Your metabolic rate or the amount of energy you expend daily is determined by three factors. These are your resting metabolic rate, the thermic effect of activity, and the thermic effect of the food you eat. It’s a combination of these three factors that determine whether that piece of German chocolate cake you ate at lunch will be burned off as heat or stored as belly fat.
What is Resting Metabolic Rate?
Resting metabolic rate is basically the energy needed to maintain all of your bodily functions at rest. Factors that affect resting metabolic rate include genetics, age, body size, and gender. Resting metabolic rate decreases by about 2 to 3% every decade during adulthood, and men have resting metabolic rates that are as much as 10% higher than women. This is partially due to their larger body size and the greater amount of lean body mass they have.
Resting metabolic rate is also influenced by hormones such as thyroid hormone. People who have hypothyroidism or an under-active thyroid typically gain weight because their metabolism slows down due to reduced levels of thyroid hormone.
Overall, resting metabolic rate accounts for between 60 to 75% of your total energy expenditure each day. That’s a big chunk.
Thermic Effect of Activity: Another Factor That Influences Your Metabolic Rate
Thermic effect of activity refers to all of the activities you do throughout the day, the workouts you do at the gym and activities you do around the house or office. It also includes all of the movement that doesn’t register in your consciousness such as fidgeting. This type of activity is referred to as NEAT or non-exercise activity thermogenesis. If you tap your foot or shake your leg while you’re working at your desk, you’re burning more calories through NEAT.
Normally, the thermic effect of activity accounts for about 20% of your daily energy expenditure, although it can be as high as 30% for people who have active jobs or spend a lot of time at the gym. Unlike your resting metabolic, which you have limited control over; you can control how much you exercise and move around during the day.
Thermic Effect of Food
Your body requires energy to break down and process food. This varies somewhat with the type of food you eat. Protein has more of a thermic effect than a similar amount of fat or carbohydrate, which is one reason why high protein diets are so effective for weight loss. Protein also increases satiety. People who are more insulin sensitive seem to have a higher thermic response to food than those who are insulin resistant. Overall, the thermic effect of food accounts for about 10% of daily total energy expenditure.
The Bottom Line?
You don’t have a lot of control over your resting metabolic rate, although you can boost it to some degree by building lean body mass through strength training. In addition, there’s evidence that resting metabolic rate may stay elevated for hours to days after a high-intensity workout. The other two components, the thermic effect of activity and thermic effect of food, are two factors you can control. Spend more time moving around even when you’re not at the gym, and eat more protein.
References:
J Am Coll Nutr October 2004 vol. 23 no. 5 373-385.
Journal of Clinical Investigation. 89(3): 824-833.
Exercise Physiology. Fifth edition. 2001. McArdle, Katch, and Katch.
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