Whole Grains Perspective: Porridge or popcorn

Terms such as "whole grains", "fiber" and "ultraprocessed food" are too broadly defined to guide specific disease prevention strategies. More precise classification may be important for meaningful application in disease prevention. We wish to discuss three underexplored issues regarding whole grain consumption and non-communicable disease (NCD) prevention: 1) which foods are broadly recognized as "whole grains"; 2) whether the apparent health benefits of whole grains reflect food choice itself or broader lifestyle choices of those who consume them and 3) whether specific types of whole grains confer distinct physiologic benefits. Of 12 major prospective cohorts (>100,000 participants), 10 assessed whole grains intakes, but only 3 whole grain foods (popcorn, oatmeal and brown rice) were common to 7 of these cohorts, and 17 of 54 whole grain foods were listed by a single cohort only. This inconsistency highlights the need for standardized classification. Furthermore, some health benefits attributed to whole grains consumption may be partly explained by lifestyle characteristics of those who consume them. For example, whole grain consumers tend to smoke less, exercise more, and have higher levels of education, all of which independently reduce NCD risk. Finally, not all "whole grains" are equivalent, and the degree of processing matters. Intact whole barley, as consumed in barley stew, produces a lower postprandial glucose response (or glycemic index) than milled barley flour used in breads. Whole grains encompass a range of carbohydrate foods whose effects on NCD outcomes vary depending on whole grain type and processing. The physiological effects of different whole grain foods require exploration to promote more meaningful use for public health and clinical application. In cohort studies, despite covariate adjustment, some observed benefits may be due to the other lifestyle habits of those who select to be "whole grain" consumers.