Metabolism is the chemical processes that occur to maintain the living state of cells in an organism. Metabolic rate is the rate at which this occurs. In humans, the metabolism is the term used to describe how our body transforms energy (i.e. burning calories) to keep all the cells and body mechanisms working to keep us alive. Our metabolic rate is therefore the rate at which the body burns calories.1
Impact of coffee and caffeine on metabolism and metabolic rate
The results shown above are from a series of 4 trials studying the effect of caffeine and coffee on metabolic rate in non-obese and obese subjects. In the first trial, 8 mg/kg of caffeine was compared against a placebo in normal weight participants. Metabolic rate increased significantly during the 3 hours after caffeine consumption. Plasma glucose levels, insulin levels, and carbohydrate oxidation did not change significantly, but plasma free fatty acid levels rose from 432+/-31 to 848+/-136 muEq/liter. Fat oxidation levels also significantly increased during the last hour of the test.
The second and third trials studied the effects of 4 mg/kg of caffeine in control and obese participants. Metabolic rate increased significantly in both groups, but significant increases in fat oxidation were only observed in the control group. Plasma free fatty acids did not change in the obese group.
The fourth trial studied the effect of coffee when consumed after a 3080 kJ meal. The thermic effect of the meal was much greater after coffee than after the placebo of decaffeinated coffee. Fat oxidation was also much higher after coffee, over decaffeinated coffee.
The conclusions of the 4 studies were that that coffee (caffeinated) increases metabolic rate in both obese and non-obese individuals, however, fat oxidation is higher in non-obese subjects.2