Body fat has a terrible PR problem. For decades, the prevailing view was "the less, the better" and we treated it as an enemy to be defeated by a number on the scale. In reality, it's an active endocrine organ – it produces hormones, stores energy, insulates organs, and in women, it plays a role in regulating the menstrual cycle. So the question "how much body fat is optimal?" is far more interesting than it seems. And the answer is nowhere near "as little as possible."

Heads up: most of the values we'll discuss today come from American studies. The reference ranges, however, are very similar in Europe and are widely used by European sports medicine and clinical bodies.

The minimum you can't function without

Of all the fat tissue in our bodies, part of it has earned the status of essential. Scientists use the term essential fat to describe the amount of body fat that allows the body to simply work. For men, that's 2–5% of body weight; for women, 10–13%. The difference is not an evolutionary whim – women need a higher minimum because, in their case, body fat supports reproductive function, hormonal balance, and the absorption of vitamins (you probably know that several of them are described as fat-soluble). Dropping below this threshold isn't "getting shredded" – it's playing with your health and risking serious disorders, which we'll come back to.

The ranges science considers healthy

The two most frequently cited institutions – the American College of Sports Medicine (ACSM) and the American Council on Exercise (ACE) – use slightly different thresholds, but the overall picture is consistent. According to ACE, the typical range for an averagely active, non-competitive adult is 18–24% for men and 25–31% for women.

Athletes sit lower: men usually between 6–13%, women between 14–20%. ACSM uses a slightly broader "healthy" range: 10–22% for men and 20–32% for women. Above these thresholds – 25% in men and 32% in women – we're talking about obesity defined by body fat percentage rather than by BMI.

The differences come down to how each body defines "optimal" and whether the goal is health, performance, or longevity. The clinical risk thresholds, however, are consistent across both systems. So are the actual numbers, more or less. :)

There's a great video on this topic on Jeff Nippard's channel, which inspired this piece.

Why women have (and should have) more body fat

TThis isn't a matter of weaker discipline or a "slower metabolism." Women naturally maintain a higher body fat percentage because it's essential for reproductive function and hormonal balance. On top of that, female fat deposits sit mostly subcutaneously – on the hips, thighs, and chest – rather than around the organs. NIH research suggests that this distribution is metabolically protective compared to the typical male pattern of accumulating visceral fat (on the belly and neck). At the same body fat percentage, an average woman will statistically have lower cardiometabolic risk than a man, and a healthier-looking body shape. Low body fat in women can also cause serious health complications, which we'll get into later.

Screen from the video What Every Body Fat % Actually Looks Like (50% to 5%)

How age changes the rules

With age (past the thirties and forties), muscle mass declines, metabolic rate slows down, and in women going through menopause, the drop in estrogen pushes body fat towards the abdomen and visceral cavity, raising cardiometabolic risk. Most reference tables therefore include age categories – the same body fat percentage means something different at 25 than at 55.

What happens when body fat is too low

This is the part fitness culture consistently ignores, and that almost no shredded influencer on Instagram talks about. Low body fat, especially combined with an energy deficit, triggers a cascade of problems that sports medicine describes as RED-S (Relative Energy Deficiency in Sport). In short – this isn't a biochemistry lecture – the body doesn't have enough fuel to maintain all of its functions, so it starts switching them off.

Hormones and fertility. In women, the most noticeable change – and one that almost every bikini fitness competitor will confirm – affects the menstrual cycle. Menstrual disturbances affect around 20% of women who train regularly, and in groups such as ballet dancers (44%) or long-distance runners (51%), the rate rises dramatically. The mechanism is well understood: reduced pulsatility of gonadotropin-releasing hormone leads to lower FSH and LH, hypoestrogenism, functional amenorrhea, and a drop in bone mass. The male counterpart is analogous – energy deficiency lowers testosterone and harms bone health.

Bones. The consequence is brutal and often delayed. Loss of menstruation disrupts the bone-building process and weakens the skeleton, making bones more prone to fractures. In the most severe cases, young female athletes can develop osteoporosis as a result of disordered eating and menstrual dysfunction. Visible abs at 25 in exchange for osteoporosis at 35 is not a trade worth making.

