Assessing Body Composition for Health and Fitness

Body Composition
Body composition refers to three key variables: body fat percentage, muscle mass, and bone mineral density. In general, having less body fat, more muscle, and higher bone mineral density is associated with better overall health.

Body Fat Percentage
While people can look different and still achieve optimal health, carrying excess body fat is clearly unhealthy. Increased fat accumulation—especially in obesity—is linked to a chronic low-grade inflammatory state. This inflammation has been associated with metabolic disturbances such as insulin resistance, type 2 diabetes, and cardiovascular disease.

Another important factor is the enzyme aromatase, which is present in adipose (fat) tissue. Aromatase converts androgens like testosterone into estrogens. In individuals with excess body fat, particularly with higher amounts of visceral fat, increased aromatase activity leads to more conversion of testosterone into estrogen. This hormonal imbalance can result in lower testosterone levels in men (sometimes leading to conditions like gynecomastia) and cause adipose tissue to become a primary source of estrogen in postmenopausal women.

Excess body fat can also make daily activities and physical pursuits more challenging. For example, losing twenty pounds of body fat—while maintaining muscle mass—can feel like removing a weighted vest, improving athletic performance and reducing stress on joints, connective tissue, and the cardiovascular system.

Based on fifteen years of coaching experience, most men tend to do best with body fat percentages in the mid-teens, while women generally thrive in the low to mid-twenties. At these levels, people often appear lean and athletic, enjoy better energy and metabolic health, and even experience improved sleep. However, going much lower than these percentages may require an overly restrictive lifestyle and can lead to decreased energy, impaired recovery, undesirable hormonal profiles, and negative impacts on fertility and mood stability. Lowering overall body fat percentage can be achieved by both reducing fat mass and increasing skeletal muscle mass.

While before and after photos like this are common in the fitness world, both of these pictures are representative of extremes and should be avoided.

Muscle Mass
While increased fat mass negatively impacts fitness, increasing muscle mass offers substantial benefits. More muscle enhances overall muscular strength—the ability to generate maximal force—which allows your body to perform a wider range of activities. Being physically capable acts as a strong defense against frailty later in life. The more you can do now and the longer you maintain that capacity, the higher your quality of life will be as you age.

It’s important to remember that many individuals enter assisted living not because of a terminal illness, but because they can no longer complete daily tasks independently. In later life, simple activities can feel like a one-rep max strength challenge. Building strength now means you’ll remain stronger as you age.

Muscle also serves as a “glucose sink,” improving metabolic health and reducing the risk of chronic diseases. With more muscle mass, you can consume more sugar and even indulge in junk food without a significant increase in health risks or fat accumulation. Additionally, extra muscle increases your basal metabolic rate and overall cardiovascular health.

Furthermore, improved muscle mass and strength benefit joint health. The stronger and more mobile the tissues surrounding a joint, the less likely you are to experience pain and dysfunction. In many cases, chronic knee, shoulder, or back pain can be alleviated by strengthening the muscles around the affected joint. Given that people tend to lose roughly 1% of their muscle mass per year after the age of 30, I encourage building and maintaining as much muscle as possible throughout life—simply put, more muscle is better.

Bone Mineral Density
The final component of body composition is bone mineral density (BMD), which measures how hard and dense your skeleton is. This is particularly important for women due to hormonal influences. A reduction in BMD is known as osteopenia, and when it becomes severe, it is called osteoporosis.

Having a denser skeleton improves your durability in the event of accidents like falls or car crashes. Being able to take a tumble and walk away with only minor injuries—as opposed to suffering a bone break—can make a dramatic difference in your longevity and quality of life.

Consider this striking statistic: the one-year all-cause mortality risk following a hip fracture in individuals over 65 is 30%. In other words, if you’re over 65, your chances of surviving the year after a hip fracture are only 70%. Maintaining a very dense skeleton can effectively eliminate the risk of fractures in nearly all but the worst accidents.

I aim for bone mineral density scores of my clients to be as high as possible on a DEXA scan, ideally with a minimum T-score of 0—preferably closer to 1.0 or even 1.5.

Measuring Body Composition
Both bioimpedance analysis (BIA) and dual-energy X-ray absorptiometry (DEXA) offer valuable insights into body composition, each with distinct advantages. BIA methods, such as InBody scans, are praised for their convenience, affordability, and ease of use. They quickly estimate metrics like total body water, fat mass, and lean mass by measuring the electrical conductivity of tissues, making them especially useful for routine monitoring in fitness or wellness settings. However, BIA accuracy can be affected by hydration status, activity level changes, and recent food intake. While at-home BIA assessments are useful for tracking trends, they may not provide the precision needed for a detailed progress evaluation.

In contrast, DEXA is considered the gold standard for body composition analysis. It provides highly precise measurements that not only differentiate between fat and lean tissue but also offer detailed information on bone mineral density. Although DEXA scans typically come at a higher cost and require specialized equipment, they deliver the accuracy needed for comprehensive assessments. National chains such as DEXA Fit and Live Lean RX are available in most major metro areas, offering DEXA scans for less than $100 each.

Overall, while BIA is a budget-friendly option for frequent at-home tracking, DEXA remains the preferred method for in-depth body composition analysis.