How do our different body components contribute to our weight?
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Knowing how much of our body is attributable to water, protein, fat, carbohydrate and minerals is interesting and helpful in certain ways. However, it is often more helpful to take it up a level and look at the contributing tissue such as muscle and fat, especially when you are trying to assess health and disease risk. In fact, the contribution of various tissues explains the relative contributions made by the different molecules and minerals. |
Muscle and fat (adipose tissue) are typically the greatest contributors to body weight. For instance, a generally lean man will be about 40-45% muscle and 14-18% body fat. That means that muscle and fat make up half to about two-thirds of his body mass. For this man, bone might contribute about 8% and the skin 2%. The rest of body weight is comprised of organs and tissue such as the heart, lungs, liver, kidneys, intestines, pancreas, brain, spinal cord and our circulations (blood, lympahatic). The American Council on Exercise (ACE) has classified body fat levels as shown in the table below (also see Body CompositionTables)
|
Description |
Women |
Men |
|
Essential fat |
10–12% |
2–5% |
|
Athletes |
13–20% |
6–13% |
|
Fitness |
21–24% |
14–17% |
|
Acceptable |
25–31% |
18–25% |
|
Obese |
32%+ |
25%+ |
Source: American Council on Exercise (ACE)
Why do we store excessive energy as fat?
Fat is how we store most of the excessive energy we consume. It is a matter of efficiency as more than double the amount of energy can be stored in a gram of fat than in carbohydrate and protein (9 calories vs 4 calories per gram). Furthermore, carbohydrate and protein attract water, thus storing excessive energy exclusively as glycogen or protein would increase body water tremendously. For instance, each gram of glycogen attracts about 3 grams of water. Thus storing energy primarily as carbohydrate or protein would make us much heavier, larger, and somewhat waterlogged. This would be a huge disadvantage, as body weight would probably triple!
How does body weight change?
Body weight changes as components of body composition change. That means that a loss of body fat would decrease weight and a gain of body fat would increase it. However it is important to realize that gains in body fat are often accompanies by minor changes in supportive tissue such as muscle, skin and bone. The same can be said of muscle. Changes in muscle mass can result in minor changes in bone, skin and blood mass as well.
For most people body weight will change largely due to alterations in either or both body fat and muscle. Increases in muscle mass results from resistance exercise. For regular exercisers and athletes,muscle mass becomes a significant consideration in understanding why they weigh what they do. Meanwhile, for most people though, the scale goes up as body fat is accumulated. In either case, changes in body weight will depend on their energy (calorie) balance. In addition, reduced physical activity, which often happens during adulthood, can reduce muscle mass and theoretically lower body weight. However, what’s more typical is that losses in muscle are paralleled by gains in fat tissue which counterbalances the weight loss or can lead to weight gain is the accumulation of fat exceeds loss of muscle.For most people body weight changes do to calorie imbalances and changes in physical activity.
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