Routes to obesity: phenotypes, food choices and activity

Gain in body weight over a number of years could be achieved through cumula tive positive energy balances. These positive balances could come about thr ough adjustments in the various components of energy expenditure or fuel ut ilization, together with shifts in food selection or eating patterns leadin g to adjustments in macronutrient intake. This means that many combinations of intake and expenditure could lead to a positive energy balance; these c ombinations can be called routes to body weight gain. However, these routes are difficult to trace by studying random samples of individuals. Previous investigations have found a clear association between high fat consumption and the occurrence of obesity, and although a high fat intake is a strong behavioural risk factor for weight gain, the relationship does not constitu te a biological inevitability. Some normal-weight and lean individuals appe ar to eat a high-fat diet. To investigate reasons for this we have studied individuals initially defined by particular clusters of dietary characteris tics related to fat and carbohydrate consumption. Habitual high-fat (HF) an d low-fat (LF) consumers have been termed phenotypes. Various aspects of en ergy expenditure (physiological and behavioural) and energy intake were mea sured in these individuals with contrasting profiles. HF phenotypes had hig h intakes of fatty foods and an overall higher energy intake than LF. Howev er, these groups of young adult males had similar BMIs and percentage body fat. The HF had a significantly higher resting metabolic rate (RMR) and a l ower RQ, together with high plasma fasting leptin levels, and a higher slee ping heart rate. In HF individuals the physical activity level was somewhat lower and they had significantly more periods of sedentary behaviour than LF subjects. Although HF individuals appear to be more vulnerable to develo ping obesity, both phenotypes carry particular risk factors and protective factors for weight gain. The use of phenotypes has allowed the identificati on of different potential routes to weight gain. Different strategies are r equired to prevent age-related increase in body weight in these quite diffe rent individuals.