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health measure by which to assess the effects of chocolate consumption, to date the literature is inadequate.

Estimates of the likely genetic component to obesity are in the order of 2040% depending on the type of study (13). Polymorphisms in the leptin gene may be one of the important genetic variables which regulate appetite. Leptin protein levels have been clearly related to the obese state in animals but less clearly so in humans (14). Despite genetic factors, the important principles are that increasing weight (adiposity) results in movement towards the obese state, and that gain in adiposity (fat mass) results from a long-term imbalance between energy intake (energy from food and drink) and energy expenditure (basal metabolic rate + thermic effect of eating + involuntary muscle activity (shivering) + voluntary activity (day-to-day living and specific 'exercise')). A review of the intricacies of food intake, energy balance and body weight control is provided by Doucet and Tremblay (15) (Fig. 11.1).

Weight gain which occurs as a result of prolonged energy imbalance is not all fat tissue: increased lean body mass is required to support the adiposity. Since the basal metabolic rate (BMR) is primarily dependent on body weight, increased weight results in a higher BMR and also a higher energy cost of activity because of the extra weight to move. Thus the total energy intake (TEI) required for weight stability goes up, and selection of energy-dense foods may be required to sustain adiposity. Such selection of energy-dense foods by the obese has been demonstrated (16,

Total energy intake comes from a range of different foods and in a typical Western culture this may be between 15 and 50 different food and drink items per day, with many more being possible. The energy from a food (or drink) is derived from the different macro-nutrient constituents: fat 37 kJ/g (9 kcal/g); carbohydrate (sugars and starch) 16 kJ/ g (3.75 kcal/g); protein 17 kJ/g (4 kcal/g); fibre 6 kJ/g (1.5 kcal/g); alcohol 29 kJ/g (7 kcal/g). As fat (whether saturated, mono- or polyunsaturated) provides over twice the energy of carbohydrate and protein per given amount, foods which are fat rich are more calorific, or energy dense, than low-fat foods. This is the basis of why fatty foods are considered 'fattening'. If a diet is predominantly made up of fat-rich foods, then there is a strong possibility of excess energy consumption (in relation to expenditure) due to its low satiety quotient (18), i.e. fat produces a poor satiety response (1921). This effect has also been called 'passive over-consumption'; however the term 'passive' is not fully appropriate in this context. Fat makes up about 55% of the energy from a chocolate bar, with about 40% from sugar and the remaining 5% from protein.

Fat Intake and Preferences

There is an association between increased fat content of the diet and obesity in adults (22, 23) and children (24). However, all intake data, and especially from

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