The Science Behind Coffee
Coffee is primarily a source of caffeine, a methylxanthine alkaloid that acts as a central nervous system stimulant. Beyond caffeine, coffee contains a complex blend of over 1,000 bioactive compounds, including antioxidants, polyphenols, and diterpenes. One cup (240ml) of black coffee is virtually calorie-free, containing less than 5 calories. Macronutrient-wise, it offers negligible amounts of protein, carbohydrates, and fats.
However, the micronutrient profile is more interesting. Coffee is a source of potassium (approximately 116mg per cup), niacin (vitamin B3, about 0.5mg per cup), and magnesium (around 7mg per cup). These contribute to various bodily functions, including nerve function, energy metabolism, and bone health. More importantly, coffee is incredibly rich in antioxidants like chlorogenic acid, quinic acid, and melanoidins (formed during the roasting process). Clinical studies show that these antioxidants can combat oxidative stress, potentially reducing the risk of chronic diseases such as cardiovascular disease and certain cancers.
The Glycemic Index (GI) of black coffee is generally considered to be very low, close to zero. This means it has minimal impact on blood sugar levels. However, additions like sugar, milk, or syrups can significantly raise the GI and impact blood sugar control. Nutrition research indicates that caffeine can influence insulin sensitivity, with some studies showing a temporary decrease in insulin sensitivity following coffee consumption. This effect may be more pronounced in individuals with pre-existing insulin resistance. The speed of caffeine absorption is relatively rapid, with peak plasma concentrations reached within 30-60 minutes after consumption. The half-life of caffeine varies significantly from person to person, ranging from 3 to 7 hours, influenced by factors like genetics, liver function, and smoking habits.
Coffee consumption stimulates the release of cortisol, the body's primary stress hormone. While a moderate increase in cortisol can be beneficial for alertness and focus, excessive or chronic elevation can lead to negative health outcomes, including impaired immune function, increased blood pressure, and disrupted sleep. Coffee also promotes the production of stomach acid, potentially leading to heartburn or indigestion in susceptible individuals. Furthermore, caffeine has a diuretic effect, increasing urine production and potentially leading to dehydration if fluid intake is not adequately increased. Finally, diterpenes such as cafestol and kahweol, found in unfiltered coffee, can elevate LDL cholesterol levels. Filtered coffee reduces the amount of these compounds.