Elite body composition testing: considerations for athlete health and performance

Few practices in professional football are as common and contentious as body composition testing and manipulation. In principle, these practices can provide valuable insight into fuelling, adaptation, and rehabilitation. Used appropriately, they inform tailored nutrition and training strategies, track physical development, and support safe return from injury.

But when misapplied, they can create anxiety, drive under-fuelling, and foster environments where appearance is prioritised above performance.

Recent testimonies from elite players highlight the risks. Fran Kirby and Alessia Russo have spoken about body shaming in elite women’s football, while Kalvin Phillips and Allan Saint-Maximin have faced public scrutiny in elite men’s football. Similar accounts exist in professional cricket and cycling, where “fat clubs,” public ranking systems, and potentially damaging practices still persist.

Too often, sport nutritionists are employed with the sole aim of working with “fat” players, while arbitrary body fat percentage targets are imposed without scientific basis, encouraging harmful practices—from low carbohydrate diets to skipped meals and snacks—in the pursuit of hitting “green zones.”

This raises two important questions: what does the evidence actually tell us about body composition, and how should assessments be conducted responsibly in elite football?

Why body composition matters and why it can harm

Body composition reflects the balance between lean tissue, fat mass, bone, and hydration.

In principle, lean mass supports strength, power, and resilience to contact; and excess fat mass can reduce efficiency and increase loading stress. Tracking changes in body composition can highlight adaptation, growth, bone health, and rehabilitation progress.

However, evidence also shows substantial risks. A global systematic review estimated that 19% of athletes report disordered eating behaviours, including restriction, binging, and purging. ^[7] These risks are heightened in youth players, female athletes, and any environment where aesthetics are emphasised over function.

The International Olympic Committee and UEFA have explicitly cautioned against the use of single body composition values as benchmarks. ^[5,10] UEFA concluded “There is no single value for either body mass or fat mass against which targets or judgements should be made.” Yet it is still common to hear senior stakeholders demand, “I want everyone under 10% body fat.”

This disconnect between evidence and practice has the potential to fuel anxiety, body dissatisfaction, relative energy deficiency in sport (RED-S), and, in severe cases, clinical eating disorders.

The bottom line is that body composition can influence player health and performance. But how it is assessed, interpreted, and communicated is what truly matters. Ironically, when clubs prioritise training quality, recovery, and nutrition support, the body composition outcomes that players, coaches, and staff so often demand usually follow naturally.

Actual data on pro footballers’ body comp

My colleagues and I collated the largest dataset of criterion values in professional male football (which is currently under review, awaiting publishing). Across 10 years, 343 players from the Premier League and English Football League completed 939 DXA scans standardised to best practice guidelines.

Among the key findings are realistic ranges. Body fat percentages typically sat between 11.6% and 15.4% depending on position, ethnicity, and league. Values below 10%, the benchmark typically imposed in practice, were rare.

Goalkeepers and central defenders carried greater mass and fat levels than midfielders and wide players. Forwards resembled defenders more than midfielders. These differences likely reflect position-specific training and match characteristics.

Looking across ethnicity, black players were taller, heavier, and had greater fat free mass, but lower fat percentage, than white players.

The Premier League players averaged lower fat mass than their EFL counterparts, likely reflecting superior support: nutrition staff, chefs, and recovery infrastructure.

Fat-free mass increased and fat mass decreased across the season. Moderate body mass gains were healthy adaptations—not the cause of concern that many believe.

Correlations with performance

Several studies have explored relationships between body composition and football performance, but it is important to emphasise that most are observational, cross-sectional, and small in scale. They generally measure body composition alongside training exposure, maturation, or seasonal change, rather than directly manipulating it. As such, the data show correlation rather than causation, and interpretation requires caution.

Sprint and acceleration

Professionals with lower body fat completed sprint tests more quickly. ^[11] Aziz et al., ^[1] reported negative correlations between fat percentage and shuttle run performance.

These results are consistent with the idea that excess fat mass increases metabolic cost. But they may also reflect that fitter, better conditioned players both train harder and present with lower fat levels. The causal direction remains uncertain.

