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Whole Grains – The Nutrition Source – Harvard University

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Whole Grain vs Refined Grain Diagram

Choose whole grains instead of refined grains.

Whole grains offer a “complete package” of health benefits, unlike refined grains, which are stripped of valuable nutrients in the refining process.

All whole grain kernels contain three parts: the bran, germ, and endosperm. Each section houses health-promoting nutrients. The bran is the fiber-rich outer layer that supplies B vitamins, iron, copper, zinc, magnesium, antioxidants, and phytochemicals. Phytochemicals are natural chemical compounds in plants that have been researched for their role in disease prevention. The germ is the core of the seed where growth occurs; it is rich in healthy fats, vitamin E, B vitamins, phytochemicals, and antioxidants. The endosperm is the interior layer that holds carbohydrates, protein, and small amounts of some B vitamins and minerals.

These components have various effects on our bodies:

  • Bran and fiber slow the breakdown of starch into glucose—thus maintaining a steady blood sugar rather than causing sharp spikes.
  • Fiber helps lower cholesterol as well as move waste through the digestive tract.
  • Fiber may also help prevent the formation of small blood clots that can trigger heart attacks or strokes.
  • Phytochemicals and essential minerals such as magnesium, selenium and copper found in whole grains may protect against some cancers.

The invention of industrialized roller mills in the late 19th century changed the way we process grains. Milling strips away the bran and germ and leaves only the soft, easy-to-digest endosperm. Without the fibrous bran, the grain is easier to chew. The germ is removed because of its fat content, which can limit the shelf life of processed wheat products. The resulting highly processed grains are much lower in nutritional quality. Refining wheat creates fluffy flour that makes light, airy breads and pastries, but the process strips away more than half of wheat’s B vitamins, 90 percent of the vitamin E, and virtually all of the fiber. Although some nutrients may be added back by fortification, other health-promoting components of whole grains such as phytochemicals cannot be replaced.

A growing body of research shows that choosing whole grains and other less-processed, higher-quality sources of carbohydrates, and cutting back on refined grains, improves health in many ways. For a closer look at carbohydrates, check out our Carbohydrate Guide.

The 2015-2020 Dietary Guidelines for Americans recommends eating 6 ounces of grain foods daily (based on a 2000-calorie diet) and getting at least half or 3 ounces of that grain intake from 100% whole grains. [1] However, due to an increasing amount of research showing the various health benefits derived from whole grains, and even a possible detrimental effect when eating mostly refined grains, it is recommended to choose mostly whole grains instead of refined grains. An easy way to tell if a food product is high in 100% whole grains is to make sure it is listed first or second in the ingredient list. Or better yet, choose unprocessed whole grains:

Amaranth Kamut  Spelt
Barley Millet  Teff
Brown Rice Quinoa  Triticale
Buckwheat  Rye  Wheat Berries
Bulgur  Oats  Wild Rice
Corn  Sorghum

Be careful when choosing foods labeled as whole grains: “Whole grain” doesn’t always mean healthy.

One study revealed that inconsistent food labeling means that foods identified as “whole grain” are not always healthy. [2]

  • The study assessed five USDA criteria that identify whole grains in a food product: 1) any whole grain as the first ingredient, 2) any whole grain as the first ingredient, and added sugars not being one of the first three ingredients in the ingredient list, 3) the word “whole” before any grain ingredient, 4) a carbohydrate-to-fiber ratio of less than 10:1, and 5) the industry-sponsored Whole Grain Stamp.
    • The Whole Grain Stamp is a widely used marker on food products. The stamp, while designed to steer consumers towards healthy whole grains, identified products with more fiber and less sodium and trans fat but that were higher in sugar and calories than whole grain foods without the stamp.
    • The other three USDA criteria had mixed results in identifying healthier whole grain products, but (criterion 4) the carbohydrate-to-fiber ratio of less than 10:1 proved to be the most effective measure of healthfulness. However, it is unclear whether this ratio is more predictive of chronic disease risk than other measures of carbohydrate quality—such as the amount/type of fiber or overall dietary glycemic index/load. Foods that met this criterion were higher in fiber and less likely to contain trans fats, sodium, and sugar.
  • Because calculating the carbohydrate-to-fiber ratio may be difficult and not readily available for a consumer reading a label, the study suggests that labeling guidelines appearing on whole-grain foods should be improved.

