We often know less than we think. Many people believe that black olives are harvested from the trees when they turn black. They would be mistaken. Black olives are harvested at the same time as green olives, and so the chemical content is exactly the same, regardless of colour. The different treatment processes received by black and green olives determine their final chemical composition. Whether black or green, olives are highly nutritious and low in calorie content, with only about 150kcal per 100 grammes. The most valuable nutritional component is its oleic acid, which protects the heart from cardiovascular diseases, thanks to its ability to reduce the levels of low density lipids or ‘bad cholesterol’ in the bloodstream and boost the amount of high density lipids or ‘good cholesterol’. Olives are also rich in the digestible fibre necessary for a healthy digestive system, and the frequent consumption of olives is an ideal way of reaching our recommended daily fibre intakes. The real difference between black and green olives lies in the mineral content. Green olives contain about twice as much salt as black olives, so the latter option is recommended for people who suffer from high blood pressure. Black olives are prepared using salts rich in iron and therefore offer health benefits to people with low levels of iron. Black olives seem to be the healthier option, although the consumption of olives of either colour is beneficial, and dietitians recommend that a healthy adult should eat about 25 grammes, or seven olive fruits each day.