LOW ENERGY AVAILABILITY
This blog is the second part of a two-part series on bone health for athletes. Loss of bone density can lead to stress fractures in the short term which is a common complaint of athletes who come to our clinic. In the long-term loss of bone density can result in osteoporosis. In the first blog we looked at the main mineral bones are made of, calcium and how your diet influences this. In this blog we look at another very important nutrition related issue – low energy availability.
For years it was thought that stress fractures were a result of the physical strain caused by high training loads, all that pavement pounding gradually damaging bones. We now know that activity such as this (running, jumping, weight lifting), that works against gravity has a positive effect on bone strength, where non-weight bearing activities (swimming, cycling) has a neutral effect.
So rather than cause damage, exercise increases bone strength and low bone density is primarily caused by low energy availability (Hilton, 2003).
Low energy availability occurs when the energy you expend during training and daily activities does not match that which is consumed in food and fluid (kilojoules / calories). This imbalance means there is not enough fuel left over to support physiological functions including metabolic rate, bone health, immunity, menstrual function, protein synthesis, cardiovascular and psychological health (Mountjoy et al. 2014). Athletes that are at risk of low energy availability are those who have high training loads (e.g. – ultramarathon, ironman), where a lean body is desirable (ballet dancer, diver, gymnast) or those who are required to make weight for competition (e.g. boxing, rowing, wrestling, jockey).
Menstrual cycle disturbances in female athletes is a common reason for visiting a sports physician. Historically this was put down to the stress of training but we now know that reproductive function and bone formation are greatly affected when energy availability drops below a certain point, and this can manifest as menstrual cycle disturbances (Loucks, 2011).
But it’s not just women that need to be concerned, hormone disturbances have also been seen in men with low energy availability (Henning, 2014).
Check out the comparison of the following two diet histories. The one on the left is a 65kg female training for a 70.3 triathlon who is not fuelling her training well. She has come to see us because she can’t seem to lose extra body fat. She has not had a menstrual cycle for the last year, she is tired and not able to keep up with the goals her coach is setting for her.
The one on the right is a 65kg female who is fuelling well, she feels good, she is meeting targets set by her coach and she is happy with her body composition. These athletes need around 450-500g of carbohydrate every day to fuel their training, and around 80g of protein.
We find that if you focus on having adequate fuel to power your training sessions at 100%, and recover well between sessions, your body composition will sort it self out.
| Not fuelling well | Fuelling well |
| Pre-training
Nothing
Breakfast 2 hardboiled eggs with sautéed vegetables Vegetable juice
Snack Cappuccino Apple
Lunch 150g roast chicken 3 cups of mixed salad
Snack Banana Tub of Greek yoghurt
Recovery Nothing
Dinner 150g salmon 2 cups stir fried vegetables
Supper 2 squares of dark chocolate |
Pre- training
Banana + 2 slice toast and honey
Breakfast 1 hardboiled egg with sautéed vegetables and 2 slices grainy toast Fruit juice
Snack Cappuccino 1 cups fruit salad with yoghurt and honey drizzled on top
Lunch 100g roast chicken 3 cups of mixed salad 1 cup cous cous
Snack (pre-training) Banana Tub of Greek yoghurt
Recovery All milk milo + muesli bar
Dinner 100g salmon 2 cups stir fried vegetables 1 cup of cooked rice
Supper 2 scoops of ice-cream |
| Total energy: 7000kJ
Carbohydrate: 100g Protein: 120g |
Total energy: 12500kJ
Carbohydrate: 450g Protein: 125g |
The biggest wins for bone health come from adequate energy in the diet. But training with low energy availability is not only bad for bone health, it has many other potential consequences such as poor performance, reduced ability to recover well, fatigue, poor immune system, reduced ability to lose body fat, poor growth and overall health. If you are unsure if you are doing the best for your bones book in to see a sports dietitian for an assessment.
REFERENCES
Loucks A. B., Kiens, B. & Wright, H. (2011) Energy availability in athletes. Journal of Sports
Sciences. Vol 29:sup1: S7-S15
Henning, P. C., Scofield, D. E., Spiering, B. A., et al, (2014). Recovery of endocrine and inflammatory mediators following an extended energy deficit. The Journal of Clinical Endocrinology and Metabolism. Vol 99(3): 956–964.
Hilton, L. K. & Loucks, A. B. (2000) Low energy availability, not exercise stress, suppresses the diurnal rhythm of leptin in healthy young women. Am J Physiol Endocrinol Metab. Vol 278(1):E43-9.
Mountjoy, M., Sundgot-Borgen J., Burke, L. et al. (2014) The IOC consensus statement: beyond the Female Athlete Triad – Relative Energy Deficiency in Sport (RED-S). British Journal of Sports Medicine. Vol 48: 491-497