Consumers should steer towards whole grain foods that are high in fiber and that have few ingredients in addition to whole grain. Moreover, eating whole grains in their whole forms—such as brown rice, barley, oats, corn, and rye—are healthy choices because they pack in the nutritional benefits of whole grains without any additional ingredients.

Whole Grains and Disease

As researchers have begun to look more closely at carbohydrates and health, they are learning that the quality of the carbohydrates you eat is at least as important as the quantity. Most studies, including some from several different Harvard teams, show a connection between whole grains and better health. [3]

  • A report from the Iowa Women’s Health Study linked whole grain consumption with fewer deaths from inflammatory and infectious causes, excluding cardiac and cancer causes. Examples are rheumatoid arthritis, gout, asthma, ulcerative colitis, Crohn’s disease, and neurodegenerative diseases. Compared with women who rarely or never ate whole-grain foods, those who had at least two or more servings a day were 30% less likely to have died from an inflammation-related condition over a 17-year period. [4]
  • A meta-analysis combining results from studies conducted in the U.S., the United Kingdom, and Scandinavian countries (which included health information from over 786,000 individuals), found that people who ate 70 grams/day of whole grains—compared with those who ate little or no whole grains—had a 22% lower risk of total mortality, a 23% lower risk of cardiovascular disease mortality, and a 20% lower risk of cancer mortality. [5]

Cardiovascular Disease

Eating whole instead of refined grains substantially lowers total cholesterol, low-density lipoprotein (LDL, or bad) cholesterol, triglycerides, and insulin levels.

  • In the Harvard-based Nurses’ Health Study, women who ate 2 to 3 servings of whole-grain products each day were 30% less likely to have a heart attack or die from heart disease over a 10-year period than women who ate less than 1 serving per week. [6]
  • A meta-analysis of seven major studies showed that cardiovascular disease (heart attack, stroke, or the need for a procedure to bypass or open a clogged artery) was 21% less likely in people who ate 2.5 or more servings of whole-grain foods a day compared with those who ate less than 2 servings a week. [7]

Type 2 Diabetes

Replacing refined grains with whole grains and eating at least 2 servings of whole grains daily may help to reduce type 2 diabetes risk. The fiber, nutrients, and phytochemicals in whole grains may improve insulin sensitivity and glucose metabolism and slow the absorption of food, preventing blood sugar spikes. [8] In contrast, refined grains tend to have a high glycemic index and glycemic load with less fiber and nutrients.

  • In a study of more than 160,000 women whose health and dietary habits were followed for up to 18 years, those who averaged 2 to 3 servings of whole grains a day were 30% less likely to have developed type 2 diabetes than those who rarely ate whole grains. [9] When the researchers combined these results with those of several other large studies, they found that eating an extra 2 servings of whole grains a day decreased the risk of type 2 diabetes by 21%.
  • A follow-up to that study including men and women from the Nurses’ Health Studies I and II and the Health Professionals Follow-Up Study found that swapping white rice for whole grains could help lower diabetes risk. Those who ate the most white rice—five or more servings a week—had a 17% higher risk of diabetes than those who ate white rice less than one time a month. Those who ate the most brown rice—two or more servings a week—had an 11% lower risk of diabetes than those who rarely ate brown rice. Researchers estimate that swapping whole grains in place of even some white rice could lower diabetes risk by 36%. [10]
  • A large study of more than 72,000 postmenopausal women without diabetes at the start of the study found that the higher the intake of whole grains, the greater the risk reduction of type 2 diabetes. A 43% reduced risk was found in women eating the highest amount of whole grains (2 or more servings daily) as compared with those who ate no whole grains. [11]

