K. M. Behall and Judith Hallfrisch, Beltsville Human Nutrition Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland, U.S.A.
OATS: Chemistry and Technology, Second Edition
Pages 255-273
DOI: https://doi.org/10.1094/9781891127649.012
ISBN: 978-1-891127-64-9
Abstract
Cardiovascular disease continues to be the number one cause of death in the United States despite numerous plans to reduce its prevalence. Interest has increased in the use of diet and lifestyle rather than drugs for the prevention and management of hypertension and cardiovascular disease. Several epidemiological or observational studies have reported that diets rich in whole grains may protect against hypertension (Ascherio et al 1992, He and Whelton 1999, Pins et al 2002), cardiovascular disease (Jacobs et al 1998, 1999; Liu et al 1999; Truswell 2002), and type 2 diabetes (Salmerón et al 1997a,b; Liu et al 2000; Meyer et al 2000; Fung et al 2002). Little or no protective association between refined grain intake and the risk of heart disease (Jacobs et al 1998) or type 2 diabetes has been reported (Liu et al 2000, Meyer et al 2000). Some research has suggested a role for dietary fiber in the management of obesity (Ludwig et al 1999, Anderson 2003).
Numerous studies have shown that grains containing a high amount of soluble fiber, such as oats, are more effective in lowering blood cholesterol in animals (Ranhotra et al 1991, Newman et al 1992, Brown et al 1999, Önning et al 1999, Wood 2001) and humans (Jenkins et al 1978, Newman et al 1989, McIntosh et al 1993, Behall et al 1997, Jang et al 2001, Jenkins et al 2002a) than grains containing predominantly insoluble fibers, such as wheat or rice (Dubois et al 1995, Önning et al 1999, Jenkins et al 2002a). Clinical studies evaluating the effects of cereal soluble fibers on blood lipids have used primarily oats, although barley is also a good soluble fiber source (McIntosh et al 1991).
On the basis of observational and clinical intervention studies suggesting that oats are effective in lowering blood cholesterol levels, the U.S. Food and Drug Administration (FDA) (1997) has allowed a health claim for oats and soluble fibers from oats. The recommended effective level of consumption is a minimum of at least 0.75 g of the soluble fiber β-glucan per serving and a daily intake of at least 3 g (four servings). A diet low in saturated fat and cholesterol in conjunction with the soluble fiber intake was specified.
Oats, barley, and their soluble fiber extracts also have been reported to have beneficial effects on glucose tolerance, especially with regard to the magnitude of the postprandial glucose and insulin responses (Braaten et al 1991, Würsch and Pi-Sunyer 1997, Hallfrisch and Behall 2000, Wood 2001, Willett et al 2002). Specific health benefits include improving glycemic control in diabetic subjects (Fontvieille et al 1992, Wolever et al 1992) and potentially decreasing the risk for development of diabetes (Salmerón et al 1997a,b). Insulin resistance has been reported to be a major factor in the development of type 2 diabetes mellitus and, for many people, is the first observed abnormality in the progression of the disease (Daly et al 1997). It is associated with obesity, hypertension, ischemic heart disease, and diabetes mellitus both independently and as part of the metabolic syndrome, a cluster of factors that includes hypertension, abdominal obesity, elevated plasma glucose and/or insulin, insulin resistance, and dyslipidemia (Daly et al 1997, Hauner 2002, Bray and Champagne 2004, Steinbaum 2004). The incidence of metabolic syndrome is increasing with the rise in obesity in the United States (Steinbaum 2004, St-Ongle et al 2004). Obesity, observed in more than 30% of the U.S. population, has been reported to be the most common condition associated with insulin resistance (Daly et al 1997). In addition, increased insulin concentrations generally indicate insulin resistance in nondiabetic individuals. The beneficial effects of consuming oats or barley or their soluble-fiber extracts are most likely to be found in subjects for whom lowering glucose and insulin is an improvement, that is, in older, overweight, and type 2 diabetic individuals.
The effects of soluble fibers on blood pressure are less well described (Swain et al 1990, Ascherio et al 1992, McIntosh et al 1993, He and Whelton 1999, Suter 1999, Hajjar et al 2001, Saltzman et al 2001, Davy et al 2002a, Pins et al 2002, He et al 2004). Many of the studies in humans have added either fiber supplements or fiber-containing foods to self-selected diets. Observational studies do not distinguish between soluble and insoluble fiber content because fiber sources generally are combined (such as all cereals together, fruits and vegetables together), making it difficult to identify a specific beneficial dietary component.
In this chapter, we discuss animal and human studies in which oats and other sources of soluble fibers or β-glucans were fed. Research examining their beneficial effects on various risk factors for diseases (including cardiovascular disease, hypertension, and type 2 diabetes mellitus) is reviewed. These risk factors include obesity and elevations in blood lipids, blood pressure, and glucose and insulin levels. We also discuss the mechanisms responsible for these effects that result from consumption of oats and oat products or, when relevant to oats, other foods containing soluble fibers.
