Sugar didn’t ruin your last run. Not eating enough of it did.
I know, I know, because a lot of stuff you have read in the general population world (aka non-runners) says that sugar causes inflammation, fat gain, brain fog, hormonal chaos, etc etc. etc. And for most people sitting at a desk, barely getting 3,000 steps per day and eating processed garbage… yeah, the sugar thing is a real toxin for them.
But you’re not most people because you’re out there grinding out the miles/kms before the rest of the world wakes up.
So, the rules change a lot for runners.
If you didn’t know, sugar is a carbohydrate (all runners know about the pre-race carb load). And carbohydrates break down into glucose, which is the immediate, usable energy your body runs on. When there’s more glucose than your body needs right now, it converts the excess into glycogen and packs it away in your muscles and liver for later.
During a run, your body taps those glycogen stores on demand, converting them back into glucose to keep your muscles firing. The more glycogen you have stored going in, the faster and farther you can go before things start falling apart.
Simple carbs (pure sugar, candy, white rice/potatoes/bread, sports drinks, soda, gels, etc.) break down fast from when you first ingest them to being used as energy. Complex healthy carbs (oats, brown/black rice, sweet potatoes, whole grains, etc.) break down more slowly. Both have a job at different times, and neither one is the enemy.
The problem isn’t sugar but instead a problem of context.
For a person doing minimal movement? Excess sugar = excess glucose = stored as fat = high chance of health problems in the long term. For a runner doing 30miles/50km (5-6 hours) or even more a week? That same sugar is disappearing into muscle glycogen stores faster than you can replace it.
These are different biological situations wearing the same nutritional label.
Now here’s some science that is quite concerning for people who run a lot and race a lot.
Up to 80% of endurance runners don’t eat enough carbs to support their training, and marathon runners average only about 22 grams of carbs per hour during races, when the recommendation is 60 to 90 grams (some pros are able to stomach 100+ grams per hour, which is a convo for another day. That’s not a small gap, but I would say it’s a bonk/wall crash waiting to happen.
Chronic under-fueling doesn’t slow you down but can also lead to stress fractures, hormonal disruption, and unintended weight gain (or weight loss). Relative Energy Deficiency in Sport, aka RED-S, is the clinical name for it. And it’s way more common than people think (I’ve had it three times and now I know the warning signs and never let it get that close).
And those runners reaching for Coke Zero/Diet Soda on a hard or long training day might want to consider getting the OG Cola instead. Diet drinks don’t restore glycogen. They just trick your brain into thinking they actually consumed carbs, which is another issue.
The fix isn’t a prescriptive do exactly this thing, but more of a process that is specific to you. Research it, get one consult with a sports dietitian/nutritionist to understand where you are and what your goals are, then experiment on yourself until you figure out what actually works. You’re a one-of-one experiment, and that’s a really dope thing.
Stop following nutrition rules written for people who don’t run at all. Sugar is a tool; tools can hurt or help people. Use it like one.
