In my last post, I laid out what metabolic health actually means — the regulatory systems that, working correctly, keep weight in a stable range without much conscious effort. Obesity is what it looks like when that regulation has broken down significantly enough to produce excess fat accumulation that starts to affect health. I want to slow down on that definition, because I think it's more precise, and more useful, than how the word gets used in everyday conversation.
The definition most people are using is incomplete
Ask most people what obesity means, and you'll get some version of "very overweight," usually anchored to a BMI number. BMI — body mass index, a simple ratio of weight to height — is the tool most commonly used to screen for obesity, mostly because it's cheap and easy to calculate at scale. But it was never designed to be a diagnostic tool for an individual patient, and it isn't one. It can't distinguish between someone carrying excess fat and someone with significant muscle mass. It says nothing about where fat is distributed, which, as I'll cover in an upcoming post on visceral fat, matters enormously. Two people with an identical BMI can be in completely different metabolic positions.
What obesity actually is, medically
Obesity is now formally classified as a chronic disease, not just a risk factor or a cosmetic concern. That classification matters, and it wasn't made casually. Obesity meets the criteria used to define a disease: it involves specific physiological dysfunction (impaired regulation of appetite, energy storage, and fat distribution), it has a predictable disease course if untreated, and it causes measurable harm to multiple body systems — cardiovascular, metabolic, orthopedic, and others.
The physiological core of it is dysregulation in the systems I described in my last post: appetite and satiety signaling that no longer tracks actual need accurately, energy storage that favors accumulation over use, and often, an inflammatory state that reinforces the problem rather than resolving it. Obesity isn't simply "eating too much." It's what happens when the systems that are supposed to regulate energy balance automatically stop doing their job, and the conscious mind is left trying to manually override signals that were never designed to be manually overridden.
Why this framing changes how it should be treated
If obesity is a disease driven by dysregulated biology, then treating it primarily as a willpower problem was always going to fail a large share of patients — which is exactly the pattern I described in an earlier post about what 25 years of surgery taught me. It also means effective treatment has to target the actual physiology: appetite regulation, energy metabolism, inflammation, and fat storage patterns, not just caloric intake through sheer discipline.
This is part of why GLP-1 medications represent such a significant shift in how obesity can be treated. They work directly on the appetite-regulation pathway that's often dysfunctional in obesity, rather than asking patients to override a broken signal through willpower alone. That's not a small distinction. It's the difference between fighting your own biology and correcting it.
What obesity is not
I think it's worth being direct about a few things obesity is not, because the public conversation gets this wrong often enough that it's worth stating plainly:
- It is not simply a matter of personal discipline or moral failing.
- It is not accurately captured by a single number like BMI, though BMI remains a useful, imperfect screening tool at a population level.
- It is not the same condition in every patient — the underlying drivers, and the right treatment approach, vary significantly from person to person.
Where this leaves us
Obesity is the most visible expression of metabolic dysfunction, which is probably why it dominates public conversation about weight. But it's one expression among several, not the whole picture. In the next post, I'll widen out to metabolic disease more broadly — the umbrella that obesity sits under, and how it connects to conditions like metabolic syndrome that don't always come with visible weight change at all.
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Medical disclaimer: This content is provided for general educational and informational purposes only and does not constitute medical advice. It is not intended to diagnose, treat, cure, or prevent any condition, and it does not create a physician-patient relationship. Every patient's medical history, health status, and treatment needs are different. Always consult your own physician or qualified healthcare provider before starting, stopping, or changing any medication or treatment, and before making any decisions based on information found here. If you are experiencing a medical emergency, call 911 or go to your nearest emergency room.