Health Benefits of Whole Grain Diets

by | May 11, 2011 | Antioxidants, Cancer, Cardiovascular Health, Diabetes, Fiber, Whole Grains

Written by Neil E. Levin, CCN, DANLA. Studies have shown that whole grain intake is proactive against cancer, cardiovascular disease, diabetes, and obesity. 

Whole grains are an essential part of a traditional whole-food-based diet that provides a wide range of nutrients.

Many of these nutrients are deficient in our typical modern fast food diet, as well as in diets that feature white rice or white bread products instead of wholegrain alternatives such as brown rice, rolled oats and oat flour.

A wholegrain typically consists of 3 main sections of the grain: the outer bran layers, the germ, and the inner endosperm consisting largely of starches. A majority of the population has consumed refined grains for only the past century as milling techniques improved their efficiency. Earlier milling techniques did not completely separate the bran and germ from the inner endosperm and produced limited amounts of highly purified refined “white” flour. But in 1873 the roller mill was introduced, which more efficiently separated the bran and germ from the endosperm. The ensuing widespread use of the roller mill created an increasing demand for refined grain products and was a significant factor causing a dramatic decline in wholegrain consumption from the 1870s through the 1970s.  (2, 3)

Studies show that only about 8% of Americans consume the recommended number of daily wholegrain servings.  Although current American nutritional guidelines call for the consumption of at least 3 servings of wholegrains daily, the typical American – adult or child – consumes less than one serving of wholegrain foods per day. Intake in other Western countries also is about one serving per day.  (1, 2)

One reason why there is such a public health emphasis on increasing the number of servings of wholegrain foods is their dense nutritional content. Whole grains naturally contain vitamins, minerals, and other constituents that are essential for human health, most of which are removed when a grain is refined. (3)

Unrefined wholegrains naturally contain high concentrations of B vitamins thiamine, niacin, riboflavin, and pantothenic acid, minerals (calcium, magnesium, potassium, phosphorus, sodium, and iron), essential amino acids arginine and lysine), and vitamin E complex (tocopherols and tocotrienols). All of these nutrients are essential for human health and life. (2)

Wholegrains are rich sources of fermentable carbohydrates, including dietary fiber, resistant starch, and oligosaccharides. These undigested carbohydrate are fermented by intestinal microorganisms to short-chain fatty acids, including butyrate, which is a preferred fuel for colonic mucosa cells. Short-chain fatty acid production has also been related to lowered serum cholesterol and a decreased risk of cancer.  (2)

Fats and oils that are present in the bran or germ layer of whole grains are unfortunately removed from the products during the process of refining them. This improves the shelf life of these processed foods, but at the expense of their nutritional value. These healthy fats from whole grains include natural vitamin E and its family of related compounds, as well as various plant sterols and other nutritionally valuable fractions.  (2, 3)

Wholegrain products provide natural chelating agents such as phytates that bond to minerals, controlling the minerals’ absorption, transport, and safety. These valuable wholegrain fractions also include natural compounds that help to regulate estrogen levels in the body. (2)

Unlike processed grains such as white rice and refined white flour, whole grains contain significant amounts of dietary fiber that aids in promoting satiety, proper bowel regularity, blood sugar control, and healthy cholesterol levels. …(2)

Oats, rye, and barley each contain about one-third soluble fiber, with the rest being insoluble fiber. Adequate soluble fiber intake is associated with healthy cholesterol levels and an improved glucose response, while insoluble fiber is associated with improved bowel regularity. (2)

All of these natural constituents of whole grains are considered to be supportive of the health of our bodies by providing a balanced nutrient profile similar to what our ancient ancestors ate. Epidemiological studies have shown that wholegrain intake is protective against cancer, cardiovascular disease (CVD), diabetes, and obesity. Published wholegrain feeding studies report improvements in biomarkers with wholegrain consumption, including weight loss, blood-lipid improvement, and antioxidant protection. The disease protection seen from wholegrains in prospective epidemiological studies far exceeds the protection from isolated nutrients and phytochemicals extracted from wholegrains. This evidences the value of eating wholegrain foods over isolated components of those foods.  (2)

Health issues associated with an over-processed diet low in whole grains may include: obesity, diabetes, cardiovascular disease, chronic inflammatory states, oxidative stress, cancer, and constipation.

