The effect of short term excess dietary fat, carbohydrate or energy on liver fat content in healthy women.

This study seeks to determine whether an excess energy diet with either a moderately high proportion of fat or a moderately high proportion of refined carbohydrate, or an isocaloric diet with either a moderately high proportion of fat or a moderately high proportion of carbohydrate (with an emphasis on refined carbohydrates) increases liver fat content in normal weight individuals with no liver disease. This is a randomised cross-over dietary intervention trial with 2 arms. One arm will consume two different isocaloric diets and the other arm will consume two different hypercaloric diets. Each experimental diet will be consumed for 4 weeks. There will be a 6-week washout period between each of the two diets. All participants will be advised to continue with their usual physical activities. To standardise baseline diet composition, all participants will be complete a 2-week standard diet based on current New Zealand dietary recommendations and results from the 2008/09 Adult Nutrition Survey (Table 1 in the Attachment). In summary the macronutrient ranges will be carbohydrate: 45-60%, protein: 15-25%, fat: 20-35% and this will also be based on the recommended servings of fruit, vegetables, wholegrains, protein foods and healthy fats. A. Pre-intervention standardised diet Participants will be asked to complete a 3-day weighed food record. The study dietitian (KS) will instruct participants how to correctly complete the 3-day weighed food record. The record of each participant will be analysed by the study dietitian (KS) using Kai-culator, a computer program developed by the Department of Human Nutrition, University of Otago, which allows New Zealand specific dietary analysis. If necessary, adjustments will be made to each study participant’s diet so their diet macronutrient composition is consistent with current NZ dietary recommendations (see Table 1 in the Attachment). The total daily calorie intake will remain the same. They will consume the standardised pre-intervention diet for 2 weeks. B. Experimental diets The macronutrient composition of each experimental diet was determined to be at the upper levels of intakes achievable by people in the longer term in everyday life (Table 2 in the Attachment). Diets will be prescribed by the study dietitian (KS) and recommended foods will be those currently found in a typical NZ diet and that are readily accessible. Each participant will be instructed at the beginning of each new diet on the types of foods to consume to achieve the macronutrient distribution in the experimental diets. Changing the macronutrient proportions within each of these diets will be done by either adding extra portions or increasing the portion size of fat or carbohydrate foods. If this is within an isocaloric diet context the opposite macronutrient will be decreased to keep energy balanced. These changes will be personalised to the participant to fit within current dietary patterns and preferences. Weekly 30 minute visits to the study dietitian (KS) will be scheduled during the 4-week experimental diet period to enhance compliance with the experimental diet. The study dietitian (KS) will also be readily contactable (via email, phone or txt) to answer any dietary questions and to provide further guidance as necessary. Other additional strategies that will be used to monitor dietary adherence will include 3-day weighed food records during each dietary phase and weekly monitoring of body weight. For those in the hypercaloric diet arm, the dietitian will provide weight loss guidance atthe conclusion of the experimental diets until the participant returns to her usual pre-study weight. Isocaloric (IC) Diets Participants in the first arm of the study will consume two different isocaloric diets. Each of the two diets will be consumed for four weeks. The calorie intake of each individual will be calculated to maintain their current bodyweight and will take into account results from their 3-day weighed food record. One isocaloric diet will have a relatively high percentage of energy (55-60%) from carbohydrate with most from refined carbohydrate sources (IC-HC). After a six week washout period participants will then consume an isocaloric diet with a moderately high proportion of energy (35-40%) from fat (IC-HF). For both isocaloric diets, the ratio of total fat to unsaturated fat will be 2.5:1, with the percentage of energy sourced from unsaturated fat being 10% for the relatively high carbohydrate diet and 15% for the moderately high fat diet. Hypercaloric (HC) Diets Participants in the second arm of the study will consume two different hypercaloric diets. The calorie intake of each individual will be calculated to be proportionally higher in energy to induce a 3-5% weight gain during each of the four week hypercaloric diet periods, This equates to an approximately 25-35% increase in energy based on each participants' 3-day weighed food record. One hypercaloric diet will have a relatively high percentage of energy (55-60%) from carbohydrate with most from refined carbohydrate sources (HC-HC). After a six week washout period, participants will then consume a hypercaloric diet with a moderately high proportion of energy (35-40%) from fat (HC-HF). For both hypercaloric diets, the ratio of total fat to unsaturated fat will be 2.5:1, with the percentage of energy sourced from unsaturated fat being 10% for the relatively high carbohydrate diet and 15% for the moderately high fat diet.