John designs an experiment to determine the role of the

John designs an experiment to determine the role of the consumption of unsaturated fats in the development of cardiac illnesses. He conducts the experiment on a group of individuals whose daily meals include large quantities of saturated fats. At the beginning of the study, the participants are all checked for any preexisting health conditions. When it is established that the group is disease-free, John starts recording the changes that occur in each of their cardiac systems with the consumption of those fats. Which type of study is John using for his research? Group of answer choices a retrospective study a cross-sectional study a prospective study a longitudinal study

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