Identifying why some people consume excess fat. A twin study.

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Obesity is a major health issue that is currently affecting millions of Australians, in addition to having a high economic cost both in this country and around the world. Some individuals are more susceptible to obesity than others; one factor may be variance in the taste system due to genetic and environmental factors such as diet. The present study aims to identify and investigate the mechanisms linking individual differences in taste with obesity. The mechanisms thought to be in play relate to our sense of taste, including taste receptors and their responsiveness to fatty acids, satiety levels resulting from consuming high fat foods, and food preferences. It is predicted that for susceptible individuals, consuming a high fat diet will negatively influence their responsiveness to fatty acids, increase their preference for high fat foods and decrease their hormonal and perceived satiety levels following food consumption. Each of these mechanisms has the potential to lead to an increase in dietary fat consumption, and BMI. Previous research has indicated that within pairs of BMI discordant monozygotic twins, the twin with the higher BMI has significantly lower taste responses to fatty acids, indicating that their diet may be related to their fatty acid taste sensitivity. This study aims to include 100 twin pairs (half monozygotic and half dizygotic) recruited from the Australian Twin Registry. These participants will be over 18 years of age. Twin pairs will be randomized into one of two weight maintenance diets (high- or low-fat). Participants will consume this allocated diet for eight weeks, with weekly diet diaries being assessed for compliance, in addition to weekly satiety questionnaires. Prior to baseline testing, participants will complete a four-day diet diary, the Cancer Council of Victoria food frequency questionnaire, the restrained eaters questionnaire, and a like-dislike questionnaire. Further testing will occur at baseline, week four and week eight. Each testing session will include a 24-hour dietary recall, taste function assessment, a fat-ranking task using custards, saliva samples, papillae density testing, preference testing for seven regular and low fat foods, anthropometry and a fungiform papillae biopsy. During baseline testing, participants will also be tested for PROP sensitivity, which is a heritable trait. Results will be compared at each time point to determine the effect of a high- or low-fat diet on fatty acid taste responses and satiety.