The active constituent in coffee that is responsible for its many health benefits is a compound called chlorogenic acid. It neutralizes free radicals, and addresses the problem of hydroxyl radicals, both of which can lead to cellular degeneration if left unchecked. Chlorogenic acid also helps regulate metabolism. Compared to green tea and grape seed extract, green coffee bean extract is twice as effective in absorbing oxygen free radicals.
One of the advantages of using the green coffee bean extract is that the negative effects of coffee are avoided. The chlorogenic acid is thought to boost metabolism by changing the way glucose is taken up by the body. And it does contain caffeic acids, which give a boost to energy levels like regular coffee does. But unlike boiled coffee, green coffee bean extract contains no cafestol, which is a diterpene. Along with its diterpene relative kahweol, cafestol increases concentrations of the 'bad' cholesterol, LDL, to levels that over a lifetime might increase the risk of coronary heart disease by as much as 20% These diterpenes also had an effect on the levels of liver enzymes measured. When these are elevated it is an indicator of stress on the liver. However the study that measured this found this was a transient effect, and also that the levels of liver enzymes were much lower than those with liver disease.
As a side note on the health effect of the diterpenes found in regular coffee, it was found that by simply drinking filter coffee, none of these effects on cholesterol levels or the liver took place. The coffee filter removed the offending diterpenes. And levels of these diterpenes in instant coffee are low.
Other benefits of green coffee bean extract include an increase in the effectiveness of pain killers, especially for migraine medications; a reduction in the risk of diabetes; and assisting the body burn a higher proportion of lipids (fats) compared to carbohydrates, which could help with muscle fatigue for athletes and bodybuilders.
Interestingly, on the subject of caffeine and liver disease, further studies have indicated it may in fact support liver health for some people. Those who were at high risk of developing liver disease due to drinking too much alcohol were found less likely to suffer liver damage if they drank more than two cups of coffee or tea a day. This was a population based study, not a clinical trial, and so is not conclusive on the subject. But it does offer some promising information. Those drinking in excess of two cups or more a day were half as likely to develop liver disease compared to those drinking less than one cup a day. Researchers do not know what caused this protective effect.
One of the criticisms of coffee in regards to health is that it leaches calcium from the bones. But this effect has been found to be overemphasized, at least in children. And adults who consume a diet with sufficient levels of calcium will be protected from the small amount of calcium that is lost due to coffee consumption.
So the old axiom that caffeine can stunt a child's growth is a myth. It was based on the fact that in older studies, caffeine was associated with low bone mass because those studies were done on elderly people who both drank a lot of coffee and had diets that were low in calcium. Recent studies in the US followed 80 teenagers over 6 years, and found no difference in the bone density of those with a high level of caffeine in their diet, compared to those teenagers who had little caffeine. Other studies determined that the amount of calcium lost from bones is small and can be balanced by having sufficient calcium in your diet.
References: Australian Healthy Food Magazine, January.