Say "coffee,” and most people think of a dark brown brew. But there’s also green coffee, which simply refers to the raw (green) coffee beans. After the beans are picked, they typically go through various water baths and are then dried and milled but not roasted. You can buy green coffee beans to roast yourself at home.
Then there are green coffee extracts (GCE) sold in capsules and as an ingredient in coffee beverages (such as Coffee Slender and CoffeeShape) and even chewing gum (SlimGum), all often promoted for weight loss. Though green coffee beans have caffeine, some GCEs are available decaffeinated.
It’s not farfetched to think that green coffee has potential health effects, just as roasted coffee does. Roasted coffee has been linked, for example, to reduced risk of diabetes, gallstones and Parkinson’s disease. Coffee beans contain hundreds of biologically active compounds, some potentially healthful and others potentially harmful. Green coffee is especially rich in chlorogenic acid, a polyphenol that has been shown in animal and lab studies to have antioxidant and anti-inflammatory properties, as well as effects on blood sugar and body weight. But the compound is mostly destroyed in roasting. On the other hand, roasting the beans creates other beneficial compounds that green coffee lacks.
A few studies have found that overweight people who take GCE lose more weight than those taking a placebo. Though caffeine slightly boosts calorie burning, chlorogenic acid may decrease intestinal absorption of sugar and increase oxidation of fatty acids, among other possible weight-loss mechanisms, researchers say. But the studies have been small and short, and most have design problems, which makes their results questionable. Some were funded by GCE manufacturers.
Interestingly, while regular coffee can temporarily increase blood pressure (especially in people not used to caffeine), GCE may lower blood pressure, due to other compounds in the raw beans. In a Japanese study of 117 men with mild hypertension published in Hypertension Research in 2005, those who consumed GCE for four weeks had reductions in blood pressure, with greater benefits seen at higher doses. Another Japanese study, in 2006, similarly found a blood-pressure-lowering effect in people with mild hypertension who took GCE for 12 weeks. According to the Natural Standard, which evaluates alternative medicine, roasting coffee beans produces a compound that inhibits the beneficial effects of chlorogenic acid on blood pressure—and this may be why only green coffee has been shown to lower blood pressure.
Bottom line: Green coffee may have some health benefits, but until there are better, larger, longer studies to assess its safety and effectiveness, we don’t recommend the extracts. The optimal dose is not known and supplements vary in their formulations. Keep in mind that if GCE lowers blood sugar, as some studies suggest, it may interact with diabetes medications. As with most dietary supplements, pregnant women should avoid GCE.