Understanding 'protein valuation - the key to reducing meat consumption?

Protein is a critical component of our diet, essential for numerous physiological processes like cell tissue maintenance (Casteneda et al., 1995). As such, protein is central to the debate about meat consumption, and consumers often have concerns about the lack of protein in vegetarian/vegan ('vegan') diets (Reipurth et al., 2019). It is likely these concerns have a biological basis. Evidence for this would support the broader concept that humans possess 'nutritional wisdom': the ability to unconsciously recognise and seek out different foods that together provide optimal nutritional intake. Three groups of protein sources will be compared: meat, meat-alternative products (e.g. the Vegetarian Butcher) and naturally-occurring plant-based sources (e.g. legumes).

Protein valuation
In non-human animals there is strong support for the ability to ensure dietary protein requirements are met. This behaviour is observed in the Chacma baboon (Johnson et al., 2013), spider monkeys (Felton et al., 2009), and even insects such as caterpillars (Dussutour et al., 2007). Many suspect that the same mechanism has been conserved and is expressed in humans. However, this remains to be demonstrated conclusively, and novel methods are needed.

One approach is to feed people a low protein-diet, placing them in a state of protein depletion. However, these studies are expensive, and the results can be difficult to interpret. For instance, Griffieon-Roose et al. (2012) reported that protein depletion caused a preference for savoury foods, but this might just reflect a general tendency to select foods that have been missing from the diet. More recently, Buckley et al. (2019) trialed a new food-choice paradigm, providing stronger evidence for 'protein valuation' in humans. Specifically, they demonstrated preferential selection of foods based on protein content and argued that this reflects a capacity to detect and respond to small differences in protein. Interestingly, they also found participants who showed stronger protein valuation were more likely to have higher fat-free muscle mass later in life.

Critical questions about protein valuation remain unanswered. Does protein valuation exist (do humans unconsciously select foods based on protein content)? Do individuals express different levels of protein valuation and what methods are best suited to detect this hidden human capacity? Theoretically, these questions are novel and exciting, and their resolution has the potential to explain resistance to a vegan diet, further exposing ways to encourage a dietary transition that delivers a healthier and more sustainable future.

Objectives
This project will be the first to systematically expose evidence for protein valuation in humans. Building on this, it will show how this understanding can be used to promote the adoption of sustainable diets.

Section 1: Methods for measuring protein valuation will be developed from online decision-making tasks. Contributions of current diet, different sources of protein, and different amino acid combinations will be examined.

Section 2: The role of protein valuation in dietary transition will be investigated in two ways:

a. A longitudinal study will investigate the temporal dynamics of dietary transition and whether this is predicted by individual differences in valuation.
b. A two-month exposure study will assess whether meat-alternative products can promote changes in protein valuation and improved or earlier dietary transition.