Mental health and cognition. The clinical symptoms of RED-S include, among others, disordered eating, fatigue, hair loss, cold hands and feet, dry skin, noticeable weight loss, delayed healing of injuries, and the cessation of menstruation. People affected by the syndrome often struggle with low self-esteem and depression as well. Irritability, mood swings (bouts of sadness or anger), and difficulty concentrating ("brain fog") are standard parts of this picture.

Immunity. Low energy availability throws the entire endocrine system out of order. It disrupts the thyroid axis, leptin levels, carbohydrate metabolism, the growth hormone / IGF-1 axis, and sympathetic-parasympathetic balance. That sounds bad, and in practice it produces uncomfortable consequences: you sleep worse, catch infections more often, recover more slowly, and training gives smaller and smaller returns. The threshold for this state is surprisingly early – in women, dysfunctions of various systems appear once energy availability drops below 30 kcal per kg of fat-free mass per day.

What happens when body fat is too high

The other end of the curve is widely known, but it's worth distinguishing two dimensions here: how much body fat, and where.

The mortality curve. The relationship between body fat percentage and mortality risk is not linear. A meta-analysis of 35 cohorts covering more than 920,000 people showed that every 10% increase in body fat was associated with an 11% increase in death risk (in adults from the general population). The NHANES analysis on a sample of 16,000 people confirmed that the mortality curve is U-shaped – risk also rises at very low values (compared to reference groups with body fat around 25–30% in men and 30–35% in women).

Insulin resistance and type 2 diabetes. The key player here is visceral fat – the kind that wraps around the organs in the abdominal cavity (it's often measured as a separate metric, which we'll get to). Visceral fat deposits are tightly linked with dyslipidemia, inflammation, insulin resistance, glycemic disturbances, fatty liver disease, and the whole picture of metabolic syndrome. A meta-analysis of 40 studies showed that out of all types of fat depots, it's visceral fat mass that correlates most strongly with insulin resistance.

Cardiovascular disease. Insulin resistance – mainly through activation of the renin-angiotensin-aldosterone system and sympathetic stimulation – leads to high blood pressure. Obesity, and visceral obesity in particular, accounts for most of the risk of hypertension. Visceral fat also acts as a factory of pro-inflammatory cytokines, which translates into accelerated atherosclerosis.

What does this mean in practice? The single strongest risk indicator is not weight itself, nor even body fat percentage alone, but waist circumference. A 2025 study published in the Annals of Family Medicine on 4,252 American adults (aged 20–49) showed that body fat percentage and waist circumference are more reliable predictors of 15-year mortality than BMI (yes, BMI is becoming a bit of a relic, dating back to a time before anyone was maxing out protein intake). BMI in the overweight/obese range (≥25) was not statistically associated with higher death risk, but a high waist circumference – over 102 cm in men and 89 cm in women – increased the risk of death from any cause by 1.59 times, and from heart disease by 4.01 times. Where you carry your body fat matters considerably more than how much of it you have in total – though it's hard not to notice some correlation here too.

How to measure body fat (and whether home scales are up to the task)

As life usually goes, most of the measurement methods we rely on come with a meaningful margin of error. Starting with the best, and least well-known:

DXA (sometimes written as DEXA) is the gold standard. Dual-energy X-ray absorptiometry is currently the reference method. DXA delivers a highly precise measurement of body fat, muscle mass, bone density, and visceral fat – in a single scan, you get a full picture of body composition. The downsides are availability and cost: the scan typically costs around 100 euro, you'll find it in sports medicine or osteoporosis clinics, and to track trends you need to repeat it every few months. Every major city has at least a few facilities offering it, and you can either pay privately or try to get a referral for a publicly funded scan.

BodPod and hydrostatic weighing. Two older methods based, respectively, on measuring body volume in an air-displacement chamber and buoyancy in water. Very accurate, but harder to access – in Europe, they're mostly used in research centres and a handful of sports labs.

Professional bioelectrical impedance (BIA). Devices such as InBody, Tanita BC, or Seca mBCA, found in medical offices and gyms. They pass a weak electrical current through the body, which travels faster through water and muscle than through fat. The resistance (impedance) the current encounters allows the device to estimate body composition. A newer, decent-quality BIA with hand-to-foot electrodes, performed on an empty stomach, without a recent workout, and at a consistent time of day, is a fair compromise between precision and accessibility.

