During a typical training week, a recreational athlete may train from five hours all the way to the elite of fifteen hours plus. Within that week, athletes will most likely consume on average 35 meals and snacks combined, totalling 1,820 eating occasions every single year.

The aim of performance nutrition is to ensure that these meals are conducive to support health, body composition, training and competitive performances.  Since nutrition can both positively and negatively affect health and performance, the number of opportunities to correct this is plentiful.

With each meal having a purpose, an outcome; whether it’s fueling, replenishing, repairing, rehydrating – athletes looking to excel at their sport and training shouldn’t ignore this avenue for progression.

With that in mind, athletes need to become excellent at the basics first. The ever so often brushed aside fundamentals come in the form of both daily and weekly energy availability. It definitely isn’t the most exciting or glamorous area of performance nutrition as it essentially encompasses the amount of calories we consume, versus the amount of calories we expend via exercise, daily activity and rest. That being said, the greatest results are always noticed when done correctly as it predictably directs changes in body composition, recovery, fuelling, immune function, injury rehabilitation, cognitive function and well being.

Energy Availability

Before jumping into the calorie business, it’s worth mentioning that I’ll interchange the use of calories and energy. They are the same thing – so when I talk about energy, it’s actually calories. For the health and performance of any athlete, the concept of energy availability is undoubtedly very important. Therefore, we need to start broad by addressing the fundamental area first.

Some Background

Loucks et al (2011) defines energy availability (EA) as the dietary intake minus the energy expended in particular metabolic demands of interest to aid; cellular maintenance, thermoregulation, growth, reproduction, immunity and locomotion.

Therefore, if insufficient energy is consumed, then deficiencies will become apparent when attempting to meet these demands. A really important thing to note about EA is that it’s an input to physiological systems after exercise;

Energy availability = Energy Intake – Energy expended in exercise

Therefore, once exercise is subtracted from the amount of food consumed, the remaining calories left over are used to maintain your normal physiological processes. EA typically lies within the range of 30-45kcal per kilogram of fat free mass, expressed as 30-45kcal/kg/FFM. If we were to take a typical male athlete weighing 80kg at 10% body fat, this would suggest that he has approximately 72kg of fat free mass (bodyweight that isn’t fat mass). EA would range between 2,160-3240kcal per day. These numbers are important because they are the reference range we need to work off.

This is why we use EA as it highlights that an athlete’s requirements differ vastly from their non-athlete office bound counterpart as one of the components, locomotion is significantly increased. For example, If the same 80kg athlete were to consume the upper range of 3,240kcal per day and expends 840kcal through exercise, EA to maintain normal bodily functions would equate to 2,400kcal per day (3,240-840=2,400kcal). If a sedentary person were to consume the same amount of food where little to no exercise was performed, then all of the 3,240kcal would be an excessive amount allocated to meet normal bodily functions – this surplus in energy will be stored as body fat. On the contrary, if the 80kg athlete consumed the lower range of 2,160kcal and continued to expend 840kcal on a daily basis, the remaining 1,320kcal for the maintenance of normal cellular function will become compromised. The resulting energy deficit will most likely not even meet requirements for resting energy expenditure. This is perhaps the single, most important issue that needs to be addressed with athletes on calorie restricted diets as a tradeoff and compromise will always exist at the expense of normal bodily functions.

Some Female Athlete Issues

Consequently, female athletes report issues with reproductive function when energy dips below 30kcal/kg/FFM as this is an insufficient amount of energy available to maintain physiological systems when at rest. This is better known as the Female Athlete Triad and consequently causes functional hypothalamic menstrual disorders, a decrease in bone protein synthesis, oestrogen, insulin-like growth factor-1 and tri-iodothyronine. The resulting lower bone mineral density (BMD) caused by a decrease in mineralization via low EA increases the likeliness for stress fractures and injury. It would be oversimplified if we simply thought that female athletes simply do not eat enough as there are often underlying reasons as to why. Most commonly reported issues stem from body image, eating disorders, disordered eating and excessive energy expenditure through training. Therefore, finding the root cause of this is essential to counsel the athlete back to full health.

Some Immunity Issues

For the immune compromised athlete, lower EA is also attributed to the increased risk of illness. The immune system forms two types of immunity to fight two types of pathogens; Type 1 fights intracellular pathogens such as viruses where Type 2 fights and defends our body against extracellular pathogens such as bacteria. During periods of heavy EA, type 1 immunity becomes suppressed which usually increases the occurrence of virus based upper respiratory tract infections (URTI). This is most commonly found in endurance based athletes with very high energy costs of exercise. For example, Lancaster et al (2005) reported that a 2,200kcal expenditure over a 2.5 hour period suppressed type 1 immunity by 65% when only 50% of the energy via carbohydrates were replenished. Although this study was designed to only replace 50% of the calorie demand, it actually replicates real world scenarios as endurance exercise typically suppresses appetite.

Some Appetite Issues

In addition to this, the high food bulk and fibre content associated with the recommended high carbohydrate diets unfortunately have appetite suppressing properties. In return compounding the EA issue and worsening the outcome.

Knowing this, hunger is not a good cue to work off for athletes with very high energy expenditures. The blunted hunger cues are caused by post exercise elevated levels of appetite suppressing hormones (PYY, GLP-1 and PP) which causes athletes to not meet their calorie need. This has been shown to consequently reduce EA by ~10kcal/kg/FFM per day or approx. 700kcal per day for a typical endurance sized athlete.

This is why meal planning for athletes is very important as it will dictate when and how much to eat in order to cope with energy demands. Evidently, delayed eating by following hunger cues does not work for athletes.

