Body Composition and Healthy Aging: What Actually Matters

Aging is inevitable. How you age is not.

The difference between someone who remains vibrant, strong, and independent into their 80s and beyond versus someone who becomes frail and dependent decades earlier often comes down to body composition - the relative proportions of muscle, fat, and bone that make up your body.

This is not about aesthetics or fitting into old clothes. It is about maintaining the physical capacity to live the life you want, reducing disease risk, and preserving cognitive function. Understanding what happens to body composition as we age - and what you can do about it - is among the most important things you can learn for your long-term health.

What Happens as We Age

Starting around age 30, most people begin losing muscle mass at a rate of about 3-8% per decade. This process, called sarcopenia, accelerates after age 60 and becomes increasingly significant with each passing decade. Without intervention, someone can lose 30% or more of their muscle mass over a lifetime.

Simultaneously, body fat tends to increase, even in people whose weight stays stable. And the distribution of fat shifts - subcutaneous fat (under the skin) decreases while visceral fat (around the organs) increases. This visceral fat is particularly problematic, associated with inflammation, insulin resistance, and increased disease risk.

Bone density also declines with age, particularly for women after menopause when oestrogen's protective effects diminish. Bone loss increases fracture risk and can lead to the stooped posture and height loss associated with ageing.

These changes are not merely cosmetic. They have profound implications for health and function.

Why Muscle Mass Matters More Than You Think

Muscle is not just about strength - though strength certainly matters for daily function and fall prevention. Muscle is metabolically active tissue that plays crucial roles in overall health.

Blood sugar regulation: Muscle is the primary site of glucose disposal after meals. When you eat carbohydrates, insulin signals your muscles to take up glucose from the blood. More muscle means more capacity to handle glucose, which translates to better blood sugar control and reduced diabetes risk.

Metabolic rate: Muscle burns more calories at rest than fat does. Loss of muscle contributes to the metabolic slowdown many people experience with age - and the weight gain that often follows despite not eating more.

Functional capacity: Everything from climbing stairs to carrying groceries to playing with grandchildren requires muscle. Loss of muscle translates directly to loss of independence and quality of life.

Resilience: Muscle serves as a reserve that your body draws on during illness, surgery, or other stress. People with more muscle mass tend to recover better from hospitalizations and survive serious illness at higher rates.

Longevity: Research consistently shows that muscle mass and strength are among the strongest predictors of lifespan. Grip strength, a proxy for overall muscle strength, predicts mortality better than blood pressure.

The message is clear: preserving muscle mass is not optional for healthy ageing. It is essential.

The Problem With BMI

Body mass index (BMI) - weight divided by height squared - has been the standard measure of healthy weight for decades. But BMI has serious limitations, particularly for assessing health as we age.

BMI cannot distinguish between muscle and fat. A muscular person can have a "overweight" BMI despite being metabolically healthy, while someone with low muscle and high body fat can have a "normal" BMI while being at significant health risk.

This matters more as we age because of the tendency to lose muscle while gaining fat. Someone might maintain the same weight - and the same BMI - while their body composition shifts dramatically in an unhealthy direction. Their scale and BMI suggest everything is fine while their metabolic health deteriorates.

For older adults, a slightly higher BMI is actually associated with better outcomes than a "normal" BMI - likely because it reflects adequate muscle mass. The very thin elderly person often has low muscle mass that puts them at risk.

Body composition assessment - through DEXA, bioelectrical impedance, or other methods - provides far more useful information than BMI for understanding health risk and guiding intervention.

The Danger of Visceral Fat

Not all body fat is created equal. Subcutaneous fat - the fat under your skin that you can pinch - is relatively benign. Visceral fat - the fat that accumulates around your internal organs - is metabolically active in harmful ways.

Visceral fat secretes inflammatory chemicals, contributes to insulin resistance, and is associated with increased risk of type 2 diabetes, cardiovascular disease, and even dementia. You can be relatively lean and still have concerning levels of visceral fat, or carry more visible subcutaneous fat while having healthy visceral levels.

The tendency to accumulate visceral fat increases with age, particularly after menopause for women. Chronic stress, poor sleep, and diets high in refined carbohydrates all promote visceral fat accumulation. Conversely, exercise - particularly strength training - and metabolically healthy eating patterns help reduce it.

Because visceral fat is invisible from the outside, assessment through DEXA or other imaging is valuable for understanding your actual risk.

Preserving Bone Density

Bone is living tissue that is constantly being broken down and rebuilt. When breakdown outpaces rebuilding - as tends to happen with age - bone density decreases. The result is osteopenia (mild bone loss) and osteoporosis (significant bone loss with high fracture risk).

Fractures in older adults are not minor inconveniences. Hip fractures in particular are associated with significant mortality - about 20% of people who break a hip die within a year. Even non-fatal fractures lead to pain, reduced mobility, and loss of independence.

Bone density preservation requires adequate calcium and vitamin D, but also weight-bearing exercise that stresses the bones and stimulates rebuilding. Walking, running, and strength training all support bone health in ways that swimming and cycling do not (though those activities have other benefits).

Hormone status also affects bone - oestrogen is protective, which is why bone loss accelerates after menopause. For some women, hormone therapy may be appropriate to support bone health, though this is an individual decision with tradeoffs to consider.

What You Can Do

The age-related changes in body composition are not inevitable at the rates typically seen. Much of what we accept as "normal ageing" is actually the result of lifestyle factors that are within our control.

Strength training is non-negotiable. Resistance exercise is the most effective intervention for preserving and building muscle mass at any age. You do not need to become a bodybuilder, but regular challenging of your muscles is essential. Twice weekly, working all major muscle groups, is a reasonable minimum.

Protein intake matters. Older adults need more protein than younger people to maintain muscle mass - approximately 1.0-1.2 grammes per kilogramme of body weight daily, and more if actively building muscle. Spreading protein intake across meals supports muscle protein synthesis better than eating it all at once.

Keep moving in general. Beyond formal exercise, general physical activity throughout the day supports metabolic health and prevents the deconditioning that comes from sedentary living. Walk, take stairs, garden, play - the specific activity matters less than that you are moving regularly.

Manage blood sugar. The dietary patterns that support healthy blood sugar - adequate protein, fibre, healthy fats, limited refined carbohydrates - also support healthy body composition. Blood sugar instability promotes fat storage and muscle breakdown.

Prioritize sleep. Sleep deprivation impairs muscle recovery, promotes fat storage, and increases cortisol - all of which worsen body composition. Quality sleep is a body composition intervention.

Manage stress. Chronic stress elevates cortisol, which promotes visceral fat accumulation and muscle breakdown. Whatever genuinely helps you manage stress supports healthier body composition.

It Is Never Too Late

If you have not been attending to these factors, you might wonder if the damage is done. Research is clear: it is never too late to improve body composition.

Studies have shown that even people in their 80s and 90s can build muscle and improve strength through resistance training. The capacity to adapt remains throughout life, even if the rate of improvement slows.

Starting earlier is better, but starting at any point is better than not starting. The body you will live in for the rest of your life is shaped by the choices you make today.

Healthy ageing is not passive. It requires intention, effort, and sometimes restructuring of priorities. But the payoff - years or decades of vitality, independence, and engagement with life - is worth it.

Your body composition is not fixed by age. It is shaped by how you live.

Want to learn more? Explore advanced body composition analysis techniques or understand exercise for metabolic health and longevity.