Low Energy Availability in Kickboxers: Why Eating Too Little Hurts Performance

You train hard, show up consistently, and still feel unusually tired. Punches feel slower. Footwork is less sharp. Concentration drops. Recovery between sessions takes longer. It is easy to blame motivation, sleep, or “not being fit enough.” Nutrition deserves a closer look.

Low energy availability (LEA) happens when the energy left after exercise is not enough to support normal body functions. When that state is severe or prolonged, it can contribute to Relative Energy Deficiency in Sport (RED-S) and affect health and performance. That matters in kickboxing because high-intensity training often sits next to making or holding a weight class.

This article is educational, not a diagnosis. Persistent fatigue, menstrual changes, repeated injuries, or suspected under-fuelling should be assessed by a qualified healthcare professional.

How common is low energy availability?

The concern is not theoretical. A 2025 systematic review and meta-analysis included 59 studies and 6,118 athletes across the studies assessing LEA prevalence. The authors found that 2,737 athletes (44.7%) were identified as having LEA — 44.2% of female athletes and 49.4% of male athletes. In eight studies assessing RED-S risk, 63.0% of athletes were identified as being at risk.

Those numbers do not mean almost half of all kickboxers have LEA. The studies covered different sports and populations. They do show why athletes, coaches, and support staff should take inadequate fuelling seriously, especially in sports where body weight matters.

What is energy availability?

Energy availability is not the same as “am I eating enough to hold my body weight?”

In simple terms: energy availability = energy from food − exercise energy expenditure, relative to fat-free mass. The energy left after training is what the body has for metabolism, hormones, bone maintenance, and other functions.

An athlete can develop LEA in two ways:

• Eating too little while keeping the same training load
• Suddenly increasing training without increasing food enough

It does not always happen because someone is deliberately starving. Lack of time to prepare food, reduced appetite after training, poor nutrition knowledge, and a sudden jump in training volume can all contribute.

Why kickboxers may be at risk

A kickboxing week can include technical sessions, pad work, bag work, conditioning, sparring, strength training, and extra cardio. At the same time, fighters may be thinking about staying in a weight class, reducing body fat, making weight, looking leaner, adding volume, or following a restrictive diet found online.

When food intake drops while training demand stays high, the gap gets large. A 2020 review on LEA notes that weight-class sports can carry extra risk because athletes may restrict food over body-image concerns or the belief that lighter always means better performance.

LEA can occur with or without an eating disorder.

Want fat-loss basics without starving your sessions? See whether kickboxing can help you lose weight.

Eating less does not automatically make you a better fighter

Body weight can influence performance in a weight-class sport. There is still a point where cutting food starts to compromise the systems that let you train and compete.

The 2020 review describes how the body can adapt to prolonged LEA by conserving energy. Resting energy expenditure and other daily energy use can change, with hormonal and metabolic adaptations. That can create a frustrating cycle:

Eat less → lose weight → weight loss slows → eat even less → recovery suffers → training quality falls.

The athlete may become lighter without becoming a better fighter. In some sports, carrying less body weight can temporarily mask the downside of LEA. Performance may hold or even improve while the athlete still never reaches full potential.

Carbohydrates are not the enemy

Cutting carbohydrates just because you want to lose weight is a common mistake. Kickboxing is repeated high-intensity work: combinations, kicks, explosive movement, footwork, defence, sparring. Those efforts need readily available carbohydrate fuel.

The 2020 review describes metabolic changes during LEA, including reduced glycolytic activity and reduced muscle glycogen (the stored carbohydrate in muscle used as high-intensity fuel). It notes a study in which only three days of LEA reduced muscle glycogen in male endurance athletes.

The better question is not “should a fighter avoid carbohydrates?” It is “how much carbohydrate does this fighter need for the training they are doing?” That answer changes with training load, body size, goals, competition phase, and individual tolerance.

Protein matters — but protein cannot fix under-fuelling

Protein supports muscle repair and adaptation. Sports nutrition is not a contest between protein and carbohydrate. If total energy is too low, extra protein alone does not fix inadequate energy availability.

A fighter needs an overall strategy:

Nutrient	Role
Carbohydrate	Training fuel
Protein	Muscle repair and adaptation
Fat	Energy and essential physiological functions
Micronutrients and fluids	Normal body function and performance

The goal is not to maximise one nutrient while neglecting the rest.

Why you may feel tired during training

LEA is not the only cause of fatigue. Poor sleep, excessive training, stress, illness, dehydration, and other medical or nutritional issues can also contribute.

Persistent fatigue plus poor recovery, declining session quality, and repeated difficulty fuelling training should prompt a check: does energy intake match training demand?

The 2025 meta-analysis found that athletes with LEA had poorer outcomes in training response, endurance performance, coordination, concentration, judgement, explosive power, and agility compared with athletes with normal energy availability. For a kickboxer, those are not minor details. Technique, reaction, decision-making, and explosive movement all matter.

Weight cutting needs a strategy — not starvation

Making weight is part of competition. Making weight and being well-fuelled are not the same thing. Structured weight management is not the same as eating as little as possible for weeks.

If an athlete spends long periods aggressively restricting food, carbohydrates, or fluids, the cost can go well beyond the number on the scale. The goal should not simply be “make weight.” It should be: make the required weight while preserving as much performance, recovery, and health as possible.

Plan weight management around the competition date, training demands, starting body composition, previous cutting history, and event rules — not improvised in the last few days.

LEA can affect more than performance

RED-S is not just a “low energy” problem. Prolonged or severe LEA can affect metabolic function, endocrine function, reproductive health, bone health, skeletal muscle, and psychological wellbeing.

