Step into a gym or open social media and you’ll hear it: cut the rice, skip the roti, carbs make you fat. That might be fine if you sit at a desk all day. If you’re training for endurance sports, it’s terrible advice.
Here’s what the research actually says about carbs, and why runners need them.
Carbs are your running fuel
When you eat rice, roti, poha or a banana, your body breaks the carbohydrate down into glucose (and, for the banana, some fructose). Some of it is used right away, and some is stored in your muscles and liver as glycogen. Think of it as petrol in the tank. When you run hard, glycogen is the main fuel your muscles draw on, though the tank is limited, which is why long runs can leave you feeling empty.
Scientists showed this back in 1967. A Swedish team had nine healthy men follow low-carb, mixed and high-carb diets for three days each, then cycle at a hard, steady pace until exhaustion. On the high-carb diet their muscles held far more glycogen, and they lasted about three times longer than on the low-carb diet.1
When the tank runs dry
You can only store so much glycogen, roughly enough for 90 minutes to two hours of hard effort. As you start to run low on glycogen, you slow down, your legs feel like concrete and your head goes foggy. Marathon runners call it hitting the wall.
Eating during long runs helps. In one well-known study, seven trained cyclists riding hard on flavoured water gave up after about three hours. With a carbohydrate drink, they kept going for another hour.2
“But isn’t low-carb better?”
Keto and other low-carb, high-fat diets are popular, and some people say they turn athletes into fat-burning machines. In 2017, researchers at the Australian Institute of Sport tested this on elite race walkers during three weeks of hard training.3
The keto group did burn a lot more fat. But they needed more oxygen to walk at race pace, which made them less efficient. The two high-carb groups improved their 10 km times by 5–7%. The low-carb group’s improvement was small and not statistically significant, even though they’d done the same training.
Similar groups of elite walkers, same hard training. The only difference was their diet, and those eating more carbs got meaningfully faster.
How much do you need?
Sports nutrition literature suggests the amount of carbs depends on two things: your body weight and how much you train.4
| Training load | Carbs per kg of body weight per day |
|---|---|
| Light / skill sessions | 3–5 g |
| About 1 hour a day | 5–7 g |
| 1–3 hours a day, moderate to hard | 6–10 g |
| 4–5+ hours a day, moderate to hard | 8–12 g |
So a 50 kg runner training 1–3 hours a day at a moderate to hard effort should aim for about 300–500 grams of carbs a day. To give you an idea, the lower end, 300 grams, is roughly two cups of cooked rice, four rotis, three bananas and a plate of poha, plus the dal, milk and fruit you’d eat anyway.
How to fuel your body
For everyday needs, Indian food has plenty of carbs.
- Before training (2–3 hours): Go for light carbs your stomach can handle, and start with small portions: poha, upma, idli, or roti or bread with light jam. Avoid oily, spicy or fatty food.
- During runs over 60–90 minutes: Aim for 30–60 g of carbs an hour.4 Try a high-carb gel or another source of carbs your stomach can handle, such as honey.
- After training: Aim to eat within 30 minutes after your workout ends. In one study, athletes who had carbs straight after exercise refuelled their muscles about three times faster over the next two hours than when they waited.5 Curd rice, roti-sabji, or dal-chawal all work well.
For women athletes
A lot of young women athletes don’t eat enough, often without realising it. Some are trying to stay “light”. Others simply don’t have enough food. When your body is short of energy, it starts switching off things it can live without. Scientists call this REDs (Relative Energy Deficiency in Sport). It can stop your periods, weaken your bones and leave you injured or ill more often.6
Eating enough, and especially enough carbs, is one of the easiest ways to protect your health and your running. If your periods stop, that isn’t a sign you’re fit. Talk to your coach or a doctor.
References
- Bergström J, Hermansen L, Hultman E, Saltin B. Diet, muscle glycogen and physical performance. Acta Physiologica Scandinavica. 1967;71(2):140–150. doi.org/10.1111/j.1748-1716.1967.tb03720.x
- Coyle EF, Coggan AR, Hemmert MK, Ivy JL. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. Journal of Applied Physiology. 1986;61(1):165–172. doi.org/10.1152/jappl.1986.61.1.165
- Burke LM, Ross ML, Garvican-Lewis LA, et al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. Journal of Physiology. 2017;595(9):2785–2807. doi.org/10.1113/JP273230
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement: Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise. 2016;48(3):543–568. doi.org/10.1249/MSS.0000000000000852
- Ivy JL, Katz AL, Cutler CL, Sherman WM, Coyle EF. Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. Journal of Applied Physiology. 1988;64(4):1480–1485. doi.org/10.1152/jappl.1988.64.4.1480
- Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine. 2023;57(17):1073–1097. doi.org/10.1136/bjsports-2023-106994
This article is general education, not personal medical advice. Athletes with specific health concerns should speak to a qualified sports dietitian or doctor.