Obesity

Whole grains may influence insulin levels through beneficial effects on satiety and body weight. People tend to gain significantly less weight over time if they consume an average of ≥3 servings whole grains/day. Whole grains may enhance satiety (delayed return of hunger following a meal) for up to several hours following a meal and appear to prevent weight gain among middle-aged women.  (2)

In the Framingham Heart Study, middle-aged adults who consumed more wholegrain foods had a lower body mass index (BMI) and central obesity than those who consumed the least.  (3)

In the Framingham Offspring Study, wholegrain intake was inversely associated with body mass index (BMI) and fasting insulin levels.  (4)

The Baltimore Longitudinal Study of Aging reported that a healthy eating pattern, including the consumption of whole grains, is associated with smaller gains in BMI and waist circumference.  (5)

Studies suggest an association between wholegrain intake and the regulation of body weight. In the Coronary Artery Risk Development in Young Adults (CARDIA) Study, whole grains were inversely associated with BMI and waist:hip ratio both at baseline and 7 years later.  (2)

Diabetes, Insulin Sensitivity, and Blood Sugar Control

Whole grains are known to affect glucose and insulin responses, partly due to their slow digestibility. The greater the intake of whole grains, the lower that fasting insulin levels are likely to be.  (2)

Oat bran can improve glycemic and insulinemic responses and beneficially influence plasma lipid levels in diabetic patients.  Oat-based meals evoked smaller glucose and insulin responses than wheat- or maize-based meals. Particle size influenced the digestion rate and resulting metabolic effects of wheat and maize, but not of oats.   (2, 15)

In a long-term study of nearly 90,000 women and a similar study of about 45,000 men, those with higher intakes of cereal fiber from whole grains had about a 30% lower risk of developing type 2 DM (diabetes mellitus) versus those with the lowest intakes.  (2, 6, 7)

In the Health Professional Follow-up Study of 42,898 men, a 37% lower risk of type 2 DM was associated with consumption about three servings of wholegrains per day. (8)

The Iowa Women’s Health Study also found that dietary fiber and wholegrain intake were protective against type 2 DM (Meyer et al. 2000). (9)

In the Nurses’ Health Study, those consuming mostly refined grains and few whole grains had a 57% higher risk of developing type 2 DM than did those consuming mostly whole grains.  (10)]

Clinical studies to date support that wholegrain consumption can improve biomarkers relevant to DM, such as reduced insulin demand. Epidemiological studies consistently show that the risk for type 2 DM is decreased with the consumption of whole grains.

Insulin sensitivity may be an important mechanism whereby wholegrain foods reduce the risk of type 2 DM and heart disease. A report on the effect of substituting whole grains for refined grains on insulin sensitivity found that fasting insulin levels were 10% lower after 6 weeks on a wholegrain diet. This suggests that a change in insulin sensitivity may be responsible for the reductions in insulin levels and risk of type 2 DM reported in epidemiological (population) studies.  (2)

Wholegrain and bran intakes are associated with reduced all-cause and CVD-specific mortality in women with diabetes mellitus. Wholegrain consumption may now be considered an important modifiable risk factor for decreasing mortality and cardiovascular risk in diabetics. Whole grains are recommended by the American Diabetes Association for DM prevention.  (2, 15)

Cardiovascular Disease, Lipids, and Heart Health

Cardiovascular disease (CVD) is the number one cause of death and disability of men and women in the USA. There is strong epidemiological and clinical evidence linking the consumption of whole grains to a reduced risk of coronary heart disease (CHD). Large prospective epidemiological studies have found a moderately strong association between wholegrain intake and decreased CHD risk.

Patients with type 2 diabetes mellitus have a 2- to 3-fold higher risk of CVD and premature mortality than the general population. A randomized crossover trial indicated that a high-fiber diet can improve glycemic control, lower excessive insulin levels, and improve blood lipid concentrations in diabetic patients.  (3)

Unsaturated fatty acids found in wholegrain wheat and oats are known to reduce serum cholesterol and are important components of a heart-healthy diet. Short-chain fatty acids, such as those found in wholegrains, have been shown to lower serum cholesterol. (2, 11)

Clinical studies to date support that wholegrain consumption can improve biomarkers relevant to CVD, such as lipid peroxidation and plasma homocysteine concentrations, in patients with coronary artery disease. (2)

…Plant sterols and stanols are found in wholegrains and are known to reduce serum cholesterol. Increased wholegrain consumption would increase total phytosterol intake, including ß-sitosterol, which is associated with cholesterol reduction. (2)

