Dietary guidelines for Americans and cancer occurrence - Diet and Cancer

Nutrition Research Newsletter, Nov, 2002 by L Harnack, K Nicodemus, D Jacobs, A Folsom

Since 1980, the US Department of Agriculture (USDA) and the Department of Health and Human Services have jointly published the Dietary Guidelines for Americans. The Dietary Guidelines, which provide advice for healthy Americans aged 2 years or more about food choices that promote health and prevent disease, serve as the basis for federal nutrition policy and nutrition education activities. To ensure that the Dietary Guidelines remain current, every five years the two agencies appoint a Dietary Guidelines Advisory Committee of experts in nutrition and health to review scientific and medical knowledge and recommend changes to the Dietary Guidelines. There is limited empirical epidemiologic data to verify that adherence to the cluster of nutrition-related behaviors recommended in the Dietary Guidelines will reduce the incidence of disease. The aim of the current study was to examine the association of compliance with the Dietary Guidelines and incident cancers. The researchers evaluated data from the Iowa Women's Health Study (IWHS), a population-based cohort of postmenopausal women in whom diet was measured before the diagnosis of cancer.

A total of 41,836 women completed a questionnaire in January 1986 and were followed for cancer incidence and mortality. The questionnaire included questions regarding diet, smoking, physical activity, anthropometrics, personal history of cancer, among other items. The average age of respondents was 61.7 years; 99% of respondents were white. Information on cancer diagnosis was ascertained through the State Health Registry of Iowa, which is part of the National Cancer Institute's Surveillance, Epidemiology, and End Results Program. Response rates for the follow-up questionnaires were 91%, 89%, 83%, and 79%, respectively. Through 31 December 1998, after 13 years of follow-up, 5038 cancers, excluding nonmelanotic skin cancer, were recorded. Subjects with a higher dietary guidelines index score were more likely never to have smoked and to report having used hormone replacement therapy compared with those with a lower index score. In addition, those with a higher index score were somewhat older and had a lower energy intake, compared with those with a lower score. As expected, subjects with a higher index score had lower intakes of sweets, total fat, saturated fat, cholesterol, and sodium than did subjects with a lower index score. Similar patterns in relative risks were found for several cancers at specific sites. Incidence of colon cancer decreased progressively with increasing scores on the dietary guidelines index. The incidence of colon cancer in those in the top quintile of the dietary guidelines index was 74% of the incidence of those in the lower quintile. Progressive decreases in relative risks across quintiles of the dietary guidelines index were also seen for incident cancers of the bronchus and lung, breast, and uterus. Relative risk suggested an inverse (non-significant) association between the dietary guidelines index and incident upper digestive tract, rectal, hematopoietic, and lymphatic cancers. In contrast, the incidence of ovarian cancer was positively associated with the dietary guidelines index. This appears to be attributable to the physical activity component of the index. In a previous analysis of data from IWHS, the incidence of ovarian cancer was found to be higher among women in the cohort with moderate and higher than with low levels of physical activity.

In conclusion, findings from the IWHS suggest that greater adherence to the cluster of nutrition-related behaviors recommended by the Dietary Guidelines for Americans may be associated with a lower risk of cancer. Specifically, risk in postmenopausal women may be reduced for cancers of the colon, bronchus and lung, breast and uterus. Better compliance with the Dietary Guidelines was associated with an increased risk of ovarian cancer, but fortunately its incidence is a small proportion of total cancer.

L Harnack, K Nicodemus, D Jacobs, A Folsom. An evaluation of the Dietary Guidelines for Americans in relation to cancer occurrence. Am J Clin Nutr 76(4):889-896 (October 2002) [Correspondence: L Harnack, Division of Epidemiology, 1300 South 2nd Street, Suite 300, Minneapolis, MN 55454-1015. E-mail: harnack@epi.umn.edu]