The association between oral fatty acid sensitivity and acute excess energy consumption in healthy weight and obese subjects

This study was designed to assess if there was an association between oral fatty acid (FA) taste sensitivity and perceived satiety following consumption of a high fat meal. Subjects were classified as hypersensitive or hyposensitive by the concentration threshold at which they identified C18:1 as an odd sample of three, using two control solutions. In sessions 1 and 6 subjects were assessed for oral fatty acid taste sensitivity and classified as either hypersensitive or hyposensitive to FA. Oleic acid (C18:1) was used for FA sensitivity tests as it is most commonly used in the food system and liquid at room temperature, therefore practical for usage. Subjects were asked to identify a sample containing C18:1 using triangle methodology. C18:1 was added in varying concentrations (0.02mM-12mM) to long life non-fat milk and each C18:1 sample was presented to subjects with 2 control samples. C18:1 was stored under N2 below 4 degrees Celsius. Viscosity and textural variations between control milk and C18:1 samples were minimised by addition of 5% (w/v) gum acacia and liquid paraffin. To prevent oxidation of C18:1 within samples, 0.01% ETDA was added. Samples were homogenized for approximately 30 sec/100ml at 7000rpm and were prepared fresh on the day of testing. Samples were presented to subjects at room temperature and detection thresholds determined using ascending concentrations of C18:1samples. If correctly identified subjects were presented with another set of samples where C18:1 remained at the same concentration. If incorrect, subjects were presented with three more samples where the C18:1 concentration was increased to the next concentration. This procedure continued until the subject identified the C18:1 sample at the same concentration 3 consecutive times. The concentration at which this occurred was defined as the subject’s oral detection threshold for C18:1. Hypersensitivity was defined by correctly identifying the odd C18:1 sample three times consecutively at less than 3.8mM while hyposensitive subjects required higher concentrations. To prevent confounding from olfactory cues, subjects wore nose clips. To minimize possible visual cues generated by the addition of C18:1, subjects were tested under red light. Subjects were tested in duplicate on both testing days to ensure consistency. During session 1, height and weight were also measured. Prior to any measurements being taken subjects were required to remove shoes, heavy clothing and items from their pockets. Body weight (kg) was measured using scales (accuracy +/- 0.1kg) and height (m) was measured using a stadiometer. Height and weight were used to calculate each subject’s BMI, using the following equation; weight (kg)/height (m^2). Subjects were categorised according to the standard definition values for BMI; healthy 18.5-25 kg/m^2, overweight 25-30 kg/m^2, obese >30 kg/m^2. During the first session subjects were also asked to complete a Deakin University FFQ to indicate their usual pattern of food intake and habitual fat consumption for the month prior to participation in the study. This questionnaire was developed based on the ABS National Health Survey 1995 and consisted of questions such as “What is your average consumption of flavoured milk drinks per month?” Subject's also completed a 4-day diet diary to indicate dietary habits (3 weekday and 1 weekend day). Subjects were asked to record all food and drink consumed within their normal eating pattern. Subjects were asked, if possible to weigh foods or provide measurement details and to specify details of brand, recipes, addition of fat and the method of cooking (E.g. frying or grilling). Diet diaries were analysed using FoodWorks. Mean energy intake (kJ), amount (g) and percentage from dietary fats, protein and carbohydrate was calculated and the type of fat used was also noted. During sessions 2-5 subjects attended the laboratory where they consumed 4 different breakfasts which varied in macronutrient contribution to energy followed by a buffet style lunch. Participants attended these 4 meal sessions over the space of 2 weeks, attending at least one per week. There was no minimum wash-out period required between meal sessions, with participants able to attend a subsequent session the following day. The macronutrient ratios of the breakfast meals were as follows; Breakfast 1: High carbohydrate, 50% carbohydrate, 25% fat, 25% protein, Breakfast 2: High fat, 50% fat, 25% carbohydrate, 25% protein, Breakfast 3: High protein, 50% protein, 25% fat, 25% carbohydrate, Breakfast 4: Balanced macronutrient, 33% carbohydrate, 33% fat, 33% protein. An egg based breakfast frittata was chosen as this was easily manipulated to vary macronutrient ratios. Dietary fibre was balanced across all breakfast meals (g) as this is a known confounding satiety factor.The liquid mass of each breakfast was calculated and to compensate for any mass variation breakfasts were equated with water. Breakfast was served in the laboratory at 9:00am in a social setting. Subjects were required to finish the entire serving and asked to return in the afternoon (12:00pm) to consume a buffet style lunch Lunch was provided in excess (8621kJ) and foods included chips, homemade potato and leek soup, pasta bake, salad with Italian salad dressing, pastries, grapes and chocolate bars. Subjects were asked to eat until comfortably full and the amount eaten was measured by weight (g) using kitchen scales and energy (kJ) as an indication of satiety. No food was consumed between breakfast and lunch (including tea or coffee) to ensure an accurate measure of satiety. Subjects were able to consume water up to an hour prior to lunch. The evening prior to the meal testing day, subjects were instructed to consume only the supplied Lean Cuisine beef lasagna at their usual dinner time as a standardized meal. Subjects were asked not to consume any other foods until attending the sensory laboratory the following day. A satiety questionnaire was filled out immediately prior and after breakfast and immediately prior and after lunch . The satiety questionnaire indicated perceived satiety using 100mm visual analogue scales (VAS) where 0 mm represented “not at all” and 100 mm represented “extremely,” in response to questions such as, “How full are you?” and “How hungry are you?” Liking of the foods presented at the buffet lunch was also assessed with a 9-point hedonic scale, as intake of food items may be driven by liking.