Eater's Digest: Managing common metabolism myths

By Scott Norgaard     3/18/10 7:00pm

We all envy people who can eat whatever they want without gaining weight. How do such people maintain their physiques? This week, we'll delve into some of the questions surrounding metabolism. What are some factors that influence our metabolisms, and how much control do we have over them? Several scientific-sounding myths claim to have all the answers regarding this process, but in how far should we trust them?

One common belief about metabolism is that eating smaller meals more often will keep the "metabolism fire burning," compared to eating larger, less frequent meals. This mentality posits that you will burn more calories throughout the day by eating more often. Monica Reinagel, an author of three health and nutrition books and a board-certified licensed nutritionist who runs a section called "Nutrition Diva" on www.quickanddirtytips.com, asserts in her column that there is some truth to this belief, but the conception is vastly overstated. Your body needs about three days to change the rate at which it burns energy, so simply eating every few hours will not enact drastic changes.

So what are the factors that have the greatest influence our metabolism?

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According to the Victorian government's "Better Health Channel" Web site, factors like age, gender, muscle mass and genetics play a role; metabolism is largely dependent on the amount of lean muscle mass you have. As people age, the muscle mass in their body usually decreases, and their metabolisms gradually slow - this loss is generally why older people need less food than younger people. Hormones can also influence a person's metabolism, and certain hormone disorders related to the thyroid can affect one's metabolism.

In one case, hyperthyroidism occurs when your body's thyroid is too active and excess amounts of the hormone thyroxine cause your basal metabolic rate, or BMR, to increase, leading to weight loss. This disease, which affects about one percent of people, can be treated with medications, surgery or radiation treatments.

Your calorie expenditure, another component of your metabolism, is largely controlled by three various means.

The first is one we've already touched on - your basal metabolic rate, which is the energy used by your body to maintain basic biological functions like keeping your heart beating and your organs functioning. You need a baseline amount of energy to stay alive, and your BMR is responsible for 50 to 80 percent of your energy expenditure each day.

The second main consumer of your calories is your physical activity, which is the energy used by your muscles. Different activities require a different number of calories. For example: A 160-lb. person bicycling for one hour burns 610 calories, but if recreationally swimming for an hour, that same person would only burn 457 calories. If they were just sitting quietly for an hour, they would burn a mere 76.2 calories. People possess different daily energy expenditures from physical activity, depending upon how active they are.

The third consumer of calories is the thermic effect of food, which is the amount of energy your body uses to transform your food into fuel it can use. Think of it as a kind of tax the body levies in order to convert the physical food you eat into a type of energy to power your cells. Depending on the nutritional value of foods you eat, your body allots a certain percentage of the food energy on digesting and metabolizing it. Fats raise the BMR by 4 percent, while proteins raise the BMR 30 percent.

Given this information, there are some things you can do to influence your metabolism. Eating every few hours in attempt to keep your body in a "burning mode" may actually be counterproductive, as your total calorie intake may increase. However, you do have some impact over your metabolism by controlling and developing your muscle mass through strength-building activities like lifting weights.

So although you may never be able to achieve that "magic metabolism" that seems to instantly digest whatever you eat, there are some things you can do, namely increasing your muscle mass, to help the rate at which your body burns food energy. Some habits like eating every few hours may not be as effective and may actually cause you to intake more food than you anticipated.

Scott Norgaard is a Sid Richardson College freshman.

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