The prevalence of overweight and obesity has also increased substantially in the nutritional transition countries, and the health burden of obesity-related complications is growing. The introduction of fast-food chains and Westernized dietary habits providing meals with fast-food characteristics seems to be a marker of the increasing prevalence of obesity. The mechanisms involved are probably that the supply of foods is characterized by large portion sizes with a high energy density, and sugar-rich soft drinks. The high energy density of foods is partly brought about by a high dietary fat content, and it has been shown that even in a Chinese population the increase from about 15% to 20% in the proportion of calories from fat is sufficient to explain some weight gain in the population. In addition, fast food from major chains in most countries still contains unacceptably high levels of industrially produced trans fatty acids that have powerful biological effects, and contribute to type 2 diabetes and coronary artery disease. New evidence also suggests that a high intake of trans fat may produce abdominal obesity, an important factor in the metabolic syndrome, type 2 diabetes and cardiovascular disease. The optimal diet for the prevention of weight gain, obesity, metabolic syndrome and type 2 diabetes is fat-reduced, without any industrially produced trans fatty acids, fibre-rich, high in low energy density carbohydrates (fruit, vegetables and whole grain products) and with a restricted intake of energy-containing drinks.