Real means, not BS. Real means intervention studies. Observational studies can be hypothesis generating, but you cannot derive definitive conclusions from them. Only through intervention studies, you can be definitively sure about the causality.
Most observational studies simply report spurious correlations, and cannot be trusted --- especially when "reverse causality" is a strong possibility. That is people who are healthier and fitter tend to exercise more, therefore they experience less disease, death etc.
Only by taking sedentary individuals, and coaching them to exercise significantly more, and comparing with a control group, you can be sure of the causal benefits.
Most observational studies simply report spurious correlations, and cannot be trusted --- especially when "reverse causality" is a strong possibility. That is people who are healthier and fitter tend to exercise more, therefore they experience less disease, death etc.
Only by taking sedentary individuals, and coaching them to exercise significantly more, and comparing with a control group, you can be sure of the causal benefits.