There is limited research to inform policies and guidelines related to disclosing conflicts of interest on social media by healthcare professionals, including Registered Dietitians (RDs). This trial investigates mock social media posts by an RD to examine the impact of varying forms of conflict-of-interest (COI) disclosures. The disclosures tested are based on the Canadian Ad Standards "Influencer Marketing Disclosure Guidelines" and are incorporated into recommendations established by the provincial dietetic regulatory bodies for RDs. Specific outcomes evaluated include the public's ability to identify a COI; trust in the RD; credibility of the RD; transparency of the social media post and; purchasing and consumption intentions of the product endorsed by an RD in the post.

This study is a randomized controlled experiment embedded within an online cross-sectional survey entitled the Canadian Nutrition and Health Survey (CNHS). A sample of 3,380 Canadian adults from all Canadian provinces (ages ≥18 years, who own a computer, and have an email address) will be recruited by Leger Marketing Inc. as part of the CNHS. Participants will be randomized to one of five experimental groups that include a mock social media post with different variations of COI reporting, based on the Ad Standards (of Canada) Influencer Marketing Disclosure Guidelines. Each participant will be randomized to view one version (group) of the mock Instagram post, all of which feature the same RD promoting the nutritional benefits of a mock soy milk product. Participants will also have the opportunity to view the RD's Instagram account profile, which is consistent across all experimental groups. All participants will have as much time as needed to view the post and account profile.

As stated previously, the experimental groups vary by the extent to which the conflict of interest is reported (see below):

• Group 1 Not an ad disclosure: COI disclosure includes @brandname and #NotAnAd in the narrative body of the social media post.
• Group 2 Basic Disclosure: COI disclosure includes @brandname and #ad in the narrative body of the social media post.
• Group 3 Basic + Paid Partnership Disclosure: COI disclosure accompanied by a branded "paid partnership" in the header and a tag for the industry partner, @brandname and #ad immediately at the beginning of the post, and #ad and #sponsored at the bottom of the narrative body of the social media post.
• Group 4 Basic + Paid Partnership + Image label: COI disclosure includes the same characteristics as Group 3, with the addition of #ad appearing on the post image itself.
• Group 5 Control group: is a control with no COI disclosure elements (i.e. no hashtags and only the @brandname included within the narrative body of the social media post).

The primary outcome is the ability of a participant to identify if COI disclosures exist within the social media post. The secondary outcomes include participants' trust in the RD in the social media post, credibility of the RD in the social media post, participants' buying and consumption intentions, and transparency of COI reporting by the RD. Tertiary outcomes include the participants' recommendation of the food item endorsed by the RD to others, participants' engagement with the social media post, and participants' view of the healthfulness of a product endorsed by the RD.

It is hypothesized that, compared to the control condition, participants will rate all experimental conditions as having a conflict of interest. The experimental conditions will be rated more transparent and trustworthy, with the RD in the social media post being rated as more credible, and with greater purchasing/consumption intentions.

Inclusion Criteria:

Participants are included if:

• are ≥18 years
• own a computer,
• have an email address
• speak/write in English/French