Dietary carbohydrate
All of the foods and fluids that athletes eat provide nutrients which have specific roles in the body.
The information in this section will provide guidelines on daily carbohydrate recommendations to support both the health and performance of female athletes. In addition, it will cover some of the barriers that female athletes may face in order to meet carbohydrate recommendations.
There are three main types of dietary carbohydrate which are:
Also known as monosaccharides or disaccharides because they are made up of single or double sugar molecule(s). Sugars can be naturally occurring (e.g., in fruit and milk) or added sugars which are those added during processing (e.g., fruit canned in syrup or sugar added to make a cookie). On food labels, sugar is often referred to by its chemical name (e.g., glucose, sucrose, fructose, lactose, maltose). Sugars are an energy source for the body.
Also known as polysaccharides because they are more complex carbohydrates made up of multiple sugar molecules joined together by glycosidic bonds. When starch is consumed, it is broken down by the body into units of glucose, which provides energy to the body.
A complex group of sugars (polysaccharides) from plant foods which cannot be digested in the small intestine. Instead, they are completely or partially broken down (i.e., fermented) by bacteria in the large intestine.
Carbohydrate use and storage
Ingested dietary carbohydrates provide energy to the muscles, brain, and nervous system. Following ingestion, carbohydrates are broken down into smaller sugar molecules, which are converted into glucose by the liver to be used for energy. If glucose in the bloodstream exceeds energy needs, glucose will be converted into glycogen and stored in the body.
The liver can store up to ~100 grams of glycogen at any given time. This glycogen is primarily used to maintain blood sugar and energy levels throughout the day. In the muscles, a larger amount of glycogen can be stored (~400 grams). The glycogen in the muscles is a secondary storage facility, carbohydrates are stored there when the liver has reached capacity. For athletes, muscle glycogen, and the breakdown of glycogen to glucose in the liver, is used by the muscles during exercise to provide energy.
Each gram of carbohydrate provides ~4 kcal of energy.
The contribution of carbohydrate to energy metabolism during exercise changes depending on exercise type (see below). During high intensity endurance or sprint-type exercise, carbohydrates are the predominant energy source. During this type of exercise, the body will use glycogen stores, and sometimes they may even become depleted. When glycogen stores run low, the body may fatigue which can result in impaired physical and cognitive performance.
The body can store ~500 grams of carbohydrate as glycogen in the liver and muscle, which can be broken down and used when energy is needed.
Daily carbohydrate recommendations
Daily carbohydrate intake recommendations are dependent upon the intensity and duration of exercise being performed (see below). The aim is to ensure that sufficient carbohydrate is consumed to provide energy to working muscles, the central nervous system, and other bodily processes.
Dietary fiber
It is recommended for athletes to consume 25-35 grams of fiber per day. Dietary fiber provides many benefits to the body including:
- Improves gastrointestinal function and bowel movements
- Supports a healthy gut microbiome
- Associated with lower risk of heart disease, type 2 diabetes, and colon cancer
While dietary fiber intake provides many health benefits, there is a reason for practitioners to be cautious if athletes regularly have a very high fiber intake (i.e., above the RDA, >35g fiber). Research in female endurance athletes found high levels of dietary fiber intake to be associated with low energy availability and functional hypothalamic amenorrhea (i.e., loss of menstrual cycle). These associations might be due to:
1
- High fiber intake increasing fecal fat excretion, which in turn can reduce energy absorption
2
- Dietary fiber increasing satiety, which when coupled with high-intensity exercise may suppress appetite, decrease hunger, and reduce the total amount of energy consumed during a meal
3
- Excessive fiber increasing the likelihood of gastrointestinal discomfort e.g., bloating and diarrhea, which in turn may impact subsequent energy intake
Therefore, while it is important for athletes to include fiber within their diet, practitioners should be aware of how much fiber female athletes are consuming. In addition, fiber intake should be limited before and during exercise to reduce the risk of gastrointestinal symptoms. (see 
for more information).
Do female athletes meet carbohydrate recommendations?
It has been shown that female athletes across a range of sports struggle to meet daily carbohydrate recommendations and do not adapt their carbohydrate intake based on their training load. This could be due to a number of reasons including:
1
- High consumption of low energy, nutrient dense carbohydrates (e.g., fresh fruits and vegetables)
2
- Body weight and/or composition fears
3
- Substituting sports drinks with low calorie sweetened drinks during high-intensity and/or prolonged exercise
4
- Lack of education regarding the importance of carbohydrates
5
- Negative perception of carbohydrates on social media
Meeting the upper end of the carbohydrate recommendations requires a large amount of food to be consumed, which may also be a contributing factor to female athletes not meeting the recommendations. For example, in food terms, 10 g/kg BM/day of carbohydrate for a 132 lb (60kg) female (= 600g carbohydrate) is equivalent to either:
11 potatoes
1.8 kg
white rice
(uncooked)
1.7 kg pasta (uncooked)
Low carbohydrate diets
Some athletes may purposefully follow a low carbohydrate diet on a long-term basis, i.e., a ‘ketogenic’ or ‘low carbohydrate, high fat’ diet.
This may be for a range of reasons including a lack of understanding of the importance of carbohydrates for performance, fad diets, social media influence, “carb-phobia”, perceived positive body composition outcomes, etc. Very low carbohydrate intake for a prolonged period can lead to a range of outcomes including:
- Premature fatigue
during exercise
- Impaired performance at higher intensities
- Poor cognitive performance e.g., reduced alertness, difficulty concentrating
- Poor recovery between bouts of exercise
Athletes should therefore be educated around the potential performance consequences of following a low carbohydrate diet. It is however worth noting that a low carbohydrate diet may be useful during very short-term periods (i.e., 3-7 days) where weight loss is required to meet a certain weight target e.g., Olympic weightlifting, wrestling, judo and boxing. This is because there is evidence that this is effective for reducing fat mass while maintaining power and strength during very short-term periods. If this strategy is used, it should be carefully planned and managed by a sports dietitian, and should not be used for long periods of time.
Carbohydrate periodization
If athletes need help adjusting their carbohydrate intake to meet the demands of exercise on a day-by-day basis, carbohydrate periodization provides a practical solution. This strategy can help to support both performance and recovery through strategic timing of carbohydrate intake.
Should athletes alter carbohydrate intake based on menstrual cycle phase?
Popular media would suggest that female athletes should alter their diet, including their carbohydrate intake, during different phases of the menstrual cycle. However, there currently is not enough research to back this statement. There is some research to suggest that glycogen storage may be reduced during the follicular phase of the menstrual cycle compared to the mid-luteal phase. Nevertheless, providing that daily carbohydrate intake is sufficient for the exercise demands, this should not have an impact on performance.
See 
for more information.
DIETARY CARBOHYDRATE
