Carb Fueling
Plan

The glycogen tank is smaller than you think

Trained, carb-loaded athletes carry roughly 500 to 600 grams of glycogen across muscle and liver. That is about 2,000 to 2,400 kilocalories of stored fuel. At marathon race pace a 70 kg runner burns 700 to 900 kcal per hour, with carbs supplying 60 to 70 percent of that energy. The math is unforgiving: without intra-race carbs you run out of stored fuel somewhere between hour 2 and hour 3. That is the wall.

This is also why marathoners famously hit the wall around mile 20. It is not a mental thing. It is a fuel-tank-empty thing.

The 60 g/hour absorption ceiling and how to break it

Your gut absorbs glucose through one transporter (SGLT1) that maxes out at roughly 60 grams per hour. Past that point, anything more sits in your stomach causing nausea, bloating, and cramps. This is why many athletes get sick when they switch from one gel an hour to two.

The way around the ceiling is to use a second transporter, GLUT5, which absorbs fructose. With a 2:1 mix of glucose and fructose, the gut can move 90 to 120 grams per hour cleanly. Most quality sports gels and drink mixes use this ratio. Honey, maple syrup, and many fruit-based foods are naturally close to it. Pure glucose tablets and pure white sugar are not.

If your fueling plan calls for more than 60 g/hr, verify that your sources are dual-source. This single check prevents most race-day GI disasters.

Train your gut like you train your legs

Gut absorption is trainable. Athletes who practice fueling at 90 g/hr during long sessions can hit those numbers on race day with no GI issues. Athletes who never practice past 30 g/hr cannot suddenly run 90 g/hr in a marathon, regardless of what their calculator says.

Practical protocol: take your race-day target into your two longest training sessions per week for at least 6 to 8 weeks before the event. Train at the rate. Use the exact products you will race with. The phrase "never try anything new on race day" applies as much to fueling as it does to shoes.

Heat and the absorption paradox

In hot weather, blood that would normally service your gut gets redirected to your skin for cooling. This reduces gut absorption capacity by roughly 10 to 20 percent. Counterintuitively, this means in extreme heat you should slightly lower your carb target while raising sodium and fluid.

Most calculators get this wrong because they assume "more sweating = need more of everything." More sodium and more fluid: yes. More carbs: no. Push the carbs and you stack the gut, lose blood flow, and start a downward spiral that ends with you walking the last 6 miles.

Where Beetroot Pro® fits

Dietary nitrate raises plasma nitrite and nitric oxide, which improves the efficiency of mitochondrial respiration. Translated: at the same pace, you use slightly less oxygen per unit of work. The AIS Sports Supplement Framework classifies dietary nitrate as Group A, the highest evidence tier.

For race day, plasma nitrate peaks 2 to 3 hours after intake. Take your final Beetroot Pro® dose with breakfast, 2.5 hours before the gun. For best results, load daily for 3 to 6 days before the event so your tissue stores are saturated.

Fueling and nitrate work on different problems. Fueling supplies the kilocalories you burn. Nitrate makes those kilocalories go further. The two are additive, not redundant.

Where Endurance360® fits

Carb fueling is acute, race-day math. Endurance360® works on the chronic side: it builds the aerobic capacity and recovery durability that determine how fast you can hold a pace in the first place. The blend includes clinically dosed creatine for high-end power, beta-alanine for buffering capacity, and adaptogens (rhodiola, cordyceps) for stress tolerance during heavy training blocks.

Beta-alanine and creatine both require multi-week loading to take effect, so daily intake during your training block is what unlocks race-day benefits. Beetroot Pro® then handles the acute oxygen-efficiency layer in the final week.

A trained athlete fueling correctly without a built aerobic base is still going to bonk. A built aerobic base without race-day fueling still hits the wall. Use the calculator above for the fueling math, and stack Endurance360® across your training block so the engine is actually capable of finishing the race you are fueling for.