Low Energy Availability in a Distance Runner Requesting Weight Loss
A 24-year-old female distance runner presents for body-composition and nutrition guidance. She is 170 cm, 58 kg, BMI 20.1, and runs 70 km per week. Dual-energy X-ray absorptiometry shows 18% body fat and fat-free mass of 45 kg. She has had amenorrhea for 8 months and two stress fractures in the past 2 years. She wants to lose 3 kg before the competitive season because she believes lighter is faster. A 3-day food recall averages 1,900 kcal/day and 70 g protein/day. Her training energy expenditure averages 700 kcal/day. She takes no medications, has no gastrointestinal symptoms, and is not taking oral contraceptives. She asks whether a very-low-calorie diet for 4 weeks would help and whether her body-fat percentage is 'too high' for a runner.
1. Calculate her energy availability. Interpret the result using current RED-S concepts and explain why body-fat percentage alone does not determine her risk.
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Energy availability is calculated as intake minus exercise energy expenditure, divided by fat-free mass: (1,900 - 700) / 45 = 1,200 / 45 = 26.7 kcal/kg fat-free mass per day. This is below the commonly used threshold of 30 kcal/kg FFM/day for low energy availability; optimal is often described as about 45 kcal/kg FFM/day.
Her clinical picture supports relative energy deficiency in sport: amenorrhea for 8 months and two stress fractures. These are signs of disrupted endocrine and bone health, not simply low body weight. Her BMI is normal and her body-fat percentage of 18% is not necessarily low for a female runner, but that does not mean she is healthy. Risk is driven by low energy availability, not by a single body-fat number.
The 3-day recall is an estimate and may underreport intake, but the combination of calculated low energy availability and clinical signs is enough to act. I would not recommend further weight loss. She needs medical and dietitian referral, and the focus should be restoring energy availability, menstrual function, and bone health.
2. Evaluate her protein intake and propose nutrition and training changes. Include whether a 4-week very-low-calorie diet is appropriate.
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Her protein intake is 70 / 58 = 1.21 g/kg/day. For an endurance athlete, a more appropriate target is about 1.6-2.0 g/kg/day, which would be 93-116 g/day. She needs roughly 25-45 g more protein daily, distributed across meals.
A 4-week very-low-calorie diet is inappropriate. It would worsen low energy availability, likely worsen amenorrhea and bone loss, increase injury risk, and impair performance. The priority is to increase energy intake to restore energy availability, not to create a larger deficit. A practical starting point is to add about 300-500 kcal/day and reduce training load while she is medically reviewed. If she insists on weight loss, it should occur only after energy availability and menstrual function are restored and with a sports dietitian and physician involved.
Training changes include reducing running volume temporarily and adding 2 days of strength training to support bone health. Screen calcium and vitamin D intake. The goal is return to menses and prevention of further stress fractures, not a faster race weight.
3. What body-composition method would you use for follow-up and why? Discuss limitations of DEXA and bioelectrical impedance in this athlete.
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I would use DEXA for follow-up if the same scanner and software are available, because it provides fat mass, fat-free mass, and regional bone data. The bone data are particularly relevant given her stress fractures. Measurements should be scheduled at the same time of day, with consistent hydration and without recent strenuous exercise, because these factors affect results.
DEXA has limitations: it involves low radiation, results vary between devices, and changes of less than about 1-2% may be within measurement error. It should not be used as a stand-alone diagnostic tool for low energy availability.
Bioelectrical impedance is convenient but is strongly affected by hydration, recent exercise, food, and menstrual cycle. It is less accurate in athletes and is not reliable for tracking small changes. Skinfolds require a skilled tester and have similar sources of error. The key point is that body composition is secondary to clinical signs, energy availability, and performance. I would avoid focusing her on 18% body fat and instead track menstrual function, bone health, energy intake, and training tolerance.