The Magical Ingredient? Carbohydrates. When you’re working out for 60-90 minutes or longer, your body needs carbohydrates, or sugar, to keep working. Yes, some will dispute me and talk about fat adaptation, train low, metabolic efficiency. It may work for some, which is GREAT! However, I haven’t seen convincing research or case reports other than anecdotal evidence that it works. What I do know, and see constantly in the athletes with whom I work is that being sure they are getting enough carbohydrates improves performance, helps them finish faster, and feel better. All of those things are a win in my book!
How much carbohydrates do you need? It depends on a few things, and I look at them together:
- Body weight: a starting point is 0.32 to 0.45 grams of carbohydrate per pound of body weight.
- Lean body mass: if someone has a lot of fat mass, the guidelines in number 1 may over-estimate the amount of carbohydrates the person needs.
- Initial recommendation of 60 grams of carbs per hour on the bike and 45 grams of carbs per hour on the run.
- Height: If you’re taller, you have more intestinal wall space (more absorption may be possible) than someone who is shorter.
- The type(s) of carbohydrates are in your preferred fuel: a 2-to-1 mix of glucose-to-fructose has a higher absorption rate than either one alone.
- The type of sport: most people can absorb more fuel when cycling rather than running and even less when swimming.
I look at these five things and develop a starting point for an athlete. Then, depending on how well the athlete feels and his/her stomach feels we’ll increase or decrease the amount of carbohydrates per hour, by 5 to 10 grams, until we find their personal fueling “sweet spot.”
Let’s look at an example or two.
Mark is a triathlete who is 5’8″ and weighs 190 pounds. He has a body fat of 38%. He is using a drink that is all glucose or glucose polymers. If I were putting together a bike and run nutrition plan for him, I’d do the following calculations based on the points above:
- Using the recommendations, Mark needs between 61 and 86 grams of carbohydrates per hour. (190 x .32 = 61; 190 x .45 = 86).
- Mark has a higher body fat %, so I’d go on the lower end because due to the extra fat mass the recommendations may be overestimating how many carbohydrates he can absorb.
- I’ll review the recommendations of 60 grams on the bike and 45 grams on the run and compare them to the calculations in step 1.
- Mark is average height which would indicate the middle to lower range of the recommendations and calculations in steps 1 and 3 may be appropriate.
- He is using an all glucose or glucose-based drink. This also puts his absorption on the lower end of the recommendations. If he had a glucose-fructose drink, he may be able to absorb more.
- He is cycling and running, so we’ll need recommendations for both.
For Mark, I’d recommend starting with 65 – 70 grams of carbohydrates per hour on the bike and 50 – 55 grams of carbohydrates per hour on the run. The bike recommendation is on the low end of the calculations and a little higher than the “standard” recommendation. I’m giving him some room due to his weight, but not going too far over the “standard.”
As far as his run, I’m going below the calculation and above the “standard.” The reason I’m making this recommendation is again, because of his weight. If he weighed below 145-150, I’d probably go lower.
Remember: these recommendations are starting points. As the athlete trains, we’ll work together to adjust his fueling strategy. I strongly recommend athletes keep a training log and note how much and what type of fuel they used along with how they felt physically and mentally and how their GI system felt. This way we can keep track of how things are going and how any adjustments work or don’t work.