Medically reviewed by Mark Strehlow, MD, Medical Director — September 2026
Body composition is important because it shows what your weight is made of: fat, muscle and bone. That tells you far more about your health than the number on the scale. Two people can weigh the same and have the same BMI, yet one carries much more fat, especially around the organs, and much less muscle.
What is body composition?
Body composition splits your body into two parts:
- Fat mass: all the fat in your body
- Fat-free mass: everything else, including muscle, bone, organs and water
It’s usually given as a body fat percentage, but where your fat is stored matters too. Subcutaneous fat sits just under the skin. Visceral fat sits deep in the abdomen, around your organs, and it’s the type most closely tied to health problems.
Why body composition matters more than weight or BMI
BMI uses only your height and weight. As the CDC notes, it doesn’t measure body fat directly and can’t tell fat, muscle and bone apart. That can mislead:
- Normal weight, high body fat. In a Mayo Clinic study of more than 6,000 adults with a normal BMI, metabolic syndrome was about four times as common in those with the most body fat as in those with the least. In women, high body fat at a normal weight was also linked to a higher risk of dying from cardiovascular disease.
- Weight loss that isn’t all fat. Part of any weight you lose is muscle and other lean tissue. A scale can’t tell you which you lost.
The health benefits of a good body composition
Less visceral fat. The American Heart Association calls excess visceral fat an independent indicator of poor cardiovascular outcomes. It also treats waist size as a risk marker separate from BMI. Visceral fat is linked to type 2 diabetes and high cholesterol too.
More muscle. Muscle clears about 80% of the glucose that enters your blood after a meal, so it’s central to blood sugar control. Adults can lose as much as 8% of their muscle each decade, starting in their 30s or 40s, and that loss is linked to falls, fractures and loss of independence.
Stronger bones. Bone density peaks in early adulthood and then slowly declines, faster in women after menopause. The lower your bone density, the more easily a bone breaks.
In large studies, a healthier body composition goes along with:
- Lower rates of heart disease and type 2 diabetes
- Better blood sugar control
- Healthier blood pressure
- Fewer weight-related sleep problems, such as sleep apnea
- More strength, balance and independence with age
- Bones that are less likely to break
These are patterns across large groups of people, not guarantees for any one person.
Why is having some body fat important?
Your body needs some fat to work properly. Fat stores and releases energy, insulates you and cushions your organs. It also helps regulate hunger, blood sugar and insulin sensitivity, and helps process sex hormones such as estrogen.
Too little fat causes problems too, and it can disrupt many of the same processes that excess fat does. In women, eating too little for the amount of exercise they do can lower estrogen, stop periods and weaken bones. Women naturally carry more fat than men, so their healthy ranges are higher.
What is a healthy body composition?
There’s no single ideal number, because healthy body fat changes with age and sex. These are the ranges we use at Rock Creek Wellness. They’re general guidelines, and your provider sets your own target based on your health, activity and goals.
Body fat percentage: women
| Age | Low/Athletic | Fitness | Acceptable | Overfat | Obese |
|---|---|---|---|---|---|
| 20–29 | < 21% | 21–24% | 25–31% | 32–38% | > 38% |
| 30–39 | < 22% | 22–25% | 26–32% | 33–38% | > 38% |
| 40–49 | < 23% | 23–26% | 27–33% | 34–39% | > 39% |
| 50–59 | < 24% | 24–27% | 28–34% | 35–40% | > 40% |
| 60+ | < 25% | 25–28% | 29–35% | 36–41% | > 41% |
Body fat percentage: men
| Age | Low/Athletic | Fitness | Acceptable | Overfat | Obese |
|---|---|---|---|---|---|
| 20–29 | < 11% | 11–14% | 15–20% | 21–25% | > 25% |
| 30–39 | < 12% | 12–15% | 16–21% | 22–26% | > 26% |
| 40–49 | < 14% | 14–17% | 18–22% | 23–27% | > 27% |
| 50–59 | < 15% | 15–18% | 19–23% | 24–28% | > 28% |
| 60+ | < 16% | 16–19% | 20–24% | 25–29% | > 29% |
Other sources publish somewhat different cut-offs, and lower isn’t always better. Treat any chart as a guide, not a verdict.
Where your fat sits matters as much as how much you have. A DEXA scan compares the fat around your middle (android fat) with the fat around your hips and thighs (gynoid fat). A higher android/gynoid (A/G) ratio means more of your fat sits around your middle, which is the pattern linked to heart disease and type 2 diabetes. These are our targets:
| A/G ratio | Women | Men |
|---|---|---|
| Optimal | < 0.8 | < 1.0 |
| Acceptable | 0.8–1.0 | 1.0–1.2 |
| Elevated risk | > 1.0 | > 1.2 |
Without a scan, your waist is a useful check: over 40 inches for men or 35 inches for women is a sign of excess abdominal fat. A healthy body composition also means enough muscle for strength and everyday life, and healthy bone density for your age. To see what each number on a scan report means, read our guide to reading your DEXA report (PDF).
