The Endurance Carb Paradox

Okay, so the biggest myth I hear from marathoners is that because they run a lot, they can just—

Eat absolute garbage? The classic I ran twenty miles, pass the donuts diet.

Exactly. The see-food diet. But the listener question today is actually about the flip side of that. How do we manage insulin sensitivity while training for endurance events? Which is a surprisingly huge deal.

It is, because as an endurance athlete, you need carbs. Like, a lot of them. But if you're just constantly hammering gels and sports drinks all day—

Right, you're riding a blood sugar rollercoaster. Constantly spiking your insulin.

Which eventually wreaks havoc on your insulin sensitivity. Even if you're super lean! I know so many guys who look incredibly fit but their fasting glucose is creeping up into pre-diabetic ranges.

Yeah, because they're treating their resting body the same as their active body. So, here is the golden rule for endurance athletes and insulin. Timing is literally everything.

Because of muscle contraction, right?

Yes! When you are actually running or cycling, your muscles are contracting. And active muscles can pull glucose out of your blood without needing insulin to unlock the door.

Wait, without insulin at all? I thought insulin was always the key.

It is the primary key, yeah. But active muscle contraction essentially forces glucose transporters to the cell surface. It is called non-insulin-mediated glucose uptake. So when you're out on a two-hour run, hitting those sugary gels is totally fine. Your body just burns it immediately.

Okay, so during the workout, sugar is just pure functional fuel. It's safe. The issue is what people do when they get home.

Right. The workout ends, your heart rate drops, and that metabolic back door slams shut. If you sit on the couch two hours later and crush a giant plate of pancakes with syrup—

Which, honestly, is the best part of a Sunday long run.

I mean, sure, it tastes great. But physiologically, you get a massive insulin spike. Because now you are relying entirely on insulin to clear all that sugar into the cells. If you do that constantly, your cells get deaf to the signal.

So how do we actually manage this? Because I am definitely not telling my athletes to do keto. That just tanks top-end performance.

No, definitely not keto. You need the carbs to go fast. The strategy is compartmentalization. Around the workout, so during, and maybe the first hour after, you have your simple, fast-absorbing carbs.

Gels, sports drinks, white rice.

Exactly. But outside of that window? The rest of the day? You have to switch gears. Go back to being a normal, health-conscious human. Complex carbs, fiber, protein, healthy fats. Keep the insulin baseline low.

What about fasted training? Like, waking up and just doing an easy Zone 2 ride with zero breakfast. Does that help sensitize the body?

It actually does. Doing low-intensity, conversational-pace work in a fasted state forces your body to get better at burning fat. It improves mitochondrial density.

Metabolic flexibility.

Exactly. Just don't try to do your high-intensity intervals fasted, or you'll—

You will completely bonk. It is miserable. I've been there.

Totally. So, to sum it up, sugar is for the saddle or the track. The rest of the day, eat like a grown-up.

Sugar for the saddle, fiber for the sofa. I like that. We should honestly make t-shirts.