Both body weight and body composition are important in developing and maintaining good health. Does one deserve more attention than the other?
When you step onto the scale, the number you see accounts for the weight of all the tissue in your body. Body composition breaks down your weight into percentages of fat mass and lean tissue mass, providing a much clearer picture of what’s inside your skin. When it comes to health risks and rewards, it’s the percentages that count.
Your overall weight can provide insight into how high your health risks are, but there’s more to it than simple cause and effect – that number can be completely misleading. Compare a 100kg/220 pound bodybuilder to an inactive office worker who is exactly the same height, and also happens to be the same weight. You’re probably imagining two very different looking bodies with very different levels of health, fitness, and overall wellbeing – all due to the amount of body fat each person carries.
Fat cells are as active as any other cells in your body, producing a variety of hormones and other molecules that can increase your blood pressure, lead to insulin resistance, diabetes, atherosclerosis, and can have a negative impact on your cholesterol and triglyceride levels. Abdominal fat cells appear to have a greater influence on these health markers. In addition, increased fat mass leading to high body weight can be hard on the body as whole, increasing stress on the heart, lungs, and joints, reducing sleep quality, and increasing mental and emotional stress. Lean body tissues, on the other hand, overwhelmingly provide support and protection to the body and your health, giving you the ability to cope with physical stress.
While there are no universally agreed upon standards for healthy body fat percentages, we do know that healthy levels vary by age range and sex. Body fat levels typically increase with age, and women generally have a higher body fat percentage than men, likely due to the role body fat plays in reproduction. The published research on body fat norms generally suggests that for health benefits, men should maintain 10-25% body fat from the age of 35 onwards, and women should maintain 23-38% body fat for the same age ranges.
There are a number of techniques available that can provide a basic body composition measurement, though these vary in ease of access, accuracy, and cost. Bio-impedance devices, like the hand-held machines or scales that provide a body fat estimate, are by far the most common commercially available options. These devices have varying degrees of accuracy, but in general are a good option for at-home measurement. Other methods include skinfold measurement, air or water displacement techniques, and the DEXA scan – the same one that is used to provide measurements of bone density for those at risk of osteoporosis.
Regardless of what method you choose, you need to stick with that method or machine to get the most accurate picture of progress, as different techniques use different equations to get your percentage. And for health reasons, it’s the fat percentage that counts. While excessive body weight is associated with many chronic health conditions, poor quality of life, and often to an untimely death, you’ll have much better control over your risk factors by keeping the body fat percentage low and not worrying as much about overall weight!
For more information:
Pescatello, L. S. (Ed.). (2014). ASCM’s Guidelines For Exercise Testing and Prescription (9th ed.). Philadelphia: Lippincott Williams & Wilkins.
Plowman, S. A., & Smith, D. L. (2017). Exercise Physiology For Health, Fitness, and Performance (5th ed.). Philadelphia: Lippincott Williams & Wilkins.