How is body composition measured?
| Method | What it tells you | Limits |
|---|---|---|
| BMI | Your weight relative to your height | Can’t separate fat, muscle and bone |
| Waist measurement | A quick check on abdominal fat | Doesn’t give a body fat percentage |
| Smart scales and handheld devices (bioelectrical impedance) | An estimate of body fat | Readings shift with hydration, meals and exercise |
| Skinfold calipers | An estimate of body fat | Accuracy depends on who’s measuring |
| DEXA scan | Fat, lean mass and bone, region by region, including the fat around your middle | An x-ray exam, so it needs an order; not done during pregnancy |
DEXA (dual-energy X-ray absorptiometry, also written DXA) is widely used as a reference method in body composition research, and its radiation dose is very low. Repeat scans on the same machine are consistent. Fat and muscle change slowly, so rescans are usually months apart, not weeks. At Rock Creek Wellness, we use a DEXA body composition scan to see where you’re starting from and whether your plan is changing fat, muscle or both.
How to improve your body composition
- Strength train at least twice a week. Federal guidelines call for muscle-strengthening work for all major muscle groups on two or more days a week, plus 150 to 300 minutes a week of moderate aerobic activity, such as brisk walking.
- Eat enough protein, and spread it across your meals. In studies of adults doing resistance training, extra protein added to muscle gains up to about 1.6 grams per kilogram of body weight a day (about 0.7 grams per pound), and no further. If you have kidney disease, ask your provider first.
- Sleep at least seven hours. That’s what the CDC recommends for adults. In one small controlled study, dieters who slept 5.5 hours a night instead of 8.5 lost less fat and more lean mass.
- Lose weight gradually, and keep lifting. Bigger calorie cuts tend to cost more muscle. In diet studies, adding resistance training cut muscle loss to half or less.
Body recomposition: losing fat and gaining muscle at the same time
Body recomposition means losing fat while you build muscle, so your shape and health markers change even when your weight barely moves. A 2020 review found it happens most readily in people who are new to strength training, are returning after a break or carry more body fat, when they combine resistance training with enough protein. The scale can say nothing changed when a lot did.
When to have your body composition checked
Consider a measurement if:
- Your weight is steady but your waist is growing
- You’re losing weight and want to know it’s fat, not muscle
- You’re starting a training or nutrition plan and want a baseline
- You’re approaching or going through menopause, when fat gain speeds up and lean mass starts to fall
- You’re concerned about your bone health
If your body composition is changing in ways that diet and exercise don’t explain, we look for the cause before we recommend anything. That usually means a DEXA scan alongside comprehensive blood testing, which covers thyroid function, blood sugar regulation and hormones. Every new patient gets a DEXA scan when they establish care. After that, Premier Care Executive members get a body composition scan and a bone density scan included every year, and Platinum members get both at a discount.
Please note: A DEXA scan requires an order, so our DEXA scans are for Rock Creek Wellness patients. To become a patient, please call the office or book a free consultation.
Individual results vary. This article is educational and is not medical advice.
Sources
Published at the end of the post, under an H2 “Sources”.
- CDC. About body mass index (BMI). Reviewed 2025.
- Powell-Wiley TM, et al. Obesity and cardiovascular disease: an AHA scientific statement. Circulation. 2021.
- Romero-Corral A, et al. Normal weight obesity. European Heart Journal. 2010.
- Heymsfield SB, et al. Weight loss composition is one-fourth fat-free mass. Obesity Reviews. 2014.
- Cleveland Clinic. Visceral fat.
- Merz KE, Thurmond DC. Role of skeletal muscle in insulin resistance and glucose uptake. Comprehensive Physiology. 2020.
- Cleveland Clinic. Sarcopenia.
- MedlinePlus. Aging changes in the bones, muscles, and joints.
- Cleveland Clinic. Adipose tissue (body fat).
- AAOS OrthoInfo. Relative energy deficiency in sport.
- Harvard T.H. Chan School of Public Health. Measuring body fat.
- HHS. Physical Activity Guidelines for Americans, 2nd edition. 2018.
- Morton RW, et al. Protein supplementation and resistance training: a meta-analysis. British Journal of Sports Medicine. 2018.
- CDC. About sleep.
- Nedeltcheva AV, et al. Insufficient sleep undermines dietary efforts to reduce adiposity. Annals of Internal Medicine. 2010.
- Barakat C, et al. Body recomposition. Strength and Conditioning Journal. 2020.
- Greendale GA, et al. Changes in body composition and weight during the menopause transition. JCI Insight. 2019.
