Question

The role of diet in promoting or preventing disease is a focus of nutritional epidemiology. In recent years, the field has embraced the idea that dietary patterns, as opposed to a single food or nutrient, are likely to have a bigger impact on health and disease prevention. The Mediterranean diet is characterized by the traditional food patterns of Mediterranean countries. The Mediterranean diet has consistently been shown to reduce the risk of all-cause mortality, cardiovascular disease mortality, and cancer mortality in several large prospective cohort studies.

Suppose that we work for the American Cancer Society, which would like to update its "Guidelines on Nutrition and Physical Activity for Cancer Prevention." Guidelines are based on current evidence, and their purpose is to provide recommendations for the general public.

We are tasked with critically evaluating one recent study that examined the association between Mediterranean diet and risk of ovarian cancer in the Nurses’ Health Study, a prospective cohort study with 121,700 female nurses (Xie et al, Journal of Ovarian Research (2014) 7:112).

In this study, dietary information was measured prospectively every 2 to 4 years by a self-administered semi-quantitative, 131-item food frequency questionnaire. For each food, a portion size was given, and women were asked to choose from 9 intake frequencies from never to >=6 servings per day averaging over the prior year’s intake. A Mediterranean Diet Score was calculated that considered consumption of certain fatty acids, legumes, cereals, fruits, nuts, vegetables, meat, dairy, and alcohol and ranged from 0 to 10.

The following excerpts are taken from the paper.

If the correlation between the food frequency questionnaire and food diaries is poor, is it more likely or less likely that this type of bias is present?

Answer 1

The Mediterranean diet's emphasis on fruits, vegetables, and olive oil and its limited amounts of meats and saturated fats has been linked to a reduced risk of cardiovascular diseases and potentially a lower risk of ovarian cancer. Its benefits are representative of the importance of dietary patterns in health and disease prevention. However, studying its effect requires accurate dietary assessment to avoid bias in research findings.

Step-by-step explanation:

The role of diet in disease prevention has become increasingly evident, and nowhere is this more apparent than in the case of the Mediterranean diet. First brought to attention by U.S. physiologist Ancel Keys, this diet emphasizes the consumption of fruits, vegetables, olive oil, and fish, while limiting the intake of meats and saturated fats. Studies, including a 12-year study of 26,000 women, have shown a significant reduction in the risk of cardiovascular disease for those adhering to the Mediterranean diet.

In the context of cancer prevention, a recent study from the Journal of Ovarian Research focused on the relationship between the Mediterranean diet and the risk of ovarian cancer within a large cohort of nurses. Prospective dietary data was collected using a self-administered food frequency questionnaire, which allowed researchers to assign a Mediterranean Diet Score to participants. If the correlation between this questionnaire and actual food diaries is weak, it could introduce bias in the study outcomes, questioning the validity of the findings.

Nutritional choices play a critical role in overall health, contributing to the prevention of diseases such as atherosclerosis, heart disease, stroke, cancer, obesity, and diabetes. It is not only the single nutrients but the overall dietary patterns, exemplified by the Mediterranean diet, that are important for maintaining health and preventing disease. Such diet patterns are based on whole foods and are low in saturated fat, sodium, and sugar, which align with the recommendations for dietary choices fostering health and well-being.