Joanne L. Slavin

Why whole grains are protective: biological mechanisms.

Epidemiological studies find that whole-grain intake is protective against cancer, cardiovascular disease, diabetes and obesity. Potential mechanisms for this protection are diverse since whole grains are rich in nutrients and phytochemicals. First, whole grains are concentrated sources of dietary fibre, resistant starch and oligosaccharides, carbohydrates that escape digestion in the small intestine and are fermented in the gut, producing short-chain fatty acids (SCFA). SCFA lower colonic pH, serve as an energy source for the colonocytes and may alter blood lipids. These improvements in the gut environment may provide immune protection beyond the gut. Second, whole grains are rich in antioxidants, including trace minerals and phenolic compounds, and these compounds have been linked to disease prevention. Additionally, whole grains mediate insulin and glucose responses. Although lower glycaemic load and glycaemic index have been linked to diabetes and obesity, risk of cancers such as colon and breast cancer have also been linked to high intake of readily-available carbohydrate. Finally, whole grains contain many other compounds that may protect against chronic disease. These compounds include phytate, phyto-oestrogens such as lignan, plant stanols and sterols, and vitamins and minerals. As a consequence of the traditional models of conducting nutrition studies on isolated nutrients, few studies exist on the biological effects of increased whole-grain intake. The few whole-grain feeding studies that are available show improvements in biomarkers with whole-grain consumption, such as weight loss, blood lipid improvement and antioxidant protection.

Health Benefits of Fruits and Vegetables

Fruits and vegetables are universally promoted as healthy. The Dietary Guidelines for Americans 2010 recommend you make one-half of your plate fruits and vegetables. Myplate.gov also supports that one-half the plate should be fruits and vegetables. Fruits and vegetables include a diverse group of plant foods that vary greatly in content of energy and nutrients. Additionally, fruits and vegetables supply dietary fiber, and fiber intake is linked to lower incidence of cardiovascular disease and obesity. Fruits and vegetables also supply vitamins and minerals to the diet and are sources of phytochemicals that function as antioxidants, phytoestrogens, and antiinflammatory agents and through other protective mechanisms. In this review, we describe the existing dietary guidance on intake of fruits and vegetables. We also review attempts to characterize fruits and vegetables into groups based on similar chemical structures and functions. Differences among fruits and vegetables in nutrient composition are detailed. We summarize the epidemiological and clinical studies on the health benefits of fruits and vegetables. Finally, we discuss the role of fiber in fruits and vegetables in disease prevention.

Concentrated oat β-glucan, a fermentable fiber, lowers serum cholesterol in hypercholesterolemic adults in a randomized controlled trial

BackgroundSoluble fibers lower serum lipids, but are difficult to incorporate into products acceptable to consumers. We investigated the physiological effects of a concentrated oat β-glucan on cardiovascular disease (CVD) endpoints in human subjects. We also compared the fermentability of concentrated oat β-glucan with inulin and guar gum in a model intestinal fermentation system.MethodsSeventy-five hypercholesterolemic men and women were randomly assigned to one of two treatments: 6 grams/day concentrated oat β-glucan or 6 grams/day dextrose (control). Fasting blood samples were collected at baseline, week 3, and week 6 and analyzed for total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, glucose, insulin, homocysteine and C-reactive protein (CRP). To estimate colonic fermentability, 0.5 g concentrated oat β-glucan was incubated in a batch model intestinal fermentation system, using human fecal inoculum to provide representative microflora. Fecal donors were not involved with the β-glucan feeding trial. Inulin and guar gum were also incubated in separate serum bottles for comparison.ResultsOat β-glucan produced significant reduction from baseline in total cholesterol (-0.3 ± 0.1 mmol/L) and LDL cholesterol (-0.3 ± 0.1 mmol/L), and the reduction in LDL cholesterol were significantly greater than in the control group (p = 0.03). Concentrated oat β-glucan was a fermentable fiber and produced total SCFA and acetate concentrations similar to inulin and guar gum. Concentrated oat β-glucan produced the highest concentrations of butyrate at 4, 8, and 12 hours.ConclusionSix grams concentrated oat β-glucan per day for six weeks significantly reduced total and LDL cholesterol in subjects with elevated cholesterol, and the LDL cholesterol reduction was greater than the change in the control group. Based on a model intestinal fermentation, this oat β-glucan was fermentable, producing higher amounts of butyrate than other fibers. Thus, a practical dose of β-glucan can significantly lower serum lipids in a high-risk population and may improve colon health.

