Fast 
 food restaurants are feeding the obesity epidemic by tricking 
 people into eating many more calories than they mean to, an important 
 study has shown. 
 Typical menus at McDonald's, KFC and Burger King contain 65 per 
 cent more calories per bite than standard British meals, making 
 it far too easy ffor customers to overindulge without realising 
 it. 
 The high "energy density" of junk food - the amount 
 of calories it contains in relation to its weight - throws the 
 brain's appetite control system into confusion, as this is based 
 on the size of a portion rather than its energy content. 
 The critical role of energy density in obesity has been revealed 
 by Andrew Prentice, Professor of International Nutrition at the 
 London School of Hygiene and Tropical Medicine, and Susan Jebb, 
 of the Medical Research Council Human Nutrition Centre in Cambridge. 
 
 In a study published in the journal Obesity Reviews, they calculated 
 the average energy density of menus at McDonald's, KFC and Burger 
 King, using nutritional data from the fast food chains' websites. 
 
 The average energy density of these restaurants' meals was 263 
 calories per 100 grams, 65 per cent more than the density of the 
 average British diet and more than twice that of a recommended 
 healthy diet. This means that a person eating a Big Mac and fries 
 would consume almost twice as many calories as someone eating 
 the same weight of pasta and salad. 
 Professor Prentice said that the human appetite encouraged people 
 to eat a similar bulk of food, regardless of its calorific value. 
 This left regular consumers of fast food prone to "accidental" 
 obesity, in which they grew fat while eating portions they did 
 not consider large. 
 Professor Prentice added: "Since the dawn of agriculture, 
 the systems regulating human appetites have evolved for the low-energy 
 diet still consumed in rural areas of the developing world, where 
 obesity is almost non-existent. Our system of appetite control 
 is completely unpicked by the junk food diet." 
 When fast food is eaten often, even small miscalculations of 
 portion size can have major effects, the study found. If a person 
 eats 200g extra of fast food with a density of 1,200kJ per 100g 
 just twice a week, he would consume an extra 250,000kJ a year. 
 This is enough to put on almost 8kg of fat. 
 Fast food outlets should reduce the energy density of their menus 
 as well as their portion sizes, the scientists said.
 (Agencies)