We’ve long accepted the idea that someone is “healthy” if their lab results are normal and they’re not taking medication. But what if that’s the wrong measuring stick? What if metabolic illness starts long before your first abnormal blood test?

Most metabolic diseases… type 2 diabetes, insulin resistance, fatty liver, etc, are present for more than a decade before a routine physical examination and blood tests will identify the issue. They are area under the curve issues… where the area is time. I discussed this concept at length in my book, Longevity Simplified.

This is one of the first papers that puts the above comment into context. It shows us that despite feeling fine… and the current labs we get being fine, there’s trouble lurking under the surface.

A new study by San Millán and colleagues makes that clear.

In this tightly controlled trial, sedentary but otherwise “healthy” individuals were compared to moderately active people of similar age and BMI. Neither group had a diagnosed disease. But metabolically, they were worlds apart.

Muscle biopsies showed dramatic reductions in:

• Mitochondrial respiration (down 36% at Complex I, 34% in total ETC capacity)

• Fat oxidation (CPT1 activity down 51%)

• Pyruvate oxidation (down 37%), despite equal GLUT4 levels

Translation: Even without high blood sugar or cholesterol, their muscle metabolism was already failing. They were burning less fat, generating more oxidative stress, and clearing lactate poorly—evidence of inefficient, stressed mitochondria. These are likely to be the earliest findings in people who will develop metabolic disease states such as diabetes, fatty liver, hypertension, heart disease, etc.

Compared to the active group, sedentary individuals had:

• Lower VO₂ max and max power output

• Poorer fat oxidation

• Much worse lactate clearance (a key marker of metabolic flexibility)

These aren’t trivial findings. They’re predictive of the diseases that shorten lives and drive modern healthcare: type 2 diabetes, cardiovascular disease, dementia, and more.

Being sedentary is not a neutral state. Even in the absence of symptoms or abnormal labs, it’s a condition of early dysfunction. The cellular machinery that keeps us metabolically flexible and disease-resistant begins to falter quietly and early.

San Millán puts it bluntly: sedentary people are not the control group. They are already metabolically impaired.

If you don’t move regularly, your metabolism is already compromised. You may feel fine, but under the surface, the foundations of long-term health are deteriorating.

If you’re not active, you’re sick. You just don’t know it yet.

The good news is that this isn’t permanent. These changes are reversible through movement, strength, consistency, and reclaiming the role your body was designed to play.

Fitness isn’t an aesthetic. It’s cellular competence.

Start moving. Stay moving. It’s the most powerful intervention we have.