High-fat and low-fat (behavioural) phenotypes: biology or environment?

It is now widely accepted that obesity develops by way of genetic mechanism s conferring specific dispositions which interact with strong environmental pressures. It is also accepted that certain dispositions constitute metabo lic risk factors for weight gain. It is less well accepted that certain pat terns of behaviour (arising from biological demands or environmental influe nces) put individuals at risk of developing a positive energy balance and w eight gain (behavioural risk factors). Relevant patterns of behaviour inclu de long-lasting habits for selecting and eating particular types of foods. Such habits define two distinct groups characterized as high-fat (HF) and l ow-fat (LF) phenotypes. These habits are important because of the attention given to dietary macronutrients in body-weight gain and the worldwide epid emic of obesity. Considerable evidence indicates that the total amount of d ietary fat consumed remains the most potent food-related risk factor for we ight gain. However, although habitual intake of a high-fat diet is a behavi oural risk factor for obesity, it does not constitute a biological inevitab ility. A habitual low-fat diet does seem to protect against the development of obesity, but a high-fat diet does not guarantee that an individual will be obese. Although obesity is much more prevalent among KF than LF, some H F are lean with BMI well within the normal range. The concept of 'different routes to obesity' through a variety of nutritional scenarios can be envis aged, with predisposed individuals varying in their susceptibility to diffe rent dietary inputs. In a particular subgroup of individuals (young adult m ales) HF and LF displayed quite different profiles of appetite control, res ponse to nutrient challenges and physiological measures, including BMR, RQ, heart rate, plasma leptin levels and thermogenic responses to fat and carb ohydrate meals. These striking differences suggest that HF and LF can be us ed as a conceptual tool to investigate the relationship between biology and the environment (diet) in the control of body weight.