The lack of consistency among designs of clinical nutrition studies seeking to answer the same scientific question (for example, the influence of dietary fiber on serum cholesterol levels) means that their results cannot be readily compared. Some study designs are flawed, lacking adequate hypotheses and control groups. In addition, compliance in dietary studies is frequently less than ideal. Studies that allow participants to select and prepare their own food, even when adhering to an 'experimental' diet, frequently do not provide reliable results. Only in tightly controlled clinical settings, in which the participants receive all food from the experimental kitchen and are known to consume it, can the influence of poor compliance be minimized.