In the large Nurses’ Health Study, wholegrain cereal intake was strongly associated with reduced risk of coronary heart disease (CHD). The age-adjusted relative risk was 77% for the quintile of women eating the most wholegrains versus the quintile of the study population eating the least amount of wholegrains. (13)

In 43,757 U.S. health professionals aged 40–75 years, cereal fiber was most strongly associated with a reduced risk for myocardial infarction, with a 71% decrease in risk for each 10 gram increase in cereal fiber intake. (14)

High intakes of wholegrains, and components such as cereal fiber and bran, might protect against systemic inflammation. (2, 15)

Wholegrain products are relatively high in antioxidant activity. Soluble antioxidants include phenolic acids, flavonoids, tocopherols, and avenanthramides from oats. In addition to vitamin E (d-alpha tocopherol), both water-soluble and fat-soluble antioxidants are found in wholegrains.

Vitamin E is an intracellular antioxidant that protects polyunsaturated fatty acids in cell membranes from oxidative damage and inhibits the formation of dangerous nitrosamines, especially in areas of low pH. Vitamin E also helps to keep the essential mineral selenium in a reduced (antioxidant) state. Selenium functions as a cofactor for the endogenous production of glutathione peroxidase; an enzyme that protects against oxidative tissue damage.  Selenium thus has a suppressive action on cell proliferation.

Phytic acid, concentrated in grains, is another antioxidant. Phytic acid forms chelates with various metals, suppressing damaging iron-catalyzed redox reactions. Colonic bacteria produce oxygen free radicals in significant amounts, but dietary phytic acid may suppress the potential oxidant damage to the intestinal epithelium and neighboring cells.

Because of their ability to efficiently deliver these nutrients to the cells lining the gut wall, wholegrains provide antioxidant protection throughout the entire digestive tract.  (2)

Cancer

Wholegrain fiber may reduce estrogen levels by increasing estrogen excretion, by inhibition of intestinal reabsorption of estrogens, and by binding unconjugated estrogens to fiber. These effects are considered protective against certain hormonal cancers.

Compounds in grains called lignans may protect against hormonally mediated diseases. Concentrated sources of lignans include wholegrain wheat and wholegrain oats. Since lignans are concentrated in the outer bran layers of the grain, only wholegrain sources contain significant amounts, not refined grain products.

There is substantial scientific evidence that whole grains reduce the risk of cancer. In one meta-analysis, whole grains were found to be protective in forty-three of forty-five mentions of whole-grain intake.  (2, 16)

Among users of postmenopausal hormones, total fiber intake and especially cereal fiber from wholegrain foods were statistically significantly associated with a 50% reduced risk for both overall and estrogen- and progesterone-linked tumors (comparing the highest to the lowest quartile. For those women not using hormone replacement therapies, multivariable-adjusted relative risks for the highest versus the lowest quartile of cereal fiber intake were 31% lower overall and 43% lower for estrogen- and progesterone-linked tumors. (17)

Constipation

Whole grains such as wheat and oats have high concentrations of dietary fiber that increases stool weight and transit speed. Insoluble fiber is especially associated with improved bowel regularity. It is well known that dietary fiber from wholegrains such as wheat and oats increases stool weight and speed transit. Wheat is higher in insoluble fiber than most grains, while brown rice contains nearly all insoluble fiber.  (2)

Conclusion

We have seen that a decrease in the amount of whole grains in the modern diet is related to a corresponding increase in health problems that are attributed to this all-too-common dietary imbalance. The resulting health issues associated with an over-processed diet which provides inadequate levels of nutrients from whole grains may include obesity, diabetes, high blood lipids, chronic inflammatory states, and an excess of oxidative stress. Strength and endurance may also suffer as a result of these nutrient deficiencies, followed by declines in energy and immunity. Good health can be more easily attained and maintained by well-informed people who want to enjoy the Health Benefits of Wholegrain Diets.

Definitions:

Biomakers-Chemicals in living systems that show the amounts of substances of interest that are hard to measure.

Chelating-The act of surrounding a substance with other materials giving the combination new properties.

Colonic Mucosa Cells-Cells rich in mucous glands on the surface of the intestines.

Fasting Insulin Levels-Body levels of insulin after an overnight fast which provides a good starting point.

Intestinal Microflora-Microorganisms such as yeast, molds, bacteria, etc., living in the intestines.

Oxidative Stress-The damage within living organisms caused by free radical aging.

 Posted May 11, 2011.

References:

  1. United States Department of Agriculture: The 2000 Dietary Guidelines for Americans
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