Am I Eating Enough for My Training? How to Know

3 days ago

5 min read

You train five or six times a week. You are careful with food. Your performance has flattened, you are tired in a way that sleep does not fix, and you have been told to eat more and also to eat less by different people in the same week.

There is a measurement that settles it, and a threshold in the sports science literature that defines what "enough" actually means.

Chart of reported prevalence ranges for low energy availability and suppressed resting metabolic rate in athletes

The concept you need: energy availability

Total calories is the wrong frame. What matters is what is left over for your body to run on after training has taken its share.

Energy availability is energy intake minus exercise energy expenditure, expressed per kilogram of fat free mass per day. It is the fuel remaining for everything that is not exercise: hormone production, immune function, bone remodelling, digestion, cognition and recovery.

The clinical threshold for low energy availability used in the literature is below 30 kcal per kg of fat free mass per day (Logue et al., Nutrients).

Work an example. Someone with 50 kg of fat free mass eating 2,400 kcal per day and burning 700 kcal in training has 1,700 kcal left, which is 34 kcal per kg of fat free mass. Adequate, but not by much. Add one more hard session per week and they drop below the threshold.

Two things immediately follow. You cannot calculate this without knowing your fat free mass, which requires a body composition measurement rather than a scale. And a number that looks generous in absolute terms can be inadequate once training is subtracted.

How common this is

More common than the fitness conversation suggests.

A 2020 narrative review of the literature reported that estimated prevalence of low energy availability in recent studies ranged from 22 to 58 per cent, and that the proportion of athlete populations at risk ranged from 14 to 63 per cent (Logue et al., Nutrients).

One observational study in the review measured 20 vocational female ballet students, mean age 18.

Finding	Result
Energy availability below 30 kcal/kg FFM/day	22%
Energy availability 30 to 45 kcal/kg FFM/day	44%
Reported menstrual dysfunction	40%
At risk of low energy availability	65%

Note that two thirds of that group were at risk, and that menstrual dysfunction was not statistically associated with energy availability in this small sample at p = 0.17. Small studies produce imprecise associations. The prevalence figures across the wider literature are the more reliable part.

This is not confined to elite or aesthetic sports. Anyone who has increased training while holding intake constant, or who has run a long fat loss phase without adjusting for training load, can end up here.

The signs, and why they are easy to dismiss

Individually every one of these has an innocent explanation. Together they form a pattern.

Performance plateau or decline despite consistent training.
Persistent fatigue that does not resolve with a rest day.
Frequent illness, particularly upper respiratory infections.
Niggling injuries, especially bone related pain such as shin or foot pain.
Loss of menstrual cycle regularity, or its complete absence.
Reduced libido.
Poor sleep quality, or waking hungry.
Low mood, irritability, or unusual preoccupation with food.
Feeling cold constantly.
Fat loss that has stalled at an intake that should still produce a deficit.

The last one is the cruel irony. Under-fuelling can stall fat loss, which drives people to eat less, which deepens the problem.

What a measured RMR adds

This is the objective test, and it works because a suppressed resting metabolic rate is one of the measurable consequences of sustained low energy availability.

The method is a ratio. Measure your resting metabolic rate by indirect calorimetry, then compare it against what your body composition predicts it should be. A measured to predicted ratio below 0.90 is used in the literature as a marker of suppressed resting metabolism.

The same review reported that prevalence of suppressed resting metabolic rate, depending on which predictive equation was used as the comparator, ranged from 25 to 80 per cent in male athletes and 35 to 100 per cent in female athletes.

That enormous range is important and it cuts both ways. It tells you the ratio is sensitive to which equation you compare against, which means a single ratio calculation is a signal rather than a diagnosis. It also tells you that suppressed resting metabolism is genuinely widespread in training populations.

The more robust use of the measurement is your own change over time. Measure your RMR now, measure it again after you have adjusted your intake, and the direction of travel is not dependent on any equation at all.

What to actually do

Step one: get the inputs. You need fat free mass from a DEXA scan and a measured resting metabolic rate. Without fat free mass you cannot calculate energy availability at all.

Step two: calculate your energy availability. Honest intake, weighed for at least a week, minus a realistic estimate of exercise energy expenditure, divided by fat free mass in kilograms.

Step three: compare your measured RMR to prediction. If it sits well below what your lean mass predicts, that supports the under-fuelling hypothesis.

Step four: increase intake deliberately, not dramatically. Adding 200 to 300 kcal per day and holding it for three to four weeks is a reasonable trial. Rapid large increases make the response hard to interpret.

Step five: retest. Retest the RMR after 8 to 12 weeks. A rising resting metabolic rate alongside improving performance is the confirmation you were under-fuelled.

If you have lost your menstrual cycle, have bone pain, or suspect a stress fracture, see a doctor. Those are clinical situations and a metabolic test is supporting information, not treatment.

Common questions

Is 30 kcal per kg of fat free mass a hard line? No. It is a threshold used in research to flag likely problems, not a cliff edge. Sitting at 32 is not safe and 29 is not catastrophic. The direction and duration matter more than the exact figure.

Can I calculate this from my body fat percentage on a smart scale? Poorly. Impedance based lean mass estimates carry enough error that the resulting energy availability figure inherits it. The whole calculation depends on the fat free mass number being right.

Does this apply to men? Yes. The reported prevalence of suppressed resting metabolic rate in male athletes ranged from 25 to 80 per cent. The symptom picture differs, with reduced libido and performance decline more prominent than the menstrual signals.

I am trying to lose fat. Does this mean I should eat more? Possibly, and this is the uncomfortable answer. If you are under-fuelled, eating slightly more with better training quality often produces better body composition outcomes than cutting further. Measure before you decide.

The short version

Energy availability, not total calories, is the number that determines whether you are eating enough. Below 30 kcal per kg of fat free mass per day is the threshold used in the literature, and 22 to 58 per cent of studied populations fall under it. You cannot calculate it without knowing your fat free mass, and a measured resting metabolic rate that sits well below prediction is objective support for the under-fuelling case.

A Metabolic Baseline at Precision Body Lab combines a DEXA scan and an RMR test for $279, which gives you both inputs in one visit. Book online or call 1300 910 163.

Am I Eating Enough for My Training? How to Know

The concept you need: energy availability

How common this is

The signs, and why they are easy to dismiss

What a measured RMR adds

What to actually do

Common questions

The short version

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