1
Introduction to Whole Grains and Human Health

Jodee Johnson1,2 and Taylor C. Wallace3,4

1 PepsiCo R&D Nutrition, Barrington, Illinois, USA

2 Quaker Oats Center of Excellence

3 Think Healthy Group, Inc.

4 Department of Nutrition and Food Studies, George Mason University, Washington, DC, USA

The existing scientific literature base indicates that the consumption of whole grains has a beneficial effect on maintaining human health over the lifespan. However, to date, most of the supporting evidence on disease prevention has been derived from observational studies. For example, in a 1992 study of 31?208 individuals in the Adventist Health Study cohort, Fraser et al. [1] found that there was a 44% reduction in nonfatal coronary heart disease () and an 11% reduced risk of fatal CHD for participants who consumed 100% whole-wheat bread compared with those who ate white bread. In 1998, the Iowa Women's Health Study investigators also found an almost one-third reduced risk of CHD death among individuals who consumed =1 serving of whole grains each day compared with those who did not consume whole-grain products [2]. In 2005, the US Institute of Medicine () Food and Nutrition Board published dietary reference intakes for dietary fiber, which were largely based on whole grain studies. An adequate intake for total fiber was set at 38 and 25?g/day for young men and women, respectively, based on the intake level observed to protect against CHD [3]. It is important to expand the number of clinical intervention studies that assess the effect(s) of specific whole grains and whole grain products, as variations in their nutritional composition (e.g., dietary fiber, micronutrient and bioactive contents), effects on glycemic load, and health-promoting properties vary.

More recent data build on the existing evidence base and indicate that whole grain consumption is a good indicator of diet quality and nutrient intake [4,5]. Studies show that consumption of whole grains as part of a balanced diet decreases the incidence of CHD and many other chronic diseases (e.g., including, but not limited to, obesity, type 2 diabetes, and certain types of cancers) and promotes gastrointestinal tract regularity and function [6,7]. The potential health-promoting effects of whole grains likely stem from synergies exhibited by the large array of essential nutrients, dietary fibers and bioactives present in the food matrix. The wide range of protective components in whole grains and potential mechanisms for protection have also been described in the scientific literature [ 6, 7].

The 2015-2020 Dietary Guidelines for Americans (s) indicate that the US population's intake of total grains is close to target amounts; however, intakes do not meet recommendations for whole grains and exceed the limits for refined grains [8]. Average intakes of whole grains are far below recommended levels across all age and sex groups. Approximately 60% of whole grain intake in the US is from individual food items, such as breakfast cereals and oats, rather than mixed dishes. The DGAs recommend that consumers shift their diet such that they consume 50% of their grains as whole grains [8]. This recommendation is based on (i) literature demonstrating the contribution of whole grains in helping individuals meet nutrient recommendations and (ii) US Department of Agriculture () Evidence Analysis Library reports (used by the 2010 Dietary Guidelines Advisory Committee to inform the 2010 DGAs [9]) showing effects of whole grain consumption on both cardiovascular disease () and type 2 diabetes. The USDA Evidence Analysis Library reports concluded that (i) there is a moderate body of evidence from large prospective cohort studies showing that whole grain intake is associated with an approximately 21% lower risk of CVD and (ii) limited evidence supports an association between whole grain intake and an approximately 26% lower risk of type 2 diabetes [10].

This chapter seeks to review the basics of whole grains, their bioactives, and related potential health-promoting properties.

1.1 History of Whole Grains

With the advent of agriculture >10?000?years ago, whole grains became a central part of the human diet [11]. The majority of the world's population has relied on whole grains as a major component of the diet for at least the last 4000?years. Refined grains were introduced to society within the last 100?years. Prior to the introduction of technologies used to process refined grains, gristmills were used to grind grains and produce limited amounts of flour. Gristmills were inefficient in completely separating the bran and germ from the white endosperm. In 1873, the roller mill was introduced; its widespread use was applied to satisfy increasing consumer demand for refined grain products. Introduction of the roller mill was a significant factor in the sharp decline in whole grain consumption observed from 1873 through the 1970s [11].

Health benefits of whole grains have been postulated since the fourth century, when Hippocrates coined the famous proverb "Let food be thy medicine and thy medicine be food." In that era, whole cereal grains (particularly barley and wheat) were the principal food throughout the Mediterranean. For thousands of years, humans consumed these foods in whole form (e.g., whole wheat berries), in cracked grains (e.g., bulgur and couscous), and in bread or baked goods. Hippocrates' healing diet consisted of eating whole grain barley, somewhat softly prepared, at every meal every day for a period of approximately 10?days. This practice became a widespread home remedy in early Western medicine.

In the last 200?years, whole grain intake has been traditionally recommended to prevent constipation. The "fiber hypothesis" was first published in 1972, suggesting that large amounts of unrefined plant foods, especially those starchy foods rich in dietary fiber, may offer protection against type 2 diabetes and diseases of the large bowel [12,13]. The inclusion of whole grains as part of a healthful diet has been a component of the DGAs since the first edition published by the USDA and the Department of Health and Human Services in 1980 [14].

1.2 Who Consumes Whole Grains?

Current dietary guidelines encourage consumers to increase intakes of both dietary fiber and whole grains. Since 2000, the DGAs have recommended that individuals consume at least 3?oz-equivalents of whole grain daily and that at least half of all total grains consumed should be whole [8]. Data from the 2009-2010 National Health and Nutrition Examination Survey () show that whole grain intakes are approximately 0.57?oz-equivalents/day for children and 0.82?oz-equivalents/day for adults. Total dietary fiber intakes in the US are directly associated with whole grain intake [15]. Only about one-third of Americans aged >12?years meet the grain intake recommendation, and only 4% meet the current whole grain intake recommendations. Mean intakes of whole grains fall well below (less than one-third) intake recommendations for all age groups. Despite increased public health messaging and the growing number and availability of whole grain-containing products, data show that there have been no significant changes in whole grain intakes for any age group over the last decade [16]. Major sources of whole grains for the US population include ready-to-eat cereals, yeast bread/rolls, hot cereal, and popcorn [ 15, 16]. Whole grain intakes are shown to be highest at breakfast (53%) [ 16,17], which is likely driven by ready-to-eat cereal intake. Intake at breakfast contributes 44%, 39%, and 53% of the total intakes of whole grains for children/adolescents, adults aged 19-50?years, and adults aged >51?years, respectively [17]. More than 19% of whole grain consumption is obtained through snack foods.

1.3 What are Whole Grains?

According to the American Association for Cereal Chemistry International [18], whole grains consist of:

intact, ground, cracked, or flaked fruit of the grain whose principal components, the starchy endosperm, germ, and bran, are present in the same relative proportions as they exist in the intact grain.

Whole grains can be present as a complete food (e.g., oatmeal or brown rice) or used as an ingredient in food (e.g., whole-wheat flour in bread). What constitutes a whole grain food is yet to be defined, which creates unique challenges for manufacturers, researchers, regulatory agencies, and consumers [19]. Foods that are only partially composed of whole grains can be problematic when assessing population intakes, since relative proportions may be proprietary information to the manufacturer. US Food and Drug Administration () regulations state that in order for a manufacturer to use the whole grain health claim on a product label, the food must contain at least 51% whole grain ingredients by weight per reference amount customarily consumed ()....