The purpose of this study is to explore how the dietary supplement L-Phenylalanine affects the production of the metabolite phenylpropionic acid (PPA) and changes fungal populations of the gut microbiome.

The human gastrointestinal tract hosts a diverse microbial community that has a role in influencing the host's pathophysiological responses. Although there is an abundance of metagenomic data available, the functional dynamics of the gut microbiota still need exploration in different conditions. The microbiota produces various metabolites from dietary products, impacting both host health and pathophysiological functions. The metabolites produced by different microbiota may selectively suppress or stimulate the growth of some components of the gut microbiome, ultimately influencing the dynamic of gut bacterial and fungal populations. Our lab is specifically interested in a metabolite, known as phenylpropionic acid (PPA) produced by a human gut resident bacteria known as Clostridium sporogenes. C. sporogenes produces PPA by metabolizing the amino acid, L-phenylalanine, which is sourced from human diet. Many studies have observed the antimicrobial and antifungal effects of PPA. Our lab determined PPA holds antifungal activity of PPA in the gut of mice colonized with Candida albicans. We are interested in investigating how diversity in the mycobiota populations, which focuses on the fungi species in the human gut, are related to changes in PPA levels.

Therefore, this study will asses whether additional oral supplementation of L-phenylalanine has an effect on the way gut mycobiota responds to this amino acid. Healthy subjects received a 14-day supply of L-phenylalanine supplements and provided stool and blood samples to the study team.

Inclusion Criteria:

• Male or female adults over the age of 18 years

Exclusion Criteria:

• History of a diagnosis of any gastrointestinal condition, such as inflammatory bowel syndrome or disease
• Antibiotic usage within the past two weeks
• Antifungal usage within the past month
• Allergy to L-Phenylalanine or individuals with phenylketonuria (PKU)
• Adults taking medications known to interact with L-phenylalanine supplements, such as Monoamine Oxidase Inhibitors (MOAI), L-DOPA, and some antipsychotic drugs (complete and extensive drug list will be provided to interested participants during screening)
• Pregnant or nursing women