The Reality Behind Metabolism Myths

By Uzelac, Ellen

So can we really change our metabolism or are we predestined to having a slugging metabolism? Can we blame our metabolism for our body weight? Does our age, gender, or race play a role in the number of calories we can eat?

Myth No. 1- We can precisely calculate what our calorie needs are based on our metabolism.

A person's basal metabolic rate is the amount of energy required to sustain basic processes required for life. With today's technological advances, a person's oxygen consumption and carbon dioxide production can be accurately measured and used to calculate a one's basal or resting metabolic rate. Basal metabolic rate only accounts for about 70 percent of total energy expenditure. A person's actual energy expenditure is more complex and dependent on a number of factors - namely thermogenesis (the process of digestion, ingestion, absorption of food and regulation of body temperature), and physical activity. Physical activity includes all movement - not just exercise. Since physical activity or energy expenditure is dynamically changing component of life, it is difficult to really calculate a person's exact energy or caloric needs.

Energy Expenditure = basal metabolic rate + thermogenesis + physical activity

Myth No. 2 - Age, gender, and race don't effect basal metabolic rate.

All three play a role in metabolism. As humans age, the metabolic rate slows about 1 to 2 percent every decade after age 20. Also, because of their greater amount of muscle and larger organs, men have higher basal metabolic rates than women. And several studies indicate that metabolic rate differences exist between races and/ or ethnicities. Researchers are working to determine why African American females have slower metabolic rates than white females.

Myth No. 3 - So if we held our physical activity and caloric intake constant, we wouldn't gain any weight? And if weight gain occurs, then calorie restriction is effective?

Unfortunately, it is not that easy. Although physical activity and calorie intake are major variables in the energy expenditure equation, other factors play a role. First, it is important to understand that small changes in either variable over a short time will have little or no effect. You see, our body is so efficient that if we decrease our food intake for a week or two without increasing our physical activity, our metabolic rate slows to compensate for our calorie deficient. In times of famine, this attribute is helpful but when weight loss is the goal, it can be stifling. Humans are much more efficient at storing fat than burning fat. For this reason, it is imperative to stop weight gain before it occurs. The body was built to protect against famine rather than fighting weight gain. In addition, shifts in hormone levels can alter satiation (the feeling of fullness after a meal) or metabolic rate. For instance, when the thyroid gland releases insufficient thyroxine hormone, the basal metabolic rate slows causing weight gain. In addition, two obesity-related hormones leptin and ghrelin appear to affect weight. Researchers report a leptin resistance and an overproduction of ghrelin in obese people. Research continues to find answers to such hormonal problems.

Myth No. 4 - So if we overindulge one day, the only way to alter the energy equation is to exercise more?

Physical activity includes may aspects of life. Occupation is a key factor. A job requiring standing or constant motion provides much more energy expenditure than a sedentary desk job. Research indicates that people who fidget burn more calories. So to combat the battle of the bulge, make changes in every day routines. Take the stairs instead of the elevator. Park in the back of the lot and walk further. Walk around the house while talking on the phone. Also, bouts of exercise in increments of 10 minutes is equivalent to a 30 minute session. So, stop making excuses and go hit the pavement! And three or four times a week add an additional 10, 20 or 30 minutes of intense physical exercise.

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