Therefore, emphasising the consequences and importance of both energy and carbohydrate availability for athletes is a must. This was also very evident in Tour de France cyclists 6 months after racing where their EA was reported (Vegot et al, 2005) to be only 8kcal/kg/FFM. That would be an unjustified and dangerously low amount of approx. 550kcal per day for an average 72kg cyclist. This severe energy restriction is mostly likely not attributed to appetite suppression, but for dramatic weight loss. Again, further exacerbating the issue and highlighting that these athletes need close monitoring so they don’t out themselves at risk.

Some Muscle Mass Issues

Moving away from EA in endurance athletes – More applicable data for strength athletes (Fagerberg , 2017) can be gathered from a recent review done in male bodybuilders during competition preparation. Although strength and bodybuilding athletes do differ greatly, it can offer an insight into the negative consequences to health, such as hormonal imbalances and muscle mass retention if prolonged energy intakes dips under 25kcal/kg/FFM (1,700kcal for an 80kg male with 15% body fat).This becomes more apparent when training load is high and the athlete reaches very low levels of body fat ~4-5% as additional strains on other physiological systems such as the cardiovascular system may become negatively affected. Subjectively, major mood disturbances are usually seen too and it may set very lean athletes up for fat overshooting as a compensatory mechanism for becoming too lean. Therefore, being too lean may actually worsen body composition in the long run.

However, unless you are a physique athlete, there is little need to drop body fat to that extent – Personally, I wouldn’t encourage this to any degree for a strength athlete with health and performance goals as they will deteriorate. It needs to be reiterated that a competition preparation phase for bodybuilders is not healthy, more so for female athletes.

Furthermore, case studies looking at bodybuilding preparation phases report that approx. 40% of the weight lost is through muscle, i.e. for every 10kg drop in bodyweight, you would expect ~4kg of muscle loss). Therefore, it is recommended that a bodybuilder or strength athlete’s calorie intake doesn’t go below 25kcal/kg/FFM if looking to lose body fat over a long period of time – especially in already lean individuals as this may result in less muscle mass loss. So, slow and steady may be more advantageous for retaining lean muscle mass and athletic performance – equating to a 0.5-1kg bodyweight loss per week. I would however be very cautious in taking female strength athletes to EA of that extent as you could postulate that the health consequences would become more severe.

Some Rehabilitation Issues

As previously covered, energy deficiency can increase the susceptibility to injury in female athletes.  However, once injured, energy availability plays an important role in dictating the rate of recovery of that injured site. If energy restriction is too severe, it will almost certainly impair the recovery process as it will accelerate muscle loss, in return impact wound healing. The process by which muscle is made; muscle protein synthesis (MPS) is a very energy expensive process and accounts for approx. 500kcal of usage in heavily muscled individuals. Therefore, aggressive calorie restrictions reduce energy availability for this task and therefore will become compromised. During periods of injury, one of the aims is to mitigate losses in lean mass by promoting MPS, therefore having low EA is not an option. In comparison to the bodybuilders during preparation phase, muscle loss is observed even with the MPS promoting abilities of weight training. Therefore, removing the stimulus of weight training and combining it with limb immobilization will only amplify this.

Conversely, an excessive calorie intake isn’t favorable either. Not only from a gain in unwanted fat mass, but due the potential  accelerated muscle mass loss during inactivity. This is somewhat contradictive; however there is some evidence to suggest that high EA combined with bed rest may increase muscle mass loss via increased systemic inflammation. However, this may not always be the case if an athlete returns to training and works  on rehabilitation and other areas of performance. In addition to EA, the macronutrient composition of the diet appears to play a large part also where evidence would suggest that overfeeding on high fat foods may impair insulin sensitivity and decrease the muscles ability to uptake amino acids to stimulate MPS. In essence, a diet that does not have too many or too few calories and has a sensible macronutrient ratio would be encouraged.

Some Final Thoughts

From my experience, energy availability is most likely the most overlooked area by athletes. Collating information on the latest and most cutting edge strategy is generally far higher on their list. In the grand scheme of things, most of the new emerging sports nutrition data is minor or still in its infant stages when compared to the major gains that seen by acknowledging the usefulness and importance of EA. As mentioned previously, it’s not the headline story that everyone wants to hear as it is very straight forward and actually somewhat boring – Nobody really wants to hear ‘make sure you eat enough food to meet the calorie demand of your sport’.  Everyone, especially athletes want to try the next best thing to improve their performance where more times than not it’s the fundamental principles of a diet that’ll really make them improve as an athlete. To re-emphasise, we need to become better at the basics.

Most athletes will have fat loss goals at some point during their career. A diet that favours fat loss needs to be restricted in calories, therefore EA will always become compromised. This is a necessary trade off and is unavoidable. However, the degree to which calories are reduced will determine both rates of fat loss and the subsequent detriments in health and performance. Athletes who have long term fat loss goals further increase the risk of inadequate EA as they will try and overcome potential fat loss plateaus by further reducing calorie intake or increasing energy expenditure.  Therefore, the boundaries of calorie restriction (30kcal/kg/FFM) needs to be considered during this period  for athletes with higher training loads where strength based athletes who prioritise aesthetic goals should be aware of the consequences of reducing calories beyond 25kcal/kg/FFM.

With this in mind, athlete education is ever so important as many of these unwanted physiological imbalances can be avoided to a certain extent with the correct supervision guidance and coaching. Therefore, it’s the duty of nutrition coaches like myself to help educate not only the athletes, but the athletes support staff also so they are in the correct nurturing environment that will facilitate their goals in the safest and most effective way possible.




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