Why your body composition is important for your health

With the current global obesity crisis and the rising prevalence of metabolic diseases such as type 2 diabetes, cardiovascular disease, and fatty liver disease, there is a growing recognition that optimising body composition—rather than focusing solely on weight or BMI—is essential for effective health management. 

Body composition refers to the proportions of the body’s major components:

• Fat mass (both subcutaneous and visceral)

• Lean mass (primarily muscle)

• Bone mass

• Water content

Quantifying these proportions gives much greater insight into an individual’s health status than simply measuring body weight. Individuals with very different fat and lean mass proportions may have identical BMIs but will have significantly different health statuses based on these differing proportions.

As a general rule it is desirable to have relatively low fat mass and high levels of muscle mass though optimal ranges differ according to sex, race and age.

Fat mass is the total amount of fat (or adipose tissue) in the body and includes subcutaneous fat, which is fat found beneath the skin, and visceral fat, which is fat deep within your abdomen, surrounding your organs. A certain proportion of fat mass is crucial to our survival as it serves many essential functions including storage of energy, protection of our internal organs, production of certain vitamins as well as regulating the health of our entire body as it is an active part of our endocrine (hormonal) system. However having too much or too little fat is detrimental to our overall health. Excessive amounts of visceral fat (fat around the organs) are particularly bad for  our health as it is this type of fat which plays an active role in regulating so many systems throughout our body. Excess visceral fat triggers low-grade systemic inflammation which increases your risk of developing numerous chronic diseases including cardiovascular disease, Alzheimer's and various cancers. 

Fat-free mass, or lean mass, is all other components including muscle mass and bone mass. In contrast to fat mass which typically increases with age, muscle mass and bone mass decline with age. Equally, whereas excess fat mass is associated with a many of chronic diseases of ageing and early death, having a high level of muscle is strongly associated with a decreased risk in mortality. 

Muscle mass does not simply provide strength, functionality and independent living into old-age, it is a metabolically active organ. For example, skeletal muscle plays a critical role in glucose uptake from the bloodstream, effectively acting as a sink for excess glucose and maintaining blood sugar levels. 

Muscle mass and muscle strength also play a crucial role in maintaining bone mineral density. Therefore maintaining muscle mass and strength is central also preventing osteopenia, osteoporosis and reducing risk fracture as we age.

Although there are no universally accepted body composition norms, there are ranges which are considered healthy, though these differ with age, sex, race and athletic level. What we do know is that age and lifestyle has a profound effect on fat mass, muscle mass and bone mass. Our body composition changes as we age - muscle mass typically starts to decline at around age 30 - 40 and fat mass generally increases with age, particularly in cases of inactive individuals with poor dietary patterns. As we have seen above, an increase in visceral fat mass is linked to many of the chronic diseases of ageing, whereas muscle mass has the opposite effect. Therefore we need to be actively striving to maintain healthy levels of body fat and maximise muscle mass as we age. Lifestyle factors, especially exercise and nutrition, have a profound effect on our body composition. They are potent tools which we can manipulate to ensure we slow down these body commotion changes and associated conditions. Being in an overall energy balance - not being in an overall calorie surplus - is fundamental to ensure fat mass does not increase to unhealthy levels. Having a nutritionally balanced dietary pattern which is sustainable is key. Being generally active in your everyday life and intentionally incorporating strength training regularly as well as eating sufficient of protein daily is key to ensuring you maintain/ build muscle mass as well as bone mineral density. 

Assessing and monitoring body composition in a timely fashion is an extremely important metric given its strong association to our health. There are various ways in which this may be measured. These include Bioelectrical Impedance Analysis (BIA) and Dual - energy X-ray absorptiometry (DEXA). BIA offers a good estimate of the relative proportions of visceral fat, subcutaneous fat and muscle mass when performed correctly whilst DEXA scans offer accurate measures of fat mass, lean mass and bone mineral density along with other useful metrics and 2D images. 

Once you have established a baseline for these metrics, regular assessments will help guide lifestyle changes; whether what you are doing is sufficient to carry into your later years whilst maintaining functional independence and avoiding many chronic diseases of ageing. 

Regular body composition assessment and monitoring is also vital when an individual is taking GLP-1 agonists such as Ozempic or Mounjaro for weight loss purposes. The rapid weight loss typically seen with these drugs is due to loss of fat but also significant loss of muscle and bone mass. It is essential that any patients who are prescribed Ozempic or Mounjaro for weight loss also engage in regular resistance training (weights) and eat sufficient amounts of protein to offset muscle and bone loss. 

If you would like to test your personal risk factors for developing chronic diseases of ageing, and find out if you have high markers of inflammation find out more about the Longevity Annual health check and download the longevity doctor guide to healthy living.