Athletes are constantly bombarded with nutritional advice professed to boost performance, most often through the lens of improving physique. Although there are many sources, social media has provided a platform where anyone can promote nutritional programs, often without scientific basis. Female athletes are particularly vulnerable to wayward nutrition advice.

Unfortunately, it’s more common than we realize. A 2022 study including more than 200 female endurance athletes found that 65 percent were at risk of low energy availability (Low EA,) 23 percent were at risk of exercise addiction, and 21 percent had disordered eating behavior. This can have a cascade of effects, particularly on hormone health in female endurance athletes.

Hormones are chemical messengers that transmit information on your physical, mental, and emotional health. Most of the time, these hormones are present in the right place, at the right time, to keep things running smoothly. But once in a while, things can fall out of balance, and too much or too little of a hormone (or multiple hormones) can cause a variety of short- and long-term health conditions.

Lots of things can cause a hormonal imbalance – poor sleep, stress management, and recovery are common causes in endurance athletes – but what you eat and how much you eat relative to your training can make a big impact on hormone health in women.

Key hormones for athletic performance

• Testosterone: Essential for building muscle mass and strength.
• Growth hormone: Important for muscle growth and repair.
• Cortisol: Regulates the body’s stress response and can affect muscle breakdown.
• Thyroid hormones (TSH, T4, T3): Regulate metabolism and energy levels.
• Insulin: Regulates blood sugar levels and affects muscle growth and repair.
• Estrogen: Plays a crucial role in bone health, and preventing injury.

SEE ALSO: The Male Endurance Athlete’s Guide to Eating for Hormone Health

Why it’s important for women to eat for hormone health

Certainly nutrition isn’t the only factor contributing to hormone health in endurance athletes – sleep, stress management, and recovery also play a role – but what you eat and how much you eat relative to your training can make a big impact on how your body functions.

Energy availability (EA) is the amount of energy that can be used for physiologic and homeostatic processes after accounting for exercise energy expenditure (EEE) and is the preferred measure of energy status for athletes. An EA of ~45-50kcal/kilogram (kg) of fat-free mass (FFM) is considered optimal for maintaining body size and mass. On the other hand, low energy availability (low EA) is defined as <30kcal/kg/FFM or having insufficient energy to meet basic physiological demands and training. Low EA causes a cascade of hormonal disruptions that results from one main factor: inadequate nutrition/energy. Regardless of the specific diet trend (keto, paleo, or intermittent fasting- to name a few), they all have similar goals: to reduce overall calories from carbohydrates and increase protein and fat intake.

What female endurance athletes, specifically, need to know

The potential health and performance consequences that can arise secondary to low EA is known as relative energy deficiency in sport (RED-S). Unfortunately, many early symptoms of RED-S are vague and can be easily attributed to causes other than energy deficiency. Furthermore, female athletes who can maintain a reasonable level of performance despite energy deficiency and hormonal disruption may not recognize the severity until the health consequences are extensive.

The hormonal effects of energy deficiency in female athletes

Menstrual dysfunction

The most notable and recognized sign of low EA is the hormonal changes that halt reproduction. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH), estrogen, and progesterone are disrupted, which under normal circumstances help regulate the menstrual cycle. Despite popular belief, it is NOT normal to lose your period in training. Additionally, a drop in estradiol (female sex hormone) and a rise in estrone (estrogen hormone that fat secretes) signals your body to store more fat. To make matters worse, the stress hormone cortisol (progesterone is converted to cortisol in periods of high stress) also signals fat storage, all in the name of our famine mechanism.

Skeletal muscle

In severe or prolonged low EA, there is a negative effect on muscular protein synthesis instigated by decreased anabolic hormones and increased cortisol, initiating skeletal muscle protein breakdown. Hence explaining chronically sore/achy muscles and poor training adaptations despite intense training.

Bone health

Strong bones require regular physical activity, adequate calcium intake, and normal hormonal levels. Of these three, hormonal balance has the most significant impact. In women, a drop in estrogen (normal levels help to preserve bone mass density) results in rapid acceleration of bone loss, @ 3-5% per year, that cannot be fully compensated for by vigorous activity and high calcium intakes. In addition, elevated levels of circulating cortisol can also lead to significant bone loss. The result includes bone stress fractures and an increased risk of osteoporosis.

