Are all calories the same? Individual differences in the valuation of protein, carbohydrate and fat

  • Sophie Austin

Student thesis: Master's ThesisMaster of Science by Research (MScR)


Humans have the ability to identify the macronutrient composition of foods using sensory signals and learned, postingestive feedback. This enables humans to regulate their macronutrient intake and based on physiological needs, protein, carbohydrate and fat are prioritised. The amount of energy metabolised from each macronutrient is different and protein, carbohydrate and fat vary in their utilisation and absorption. However, it is unclear whether protein, carbohydrate and fat are valued equally and whether individual differences influence macronutrient valuations.
The first studies in this thesis developed a novel binary forced-choice task to measure the relative value that individuals place on protein, carbohydrate and fat, calorie for calorie. The binary forced-choice task was an effective measure of macronutrient valuations and there was excellent test-retest reliability. Protein, carbohydrate and fat were not valued equally and there was considerable variation in value across individuals. An additional food category was then added to investigate whether individual’s macronutrient valuations are similar for foods consumed at breakfast time and lunchtime. Macronutrient valuations were not consistent across the two meal times suggesting that protein, carbohydrate and fat are valued differently during the day. However, there were concerns with the familiarity of the breakfast food stimuli in this study. The final study investigated whether perceived social status influences the amount of value an individual places on a calorie of protein, carbohydrate and fat. People with lower perceived social status valued protein, carbohydrate and fat to a great extent than people with higher perceived social status.
The experiments in this thesis provide a novel perspective on the ability to identify the macronutrient composition of foods and introduce the idea of macronutrient valuation. Together, the results provide evidence that macronutrients are not valued equally and that the value placed on protein, carbohydrate and fat is moderated by individual differences.
Date of Award23 Jan 2019
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorJeff Brunstrom (Supervisor)

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