Curious about how your menstrual cycle may affect your carbohydrate needs?
Estrogen has the effect of increasing glycogen uptake and storage in the muscle and glycogen sparing and increased fat utilization during exercise.
So, when estrogen is low, your body should be able to utilize relatively more endogenous carbohydrate (stored glycogen) to fuel exercise. Practically, this means you really need to pay attention to carbohydrate loading and post-exercise carbohydrate recovery to ensure you have adequate glycogen stores, particularly when you have back-to-back training days.
When estrogen is higher, your body should be able to oxidize relatively more fat compared to endogenous carbohydrate (glycogen) during exercise. Does this mean that you should be on a lower carbohydrate diet during these phases? NO! Not if you are still attempting to complete training sessions that include some intensity. This means you may need to increase the amount of exogenous carbohydrate you are taking in just before and during your training sessions to support higher intensity work. Remember, when carbohydrate intake rates are higher than 60 g/h, you are better off taking in mixed glucose-fructose carbohydrate sources to allow your GI tract to effectively absorb the carbohydrate for oxidation. Taking in high rates of carbohydrate also requires practice!
Final point, not all women are the same so MC and fueling needs can differ between individuals. It’s a great idea to start tracking your menstrual cycle and make notes on how you are feeling during training and recovery, and then start adjusting fuel as needed.
How do I use sports drinks?
We’ve talked about carbohydrate recommendations during training and racing, but sometimes it’s hard to EAT 60+ grams of carbs per hour, especially if you are out for a long/hard ride.
Did you know you can also meet (at least a portion) of your hourly carbohydrate goals with a carb-electrolyte drink (CHO-E)? But, before you go that route, you want to know the contents of what you are drinking, the mixing instructions, and scale the serving size information from the nutrition label to the amount of fluid in the bottle you are using.
If you are also using gels or chews, make sure you are factoring in the total grams of carbohydrate and milligrams of sodium the products are providing you together, with your CHO-E drink. Here are some of the more common drinks and their CHO and sodium content per 24 oz (710 ml).
Skratch Hydration: 31 g CHO, 570 mg sodium
Skratch Superfuel: 120 g CHO, 480 mg sodium
Tailwind Endurance Fuel: 50 g CHO, 600 mg sodium
Gu Roctane: 69 g CHO, 366 mg sodium
SWORD Performance: 45 g CHO, 600 mg sodium
As always, try it first during training, try it at race pace, and over time in multiple environmental conditions before you settle on a race day plan!
What are multi-transportable carbs and why do I need them?
Multiple transportable carbohydrates, aka different types of single carbohydrates (i.e. glucose, fructose, maltodextrin) can be beneficial during endurance activity lasting >2.5 hours in duration. Currently recommended practices for carbohydrate intake during endurance exercise include:
Optional CHO mouth rinsing during exercise 30-75 min
30–60 g/h during 1–2.5 h of endurance exercise
Up to 90 g/h of multi-transportable CHO (e.g. glucose or maltodextrin:fructose blends) for exercise >2.5 h.
Previously it was thought that the body could only utilize 1 g of CHO/min (60 g/h) during exercise. However, this was based on research examining a glucose-only solution. When researchers started adding different single CHOs (ie fructose) to the mix, carbohydrate delivery and oxidation rates increased.
Intestinal absorption of carbohydrate is the limiting factor when it comes to how much exogenous carbohydrate your body can utilize during exercise. Glucose and fructose rely on different transport proteins (SGLT1 and GLUT5) for absorption in the gut. Because the glucose transporter is saturated when glucose ingestion exceeds > ~60 g/h, multiple transportable CHO (e.g. glucose-fructose) solutions are recommended when CHO intake rates are higher than ~60 g/h. The ideal solution is proposed to contain a 2:1 glucose to fructose, or maltodextrin to fructose ratio (ie 60 g of glucose or maltodextrin, and 30 g of fructose). It should be noted that the fructose addition to glucose provides benefit after the glucose transporter is saturated at ~60 g/h.
Finally, research has suggested that multiple transportable CHO vs. single CHO can result in performance improvements. One study in particular found an 8% performance improvement with a glucose:fructose solution (56.1 min) compared to a glucose only solution (60.7 min) during a 40 km bike time trial that followed 2 hours of cycling at 55% of max in trained male cyclists. Evidence also suggests reduced GI discomfort with multiple-transportable CHO mixtures compared to glucose alone. Athletes can choose CHO-based sports nutrition products in the form of liquids, gels, or solids based on personal preference, environmental conditions, and demands of the course and event.
PMID: 26373645; 22468766; 20574242; 18202575
Do we need sex-specific carb intake recommendations during endurance exercise?
Ingestion of ~90 g CHO/h in the form of glucose or maltodextrin-fructose can increase exogenous CHO utilization and improve endurance performance. However, the majority of research in this area has been completed in males, but do women require different CHO intake recommendations during endurance exercise?
In general, women are able to oxidize a greater percentage of fat versus stored CHO (glycogen), compared to men completing endurance exercise at the same relative intensity. However, current research does not suggest a sex-difference in exogenous CHO oxidation during exercise after ingesting a glucose solution. What about the ingestion of multiple-transportable CHO (e.g. glucose-fructose solution) > 60 g/h?
A recent study provided elite male and female cross-country ski athletes an 18% maltodextrin and fructose hydrogel beverage at a rate of 2.2 g/min (132 g/h) during a 2 h roller skiing protocol in cold ambient conditions at 70% max. Neither group experienced GI symptoms and there were no significant differences in glycogen utilization change, peak rate of exogenous CHO oxidation (though females tended to have lower peak oxidation rates than males, 1.2 vs 1.5 g/min), RPE, or performance between males and females in response to CHO ingestion.
Results from other studies measuring exogenous CHO oxidation in females vs. males are mixed. Some indicate that exogenous CHO oxidation is ~2-4% higher in females compared to males while others found the opposite or no difference. More research is needed to answer this question specifically, but at this point there is insufficient evidence to indicate CHO intake recommendations should be different for females and males engaging in endurance exercise. Further, it has been demonstrated that both male and female athletes can tolerate high rates (>90 g/h) of CHO (glucose-fructose) intake without experiencing GI symptoms in cool conditions.
Finally, because hormonal changes throughout the menstrual cycle may iinduce changes in fuel utilization, eating a pre-exercise CHO meal in addition to ingesting ~90 g of multiple transportable CHO per hour during endurance exercise > 2.5 h may help minimize hormonal effects and help support performance.
PMID: 10953068, 12070184, 14750011, 14967866, 16278245, 20019632, 31655603, 34015236
