Background: Nutrition science is currently facing issues regarding the public’s perception of its credibility, with social media (SM) influencers increasingly becoming a key source for nutrition-related information with high engagement rates. Source credibility and, to an extent, authenticity have been widely studied in marketing and communications but have not yet been considered in the context of nutrition or health communication. Thus, an investigation into the factors that impact perceived source and message credibility and authenticity is of interest to inform health communication on SM. Objective: This study aims to explore the factors that impact message and source credibility (which includes trustworthiness and expertise) or authenticity judgments on SM platforms to better inform nutrition science SM communication best practices. Methods: A total of 6 databases across a variety of disciplines were searched in March 2019. The inclusion criteria were experimental studies, studies focusing on microblogs, studies focusing on healthy adult populations, and studies focusing on either source credibility or authenticity. Exclusion criteria were studies involving participants aged under 18 years and clinical populations, gray literature, blogs, WeChat conversations, web-based reviews, non-English papers, and studies not involving participants’ perceptions. Results: Overall, 22 eligible papers were included, giving a total of 25 research studies. Among these studies, Facebook and Twitter were the most common SM platforms investigated. The most effective communication style differed depending on the SM platform. Factors reported to impact credibility included language used online, expertise heuristics, and bandwagon heuristics. No papers were found that assessed authenticity. Conclusions: Credibility and authenticity are important concepts studied extensively in the marketing and communications disciplines; however, further research is required in a health context. Instagram is a less-researched platform in comparison with Facebook and Twitter.

This article introduces the celebrity capital life cycle as a structuring framework for the literature on celebrity endorsement. This framework comprises four stages: acquisition, consolidation, abrupt downfall/slow decline, and redemption/resurgence. The celebrity capital life cycle framework accounts for the ups and downs of celebrities’ career journey through fluctuations in their celebrity capital (i.e., accumulated media visibility; Driessens 2013 Driessens, Olivier (2013), “Celebrity Capital: Redefining Celebrity Using Field Theory,” Theory and Society, 2 (5), 543–60. [Crossref] , [Google Scholar] ). We provide first a brief overview of the literature highlighting relevant research gaps, followed by an exposition of the conceptual underpinnings of the celebrity capital life cycle. We then develop future research directions for each stage of the celebrity capital life cycle that address the existing knowledge gaps.

Communicating evidence-based nutrition messages to the public is challenging and is often in conflict with popular opinions, particularly from social media influencers (SMIs). In order to increase engagement with nutrition professionals (NPs) on social media, we aimed to explore young adults’ perceptions of the authenticity and trustworthiness of SMIs and NPs Instagram posts. A cross-sectional questionnaire was administered to students (n = 149) from an Australian University. Participants viewed a real-life Instagram profile and one post from both a NP and a SMI. Main outcomes were post authenticity and trustworthiness, and emotional message appeals measured on five-point Likert scales. Regression models were developed to assess whose post (the NP or SMI) was perceived to be more authentic and trustworthy. Participants were young adults (median age (25th, 75th percentiles): 20 (19,21)), with approximately half identifying as female. A high heroic message appeal (+1SD above mean) significantly increased the perceived authenticity of the NPs post only (p = 0.01). Post authenticity enhanced post trustworthiness, but only when a heroic message appeal was used by the NP. When appropriate, NPs should convey positive emotions such as bravery and success to enhance the authenticity and trustworthiness of their posts.

This study provides advertisers with a simple positive facial cue—the Duchenne (or genuine) smile—to enhance the authentic persuasive appeal of a celebrity endorser whose standing has slipped. The authors examined the effect of celebrity attitude on consumer perceptions of celebrity genuineness, and in turn, consumer attitude toward the advertisement and purchase intention. They also investigated whether a negative attitude toward a celebrity can be overcome, resulting in positive advertisement attitude and purchase intentions. Results showed that exposure to a celebrity displaying a Duchenne smile significantly boosts consumer perceptions of celebrity genuineness when consumers have a negative attitude toward the celebrity.