by Lily Grace
ave you been trying to lose weight lately, only to find that it’s a bit harder than it used to be? It’s not uncommon. Unfortunately, it’s a natural part of aging—not just metabolism as many believe.
Many studies have been done to understand why people gain weight as they age and the answer is clear—the change in body composition accounts for the vast majority of the decline in metabolism (the process by which your body converts what you eat and drink into energy).
There are also a growing number of studies, however, that suggest that body composition does not account for all of the weight gain associated with aging. A decrease in the number of calories used by the body’s organs, such as the heart and liver, also occur as the body ages.
Of course, physical activity plays a role in both body composition and metabolism during the aging process. Research shows that most individuals gradually reduce their level of physical activity as they age, which further reduces their number of calories needed to maintain weight. Decreased activity also means less use of the body’s muscles, which contributes to the general decline in muscle mass and subsequent changes in body composition.
Overall, these age-related changes mean that the average 50 year-old woman needs around 300-500 fewer calories per day than she did in her 20s to maintain the same body weight. So for those who gain weight while aging, the reason is not necessarily eating more, but rather eating the same while needing fewer calories.
So why can’t I lose weight?
Essentially, even when you’re at rest, your body needs energy for all of its “hidden” functions, such as breathing, circulating blood, adjusting hormone levels and growing and repairing cells.
The number of calories your body uses to carry out these basic functions is known as your basal metabolic rate—what you might call metabolism. Several factors determine your individual basal metabolic rate, including:
»Your body size and composition. The bodies of people who are larger or have more muscle burn more calories, even at rest.
»Your gender. Men usually have less body fat and more muscle than do women of the same age and weight, burning more calories.
»Your age. As you get older, the amount of muscle tends to decrease and fat accounts for a higher portion/percent of your weight, slowing down calorie burning.
Energy needs for your body’s basic functions stay fairly consistent. Your basal metabolic rate accounts for about 70 percent of the calories you burn every day. In addition to your basal metabolic rate, two other factors determine how many calories your body burns each day:
Food processing (thermogenesis). Digesting, absorbing, transporting and storing the food you consume also takes calories. This accounts for 100-800 of the calories used each day. For the most part, your body’s energy requirement to process food stays relatively steady and isn’t easily changed.
Physical activity. Physical activity and exercise—such as playing tennis, walking to the store, chasing after the dog and any other movement—account for the rest of the calories your body burns up each day. Physical activity is by far the most variable of the factors that determine how many calories you burn each day.
The Blame Game
It may be tempting to blame your metabolism for weight gain. But because metabolism is a natural process, your body has many methods that regulate it to meet your individual needs. Only in certain cases do you get excessive weight gain from a medical problem that slows metabolism, such as Cushing’s syndrome or having an underactive thyroid gland (hypothyroidism).
Weight gain is complicated. It is likely a combination of genetic makeup, hormonal controls, diet composition and the impact of environment on your lifestyle, including sleep, physical activity and stress. All of these factors result in an imbalance in the energy equation. You gain weight when you eat more calories than you burn—or burn fewer calories than you eat.
While it is true that some people seem to be able to lose weight more quickly than others, everyone will lose weight when they burn up more calories than they eat. Therefore, to lose weight, you need to create an energy deficit by eating fewer calories, increasing the number of calories you burn through physical activity, or both.