Dose–response effects

Leaner players tolerated higher training loads and performed better on the Yo-Yo test. ^[4] However, this likely reflects bidirectional processes: players who can sustain higher training demands may adapt by becoming leaner, while leaner players may also move more efficiently during endurance tasks.

Distinguishing between these explanations is challenging.

Power and jump ability

Players with greater lean mass and lower fat mass achieved higher countermovement jump scores and displayed better resting muscle oxygenation. ^[13] Similarly, regional lean tissue and intracellular water were associated with neuromuscular performance. ^[2]

These results align with physiological principles that muscle mass supports power. However, neuromuscular efficiency, fibre type distribution, and training quality likely explain as much of the variance.

Overall, excess fat mass is consistently correlated with lower sprint, endurance, and jump scores, while lean mass often correlates with better explosive and endurance performance. However, body composition should be understood as a marker or covariant of adaptation to training, nutrition, and recovery. It is not a standalone performance driver.

At extremes, composition may influence efficiency. But within normal elite ranges, other factors like training quality, good nutrition, sleep, and genetics are far stronger determinants of performance.

Health markers associated with body comp

Similar caution is required when interpreting health-related outcomes. Many studies report associations between body composition and physiological markers. In most cases, these changes may reflect the impact of training withdrawal, energy availability, recovery cycles, or maturation, rather than body composition in isolation.

Bone and endocrine health

Fourteen professional players experienced reduced bone formation, increased resorption, and altered hypothalamic–pituitary–gonadal (HPG) axis activity during six weeks of detraining. ^[9]

Although body composition shifted during this period, the physiological changes were more clearly attributable to reduced training stimulus and altered energy balance than to fat or lean mass, per se.

Haematology

Bussollaro et al., ^[3] observed seasonal shifts in haemoglobin and haematocrit, coinciding with changes in body composition.

These results likely reflect fluctuations in training intensity, match demands, and recovery, with composition shifting in parallel rather than driving the haematological changes.

Gastrointestinal hormones

Lower fat mass was associated with reduced leptin and higher ghrelin in 32 professionals. ^[12] This is consistent with energy availability theory, but as a cross-sectional study, it cannot determine whether low fat drives hormone changes or whether endocrine differences influence fat mass.

Youth development

Somatotype, hormone profiles, and performance were linked in adolescent players. ^[8] However, somatotype is itself dynamic during adolescence. The observed relationships likely reflect natural growth and maturation alongside training, rather than composition acting as an independent sole driver.

In most cases, body composition functions as a proxy variable for the more fundamental drivers of adaptation to training: training load, fuelling, recovery, and growth.

The main health risks emerge at the extremes. Very low energy availability can compromise bone and endocrine health, while excessive adiposity can contribute to inefficiency and increased injury risk. For practitioners, the priority is to safeguard players from under-fuelling or unhealthy weight control practices, while supporting robust training, nutrition, and recovery.

Safe manipulation of body composition

Our 2025 scoping review synthesised 73 expert papers across 25 countries. ^[6]

Body mass and composition targets must reflect position, age, sex, genetics, and season phase. Safe minimums are ~5% body fat for males and ~12% for females. If the multidisciplinary team, in conjunction with the athlete, decide to alter the athlete’s body composition, the changes must be gradual. Fat loss should not exceed 0.5–1.0 kg/week, while the concomitant increase in lean mass should be 0.25–0.5 kg/week.

Fuelling for lean mass gain should be an additional 500–1000 kcal/day, consisting of 1.6–2.2 g/kg protein, carbohydrate intake periodised to training load (3–12 g/kg/day), and quality fats. Supplement these where appropriate with batch tested creatine and whey protein.

For fat loss, the calorie deficit should be 250–1000 kcal/day, maintaining ≥30 kcal/kg FFM/day to protect health. Protein should be 1.6–2.4 g/kg/day, with carbohydrates rarely below 3 g/kg/day, and fats at 15–30% of intake.

