The Truth About Carbs for Athletes and Lifters

We recently debunked the idea that carbs alone make you fat.

But what about performance? Do high- or low-carbohydrate diets change how your body performs?

It depends on what you’re training for — and how long, how hard, and how fast you’re working.

Let’s unpack it.

Do You Need Carbs to Get Strong?

A classic strength plan includes lifting heavy weights for a handful of reps and then plopping down in a chair until it’s time for your next effort.

That snail-like pace gives your body ample time to replenish fuel stores between maximal contractions.

Because of that, you can get by on a lower-carbohydrate diet if your primary goal is maximal strength.

Research comparing Olympic lifters and powerlifters on high- and low-carb diets found similar strength gains between groups.

However, if your version of strength training means chasing muscle size and pumps, a low-carb approach becomes more challenging.

Hypertrophy-style training typically:

• Increases density (shorter rest periods)

• Links supersets together

• Pushes sets closer to failure

This raises glycolytic demand and increases reliance on carbohydrate stores.

Insulin may also play a role. It’s an anabolic hormone that supports muscle protein synthesis. In research on natural bodybuilders, those following a ketogenic diet lost fat and gained strength but did not gain as much muscle as those consuming higher carbohydrate intakes.

There’s also the issue of amino acids. When carbohydrate availability is low, the body may increase amino acid oxidation for fuel. Adequate protein becomes essential if you’re pursuing a lower-carb strategy.

That said, as Luis Villasenor from @ketogains demonstrates, you can absolutely build muscle eating low carb — it just requires tighter nutritional planning.

Do You Need Carbs to Go Fast?

Most sports require repeated short bursts of intense, all-out effort.

During these maximal efforts, carbohydrate is the primary fuel source because it can be metabolized rapidly — even when oxygen availability becomes limiting.

I dug through the literature and anecdotes looking for an elite sprint or power athlete thriving long-term on a strict ketogenic diet.

I couldn’t find one.

There were media reports of LeBron James going “keto,” but those appear overstated. He reduced processed carbohydrates during the offseason for weight loss — far from the 60–70% fat intake typically seen in true ketogenic diets.

If your training involves repeated all-out efforts — HIIT, CrossFit-style workouts, sprint intervals — carbohydrate availability becomes far more important.

Do You Need Carbs to Go Long?

You’d assume endurance athletes top the carb-dependency list.

Pre-race pasta dinners, sports drinks, gels, and Costco-sized bags of bagels would suggest so.

But this one is more nuanced.

Carbohydrates are critical for higher-intensity endurance efforts. Even marathon racing occurs around 75–80% VO₂ max — a pace that relies heavily on carbohydrate metabolism.

When glycogen stores run low, you hit the dreaded bonk.

However, endurance athletes also benefit from improving fat oxidation. Fat stores are essentially limitless compared to glycogen.

This has led to strategies that:

• Train low (reduced carb availability in select sessions)

• Race high (fully fueled for competition)

Research shows high-fat, low-carb adaptations can significantly increase fat utilization within 3–4 weeks — sometimes nearly doubling fat oxidation rates at higher intensities.

However, the evidence is mixed on whether that actually improves performance?

If there’s a benefit, it appears most relevant for:

• Elite, highly trained athletes seeking marginal gains

• Ultra-endurance athletes operating at lower percentages of VO₂ max

Personally, when I attempted low-carb endurance training during 70-mile weeks, performance and recovery suffered. Getting carbohydrates in before, during, and after runs was critical.

That said, I did find benefits to being more strategic:

• Training occasionally in a slightly depleted state improved durability.

• Not slamming gels every 30 minutes helped develop metabolic flexibility.

• Concentrating higher carb intake in the post-run window helped control total caloric intake.

Carbs & Performance: The Takeaway

Restricting entire food groups can sometimes help control calorie intake.

But performance is more nuanced.

• Pure strength athletes can maintain strength on lower carbs.

• Hypertrophy and high-intensity athletes generally perform better with higher carb availability.

• Endurance athletes benefit from strategic carbohydrate manipulation — but extreme restriction isn’t clearly superior.

Ultimately, your ideal intake depends on your sport, intensity, volume, and goals.

Next week, we’ll wrap up this series by examining how carbohydrate intake impacts long-term health.