2.1. Diet Intervention Study Design
DISEASES
The study was designed as a randomized, parallel-group, whole-diet controlled trial involving a 6-week dietary intervention and a 4-week tracking period (Korean adults aged over 18 without underlying diseases were recruited at SNU, and screening tests (at week 0) were conducted five weeks before the start of the intervention (at week 1). SCL, body mass index (BMI), and waist circumference were measured to analyze their initial status in week 0 and week 1. The participants were informed that they could withdraw from the study at any time if they were willing to stop participating, developed symptoms related to COVID-19, or came into contact with an infected individual. After screening based on eligible criteria (During the 6-week intervention period, the HG was provided with a high-carotenoid diet (including average total carotenoids contents: 21.0 mg/2000 kcal per day), while the CG was provided with a control diet (including average total carotenoids contents: 13.6 mg/2000 kcal per day). The experimental diet amount was provided in proportion to the design content according to the calories closest to the estimated energy requirements of each participant. In compliance with the Helsinki Declaration guidelines, the level of carotenoids in all diets was designed not to exceed the upper limit of vitamin A intake in consideration of the conversion of carotenoids to vitamin A, and the lowest level was above the estimated average requirement of Dietary Reference Intakes for Koreans (KDRI) [After the 6-week diet intervention period, the participants were instructed to maintain their typical lifestyle habits and diet to detect changes during the 4-week tracking period. Restricting the carotenoid intake during the follow-up period could negatively affect health in research ethics; hence, rather than limiting the carotenoid intake during the follow-up period, they were instructed to return to a routine diet to ensure that it could return to the baseline level after a controlled diet. The details of the eligibility criteria and experimental diets are described in the 