"There are various types of scientific studies on humans that can be used to provide supporting evidence for a particular hypothesis. These include epidemiological studies, interventional clinical trials, and randomized clinical trials. Valuable nutrition knowledge also is obtained from animal studies and cellular and molecular biology research.\n\nEpidemiological studies are observational studies of populations around the world and the impact of nutrition on health. For example, diets with a high consumption of saturated fat are associated with an increased risk of heart attacks. Epidemiological studies do not determine cause-and-effect relationships.\n\nIntervention clinical trials are scientific investigations where a variable is changed between groups. For example, researchers may test the effect of different diets on blood pressure. One group consumes an American diet, group 2 eats a diet rich in fruits and vegetables, and group 3 eats a combination of groups 1 and 2. If done correctly, an intervention clinical trial does determine cause-and-effect relationships.\n\nIn randomized clinical trials, participants are assigned by chance to separate groups that compare different treatments. Neither the researchers nor the participants can choose which group a participant is assigned. For example, researchers may test the effect of calcium supplements on women with osteoporosis by giving participants a pill daily containing either a placebo or calcium supplement. Neither the participant nor the researcher knows what group the participant is in. Randomized clinical trials are considered the “gold” standard for scientific studies.\n\nAnimal and cellular biology studies are conducted on animals or on cells. Examples include testing the effects of a new blood pressure drug on guinea pigs or on the lipid membrane of a cell. These studies are less expensive than human trials, but the study is not on whole humans so it may not be applicable."