Obesity, long recognized as one of the most complex and costly global health crises, is finally getting the attention—and funding—it has long warranted. With blockbuster drugs like glucagon-like peptide-1 (GLP-1) receptor agonists such as Novo Nordisk’s Wegovy (semaglutide) and Eli Lilly’s Zepbound (tirzepatide) taking center stage, pharma giants and investors are rushing to stake their claim in a market projected to be worth hundreds of billions. However, as history often demonstrates, rapid hype can obscure long-term strategy and patient needs.

In this shifting landscape, few voices are as grounded—and forward-looking—as that of Mark Bagnall, CEO of Phenomix Sciences. A biotech veteran who’s lived through boom-and-bust investment cycles in gene therapy, artificial intelligence (AI), and beyond, Bagnall is now betting on precision medicine to reshape how we diagnose and treat obesity. Rather than viewing obesity as a monolithic condition treated by a one-size-fits-all solution, Bagnall advocates for stratifying patients based on their biology, offering therapies tailored to distinct subtypes of the disease.

Phenomix has developed a test to help clinicians determine which treatment, whether GLP-1s, other medications, or behavioral interventions, is most likely to be effective for a given patient. That platform is already gaining traction among obesity specialists, pharma companies, and payers alike.

In this wide-ranging conversation, Bagnall discusses the perils of following biotech fads and the emerging science behind obesity subtypes.

This interview has been edited for clarity, consistency, and length.

Phalguni Deswal (PD): GLP-1s are being hailed as a breakthrough. But you’ve seen this kind of excitement before. What feels different—or familiar—about this moment?

Mark Bagnall (MB): GLP-1s have been around for a while. I remember over a decade ago, you didn’t have to be a billionaire to acquire a clinical-stage GLP-1 asset. The science was known, and people were seeing weight loss, but obesity wasn’t fully recognized as a disease—it was still seen through an aesthetic lens.

Now, the hype is massive, reminiscent of Redux in the ’90s or gene therapy in the early 2000s. Every few years, biotech sees a new shiny object—be it gene therapy, AI, or combinatorial chemistry. GLP-1s just happen to hit all the sweet spots: a massive untapped market, clinical validation, minimal side effects, and viral consumer adoption, thanks in part to social media. But as always, hype needs to be tempered with a strong business model.

PD: So what makes a company sustainable in a “shiny object” cycle?

MB: A good company must meet three criteria: a clearly defined problem, a viable solution, and someone willing to pay for it. Too often, startups check only two boxes. You may have a great product that addresses a real need, but if payers won’t cover it, you’ve got a problem.

With obesity, we have all three—clearly. But now, we’re entering a phase where differentiation matters. GLP-1s are great, but not for everyone. That’s where Phenomix steps in. We believe that just like in oncology, where we now recognize subtypes of cancer, obesity isn’t one disease. It’s a collection of biologically distinct conditions requiring distinct interventions.

PD: Is there growing acceptance of the idea that obesity should be treated based on individual biology?

MB: Yes, we’re already seeing it. A significant portion of obesity specialists are aware of Phenomix and our testing platform. Around 20% of that group are using our test in practice. These clinicians have seen firsthand that not all patients respond to GLP-1s. Some lose only a few pounds and say, “I could’ve done that with diet alone.” Then we test them and find they’re in the “hungry brain” subtype—better suited to a different drug like Qsymia.

This isn’t theoretical anymore. We have patients losing 30, 40, even 50 pounds after switching based on test results.

PD: What kind of traction are you seeing beyond clinicians, say, with pharma or payers?

MB: There’s strong interest from both. Pharma companies want to optimize clinical trial design. If you’re developing a GLP-1, why not select patients who are most likely to respond? Conversely, if you’re working on a novel mechanism—say, mitochondrial modulation—you want to exclude those who will do well on existing therapies.

We’ve also announced a collaboration with Novo Nordisk’s Transformational Prevention Unit. They’re exploring how our tech can identify people on the path to obesity before it becomes full-blown.

On the payer side, it’s about cost containment. These drugs are expensive, and when millions of people start using them, budgets get blown. Our tests can help ensure that only those likely to benefit receive them, improving outcomes while keeping costs manageable.

PD: Looking ahead, how do you see the obesity treatment paradigm evolving?

MB: We’re on the cusp of a major shift, from viewing obesity as a single disease to seeing it as a multifactorial condition with biologically distinct subtypes. As more drugs with varied mechanisms enter the market, the variability in response will become more apparent. That’s when the precision model becomes essential.

Phenomix’s platform enables that shift. Our tests help identify which patients will respond best to which treatment – be it GLP-1s, dual agonists, diet, devices, or surgery. That benefits everyone: patients, payers, providers, and even pharma companies with drugs further back in the pipeline.

PD: What’s the one big message you’d like readers to take away?

MB: If I can give two, I’d say: First, obesity isn’t just a disease, it’s a spectrum of diseases. Treating it with a single class of drugs is like trying to cure all cancers with one chemo agent.

Second, we need to shift decision-making from social media buzz to biological reality. Phenomix is betting that biology should guide obesity treatment. And I don’t think that’s a radical proposition, but common sense.