The idea that different types of bacteria in the human gut play a role in health and disease is driving a new trend in consumer-oriented health-care kits.

Startups are offering new services to analyze the complex community of microörganisms that live in the digestive tract—called the microbiome. Customers receive test tubes in the mail and send them back with fecal swabs to be analyzed in a lab. The companies say they can do things like make diet recommendations and predict risk for certain diseases based on a person’s unique microbial makeup.

The hype is ahead of the science when it comes to gut microbiome test kits consumers use at home and then send out for lab analysis, scientists said. Although the tests may be able to show a serious bacterial infection, experts said they are not able to diagnose diseases and may not provide reliable personalized information.