Term	Definition
Authenticity [71]	Being true to the self in terms of an individual’s thoughts, feelings, and behaviours reflecting their true identity.
Celebrity endorsement [72]	Brands utilising a celebrity/well known persona in their advertising campaigns to materially improve financial returns.
Heroic message appeal [16]	Conveys bravery, nobility, and admiration.
Engagement [11]	Refers to social media activities that including browsing, liking, commenting and sharing content. Also referred to as passive and active social media use.
Herd behaviour [69]	The phenomenon of individuals deciding to follow others and imitating group behaviours rather than deciding independently and atomistically on the basis of their own, private information.
Instagram [73]	A social networking site that involves posting photos with the option of using enhancement filters, and nonreciprocal following of other users.
Nutrition Professionals [74]	An individual who holds a degree in Nutrition, with 3+ years experience working within the field.
Parasocial relationship [75]	A one-sided interaction where the consumer feels as if they know the celebrity well, whilst being completely unknown in return.
Post-truth era [13]	Relating to a situation in which people are more likely to accept an argument based on their emotions and beliefs, rather than one based on facts.
Self-Determination Theory [24] Autonomy Competence Relatedness	A theory of human motivation. Has three components: Autonomy: person’s need to feel that his or her activities are self-chosen, self-governed, and self-endorsed. Competence: A person’s innate, life-span tendency to seek feelings of effectiveness, achievement, and challenge in his or her activities Relatedness: A person’s need to feel a sense of closeness with others. This paper focuses on the perception of others being true to themselves (i.e., authentic).
Social media [18]	Any web-based communication channel, dedicated to community-based input, interaction, content-sharing or collaboration.
Social media influencer [18]	Individuals or groups of individuals who can shape attitudes and behaviours through online channels.
Source credibility [27]	A communicator’s positive characteristics that affect the receiver’s acceptance of a message. Includes the speaker’s attractiveness, trustworthiness, and expertise.