Energy availability: the reason you can be eating “well” and still not be eating enough

A lot of people might think under-fuelling looks obvious.  Imagine someone training huge hours, deliberately restricting food intake, losing lots of weight and eating small meals of mainly fruits and vegetables - sometimes it does look like that, for sure.

But low energy availability can be much more ninja.  It can happen when you start training a bit more, start missing meals because you're busier at work or with kids, try to “clean up” your diet, cut back because you want to lose a few kilos, or simply fail to increase your food intake when your training increases.

You can be eating healthy food. You can be eating three meals a day. You can even be weight stable.  And you can still be under-fuelled.

What is Energy Availability?

Sports nutritionists prefer to look at energy adequacy through the lens of energy availability rather than just energy balance. 

Energy balance is whether you've consumed more, less, or the same amount of energy as you've expended throughout the day. 

Energy availability, or EA, is the amount of energy your body has left to run everything else after the energy cost of exercise has been accounted for relative to your individual fat free mass (which is your body weight minus your body fat — basically, it's the tissues, muscles, bones and organs that need energy to function).  Let me walk you through it. 

• Food labels in NZ use 8700kJ/day as the average adult diet reference value, which is around 2,080 kcal/day. 

• If you eat 2,080 kcal in a day but use about 600 kcal of this for training (e.g. a 10km run or 90 minutes on the bike), your body does NOT have 2,080 kcal available for normal physiological function. It only has the remaining 1,480 kcal. 

• That 1,480 kcal has to support everything else your body is trying to do: repair tissue, maintain bone, produce hormones, support your immune system, maintain reproductive function, recover from training, and keep your brain and organs functioning properly. 

This is why considering EA is more useful for athletes than just monitoring calorie intake or energy balance alone. 

Low Energy Availability, or LEA, develops when the gap between what you eat and what you use during exercise leaves too little energy available to adequately support the rest of the body.

Importantly, LEA does not have to be intentional.  You don't need to have an eating disorder. You don't even need to be consciously dieting.

It can happen because:

• you increase your weekly training but keep eating exactly the same;

• you train early and don't eat much or at all until morning smoko or lunch;

• you're trying to lose weight while maintaining a high training load;

• work gets busy and meals become smaller or get skipped;

• you've increased the amount of fibre and/or protein in your diet and become too full to meet your energy requirements;

• long training sessions suppress your appetite;

• you don't fuel during exercise because you're trying to “burn fat”;

• you add another gym or training session without adding food around it.

High Performance Sport New Zealand (HPSNZ) defines LEA as a mismatch between dietary energy intake and exercise energy expenditure that leaves insufficient energy to support optimal health and performance. It also explicitly says that in many athletes, LEA happens accidentally, including when training volume/intensity increases without a matching increase in food intake, when there is poor food planning, or when foods/food groups are eliminated.

LEA is also not necessarily accompanied by weight loss, because the body can conserve energy and maintain body weight even while there is insufficient energy available for normal physiological functions. 

The body is very good at keeping you alive.  If there isn't enough energy available, it starts making decisions about where that energy is most important.

Running your heart and brain? Essential.

Reproductive function? Less essential for immediate survival.

Building strong bones? Can be compromised for a while.

Adapting optimally to today's training session? Not the body's top priority when energy is scarce.

Chronic or severe LEA can lead to Relative Energy Deficiency in Sport, or RED-S.  RED-S can affect reproductive and menstrual function, metabolic and endocrine (hormone) function, immunity, cardiovascular and gastrointestinal function, psychological health, protein synthesis, athletic performance, and can result in permanent loss of bone mineral density.  So it’s definitely something that you want to avoid at all costs.  

Signs you may not be eating enough for your training

Things to pay attention to include:

• training performance plateauing or going backwards despite consistent training;

• feeling unusually flat or heavy during sessions;

• poor recovery between workouts;

• recurrent illness;

• recurrent injuries;

• bone stress injuries;

• persistent fatigue;

• menstrual cycles becoming irregular or disappearing;

• reduced libido;

• declining strength;

• feeling cold;

• disrupted mood or concentration;

• difficulty increasing training without falling apart;

• unintended or rapid weight loss.

But remember: weight stability does not rule LEA out. Your body can adapt to reduced energy availability in ways that allow weight to stabilise while physiological functions are still being compromised.

What to take away

LEA doesn’t always look dramatic, and it doesn’t only happen to people who are deliberately under-eating. Often, it creeps in when training goes up but food intake doesn’t, or when “healthy eating” becomes too low in energy for the amount of work you’re asking your body to do.  The good thing is that it’s usually preventable once you know about it. 

In the next article, I’ll cover the practical side: how to reduce your risk of LEA without obsessively tracking calories.