Your body undergoes many changes as it ages, transforming almost every bit of you from -- from hair, nails, skin, bones, heart, lungs, and more – and whether you begin as an apple or a pear, your overall body shape will also probably shift, with time. This metamorphosis is due to factors that fall into two main categories: those you can’t control, and those you can. In particular, the rate at which body shape changes occur, are closely connected to lifestyle factors like exercise, smoking and diet.
Our bodies are made up of several components, primarily bones, muscles, fat, and water. Changes in body composition -- that is, the relative proportion of weight made up by each of these components, typically happen with age – even when there’s no overall change in body weight.
Generally, fat increases, and muscle mass, or lean tissue, and mineral bone density, decrease with age.
Fat: The percentage of the human body made up of fat is the focus of much concern because of a growing obesity problem. Healthy body fat percentages for men range from 8-20% (age 20-39 yrs) and 11-22% (age 40-59 yrs). For women, healthy body fat percentages range from 21-33% (age 20-39 yrs) and between 23-34% (age 40-59 yrs). These figures, published in the American Journal of Clinical Nutrition, are based on U.S. National Institutes of Health (NIH) recommendations of a healthy body mass index range between 19-25.
Total body weight fluctuates according to the number of calories (energy) consumed. If you eat more than you burn off, you’ll gain weight over time. Without exercise, that extra weight will be stored on your body as fat, rather than muscle, increasing the proportion of your body weight made up of fat. This shifting body composition can in turn accelerate fat gain over time, because muscle is more metabolically active than fat tissue, and burns more energy.
- Read more: What causes weight gain?
The location of fat, as well as the proportion, typically changes with age. In women, a drop in estrogen levels with menopause coincides with a shift of fat from the lower portion of the body (a "pear" shape), toward the midsection (an "apple" shape). This "belly fat" is comprised of both subcutaneous fat under the abdominal skin, as well as fat that accumulates around organs, called visceral adipose tissue, deep within the abdomen. Belly fat creates an apple-shaped form that has been associated with a higher risk of cardiovascular disease and diabetes.
For example, a 2008 review by researchers from the NIH and Harvard University looked at data from more than 44,000 women in the Nurses’ Health study over a period of 16 years. It concluded that women who had a greater waist circumference were more likely to die of heart disease and cancer than women with smaller waists. Specifically, women with a waist size greater than 35 inches had approximately double the risk of heart disease and cancer, relative to women with a waist circumference of less than 28 inches.
More recently, a review of more than 221,000 people in 17 countries, published in The Lancet, found blood pressure, lipids, and diabetes history to be more reliable than body shape, in predicting cardiovascular disease. Still, the NIH recommends a waist circumference no greater than 35 inches for women; for men, no greater than 40 inches.
In men, a drop in testosterone levels probably also affects fat distribution, and hip circumference commonly decreases as men age.
What you can do: Maintain a healthy weight as you get older, to help prevent the accumulation of fat in your midsection. Both subcutaneous fat and visceral fat can be reduced through diet and exercise.
- Read more: Can meditating help you lose belly fat?
Muscles: Skeletal muscles account for about 40-50% of total body weight in a healthy adult. Loss of muscle tissue and strength, or sarcopenia, is a result of lack of activity that challenges your muscle system. Some researchers estimate a yearly 1% loss of muscle mass, after the age of 30. Since muscle burns more calories than fat, a smaller proportion of muscle on your body has implications for your overall weight and health, as well as a loss of overall strength, and increased disability.
What you can do: Remain physically active and include resistance exercise in your regimen, which will help to maintain muscle mass throughout your life. Even seniors in their 80s and 90s have been shown to gain strength through mild resistance training.
Height Loss: Not only can you get wider, but you can get shorter as you age. Bones make up about 20% of total body weight. Due to changes in bone mass, as well as in muscles and joints, a height loss of about 0.4 inches (1 cm) every 10 years usually occurs, with the loss accelerating after the age of 70. A person may lose between 1-3 inches in height, over their lifetime. This is a tendency seen in all races, and in both sexes, according to the NIH.
What you can do: Bone mineral density peaks around the age of 30, then may diminish -- especially in women in the first years after menopause -- putting you at risk of bone-thinning diseases like osteopenia, and osteoporosis. Reduce the loss of bone mass by avoiding smoking, consuming adequate calcium, and including weight-bearing exercises like resistance training and walking in your activity plan.
Further research is ongoing to determine how shifts in body composition affect health, as well as how body composition may change with age, among different races. In the meantime, remember that major changes in body shape are not inevitable, if you continue to exercise, eat a healthy diet, and steer clear of tobacco.
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Marie-Pierre St-Onge and Dympna Gallagher. “Body composition changes with aging: The cause or the result of alterations in metabolic rate and macronutrient oxidation?” Nutrition. 2010 February ; 26(2): 152–155. doi:10.1016/j.nut.2009.07.004.
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