Endocrine and metabolic system downregulation

There is a decrease in insulin, leptin (a hormone that regulates satiety), insulin-like growth factor 1 (IGF-1) strongly associated with energy deficit, estrogen, progesterone, and triiodothyronine (T3). This cascade of changes leads to hypothyroid symptoms, reduced resting metabolic rate, bradycardia, orthostatic hypotension (blood pressure drops when you stand up), lower circulating glucose, higher free fatty acids (FFA), higher glycerol, higher cholesterol and β-hydroxybutyrate (a clinical indicator of ketosis).

An increase in growth hormone (GH), a pituitary peptide necessary for muscle and bone anabolism, and the metabolism of carbohydrates, protein, and lipids is elevated in low EA to maintain euglycemia in states of energy deficiency by withdrawing energy sources from fat stores.

Dietary intake regulating hormones

Ghrelin, which acts on the hypothalamus and pituitary and is a marker of energy status, is elevated in female athletes with low EA, increasing appetite, and hunger. Peptide YY, a hormone released by the intestinal cells in response to caloric intake, decreases appetite and is elevated in low EA, enhancing appetite to encourage caloric intake.

Recognizing the telltale signs of low energy availability is crucial before it becomes a serious health issue.

• Irregular or missing menstrual cycles
• Fatigue
• Mood problems, including irritability and depression.
• Frequent illness
• Frequent injuries, especially stress reactions and fractures
• Decreased libido
• Increase in GI issues.
• Poor or decreased training adaptations

Providing enough energy (carbs) for your body will have the most significant impact on your health and performance. The first line of offense for a female athlete is to eat/fuel in and around training. Delaying or avoiding food intake during and after a training session causes the body to remain in a catabolic (breakdown) state. Your brain interprets this as not having enough energy to support adaptation and health, decreasing resting metabolic rate and breaking down muscles for energy.

Secondly, avoiding the low carb/keto diet trend is critical. Research shows that consuming adequate carbs helps you avoid low EA even when your overall energy availability is lower than optimum. For more on this, check out: Studies Are (Again) Showing How Badly Athletes Need Carbs.

Third, increase your intake in and around training and throughout the day, then compare how you feel and perform when you are in energy balance. Tracking macros and calories for three to five days is a worthwhile exercise to get a live snapshot of exactly how much energy you are taking in. Chances are you may be surprised.

How to determine energy availability (EA)

If you know your body composition, use this formula:

Dietary energy intake minus your exercise energy expenditure (kcal) and divided by your Fat Free Mass (FFM). For example, a 68kg/150lb female with 20% body fat and burns 600 calories daily in training would need 3,100 calories a day to be slightly above the 45 calorie/kg/FFM benchmark. On a 1.5-hour training day, this female athlete would require at least 400g carbs.

Fueling guidelines

In and around training sessions

• Aerobic sessions lasting <75 min – water with electrolytes is acceptable. But if there are multiple training sessions in a day, consume 30-60g carbohydrates (carbs) per hour and 20-32oz fluid/hr.
• Sessions lasting up to 2.5 hours consume 30-60g carb/hour and 20-32oz fluid/hr.
• Sessions lasting >2.5 hours consume up to 90g/hour. And 20-32oz fluid/hr.

Post-workout fueling guidelines

• Training/race <2 hours; consume 1.2g carb/kg/hr in the first two hours.
• Training/race 2+ hours; consume 1-1.2g carb/kg/hr in the first four hours. As a simple rule, aim for 50-90g carbs, 15-25g protein, and a small amount of fat each hour for the first four hours.

Daily carb needs based on activity

Increased carbohydrate availability supports positive training adaptations and optimal health.

• Light activity up to one hour: 3-5g carb/kg/day
• 1-3 hours: 6-10g/kg/day
• >4 hours: 8-12g/kg/day

Altering energy intake, specifically carbohydrates, to be a leaner, faster athlete chasing a performance advantage can be risky business. The line between discipline and disorder is thin, and it’s easy to cross without realizing the danger until bodily functions and quality of life deteriorate. The good news is it can be prevented if you heed the body’s warning signs and provide enough fuel (carbs) to support health and training. If you are suffering from low EA or disordered eating, consult a medical practitioner for a health evaluation and a sport dietitian for a personalized nutrition plan adequate in energy, macronutrients, and micronutrients.

The importance of protein for hormonal balance

A balanced diet with adequate protein can help support muscle growth and repair.  Protein is essential for hormonal balance, as it provides the building blocks for hormones such as thyroxine, estrogen, and steroid hormones. Adequate protein intake is also necessary for maintaining muscle mass, which is important for athletic performance. For more on protein intake, see Ask Stacy: How Much Protein Does a Triathlete Need Each Day?