Do not reduce it to “I’m tired because I’m cutting weight.” Repeated fatigue, declining performance, frequent injuries, menstrual disturbances, or other concerning changes deserve proper attention. They are not automatically a normal part of fighting.

Female fighters: menstrual health matters

Female athletes need particular attention because LEA can disrupt reproductive hormone function and negatively affect bone health. The 2020 review describes suppression of reproductive function with low energy availability and links low oestrogen and menstrual disturbances with impaired bone health.

Irregular or missing cycles, persistent fatigue, declining performance, repeated injuries, or prolonged recovery problems should not be dismissed as “normal because I train hard.” They may be signals to assess energy intake, training load, and overall health.

Male fighters

LEA is not exclusively a female-athlete problem. The 2020 review describes endocrine and bone-related consequences in male athletes as well, though the male evidence base is more limited in some areas. Male fighters can also fall into restrictive dieting when trying to drop body fat or make a weight class.

Nutrition around training

The solution is not simply “eat more.” Match food to the athlete and the training day.

Before training

Arrive with adequate fuel rather than starting a hard session already depleted. Depending on timing, simple options can include banana with honey and a pinch of salt; dates with a small amount of chocolate; fruit with coconut water; or toast with jam or honey. Amount depends on the athlete, time available, and session intensity and duration.

During training

For a normal short session, water may be enough. Longer or particularly demanding sessions can have different carbohydrate and fluid needs. Do not treat every session as if it has the same requirements.

After training

Recovery should include adequate food, with particular attention to carbohydrate and protein after demanding sessions — replenish fuel, provide amino acids for repair, and prepare for the next session.

For personalised planning at the academy, see nutrition coaching with Sneha Keerthana.

What should coaches and fighters look out for?

One symptom does not diagnose LEA or RED-S. A pattern deserves attention:

• Persistent or unexplained fatigue
• Declining training quality
• Poor recovery between sessions
• Reduced concentration or coordination
• Repeated injuries or bone stress injuries
• Frequent illness or missed training
• Unexplained body-weight changes
• Persistent food restriction despite high training demands
• Menstrual disturbances in female athletes
• Excessive concern about weight or body composition

The 2025 meta-analysis found that athletes with LEA had an increased likelihood of absence from training due to illness, and that most studies examining injury found impaired bone health and greater risk of bone stress injuries.

These signs do not mean an athlete definitely has RED-S. They mean it may be time to look at nutrition, training load, recovery, and — where appropriate — assessment from qualified healthcare professionals.

The role of a sports nutritionist

Sports nutrition is not simply making a fighter lighter. A good strategy answers four questions:

1. Am I eating enough for my training?
2. Am I fuelling the sessions that matter?
3. Am I recovering well enough to train again?
4. Can I manage my weight without compromising health and performance?

For competitive fighters, nutrition should change with the phase. A hard block, a normal week, a recovery period, and fight camp should not necessarily look identical.

Your goal is not just to be lighter. It is to be a better fighter: train hard, recover, adapt, train again, perform when it matters.

If you are constantly tired in kickboxing, do not automatically assume you need more motivation. Sometimes the body needs more fuel, better timing, and a more structured nutrition plan.

From the nutritionist at Lethal Kickboxing Academy

I am Sneha Keerthana, the nutritionist at Lethal Kickboxing Academy in Perambur. My job is not simply to make athletes lighter for the scale. It is to help fighters fuel training, recover properly, manage weight intelligently, and perform without compromising long-term health.

If you train kickboxing, boxing, or Muay Thai here and want structured support, start with our nutrition programs or contact the academy.

Address: 98, Paper Mills Road, Sembiyan, Perambur, Chennai - 600011

Research

If you want to go deeper than this athlete-friendly explanation:

1. Gallant TL, Ong LF, Wong L, et al. (2025). Low Energy Availability and Relative Energy Deficiency in Sport: A Systematic Review and Meta-analysis. Sports Medicine, 55, 325–339. Prevalence and performance/injury findings across 59 studies.

2. Wasserfurth P, Palmowski J, Hahn A, et al. (2020). Reasons for and Consequences of Low Energy Availability in Female and Male Athletes: Social Environment, Adaptations, and Prevention. Sports Medicine - Open, 6, 44. Why LEA develops, metabolic and hormonal adaptations, performance consequences, and prevention.

Frequently asked questions

What is low energy availability (LEA) in kickboxers?

LEA occurs when the energy left after exercise is not enough for normal body functions such as metabolism, hormones, and bone maintenance. It can happen if you eat too little for the same training load, or if training jumps up without enough extra food.

Can eating too little hurt kickboxing performance?

Yes. Becoming lighter does not automatically make you a better fighter. Prolonged LEA can slow recovery, reduce training quality, and affect coordination, concentration, explosive power, and agility. The goal is to make weight while preserving performance and health.

Should fighters cut carbohydrates to lose weight?

Not by default. Kickboxing uses repeated high-intensity efforts that rely on carbohydrate fuel. Cutting carbs just to get lighter can reduce muscle glycogen. The better question is how much carbohydrate this fighter needs for this training load.

Is LEA only a problem for female fighters?

No. Female athletes need particular attention for menstrual and bone health, but male fighters can also under-fuel when cutting weight or body fat. LEA can occur with or without an eating disorder.

What warning signs of LEA should kickboxers watch for?

One symptom does not diagnose LEA or RED-S. A pattern of persistent fatigue, poor recovery, declining training quality, reduced concentration, repeated injuries or illness, menstrual changes, or ongoing food restriction despite hard training deserves a closer look with a qualified professional.