CARB TRUTH 🔬

Debunking Diet Culture Lies

Author

Brian Gryn
July 25, 2025

Carbohydrates aren't the villain they've been made out to be. Despite decades of diet culture demonizing carbs, cutting-edge research reveals why your body actually prefers burning carbohydrates over fat during exercise—and why this preference makes perfect biological sense. I recently did a video on this if you prefer to watch over read!

🔥 THE ATP ADVANTAGE

When it comes to producing energy (ATP), carbohydrates are your body's premium fuel. The rate of ATP production from carbohydrates is two times higher than fat oxidation, making carbs the clear winner for efficient energy delivery.

The numbers don't lie: To produce 100 ATP molecules requires 34.5 glycogen molecules via anaerobic energy production or 2.9 glycogen molecules via aerobic energy production—showcasing carbohydrates' superior efficiency in both energy systems.

⚡ THE INTENSITY FACTOR

As exercise intensity increases, your body naturally shifts toward carbohydrate oxidation for good reason. During high-intensity exercise, carbohydrate oxidation provides roughly two-thirds of the total energy need, while fat oxidation becomes increasingly limited.

Fat oxidation is limited at higher exercise intensities due to limitations within fatty acid transport across the cell and mitochondrial membranes. Exercise intensities that exceed the crossover point (~65% VO2max) utilize carbohydrates as the predominant fuel source.

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CARB MYTHS DEBUNKED

MYTH #1: "All carbs are bad"

Reality Check: Carbohydrates are a crucial source of energy for your body and for your brain. It is the type of carbs you consume that matters. Choose whole grains, fruits, and vegetables, and limit refined ultra processed carbohydrates.

MYTH #2: "Carbs make you gain weight"

The Science: Complex carbohydrates, like those found in whole grains, vegetables, fruits and legumes, are vital for sustained energy, brain function, and digestive health. Weight gain occurs from excess calories—regardless of source.

MYTH #3: "Fat burning is always better"

The Truth: Although exercise improves the capacity of muscle to oxidize fat, moderate duration exercise (≤ 1 hr) has little impact on 24-h fat oxidation. Your body's preference for carbs during exercise is metabolically intelligent.

BY THE NUMBERS

🏃‍♀️ Elite Endurance Athletes Average whole-body total carbohydrate oxidation rates of 2.70–3.16 g/min and fat oxidation rates of 0.14–0.33 g/min during running performance tests at 70% VO2max

⏱️ The Speed Factor Fat mobilization and oxidation are slow complex processes with a 10–20 minute lag time after exercise onset until fat metabolism can catch up with carbohydrate metabolism

🧠 Brain Power Carbohydrates are the body's main supply of energy and the brain's preferred energy source

WHAT THE EXPERTS SAY

Dr. Lawrence Spriet, Exercise Metabolism Researcher: "The regulation of fat metabolism in skeletal muscle has been designed to reduce the reliance on fat-derived ATP at intense aerobic power outputs."

The Takeaway: Fat and carbohydrate are important fuels for aerobic exercise and there can be reciprocal shifts in the proportions, but the interaction depends on exercise intensity and duration.

THE PRACTICAL ADVANTAGE

🎯 Performance Benefits

  • Immediate availability: Carbs provide instant energy without the metabolic lag time of fat oxidation

  • High-intensity support: Essential for performance above 65% VO2max

  • Brain function: Many plant foods are rich in the vitamins, minerals, phytochemicals and fiber that are vital to good health

🔬 Metabolic Efficiency

When you exercise, your body expertly manages its fuel selection by ramping up the breakdown of sugars, thereby reducing the reliance on long-chain fatty acids. This strategic choice ensures the most efficient use of energy.

BOTTOM LINE

The carb-phobia epidemic has gotten it backwards. While fat oxidation has its place during low-intensity, long-duration activities, carbohydrate oxidation reigns supreme for athletic performance, brain function, and metabolic efficiency.

Your body's preference for carbs isn't a flaw—it's a feature. Embrace quality carbohydrates as the high-octane fuel they are, not the dietary demons they've been painted to be.

To a healthier you,

Brian

P.S. If you're ready to stop making excuses and start making real changes, the Stepladder System is your answer. This proven method helps busy middle-aged adults lose inches and gain energy—one manageable step at a time.

Your future self will thank you for taking action today.

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