Can Diet and Exercise Really Change Metabolism?

, University of Alberta

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In This Article

What Factors Influence Metabolic Rate?

The major determinants of REE and RMR appear in prediction equations of energy expenditure and include such factors as body surface area (a calculation based on height and weight), age, and gender (Fig. 2). The greater the body surface area, the greater the RMR. Resting metabolic rate gradually declines with age, although a large component of this decline may be due to a decrease in muscle mass. For example, males have a higher RMR than females, primarily because of greater muscle mass. Fat-free mass (FFM) is a better predictor than surface area of oxygen consumption in young men.[3] Together, FFM, fat mass (FM), age, and gender account for approximately 80% of variance in RMR.[4]

Figure 2. Comparing two 30-year-old women of the same height and medium frame, the obese woman has a lower resting energy expenditure (REE) per kg of body weight than the average-weight woman. But the REEs are about the same when the average-weight woman's higher proportion of fat-free mass (FFM) is included in the calculation.

Other determinants of resting metabolism include thyroid hormones and catecholamines,[5,6] genetics,[7] body temperature,[8] and in women, the phase of the menstrual cycle.[9,10] An increased release of thyroid hormones or catecholamines increases RMR. Conversely, a reduction in energy intake specifically decreases triiodothyronine (T3) levels[11] and norepinephrine release,[12] which can subsequently decrease metabolic rate. An individual's RMR is, to a certain extent, genetically determined, and it can also increase in response to extremes in body temperature. In addition, it has been estimated that during the luteal phase of the menstrual cycle, there may be up to a 5% increase in RMR.[9] Although most factors are beyond the control of the individual, it is believed that voluntary behaviors, specifically dietary intake and exercise, can also influence resting metabolism.[6]

Although there is a significant amount of information in both the scientific literature and in the public media regarding metabolic rate, this information is often contradictory. Whether metabolic rate can be altered and the extent to which it can be altered are not well-defined. In general, it is widely believed that dieting decreases metabolic rate and exercise increases it.

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