Some things simply cannot be researched by traditional empirical means on humans because of ethical concerns; for instance, it would be unethical to feed a test group of children an unhealthy diet just so you could study how their bodies reacted. Consequently, the health sciences use a wide variety of research methodologies that are indirect.
One example would be survey research. This would be done by asking questions of a variety of people about their health and their usual behavior, and then analysing the data for correlations. This type of study is fast and relatively inexpensive to do, but the researcher is relying on the subjects to recall information accurately and report it honestly.
A longitudinal or cohort study follows a group of people through time, and is typically used to evaluate how lifestyle changes or medications effect health conditions. These studies are time consuming and there is always a concern with losing participants over time.
Cross sectional studies sample a large group of people at a specific point in time, without following the group. This can be done rapidly, but is can be difficult to sort out various causes and effects from such studies.
every research in present days are viewing the human body as lump of biological flesh. our health is very much based on the state of mind. 75% of disesage is man made. since the world is profit oriented, the diseases are invented and medicenes are made. every one wants to live long is the fundamental source to researchers to go in commercial basis. the spiritual approach is the best path to maintain healthy planet.