Whole-grain foods have been touted as a key component of healthy eating. They are found in many foods, including dark bread, whole-grain breakfast cereals, popcorn, oatmeal, and brown rice. Whole grains contain endosperm, germ, and bran. Refined grains, in contrast, lose the germ and bran during the milling process, and therefore only contain the endosperm. As a result, compared with refined grains, whole grains contain higher amounts of dietary fiber, magnesium, phytochemicals, and other nutrients.
Published in the November 2016 issue of Advances in Nutrition, "Whole-Grain Intake and Mortality from All Causes, Cardiovascular Disease, and Cancer: A Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies," evaluates the current body of research to determine what conclusions, if any, could be made about the relationship between whole-grain consumption and mortality. The authors of this review evaluated the methodology and results of 20 prospective cohort studies that examined the relationship between whole-grain intake and risk of mortality from all causes, cardiovascular disease, and cancer. These cohort studies varied in duration from 5-1/2 years to 26 years, allowing reasonable time to assess the effects of whole-grain intake compared to processed grains.
One difficulty that the authors had was the lack of a standard definition of what was or was not a whole-grain food. Some studies defined a whole-grain food by the ratio of whole grains to processed grains, whereas others avoided the need to define what was a whole-grain food by simply measuring total whole-grain intake. In addition, some studies looked at one specific whole-grain food, making it difficult to determine whether the noted effect was a result of the particular whole-grain food or whole grains in general. The authors believe that "applying a unified definition and serving size for whole-grain intake in future studies might be helpful in comparing their findings."
Despite the difficulties in comparing study results and reaching generalized conclusions, the authors believe that there is strong evidence pointing to a relationship between a greater intake of whole grains to a lower risk of all-cause mortality as well as cardiovascular disease and cancer. For example, an increase of three servings of whole grains per day was associated with a 17% lower risk of mortality from all causes, 25% lower risk of mortality from cardiovascular disease, and 10% lower risk of total-cancer mortality.
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