Restricting Carbs Hurts Performance and Health

carbohydrate fueling Nov 29, 2023

 Want to avoid LEA and REDs?

Eat enough carbohydrates.

As fasting, keto, and carb-phobia continue to be promoted across social media, we’ve seen an uptick in low energy availability (LEA) across the spectrum of athletes. In my own work, I’ve found about 55 percent of individuals who are training every day are in low energy availability. And females are especially at risk

As I’ve written about previously, LEA is a problem I see every day, and if it isn’t caught in time, it can sometimes lead to irreversible damage to your health, such as dangerously low bone mineral density. Avoiding LEA starts with eating enough.

If you know your body composition, you can start with using the equation for determining energy availability (EA), which is your dietary energy intake (kcal) minus your exercise energy expenditure (kcal) divided by your fat free mass (FFM) in kilograms (kg). You want the final number (EA) to be over 45 calories per kilogram of FFM; 50 calories per kilogram FFM is a good number to aim for if you train regularly. Anything less than 30 calories per kg is defined as LEA, and at that point you start experiencing health risks after only five days

But let’s take it one step further and hone in on carbohydrate intake. Current research is suggesting that athletes (especially female athletes) are not meeting their carbohydrate recommendations and that they may actually be experiencing additive detrimental effects of low carbohydrate availability (LCA) on top of the health and performance consequences of LEA.

What is Low Carbohydrate Availability?

As we discussed in our International Society of Sports Nutrition Female Athlete Position Stand, eating sufficient carbohydrates can help you avoid LEA. For endurance training that means 4.5 to 7 grams of carbohydrates per kilogram of body weight a day. Women doing moderate training and/or short intense days (like CrossFit training) still demand about 3.5 to 5 grams of carbs per kilogram of body weight per day.  

Research shows women by and large are not meeting those marks. One retrospective study of young and elite female athletes found that nearly half of the young female athletes and a third of elite female athletes had carb intakes below 4 g/kg of body weight a day. Anywhere from 45 to 98% of female athletes across an array of sports may not be meeting their carbohydrate needs. 

As I’ve written about previously, women are especially sensitive to low nutrition, especially carbohydrates. When we fall short, we have a marked reduction in the expression of kisspeptin, a neuropeptide that’s responsible for sex hormones and endocrine and reproductive function, which also plays a significant role in maintaining healthy glucose levels, appetite regulation, and body composition. As I wrote about here, reduced kisspeptin expression can increase our appetite, decrease our energy expenditure, and reduce glucose-stimulated insulin secretion. 

The consequences of falling into a prolonged state of LCA include decreased endurance performance, decreased coordination, decreased glycogen stores, depression, irritability, decreased concentration, decreased muscle strength, impaired judgment, decreased training response, and increased injury risk. 

Moreover, for all of us trying to build lean mass and nail our sprints, LCA impairs the feedback for gaining those adaptations (primarily by increasing BCAA oxidation)! The combination of LCA and LEA creates a magnified effect of the hormone profile associated with compromised adaptation, performance, and health; all from not eating enough carbs!

Eating enough carbohydrate also helps us maintain a healthy immune and stress response to exercise and helps moderate cortisol, improving adaptations and recovery.

Because female athletes remain underrepresented in sports science research, current carbohydrate recommendations also may fail to consider female-specific adaptations and hormonal responses associated with the menstrual cycle. 

My recommendations for avoiding LCA are pretty basic:

First and foremost, fuel for the work required! This means providing enough carbohydrate relative to your upcoming session, but finishing that session not fully depleted and eating as soon after exercise as possible. With the limited data available, it is recommended female athletes should focus on rapid consumption of at least 1.2 g of carb with minimum 0.38g protein per kilogram of body weight following prolonged exercise in order to restore spent muscle glycogen. And peri and post-menopausal women should focus on rapid consumption of at least the same, but within 30 to 40 minutes (to take advantage of the non-insulin dependent first phase of glycogen synthesis). 

Next, ensure you are aiming to have carbohydrate and protein at every meal (~25% of your carb needs with ~35-40g protein), and if you have double sessions, ensure you have a carbohydrate rich snack (~30g) before your second session. 

Nutrition is a nuanced field, but overall by aiming to fuel appropriately from breakfast to dinner, then stopping eating about 2 hours before bed, you are on the right track for optimal recovery, adaptations, and health. 


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