Carbohydrates, Low Energy Availability & Why So Many Athletes Are Under-Fuelled

Yet research consistently shows that carbohydrate intake is one of the most common nutritional gaps in sport, particularly among female and endurance athletes. This gap often contributes to Low Carbohydrate Availability (LCA), which can sit underneath Low Energy Availability (LEA) and Relative Energy Deficiency in Sport (REDs).

Understanding this matters — because many athletes experiencing fatigue, recurrent injury, illness, or stalled performance are not underperforming due to a lack of effort. They simply aren’t fueling enough.

What carbohydrate availability actually means

Carbohydrate availability refers to the amount of carbohydrate accessible to support:

• Exercise metabolism

• Glycogen resynthesis

• Hormonal signalling

• Recovery processes

• Immune and bone health

It is distinct from simply “eating carbs.”

An athlete can:

• Eat regularly

• Meet protein targets

• Consume sufficient total calories

…and still experience low carbohydrate availability if carbohydrate intake does not match training demand.

This is particularly relevant for athletes training multiple times per day, training fasted, or restricting intake around sessions.

 

Carbohydrates and energy availability

Energy Availability (EA) is defined as:

Energy intake minus exercise energy expenditure, normalised to fat-free mass (FFM)

Clinical thresholds:

• LEA: < 30 kcal/kg FFM/day

• Reduced / subclinical EA: 30–45 kcal/kg FFM/day

Low carbohydrate intake is one of the fastest ways athletes fall below these thresholds, even unintentionally, because carbohydrates are the body’s preferred and most efficient fuel for exercise.

When carbohydrate availability drops, the body compensates by:

• Reducing metabolic rate

• Altering endocrine function

• Increasing reliance on stress hormones

• Downregulating “non-essential” systems (e.g. reproduction, bone turnover)

This is the physiological basis of REDs

 

How common is low carbohydrate intake?

Across multiple studies and sports:

• 45–98% of female athletes fail to meet current daily carbohydrate recommendations

• 85% of female collegiate distance runners consume less than recommended

• Average intakes often sit around ~4–5 g CHO/kg/day, despite endurance needs of 6–10 g/kg/day

• In retrospective analyses, >70% of young and elite athletes consumed <6 g CHO/kg/day

• Up to 98% failed to meet higher-end carbohydrate targets (≥8 g/kg/day)

These findings consistently show that low carbohydrate intake is the norm, not the exception.

 

What the science shows happens with low carbohydrate availability

Low carbohydrate availability has been associated with:

Metabolic & performance effects

• Reduced glucose utilisation

• Increased perceived exertion

• Earlier onset of fatigue

• Reduced training quality

• Decreased time-trial performance and power output

Hormonal & endocrine effects

• Suppressed leptin

• Altered growth hormone and reproductive hormone signalling

• Disruption to luteinising hormone (LH) pulsatility in some studies

Bone & injury outcomes

• Increased risk of bone stress injuries

• Reduced bone formation markers

• Decreased bone mineral density, even when total energy intake appears adequate

Immune & recovery effects

• Small but unfavourable changes in immune markers

• Increased illness and injury risk (~9% higher in athletes practising carbohydrate restriction in some cohorts)

Importantly, many of these changes occur before overt REDs symptoms are diagnosed.

Carbohydrates, LEA and REDs

REDs (Relative Energy Deficiency in Sport) describes the multisystem consequences of chronic low energy availability.

Low carbohydrate availability often acts as:

• An early driver

• A masking factor (athletes feel “fine” until systems fail)

• A practical bottleneck to restoring energy availability

This is why many athletes with REDs report:

• Adequate protein intake

• “Healthy” eating patterns

• Confusion about why symptoms persist

Energy — particularly carbohydrate energy — is still insufficient.

Recommended carbohydrate intakes (context matters)

Current sport nutrition guidelines broadly recommend:

• 5–12 g CHO/kg body weight/day, depending on training load

• 6–10 g/kg/day for most endurance athletes

• Up to 10–12 g/kg/day during very high training volumes

• Post-exercise refuelling of ~1.2 g CHO/kg/hour for 4–6 hours after glycogen-depleting sessions

These numbers are far higher than what most athletes consume — not because they are undisciplined, but because these needs are rarely taught or supported.

Why RED-Scue exists

Most athletes don’t lack motivation.
They lack accessible energy.

RED-Scue exists to address the carbohydrate gap that research keeps highlighting:

• High-carbohydrate

• Easily digestible

• Portable

• Designed to support energy availability when appetite, time, or knowledge are limiting factors

Not as a replacement for meals.
But as a practical fuelling tool to help athletes meet physiological needs in the real world.

The takeaway

Low carbohydrate availability is widespread, under-recognised, and physiologically significant.

It contributes to:

• Low energy availability

• REDs

• Injury

• Illness

• Performance decline

Athletes are not broken.
Their fuelling systems are.

And until sport culture changes, making carbohydrate intake easier, more normalised, and more athlete-friendly matters. That is why I built RED-Scue.