As popular as the latest drugs being touted for weight loss, including Ozempic, Mounjaro, and Wegovy, are on social media, like any medications, they don’t work in the same way for everyone. Not all are even approved to treat obesity, but are being used off label as a relatively easy way to shed pounds. While some users lose up to 20% or more of their body weight on these drugs, others struggle to shed single digit percentages.

That shouldn’t come as a surprise, since obesity isn’t a monolith and the factors that contribute to extra pounds are different for different people. In the same way that cancer doctors are now bringing more precision to which treatments they use by learning about the genes that drive people’s cancers, doctors who treat obesity are beginning to figure out the major contributors to an individual person’s obesity. That’s been catalyzed by the new class of more effective weight loss drugs that have been recently approved, with more on the way. Now that those medications are available, doctors are focusing on directing patients to the best treatments for them, whether it’s one of the newer drugs, some combination of older drugs, or a keener attention to diet and exercise.

While obesity and diabetes specialists have been applying this tailored approach to helping their patients lose weight for many years, it’s not as familiar for medical professionals who aren’t in these specialty fields, but are often people’s first medical contact when it comes to trying weight loss treatments. For them, having additional tools to differentiate between patients who are most likely to respond to the newest drugs, for example, and those who aren’t, could save people time, money, and frustration.

Dr. Andres Acosta, assistant professor of medicine at Mayo Clinic, has dedicated the past decade to developing such a tool. He and his team divide obesity into what he calls four phenotypes, or categories based on certain genetic factors that are primarily responsible for causing obesity:

• Hungry Brain: people who never feel full
• Hungry Gut: those who eat until they’re full but get hungry again within an hour or so
• Emotional Hungry: those who eat to reward themselves or cope with emotional issues rather than based on physiological hunger
• Slow Burn: those whose metabolism makes it difficult for them to burn calories properly.

What drives obesity, he says, should also drive which treatments people receive. Those who never feel full, for example, will struggle more with diet interventions, while those with metabolic imbalances might never lose enough weight even if they exercise to exhaustion.

In 2021, Acosta co-founded a company, Phenomix, which took his years of research and developed a saliva test, called MyPhenome, that can distinguish the four types of obesity by analyzing a set of genes related to obesity that Acosta identified. In March, the company soft-launched its first test, for Hungry Gut, and this week launches Hungry Brain. Together, says Acosta, the two tests should identify the main contributor of obesity in about half or more of people with the condition. And the two tests will give doctors and patients clearer guidance about whether drugs like Wegovy and Rybelsus, and even the diabetes medications Ozempic and Mounjaro, will help them lose weight.

How the test could change obesity care

“When I see patients and talk about the options they have, and discuss how they are used, their cost, and the possible side effects, I always tell them that it doesn’t matter what they choose because at the end of the day, using the medications is like shooting in the dark,” says Dr. Daniela Hurtado, an endocrinologist at Mayo Clinic who worked with Acosta to develop and test the different obesity types. “We try something, and if it works, great. If it doesn’t, then we discontinue it and try another medication. It’s really trial and error.”

The practice is pretty widespread in the obesity field, similar to the way doctors cycle through drug treatments for hypertension and depression, making educated guesses about which medication might work best for each patient based on their health history and symptoms. Even more entrench