The most obvious difficulty with the notion that a retarded metabolism ... is that it never had any evidence to support it. ... Magnus-Levy had reported that the metabolism of fat patients seemed to run as fast if not faster than anyone else's. .... The obese tend to expend more energy than lean people of comparable height, sex, and bone structure, which means their metabolism is typically burning off more calories rather than less. When people grow fat, their lean body mass also increases. They put on muscle and connective tissue and fat, and these will increase total metabolism...
For example, from Fitday, I, at 5'4" and 8 stone 3lbs, with a sedentary type of job require 2050 calories per day, whereas if I was 12 stone, I would need 2432 calories. As predicted, the metabolic rate for the subject of this segment came up perfectly normal.
the term doubly-labeled water test refers to a particular type of test of metabolic rate, in which average metabolic rate of an organism is measured over a period of time.and:
Energy expenditure measurements are easier to perform since the development and application of the doubly-labelled water technique.*
The carbohydrate hypothesis of obesity basically says that carbohydrate intake promotes insulin release which promotes fat storage and the conversion of excess glucose (all starch breaks down into glucose) into fat for storage. So a person who eats a 'healthy diet' that would be 50-60% 'healthy' carbohydrates - 6-11 servings a day of cereals anyone? plus lots of fruit but is quite sensitive to this effect of insulin would convert all the excess to fat and store it. If they are unlucky their insulin stays relatively high preventing their body accessing this stored fat. Now they are 'growing' (but outwards) and as long as enough carbohydrates are consumed to keep insulin 'too high' for fat burning, their appetite tells them they need to eat more and so on it goes.
And that is why all nutritionists and dieticians and doctors should read Gary Taubes' book Good Calories, Bad Calories - published as The Diet Delusion in many countries.
*from Invited Commentary, Energy requirements assessed using the doubly-labelled water method, Klaas R. Westerterp, British Journal of Nutrition (1998), 80, 217–218. Available here.