some of which have lasted decades.

“That really transformed my life and my viewpoint of what I want to do with my research,” Greathouse said. “What I understood from going through that experience is how important nutrition is to your cancer recovery process. I wanted to dig further into that and understand what type of lifestyle modifications, including nutrition, could improve response to cancer treatment, improve quality of life, and improve survival overall.”

Greathouse earned a cancer prevention fellowship at the National Cancer Institute (NCI). It provided her opportunities to understand different perspectives on nutrition, the gut microbiome, and how it relates to cancer development and cancer treatment response. During the fellowship she worked with two prominent scientists, one at the NCI and one at the National Human Genome Research Institute (NHGRI).

“I was very lucky,” Greathouse said. “Both scientists shepherded me, and they each helped me understand how to do microbiome research and cancer biology research.”

Greathouse’s current microbiome study is helping her understand how diet can possibly increase or decrease a person’s risk of cancer. Also, she hopes it can potentially improve treatment response for patients. On the molecular level, the research is focused on understanding how nutrition and the microbiome interact to produce different chemicals, some of which are healthy and others that are bad for our body. On the translational level, the study is focused on how these chemical interactions affect cancer patients’ response to treatment.

“One of the clues we’re starting to understand is how important nutrition is, and the gut microbiome, together, in reducing the risk for these side effects and reducing the overall link in severity of these side effects,” Greathouse said. “We are collecting dietary information and stool samples from cancer patients, as soon as they are diagnosed and throughout treatment, to be able to develop biomarkers or predictions that we can use in the clinic to help these cancer patients either avoid these side effects or reduce the severity of those in general.”

Greathouse is hopeful that the research will help to improve precision nutrition therapy, so it can be used along with standard first-line therapy, such as chemo therapeutics or immunotherapy. Each person, and each type of cancer, may have a different response to certain foods. Because of this, nutrition should be tailored to a patient’s needs. Following a precise, healthy diet can improve a person’s response to cancer treatment and reduce side effects.

“This is how to improve how your gut microbes work,” Greathouse said. “If it doesn’t have enough of the right nutrients or chemicals to work properly, it can’t educate the immune system to respond to immunotherapy.”

When combined with nutrition therapy, using precision probiotics can be useful. In collaboration with the original inventor, Chris Kearney, PhD, Associate Professor for the Department of Biology, these probiotics are created in a lab and mirror beneficial bacteria that live in the gut but are armed with the ability to kill specific pathogens as well. They are created specifically for a patient, and because it is precisely engineered, the precision probiotics can eliminate harmful pathogens. This precision often reduces the use of broad-spectrum antibiotics, which helps a patient avoid developing an anti-microbial resistance during treatment.

“By using very specific types of precision, or engineered probiotics, we only kill certain pathogens, or a collection of pathogens, once we know what the infection looks like,” Greathouse said. “I’m really excited about this opportunity to add together with what we’re doing on the nutrition side of things to really improve precision medicine, or personalized medicine, for cancer patients.”

In 2021-2022, Greathouse was honored to participate in the Baylor Fellow Program, which recognizes professors who “exemplify excellence in teaching.” Through the fellowship she partnered with Erika Abel, PhD, Clinical Professor for the Department of Biology, and along with Abel’s biology class, they developed a project to research how vitamin D supplementation affects the microbes in the gut, and ultimately, chronic diseases.

They piloted a 12-week study with 43 individuals, including many Baylor students. Each participant was asked to take four vitamin D gummies, a moderate dose, each day for 12 weeks. Then participants were asked to provide dietary history and stool samples for 14 days. Despite the sample collection being a “big ask,” they had 98% compliance, and Greathouse credits it to one of her graduate students skilled in running clinical trials.

“This was all undergraduate-initiated research. We had some undergraduate students, one of them who is now a Fulbright Scholar, as part of that study and they helped to analyze that data,” Greathouse said. “We had some really interesting results from that study, and we are almost ready to publish a paper.”

To further the research, Greathouse is now collaborating with Malak Tfaily, PhD, at the University of Arizona, in an attempt to understand which bacteria metabolize vitamin D and which chemicals are produced when microbes come into contact with large doses of vitamin D.

“How do microbes in your gut metabolize, or utilize vitamin D, or activate vitamin D? That’s completely unknown,” Greathouse said. “We have some clues, based on the structure of vitamin D, but I’m really excited to answer this question about how vitamin D affects your gut microbiome, and ultimately, your immune system.”

Through research, Greathouse can mentor the next generation of scientists—something she loves doing.

“It’s just so rewarding to see young students or graduate students growing in their scientific abilities, growing in their faith, and developing those personal relationships with them,” Greathouse said. “I wasn’t blessed to have any children of my own, so I kind of feel like those are my kids. I try to impart the wisdom that I’ve learned. Helping them grow as a person, and as a scientist, is just the biggest and best reward.”

Greathouse considers her cancer diagnosis to be a blessing because that trial in her life strengthened her faith. Every day she strives to be the “best representative of Christian faith,” and when colleagues or strangers reach out during their own cancer treatments, she attempts to shepherd them through that period of life.

It's important to Greathouse that her students and colleagues realize faith, life, and science can blend seamlessly. The combination feels only natural to Greathouse, and she hopes her research will eventually help make someone’s life more comfortable during their own cancer treatment.

“You can do really good science and be a really strong Christian at the same time,” Greathouse said. “They are not mutually exclusive.”