C Randomized Clinical Trial
Two study arms are present. In the first one, only the conventional therapy is present. In the second, diet and exercise are added to conventional therapy. This is, therefore, an experimental study. The patients are assigned to only one of the two study arms. Due to the nature of the intervention (diet plus exercise), patients are unblinded to their study group. This is a Randomized Clinical Trial.
In a cross-over study, patients are assigned to one of the study arms for a period of time and then assigned to the other study arm for the same length of time.
The other study designs mentioned are all observational studies. In case-control studies, people with and without a specific outcome are chosen. Then, looking backward in time, one tries to detect possible causes or risk factors. In cross sectional studies, data is collected at one time. Large governments surveys are good examples of cross sectional studies. In a cohort study, people are selected and followed over a period of time. At the beginning of the study, people are defined as being exposed or not exposed to certain risk factors. They are observed over time for the development of outcome. The outcome is then compared to exposure to risk factors.