When it comes to sports nutrition, most athletes pride themselves on eating in a way that optimizes performance. Despite this commitment to fueling for performance, women and girls are at substantial risk of underfueling. Research shows that many female athletes are involved in a cycle of chronic dieting that leads to low nutrient intake and impaired physical and mental performance.
Surveys suggest that a staggering 2/3 of collegiate female athletes are actively dieting in an effort to lose weight. Scientists have identified the condition of underconsuming calories as Low Energy Availability. Low Energy Availability is defined as eating fewer than 30 calories per kg of fat free mass a day. Optimal calorie intake is defined as around 45 cal/kg of fat free mass daily.
Who Is At Risk Of The Dangers of Chronic Dieting?
Athletes in aesthetic and relative strength sports are at greatest risk of undereating, but there is evidence that this phenomenon is prevalent in team sports as well:
- One sample of 109 active adult women found that almost half reported Low Energy Availability.
- In a study of Division 1 female runners, 52 percent reported consuming lower than the 30 cal/kg minimum.
- Among Division 1 female soccer players, 33 percent reported Low Energy Availability, which was associated with greater body dissatisfaction.
How Does Regular Dieting Impact Performance?
Surveys suggest physical performance in female athletes declines by as much as 10 percent in response to chronic dieting. One study found that in elite adolescent swimmers, those with Low Energy Availability had a 10 percent decline in swim speed over a 12-week training session. In comparison, a group that had adequate nutrition and calories had an 8.2 percent improvement in performance. Another study found that reaction time worsened by 7 percent in a group of female athletes in response to Low Energy Availability.
Undereating negatively impacts physical performance in multiple ways:
- Leads to hypoglycemia and blood sugar irregularities.
- Supresses thyroid function, causing lower levels of T3 thyroid hormone that governs growth, development, and reproduction. This leads to a decrease in resting metabolic rate so that the body conserves energy and burns fewer calories daily.
- Leads to a drop in estrogen levels, which impacts fat burning, exercise recovery, and bone metabolism.
- Leads to inadequate intake of nutrients including iron, vitamin D, and calcium that are necessary for energy metabolism and exercise recovery. For example, low iron compromises hemoglobin—the oxygen carrying molecule that fuels physical performance. Lack of hemoglobin also impairs bone health, increasing bone breakdown.
What Can You Do To Overcome Low Energy Availability?
Experts call for female athletes to work with experienced sports nutritionists to devise an eating plan that optimizes performance and body composition. In some cases, counseling can be helpful to aid female athletes in navigating the social messages and norms that lead to chronic dieting. What follows are general nutrition recommendations that athletes and coaches can use when designing nutrition programs:
Estimate calorie needs and hit energy intake goals daily.
Scientists recommend the ideal calorie intake is between 39 and 45 cal/kg fat free mass/day. Endurance athletes or those who burn large volumes of energy during training may need to add exercise energy expenditure on top of that. For example, a 55 kg middle distance runner would have baseline energy needs ranging from 2145 to 2420 a day. Running 5 to 6 miles a day could bump that up to 2745 to 3020.
Get adequate protein.
It’s commonly believed that female athletes don’t require as much protein as male athletes. In fact, women have decreased protein synthesis rates after exercise, which suggests women may need more protein after muscle-damaging training. Scientists recommend a protein intake in the range of 1.3 to 1.8 g/kg of protein for omnivorous female athletes to maintain nitrogen balance. Vegetarians may require on the upper end of this range,
Prioritize healthy fat.
Due to a preoccupation with body composition, many female athletes opt for lower fat diets. Research shows that because women rely more on fat for fuel during training, a dietary fat intake of 30 to 35 percent of calories is necessary to optimize performance.
Customize carb intake.
Studies show that many women involved in endurance sports who have Low Energy Availability are not eating sufficient carbs to restore glycogen and fuel training. On the other hand, women shouldn’t rely on carb recommendations for male athletes because women burn less glycogen during exercise and may have lower carb needs than a male doing the same workout. Therefore, female athletes should experiment with carb intake guidelines to identify the optimal dose since most recommendations are based on male physiology. Similarly, the percentage of total calories from carbs may need to be reduced in favor of fat and protein in order for women to feel the best and get the most out of their training. Don't be afraid to experiment.
Optimize iron intake.
Iron is necessary to allow red blood cells to effectively carry oxygen to working muscles. Women have higher iron needs than men and they tend to lose iron via blood loss during their monthly cycles. Risk of iron deficiency anemia is greatest in vegetarians because plant-sources of iron (called non-heme iron) have poor bioavailability. A daily intake of 11 mg of iron is recommended for meat eaters and 18 mg of iron for plant-based diets.
Monitor vitamin D.
Vitamin D deficiency rates are high for female athletes, ranging from 33 to 42 percent and may be even higher depending on the season and type of sport. Vitamin D is necessary for muscle function and immunity in addition to bone health. Female athletes are strongly recommended to test vitamin D levels quarterly and supplement with up to 5,000 IUs to maintain a blood value of above 30 ng/ml.
Ensure adequate calcium.
Most female athletes who eat plenty of leafy greens, meat, and fish with some dairy have no problem fulfilling calcium needs. However, women who don’t get their period appear to require more calcium—at least 1000 mg/day, taken in two 500 mg doses from calcium carbonate or citrate.