Metabolism is the collective term used for all processes in the body producing and using energy, such as digestion, circulation, respiration, movement and sleep. Therefore, your metabolism is based on the energy your body requires to function. In moderate amounts and in combination with other, healthful approaches, caffeine, a central nervous system stimulant, might stimulate metabolism and thermogenesis, the heat and energy produced from digestion.
Coffee
A classic and often-cited study published in the May 1980 issue of "The American Journal of Clinical Nutrition" involved four trials measuring metabolic response through varying amounts of caffeine and caffeine-free products. The trials varied in caffeine dose, the body composition of the participants and meal consumption. Metabolism increased as much as 16 percent more in normal weight participants consuming caffeine than those taking placebo. Metabolic rates in obese participants were not affected with or without caffeine. The participants who consumed caffeinated coffee with their meal experienced an average 10 percent increase in metabolism over the participants without a meal and those consuming a meal with decaffeinated coffee. All metabolic increases occurred within three hours of ingestion of caffeine. Researchers explained that caffeine added to the digestion of food produced more energy output, and therefore that caffeine in reasonable quantities adds an advantage for people participating in a "weight reduction regime."
Thermogenesis
A follow-up study on coffee and thermogenesis was published in 1990 in the same journal. Test subjects included 12 medical students of normal weight, each of whom was given either a caffeinated, gelatin capsule or placebo. Energy expenditure was measured, revealing that thermogenesis was significantly higher in those who had consumed caffeine. The authors concluded that moderate caffeine consumption provokes a "linear" response directly related to dosage; the higher the dosage of caffeine, the higher the thermogenic response, especially when combined with physical activity.
Metabolic Evidence
A study published in January 2004 in the "American Journal of Clinical Nutrition" also measured the effects of caffeine on energy expenditure and agreed with earlier studies finding caffeine consumption increased energy output in participants by an average of 13 percent over placebo. The authors stated that caffeine not only increased thermogenesis but also stimulated the metabolism at rest by "influencing whole-body thermogenesis" on a cellular level. Not all mechanisms are known, however, and more studies are needed for more definitive answers.
Considerations
These studies were limited by the number of subjects involved and the cost of the procedures. Larger-scale, cost-efficient, modern study designs are needed for further evaluation of the metabolic and thermogenic effects of caffeine. The studies revealed other variables along with caffeine consumption that might contribute to metabolic stimulation, such as the thermogenic effects of meals, physical activity and weight reduction efforts. Two to four cups per day, or 200 to 300 mg, of caffeine is considered moderate. Some health conditions limit the amount of caffeine determined to be safe. Caffeine affects people differently; some side effects include restlessness, insomnia, anxiety, irregular heartbeat and headaches. valuate your caffeine use and lifestyle habits with a qualified health care professional prior to making changes in caffeine consumption.
References
- "Physiology of Sport and Exercise"; Jack H. Wilmore, et al; 2008
- "The American Journal of Clinical Nutrition"; Caffeine and Coffee: Their Influence on Metabolic Rate and Substrate Utilization in Normal Weight and Obese Individuals; K. J. Asheson, Ph.D., et al; May 1980
- "The American Journal of Clinical Nutrition"; Caffeine: A Double-Blind, Placebo-Controlled Study of its Thermogenic, Metabolic and Cardiovascular Effects in Healthy Volunteers; Arne Astrup, et al; 1990
- "The American Journal of Clinical Nutrition"; Metabolic Effects of Caffeine in Humans: Lipid Oxidation or Futile Cycling?; Keven J. Asheson, et al; January 2004
- MayoClinic.com; Caffeine: How Much is Too Much?
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