Jordi Girona, 18-26,   08034 Barcelona (SPAIN) 
Carbohydrates & Nutrition Carbohydrates are essential for physical activity. In addition, the brain uses 25% of our energy supply in the form of d-glucose. During the Pliocene period 6 million years ago, the human brain, which uses a  lot of energy, underwent dramatic enlargement. In fact, as the animal with the largest brain/body  ratio we require an easy-to-chew, high-quality, high-energy diet. Original sources of sugar were fruits and berries, then agriculture led to the growth of cereal crops,  and animal husbandry increased the range of diet still further. The advent of bee keeping 7,000 years  ago led to the domestication of sugar production. 8,000 to 6,000 years ago sugar cane was recorded as  grown in New Guinea. It was only in the 19th century that potatoes and other high glycemic index (GI)  foods such as refined sugar were introduced. For millennia sugar was hard to come by and physical  activity was part of daily life, but 50 years ago the sedentary office lifestyle took over worldwide.   We evolved from our ancestors in an environment where food was scarce and most people were  involved in hunting and farming, giving rise to the so called thrifty genotype: storing fat for leaner  times in times when food is plenty. Now that refined pure sugar is so easy to get, this genetic tendency may lead to obesity and  disease. A preference for  sugar and sweet things is a  legacy of our evolutionary  past that must not be  demonized; it is our main  nutrient after all, but it  must be controlled if we are  to live a healthy life. In this  age of increasing obesity all  over the world we need to  learn how to manage our  calorie intake to avoid  disorders.