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)