Smart home scales. Home scales with a body composition feature use the same BIA technology, but with major simplifications. The accuracy of bioimpedance scales is generally lower than methods like DXA or professional BIA, and they provide an estimate based on assumptions that won't fit everyone. BIA, for example, assumes a specific hydration level in fat-free tissues; dehydration, a recent meal, or a recent workout can throw the reading off.

The research backs this up with concrete numbers. A 2021 study published in JMIR mHealth found that several popular scales systematically underestimated fat mass by around 2–4 kg compared to DXA. A French observational study comparing three commercial scales with DXA in hospital patients delivered an even sharper verdict: home scales are accurate enough for body weight, but not for body composition, and should not replace DXA in patient care.

What about watches and fitness bands with a BIA function? Independent validation of every new generation of devices is essential, because differences in hardware, sensor placement, and proprietary algorithms are significant between models. Don't assume that a reading from your watch matches a reading from a medical analyzer, even if both have "BIA" in the spec sheet.

A tape measure. The most underrated tool. Waist circumference (measured halfway between the lower rib and the iliac crest) is cheap, simple, and an excellent predictor of risk. The waist-to-hip or waist-to-height ratio adds extra information about fat distribution. It takes 30 seconds to measure, requires nothing but a tape, and you can't "cheat" the result with hydration tricks.

A practical strategy. If you're a data freak and want to keep close track of your weight and body composition, get a DXA scan every one to two years as your reference point. For day-to-day trend tracking, a home BIA scale will do the job. Always measure under the same conditions: in the morning, on an empty stomach, after a trip to the bathroom, without a recent workout. And average several readings rather than reacting to every single number :)

Where creatine fits in

We're a creatine producer, so it's time for a small product placement. Creatine, combined with resistance training, supports the building of muscle mass and favourable changes in body composition – because, logically, more muscle translates into a lower body fat percentage – though creatine itself is not a fat burner.

A short summary, for those who didn't read but scrolled to the end

If we had to sum up what the data actually shows: for most people, the "optimal" range is not the one that looks best in Instagram photos. It sits around 18–24% for men and 25–31% for women (adjusted for age), provided that visceral fat doesn't get out of hand. You can go lower if your body tolerates it well, your period doesn't disappear, your bones are in order, your sleep and recovery hold up, and your blood work stays clean. But "lower" doesn't always mean "healthier" – and that's the takeaway fitness Instagram has been skipping over for two decades.

If you weigh yourself at home, take individual readings with a grain of salt. Track trends across months, not days. Check your waist circumference, and every once in a while get a DXA scan to see how your home scale compares to reality.

Sources:

• American Council on Exercise (ACE) i American College of Sports Medicine (ACSM) – kategorie referencyjne tkanki tłuszczowej.
• Lichter L. et al. (2025). Body Mass Index vs Body Fat Percentage as a Predictor of Mortality in Adults Aged 20–49 Years. Annals of Family Medicine, 23(4), 337. link
• Jayedi A. et al. (2022). Body fat and risk of all-cause mortality: a systematic review and dose-response meta-analysis of prospective cohort studies. International Journal of Obesity. PubMed
• Zong G. et al. (2018). Joint association between body fat and its distribution with all-cause mortality (NHANES 1988–2011). PLOS One. link
• Dipla K. et al. (2021). Relative energy deficiency in sports (RED-S): elucidation of endocrine changes affecting the health of males and females. Hormones, 20, 35–47. link
• Cabre H.E. et al. (2022). Relative Energy Deficiency in Sport (RED-S): Scientific, Clinical, and Practical Implications for the Female Athlete. Frontiers in Endocrinology. PMC
• Bagheri R. et al. (2023). Visceral adipose tissue and residual cardiovascular risk: a pathological link and new therapeutic options. Frontiers in Cardiovascular Medicine. PMC
• Lemos T. & Gallagher D. (2017). Current body composition measurement techniques. Current Opinion in Endocrinology, Diabetes and Obesity, 24(5), 310–314.
• Frija-Masson J. et al. (2021). Accuracy of Smart Scales on Weight and Body Composition: Observational Study. JMIR mHealth and uHealth. PMC
• Campa F. et al. (2021). Assessment of Body Composition in Athletes: A Narrative Review of Available Methods with Special Reference to Quantitative and Qualitative Bioimpedance Analysis. Nutrients, 13(5), 1620. PMC