he old obesity paradigm suggests that a positive energy balance causes accumulation of energy which is subsequently stored as fat in adipose tissue. However, recent evidence suggests that the situation is far more complex than this. It is considered that the current obesity epidemic is caused by a number of behavioural and physiological factors that reflect change to the diet and lifestyle that have occurred in the last 100 years. Many of these changes are complex and not fully understood. In addition, recent evidence suggests that fat distribution and storage are far more complex than was previously considered, with compartmentalisation of energy to upper and lower body subcutaneous and abdominal adipocytes being regulated by unknown mechanisms. The growth and depletion of subcutaneous and abdominal (visceral) fat cells may differ between upper and lower body sites suggesting that they serve different functions.
Researchers have attempted to understand how adipose tissue prioritises regional gains and losses in fat stores by investigated weight gain and loss in healthy individuals. For example, in one study1, participants with a mean body mass index of 23.6 kg/m2 were deliberately overfed for 8 weeks to cause the accumulation of body fat. The subjects then followed a reduced calorie diet that caused a reduction in weight loss. The subjects gained 3.7 kg of body weight but only lost 2.8 kg probably due to their high sugar overfeeding. While both the upper subcutaneous and abdominal fat stores returned to their baseline sizes with dietary changes, the lower subcutaneous fat stores remained elevated, explaining the gain in body fat. The sizes of the abdominal and subcutaneous fat cells shrank, but their numbers remained constant, whereas the upper subcutaneous fat stores shrank in both number and size.
One of the interesting findings of this study was the assumption that the weight gain was caused by the extra calories provided to the subjects. Consumption of a baseline diet containing 40 % fat, 40 % carbohydrate and 20 % protein was changed during the weight gain period to include more energy. However, the foods that were used to cause the 5 % increase in weight were ice cream, chocolate bars and energy drinks, all rich sources of sucrose (table sugar). That the authors chose to use these foods, rather than simple increase the energy intake from the normal diet of the subjects suggests that the latter strategy would not have caused a 5 % increase in weight. In order to lose the weight gained the researchers had to remove the foods that contained the sucrose. This adds further evidence that the cause of weight gain is eating fructose containing sucrose, and not overconsumption of calories.
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