As we might expect, adjustments are safest in the off-season or preseason. Drastic changes during competition carry higher risks.

How to assess and use body composition ethically

At a recent invite-only event with sport nutritionists across UK football, we developed consensus guidance on best practice. These outcomes highlight how senior accredited sport nutritionists recommend assessing body composition responsibly and ethically in elite men’s and women’s football.

Education is the foundation. All stakeholders—players, coaches, medical staff, executives, and, in youth settings, caregivers—must understand why we conduct assessments, what they measure, and their risks and benefits. Education should explicitly cover RED-S, disordered eating, body image, data use, and the athlete’s right to opt out.

Clubs should have a written body composition policy and standard operating procedure, covering timing, consent, follow-up, and communication. Governing bodies should endorse and audit these policies, escalating safeguarding breaches where required.

Stage 1: Test only when appropriate

Assessments should only occur with a clear rationale, such as rehabilitation, growth and maturation, or supporting performance goals. They should never be used to judge aesthetics, professionalism, or discipline.

Decisions should be agreed within the multidisciplinary team and revisited each season.

Stage 2: Check readiness

Players must be physically and psychologically ready. This involves screening for RED-S, disordered eating risk, menstrual health, recent illness or injury, and nutrition status. Clubs must also be ready, ensuring trained assessors, calibrated equipment, private facilities, and clear SOPs. Sex-matched assessors should be offered where possible.

Stage 3: Informed consent

Consent must be informed, voluntary, and ongoing. Written consent should be obtained at the start of each season, with verbal assent before each test. Players must know they can withdraw consent without consequence.

For under-18s, assessments should only occur if medically justified, with guardian and player consent.

Stage 4: Choose the right method

The method should match the purpose: DXA for bone and lean mass tracking, ISAK skinfolds for monitoring trends, and BIA only when resources are limited.

For players under age 16, assessments should be limited to height, mass, and markers of maturation. For ages 16-18, DXA or skinfolds should only be conducted if medically justified.

Stage 5: Collect data safely

Standardisation is critical: ideally test in the morning, when the athlete is fasted, rested, and euhydrated. Testing must be private, equipment calibrated, and athletes offered a chaperone. All results should be treated as confidential medical data.

Stage 6: Interpret with context

Results should never be presented in isolation. Context—including position, training load, injury history, and health—matters. Avoid leaderboards, colour-coded systems, or negative labels.

Results should be explained to the athlete first, and the athlete decides who else can access them.

Stage 7: Report and communicate

Athletes must always receive their results in a clear and timely way. Clubs should pre-agree who else will see data and never share results in team meetings or group formats.

Stage 8: Act and monitor

Data should only be used to inform a clear performance or health need. Re-testing should typically occur every 8-12 weeks, with DXA capped at six scans per year under IR(ME)R regulations. Athlete feedback should be collected each season to monitor the process’s impact.

Female-specific considerations

Always record and factor menstrual cycle phase and contraceptive use. Pregnancy is a contraindication for all forms of testing; and DXA is not suitable during breastfeeding. Post-partum players should only be assessed with medical clearance, focusing on health and gradual return to play.

Youth specific considerations

Avoid assessments with youth players unless medically necessary. The absolute priorities are growth, maturation, and bone health. Communication with both caregivers and players is essential.

The process matters more than the numbers. Done responsibly, assessments can reassure players, guide training and nutrition, and build trust. Done poorly, they risk fuelling stigma, disordered eating, and mental health challenges.

Towards safer, smarter practice

The evidence shows that body composition is likely relevant for football performance and health. But it is difficult to measure with precision and almost impossible to manipulate causally, as it reflects downstream outcomes of training, nutrition, genetics, sleep, and context.

Assessments can be helpful when used ethically and responsibly, but mismanagement risks fuelling RED-S, under-fuelling, body dissatisfaction, and eating disorders.

As practitioners, our responsibility is clear: assessments should serve performance and health. They should never be the basis for any comment or implication about appearance, stigma, or arbitrary benchmarks.