Inside Thousands of Metabolic Tests

Caroline Kavanagh | February 3, 2026

After years spent measuring real-time substrate use and glucose responses, one thing is certain: lasting progress isn’t the result of quick fixes or trendy hacks. The real story is about how the body selects fuel, how movement and nutrition interact at a cellular level, and how adaptation emerges gradually—sometimes invisibly—over months and years.

Here’s what the data actually reveals. Most people, even during the lightest activities, default to using carbohydrates for energy when their bodies could (and should) be relying more on stored fat. Through frequent, low-intensity movement—think walking or gentle cycling—we can retrain this system. The downstream effects are tangible: steadier glucose, preserved glycogen for when it’s truly needed, and consistently lower risk markers.

Endurance and resilience aren’t forged in endless “medium” efforts. The most profound adaptations come from spending time in the easy zones, below the aerobic threshold, where lactate stays flat and the body learns real efficiency. By contrast, the all-too-common approach—where every workout is “sort of hard”—shows up in the lab as stalled adaptation and creeping fatigue.

High-intensity sessions, when used with intent and separated by real recovery, can drive powerful changes. But used indiscriminately, they’re just noise. Resistance training, on the other hand, is non-negotiable. Decades of data show that maintaining and building muscle mass is the single most effective intervention for supporting glucose control, metabolic rate and long-term health, regardless of age or background.

A question that comes up often: are women better at utilizing fat for energy than men? The evidence says otherwise. When you account for fitness and training status, differences between men and women in substrate use during exercise are minimal. The major drivers are how well someone is trained and how they fuel—not their sex.

The practical takeaway is straightforward, but not simplistic: nutrition should reflect the demands of the day. Lower-intensity work allows the body to use its own stored fuel, while higher-output efforts require accessible carbohydrate. No formula works for everyone; sleep, stress and day-to-day intake all shape individual responses. This is why regular, personalized assessment isn’t a luxury—it’s essential.

If there’s one thing all this data makes clear, it’s this: lasting metabolic health isn’t built on hacks or hype. It comes from doing the simple things well—moving often, training with intent, prioritizing strength and matching nutrition to your actual effort. Listen to your body’s responses and use real data to guide your adjustments.

That’s what works. Not because it’s trendy, but because, measured over years and thousands of tests, it’s the only approach that consistently delivers results.

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