The role of whole grains in disease prevention

Despite universal acceptance of the importance of whole grains in the diet, consumer knowledge of the benefits of whole grains and intake of these foods are low. This review summarizes the research supporting whole-grain consumption and gives practical suggestions about how to increase whole-grain intake. Whole-grain foods are valuable sources of nutrients that are lacking in the American diet, including dietary fiber, B vitamins, vitamin E, selenium, zinc, copper, and magnesium. Whole-grain foods also contain phytochemicals, such as phenolic compounds, that together with vitamins and minerals play important roles in disease prevention. The exact mechanisms linking whole grains to disease prevention are not known but may include gastrointestinal effects, antioxidant; protection, and intake of phytoestrogens. Dietary intake studies indicate that consumption of whole grains is far less than the recommended intake of 3 servings a day, with an average daily intake of 1 or fewer servings a day. A new whole-grains health claim, allowed in July 1999 by the Food and Drug Administration, and inclusion of a whole-grain recommendation in the 2000 revision of the US Dietary Guidelines for Americans, should help increase whole-grain consumption.

Effects of dietary inulin on serum lipids, blood glucose and the gastrointestinal environment in hypercholesterolemic men

Abstract Inulin is a complex carbohydrate that belongs to a class of compounds known as fructans. Inulin has been consumed in plant sources by mankind for centuries, and is most concentrated in chicory, Jerusalem artichoke, garlic, leek and onion. It can be extracted from purified concentrated sources such as chicory root, and used to enhance the technological and nutritional properties of foods. Inulin is thought to share many of the properties of soluble dietary fibers, such as the ability to lower blood lipids and stabilize blood glucose. Additionally, inulin has been shown to enhance the growth of bifidobacteria and lactobacilli and enhance the gut environment. The objective of this study was to examine the effect of a commercially available inulin from chicory root (degree of polymerization (DP) ranging between 2 and 60, modal DP=9) in men with hypercholesterolemia on serum parameters and fecal composition. The study was a randomized, double blind, crossover design with no washout period. Twelve men were randomly assigned to two controlled diets that differed only in that the control diet contained one pint of vanilla ice cream made with sucrose while the inulin containing diet was supplemented with one pint of vanilla ice cream made with 20 grams of inulin. Subjects consumed each controlled diet for three weeks. Daily intake of 20 g of inulin significantly reduced serum triglycerides by 40 mg/dL (p=0.05). A trend toward a reduction in serum cholesterol was observed. Trends toward short chain fatty acid (SCFA) profile changes were observed after inulin administration. Transit time did not differ significantly between treatments. These data suggest that dietary inulin supplementation may improve blood lipid profiles and alters the colonic environment in a manner that may be beneficial. Because inulin is easily incorporated into an acceptable food like low-fat vanilla ice cream, it shows promise as a functional ingredient in many processed foods.

Greater satiety response with resistant starch and corn bran in human subjects.

Some studies suggest high-fiber foods are more satiating than foods with little or no fiber. However, we hypothesized that certain types of dietary fiber may enhance satiety more than others. Healthy men and women (N = 20) participated in this acute, randomized double-blind, crossover study comparing the effects of 4 fibers and a low-fiber (LF) treatment on satiety. On 5 separate visits, fasting subjects consumed either a LF muffin (1.6 g fiber) or 1 of 4 high-fiber muffins (8.0-9.6 g fiber) for breakfast. The subjects used 4 questions on 100 mm visual analogue scales to rate satiety at baseline and at regular intervals for 180 minutes after muffin consumption. Responses were analyzed as area under the curve and significant differences from baseline. Satiety differed among treatments. Resistant starch and corn bran had the most impact on satiety, whereas polydextrose had little effect and behaved like the LF treatment. Results from this study indicate that not all fibers influence satiety equally.

