Human metabolism is the sum of the chemical reactions taking place in the body. Metabolism subdivides into two categories--anabolism, which consists of reactions that build larger molecules from smaller ones, and catabolism, which consists of reactions that break down larger molecules. Generally, catabolism generates energy, while anabolism requires it. As such, the faster metabolic processes run in the body, the more energy an individual will burn or require from food. Several factors speed up metabolism.
Caffeine
Used frequently for its stimulant and attention-increasing effects, the caffeine in coffee, tea and soda also increases metabolic rate. This effect is not necessarily universal, however, notes a study by Dr. Bracco, et al, published in 1995 in "The American Journal of Physiology--Endocrinology and Metabolism." Authors examined the effect of caffeine upon lean and obese subjects, and found that while metabolic rate increased significantly in lean subjects, the effects were much less pronounced in obese subjects. In particular, authors noted that obese subjects generated less heat and burned less fat than lean subjects; both effects were pronounced in lean study participants.
Exercise
The effect of exercise on metabolism, particularly where it relates to carbohydrate metabolism, is clear. Exercise increases the metabolic burn of carbohydrate as a source of energy for working muscles. Since muscles can also burn fat as fuel under certain exercise conditions, there is some increase in fat burning during and immediately after exercise, as well. A 1993 study by Dr. Romijn, et al, published in "The American Journal of Physiology--Endocrinology and Metabolism" reports that the effect is particularly pronounced with regard to carbohydrate metabolism, presumably because certain muscles preferentially burn carbohydrate under many exercise conditions. Further, exercise depletes carbohydrates stored in muscles, and muscles work to replenish this carbohydrate source after exercise.
Muscle Mass
One characteristic of body composition--increased muscle mass--significantly affects metabolic rate. The reason for this is that muscle is very active tissue, and burns more calories even at rest than other, less active, tissues like fat, explains Dr. Lauralee Sherwood in her book "Human Physiology." As such, an individual's metabolic rate is in direct proportion to his muscle mass, where more muscle leads to increased metabolism.
References
- "The American Journal of Physiology--Endocrinology and Metabolism"; Effects of Caffeine on Energy Metabolism, Heart Rate, and Methylxanthine Metabolism in Lean and Obese Women; D. Bracco, et al; 1995
- "The American Journal of Physiology--Endocrinology and Metabolism"; Regulation of Endogenous Fat and Carbohydrate Metabolism in Relation to Exercise Intensity and Duration; J. Romijn et al; 1993
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
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