Dozens of yogurt brands lining grocery store shelves claim to contain probiotics. These live bacterial cultures which been paraded as dietary supplements to promote healthy gut microbiota and aid digestion.

But according to integrative biology professor Howard Ochman, consuming anything that claims to change the body’s community of microorganisms may not have the advertised effects. On Wednesday, Ochman explored the complexities of the human microbiome during a talk that was part of the Dell Medical School’s lecture series Advances in Medicine and Research.

According to Ochman, the largest number of microbes in the body reside in the gut and perform several functions including harvesting nutrients and protecting against toxins. Ochman said his research began with the question of whether great apes, because of their genetic relationship to humans, could be used to learn more about the human microbiome.

Ochman said his research was challenging because it required going out into the field and collecting fecal samples from chimps, bonobos, and other primates. DNA then had to be extracted from the samples and characterized. 

“You isolate the DNA from the samples, which is easy because there’s a lot of DNA from fecal material … (and) you basically sequence until your money runs out,” Ochman said.

Ochman used the extracted bacteria to create a phylogenetic tree, a chart that displays the inferred evolutionary relationships between species. He said the tree demonstrated something shocking — the differences between human and ape microbiomes had diverged throughout evolutionary time, indicating that genetics, not diet, determines one’s microbiome.

“When this came out, no one believed it … because everyone wants to believe that diet contributes to the microbiome,” Ochman said. “[Companies] want you to eat bacteria to make your microbiome better.”

The major pushback was from companies that didn’t want to believe that genetics contributed to the microbiome makeup, Ochman said. He added that probiotics don’t necessarily change one’s microbiome, just as glasses can’t change one’s genetically determined loss of vision, but they can supplement it.

Ochman also found evidence that the diversity of microbiomes has decreased throughout human lineage. Despite the popular idea that this is due to increased antibiotic usage, Ochman said antibiotics and a modern diet aren’t completely to blame, as divergence occurred early in evolutionary history.

Additionally, Ochman discussed current research on enterotypes, which define gut microbiomes based off of a person’s predominant bacteria. Peer Bork of the European Molecular Biology Laboratory classified different enterotypes through his article “Enterotypes of the human gut microbiome,” published in 2011.

“We identified three robust clusters (of microbial ecosystems) … that are not nation or continent-specific,” Bork said in his article.

According to Ochman, enterotypes and microbiomes are a huge point of controversy because scientists argue about the validity of their existence and their significance. 

Andrew Moeller, a Miller Research Fellow at UC Berkeley and former student of Ochman’s who continues to study the microbiome, emphasized the potential importance of this research to human health.

“The gut microbiota is deeply integrated with the digestive, immune, and neuroendocrine systems of the host, so studying the microbiome may lead to a better understanding of the factors influencing human health,” Moeller said. “The most challenging aspect … is wrapping one’s head around the immense complexity of the system.”