Mechanisms for the Impact of Whole Grain Foods on Cancer Risk

Dietary guidance recommends consumption of whole grains for the prevention of cancer. Epidemiologic studies find that whole grains are protective against cancer, especially gastrointestinal cancers such as gastric and colonic, and hormonally-dependent cancers including breast and prostate. Four potential mechanisms for the protectiveness of whole grains against cancer are described. First, whole grains are concentrated sources of dietary fiber, resistant starch, and oligosaccharides, fermentable carbohydrates thought to protect against cancer. Fermentation of carbohydrates in the colon results in production of short chain fatty acids that lower colonic pH and serve as an energy source for the colonocytes. Secondly, whole grains are rich in antioxidants, including trace minerals and phenolic compounds, and antioxidants have been proposed to be important in cancer prevention. Thirdly, whole grains are significant sources of phytoestrogens that have hormonal effects related to cancer protection. Phytoestrogens are thought to be particularly important in the prevention of hormonally-dependent cancers such as breast and prostate. Finally, whole grains mediate glucose response, which has been proposed to protect against colon and breast cancer.

Gastrointestinal Effects of Low-Digestible Carbohydrates

Low-digestible carbohydrates (LDCs) are carbohydrates that are incompletely or not absorbed in the small intestine but are at least partly fermented by bacteria in the large intestine. Fiber, resistant starch, and sugar alcohols are types of LDCs. Given potential health benefits (including a reduced caloric content, reduced or no effect on blood glucose levels, non-cariogenic effect) the prevalence of LDCs in processed foods is increasing. Many of the benefits of LDCs are related to the inability of human digestive enzymes to break down completely the carbohydrates into absorbable saccharides and the subsequent fermentation of unabsorbed carbohydrates in the colon. As a result, LDCs may affect laxation and cause gastrointestinal effects, including abdominal discomfort, flatus, and diarrhea, especially at higher or excessive intakes. Such responses, though transient, affect the perception of the well-being of consumers and their acceptance of food products containing LDCs. Current recommendations for fiber intake do not consider total LDC consumption nor recommend an upper limit for LDC intake based on potential gastrointestinal effects. Therefore, a review of published studies reporting gastrointestinal effects of LDCs was conducted. We included only studies published in refereed journals in English. Additionally, we excluded studies of subjects with incomplete or abnormal functioning gastrointestinal tracts or where antibiotics, stimulant laxatives, or other drugs affecting motility were included. Only in studies with a control period, either placebo treatment or no LDC treatment, were included. Studies must have included an acceptable measure of gastrointestinal effect. Sixty-eight studies and six review articles were evaluated. This review describes definitions, classifications, and mechanisms of LDCs, evaluates published human feeding studies of fifteen LDCs for associations between gastrointestinal effects and levels of LDC intake, and presents recommendations for LDC consumption and further research.

Whole grain intake and cancer: a review of the literature.

There has been little research concerning the health effects of whole grain intake in humans. We have synthesized 15 american and European case-control and prospective studies of whole grain intake. Most subjects were middle aged or older. The studies employed disparate dietary methods, and the foods referred to and quantities eaten are ill defined. Nevertheless there is a striking consistency in reduced risk for colorectal and gastric cancers associated with intake of whole grain, also found in isolated studies of endometrial cancer and coronary heart disease. Because reduced risk was not associated with refined grain intake, these findings do not appear to be confounded by participant confusion concerning refined vs. whole grains. The independence of these findings from reduced risk associated with fruit and vegetable intake is not established. There should be further research to establish whether whole grain intake is protective against chronic disease.

Partially hydrolyzed guar gum: clinical nutrition uses.

OBJECTIVE This paper provides a review of research on partially hydrolyzed guar gum that is relevant to clinical nutrition practice. METHODS All relevant papers published on partially hydrolyzed guar gum were reviewed and the results summarized. RESULTS Partially hydrolyzed guar gum (PHGG) is a water-soluble dietary fiber with a wide range of uses in clinical nutrition. Its low viscosity allows its use in enteral products and beverages. PHGG can be added to enteral formulas and food products as a dietary fiber source. PHGG provides the benefits associated with dietary fiber ingestion. Addition of PHGG to the diet reduced laxative dependence in a nursing home population. PHGG also reduced the incidence of diarrhea in septic patients receiving total enteral nutrition and reduced symptoms of irritable bowel syndrome. PHGG also increased production of Bifidobacterium in the gut. CONCLUSION The ease of use of PHGG and its clinical effectiveness make it a good choice in clinical nutrition practice.