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The two other types of research are defined as either observational (where no particular change is made to a person’s lifestyle) or interventional (where those being studied are asked to follow a new diet plan). Observational studies allow us to evaluate what issues might exist that best promote health while interventional research studies which changes work best.


 

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Each new research study is a guide



Most studies of diet are conducted in one of two ways. The first type of study is a "prospective" look at the effect of diet, where those in study are asked to follow a particular menu plan designed by researchers. The drawback is that these are very expensive studies and often utilize smaller study groups.

The other is a study where participants are asked to recall what they have eaten in the past. This "retrospective" look at diet has its advantage in that it is easier to involve a large group of participants. The down side is that people don't always remember well what they have consumed. While there is a known margin for error, most of these studies are able to address how individuals eat over a long period of time more economically.

Flora Lubin and her colleagues have been looking at dietary studies from a different viewpoint. They created a dietary recall method that looks at the change in a person's diet over time. Their food frequency questionnaire provides a structure for looking at the consumption of over 180 food items at 1, 2, 5, 7 and 20 years prior to the interview. Such a technique allows for evaluation of alteration in intake over time and the reason for changes.

In a study reported recently, this technique was applied to evaluate whether a change in diet had any impact on a woman's risk for ovarian cancer (J Nutr 2006;136(9):2362-2367). The researchers studied 631 women with a diagnosis of ovarian cancer and matched them with 2 healthy controls. The researchers found that substituting animal fat with non-animal fat was associated with a reduction in risk of ovarian cancer. It may be that the same effect can be achieved by replacing animal fat with either carbohydrate or animal protein.

Such retrospective studies are not conclusive. The key is the word "association," meaning that there might be a link between decreasing intake of animal fats and the decreased incidence of ovarian cancer. While this study has a large group of participants, research such as this is evidence to argue for a prospective study of women and the effect of change in diet on ovarian or other cancers.

What this means for you:

Few research studies are conclusive and the first question you should ask is whether the study reported on the nightly news is prospective or retrospective. Such a retrospective study as this (with its excellent design to evaluate change in diet) indicates an association with less ovarian cancer in women who changed their diets to consume less animal fat. Confirmation of this association can only come with a prospective study.

First posted: August 23, 2006