Body weight/composition has always been one of the main concerns of any endurance athlete, male or female. Being leaner and lighter is often associated with improved performance, especially in running.The “Female Athlete Triad”, encompassing one or more manifestations of restrained eating, menstrual dysfunction and poor bone health is relatively common among female endurance athletes with varying degrees of severity.

Many female athletes, most often unknowingly, fail to obtain appropriate energy intake and will function in a low energy state.  Low energy availability – when energy intake is too low to meet the body’s energy need due to increasing demand from heavy training schedule coupled with restrictive eating or poor nutrition recovery often leads to a significant negative energy balance.

A significant negative energy balance becomes of concern when it affects health and performance. 
Reduction in metabolic rate, increase risk of illness and injury (which in severe cases often leads to hormonal imbalances), menstrual dysfunction and suboptimal bone health are some of the negative consequences of chronic energy deficit.

Although the term “endurance runners” was not clearly defined, the following recommendations are still relevant for most of female triathletes/runners who train at least 3-4 times/week (or >8hrs/week). I have summarised the key take-away points here.

Energy Intake Requirement
The recommended intake for daily total calories is45kcal/kg of fat free mass plus the energy expended during training That means if you weigh 60kg with 20% of body fat, the minimum daily intake is 2160kcal/day.After an average of 500-600kcal energy expended during exercise, the recommended daily intake is 2600-2800kcal/day.
I would recommend calculating the daily intake in terms of g/kg for each macronutrient (carbohydrate, protein and fat).

 

Protein Recommendation
The daily protein intake may vary depending on the amount of carbohydrate taken and the type of training performed on the day.
The general recommendation for female endurance runner has been 1.2-1.3g/protein/kg/day. However, the latest estimated protein requirement for female athletes has been shown to be much higher 1.6g/kg/day.

Sources of protein:

• 1 egg – 5-6g
• 250g yogurt – 11-13g
• 120g cooked chicken/beef (1 palm size) – 20-25g
• 100g tofu – 12g
• 1 cup/250ml milk – 8-11g
• 100g rolled oats – 11-14g
• 4x3x2cm hard cheeses (40g) – 8-10g
• 1 cup cooked white rice – 2.1g
• 2 slices bread (white & whole meal) – 2-6g

 

Iron
Iron is an important component of haemoglobin and myoglobin, the protein transporter of oxygen. Lower level of haemoglobin has been shown to reduce maximal oxygen consumption, hence endurance performance.
The recommended daily intake of iron for premenopausal women in 18mg/day and 8mg/day for men.
Female athletes have a higher risk of iron deficiency due to blood loss from menstruation, increased acute inflammation effect of strenuous exercise which affects iron absorption, iron losses due to hemolysis (rupturing of red blood cells) or gastrointestinal bleeding, which may occur as the pounding effect in distance running.

Iron supplementation should be taken with caution. It DOES NOT increase performance. Proper diagnosis and testing for  iron deficiency or iron deficiency anemia needs to be done and the root cause of deficiency analysed before supplementation is needed.

Iron deficiency may occur due to

• lack of consumption of iron-rich foods,
• lack of absorption (deficiency in copper or vitamin D),
• drug/nutrient interaction (antibiotics, aspirin, NSAIDS, synthetic anabolic steroids, heavy metal toxicity decrease iron absorption),
• inadequate production of red blood cells (vit B12, B6, folic acid, copper deficiencies).

Change in diet by consuming more iron-rich foods combined with vitamin C may be enough to reverse iron deficiency symptoms without the need for supplementation. All vegetarian athletes (or those mainly consume a plant-based diet) will have 1.8x iron requirement as bioavailability of iron in plant-based diet is only 10%, versus 18% in a mixed diet.
Good sources of iron in diet: (Linus Pauling Institute, 2012)

• 6 medium oysters – 5mg
• 120g cooked beef – 3.3mg
• 1 medium baked potato with skin – 1.87mg
• 1 tbs black-strap molasses – 3.5mg
• 1/3 cup tofu – 2.15mg
• 85g canned tuna – 1.3mg
• 85g cooked dark meat chicken – 1.13mg
• 1 small box (42g) raisins – 0.81mg
• 28g cashew nuts – 1.89mg

 

Vitamin D 
Vitamin D plays an important role in maintaining calcium level as its adequate level is necessary to increase intestinal calcium and phosphate absorption.
In addition to its effect on bone health, vitamin D plays an important role in immune system, muscle functions and sports performance.

Our main source of vitamin D is synthesised by the skin when exposed to the sun, forming vitamin D3 (cholecalciferol). Just because we live in a sunny environment, it does not guarantee we have adequate vitamin D synthesis. Some of the factors that can limit vitamin D production includes regular sunscreen use, clothing coverage, cloud cover, time of being outdoor and latitude.

5-30mins of direct sun exposure between 10am to 2pm on arms and legs several times a week is recommended to ensure adequate vitamin D synthesis. We can also obtain vitamin D from our diet, though the sources are rather limited. Some vitamin D3-rich foods include fatty fish (salmon, sardines, herring, cod), cod liver oil, fish oil and egg yolks. Mushrooms also contain another per-cursor of vitamin D: ergosterol. When  sun-dried, it is converted to ergocalciferol (vitamin D2).

Even though low vitamin D level may impair athletic performance, there is limited scientific evidence that supplementation of vitamin D will improve athletic performance on athletes who are not deficient.

RDA for vitamin D is measured via serum concentration of  25(OH)D or calciferol, the major circulating form of vitamin D, It is converted from vitamin D2 and D3 in the liver. It needs to be further converted into the biologically active form, calcitriol, in the kidneys.

The 2016 global recommendations for vitamin D serum concentration:
25(OH)D level  30nmol/L or 12ng/ml as deficient
25(OH)D level  between 30-50nmol/L or 15-20ng/ml as insufficient
25(OH)D level  50nmol/L or 20ng/ml as sufficient

For athletes, the cut-off of 75nmol/L or 30ng/ml is suggested for vitamin D sufficiency and 50nmol/L or 20ng/ml for sufficiency.

Daily vitamin D intake recommendations vary depending on “age, geographic location, skin pigmentation, physical activities, and season”
<18yrs : 600-1000IU, Upper Limit 4000IU
19-70yrs: 1500-2000IU, Upper Limit 10000IU

 

Calcium
Dietary assessment is the only way to assess calcium status. Serum calcium is very tightly regulated and are its levels are not correlated with acute calcium intake or changes in dietary intakes (unless intake is severely restricted). Clear biochemical indeces to measure calcium status are lacking as the body uses bone tissue as calcium source to maintain constant concentrations of calcium levels in blood, intercellular fluids and muscle.

 

References

Review Paper:
Deldicque L, Francaux M. Recommendations for Healthy Nutrition in Female Endurance Runners: An Update. Frontiers in Nutrition. 2015;2:17. doi:10.3389/fnut.2015.00017.