The fat-fueled runner

A friend from our running group messaged last week, excited. He had finally tried carnivore — meat, eggs, a little salt, nothing else — after months of hearing me talk about it.

A few days in, his pants were already looser. He could hardly believe the lack of bloating, the mental clarity, how strange it felt to not be hungry every two hours. I recognized the excitement immediately. It was the same thing I felt eight years ago, when I first stopped treating carbohydrate as the default fuel for a runner’s body.

That conversation is the reason for this column. Because the running world still operates on an assumption that deserves a second look: that carbs are king, and that the more of them you eat — before, during, and after a run — the better you’ll perform.

Every runner has felt it — the wall, the bonk, the sudden emptiness in the legs around the 30-minute mark of hard effort when glycogen stores start running thin. That’s the fundamental problem with a body trained to run on sugar: glycogen is a small, quickly-depleted tank. Ketones, by contrast, are what your body produces when it’s fat-adapted — efficient, steady, and drawn from a fuel source (body fat) that even lean runners carry tens of thousands of calories of. A fat-adapted runner isn’t chasing a tank that empties every half hour. They’re running on a reserve that barely moves.

That’s the real goal: not carbo-loading, but becoming fat-adapted — turning the body into an efficient fat-burning machine that doesn’t panic when glycogen dips, because it was never dependent on glycogen as the primary fuel to begin with.

Watch any race expo and you’ll see runners tearing into sugary gels every 20 to 30 minutes — even in a 10K, a distance that shouldn’t require external fueling at all for most healthy adults. That’s not a fueling strategy. That’s a sign of a body so dependent on constant glucose that it can’t trust its own fat stores to carry it.

Short-term, sugar-dependent runners can get away with it — the gel hits, the energy spikes, the race gets finished. But it’s a habit with a bill that comes due: chronically high insulin and glucose loads are increasingly showing up in runners as fatty liver, elevated blood pressure, and high uric acid — problems people associate with sedentary lifestyles, not marathoners.

Here’s what carbo-loading culture misses: running is catabolic. Every long run breaks muscle down. What rebuilds it is protein — specifically, amino acids for muscle protein synthesis — and a body preoccupied with processing carbohydrate tends to prioritize that over adequate protein intake.

This is also where the type of protein matters enormously. Plant protein is incomplete; animal protein — meat — provides the full amino acid profile the body needs to actually repair and build muscle.

For long-distance runners breaking down tissue mile after mile, that distinction isn’t academic — it’s the difference between recovering and slowly grinding yourself down.

The same is true for iron. Runners are notoriously prone to anemia and low ferritin, and heme iron — the highly bioavailable form found only in meat — is what the body actually absorbs efficiently. Plant-based “iron-rich” foods can’t compete on bioavailability, no matter how the marketing reads.

It’s tempting to treat nutrition as pure arithmetic: burn more than you eat, and you’re fine.

But the body doesn’t experience food as a spreadsheet. A 400-calorie serving of ultra-processed food and a 400-calorie serving of steak produce wildly different hormonal, inflammatory, and recovery responses. Refined sugar (that includes rice, bread, pasta, and a lot of so-called “protein powders”) drive inflammation that competes directly with the repair processes your muscles need after a long run or a hard trail session. So even a runner who is technically in calorie balance can be running poorly fueled — tired, inflamed, and undernourished in the ways that actually matter for endurance.

I’ve been a carnivore for eight years now, through marathons, trail races, and ultras that would have seemed unthinkable on a sugar-dependent body. No bonking, no gels, no glycogen panic at mile 20 — just a body that knows how to burn what it’s carrying.

My friend is only a few days into his own version of that discovery, and already sold on what his body is telling him. It’s a familiar excitement. I suspect it won’t be long before he, too, stops reaching for the gels — and starts trusting the fat he’s already fueled by.

You can’t outrun a bad diet. But you can absolutely run further, longer, and stronger by teaching your body to burn what it already has.