Cancer

The data on cancer are mixed, with some studies showing a protective effect of whole grains and others showing none. [12,13]

  • A large five-year study among nearly 500,000 men and women suggests that eating whole grains, but not dietary fiber, offers modest protection against colorectal cancer. [14,15] A review of four large population studies also showed a protective effect of whole grains from colorectal cancer, with a cumulative risk reduction of 21%. [16]

Digestive Health

By keeping the stool soft and bulky, the fiber in whole grains helps prevent constipation, a common, costly, and aggravating problem. It also helps prevent diverticular disease (diverticulosis) by decreasing pressure in the intestines. [17]

  • A study of 170,776 women followed for more than 26 years looked at the effect of different dietary fibers, including that from whole grains, on Crohn’s disease and ulcerative colitis. Though a reduced risk of Crohn’s disease was found in those eating high intakes of fruit fiber, there was no reduced risk of either disease found from eating whole grains. [18]

Some grains contain the naturally-occurring protein, gluten. While gluten can cause side effects in certain individuals, such as those with celiac disease, most people can and have eaten gluten most of their lives—without any adverse reaction. However, negative media attention on wheat and gluten has caused some people to doubt its place in a healthful diet, though there is little published research to support such claims. For further information on gluten and health, see: Gluten: A Benefit or Harm to the Body?


References

  1. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015 – 2020 Dietary Guidelines for Americans. 8th Edition. December 2015. Available at http://health.gov/dietaryguidelines/2015/guidelines/
  2. Mozaffarian RS, Lee RM, Kennedy MA, Ludwig DS, Mozaffarian D, Gortmaker SL. Identifying whole grain foods: a comparison of different approaches for selecting more healthful whole grain products. Public Health Nutr. 2013;16:2255-64.
  3. Wu H, Flint AJ, Qi Q, et al. Association between dietary whole grain intake and risk of mortality: two large prospective studies in US men and women. JAMA Intern Med. 2015;175:373-84.
  4. Jacobs DR, Jr., Andersen LF, Blomhoff R. Whole-grain consumption is associated with a reduced risk of noncardiovascular, noncancer death attributed to inflammatory diseases in the Iowa Women’s Health Study. Am J Clin Nutr. 2007;85:1606-14.
  5. Zong G, Gao A, Hu FB, Sun Q. Whole Grain Intake and Mortality From All Causes, Cardiovascular Disease, and Cancer: A Meta-Analysis of Prospective Cohort Studies. Circulation. 2016;133:2370-80.
  6. Liu S, Stampfer MJ, Hu FB, et al. Whole-grain consumption and risk of coronary heart disease: results from the Nurses’ Health Study. Am J Clin Nutr. 1999;70:412-9.
  7. Mellen PB, Walsh TF, Herrington DM. Whole grain intake and cardiovascular disease: a meta-analysis. Nutr Metab Cardiovasc Dis. 2008;18:283-90.
  8. Aune D, Norat T, Romundstad P, Vatten LJ. Whole grain and refined grain consumption and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies. Eur J Epidemiol. 2013;28:845-58.
  9. de Munter JS, Hu FB, Spiegelman D, Franz M, van Dam RM. Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. PLoS Med. 2007;4:e261.
  10. Sun Q, Spiegelman D, van Dam RM, et al. White rice, brown rice, and risk of type 2 diabetes in US men and women. Arch Intern Med. 2010;170:961-9.
  11. Parker ED, Liu S, Van Horn L, et al. The association of whole grain consumption with incident type 2 diabetes: the Women’s Health Initiative Observational Study. Ann Epidemiol. 2013;23:321-7.
  12. Aune D, Keum N, Giovannucci E, et al. Whole grain consumption and risk of cardiovascular disease, cancer, and all cause and cause specific mortality: systematic review and dose-response meta-analysis of prospective studies. BMJ. 2016;353:i2716.
  13. Jacobs DR, Jr., Marquart L, Slavin J, Kushi LH. Whole-grain intake and cancer: an expanded review and meta-analysis. Nutr Cancer. 1998;30:85-96.
  14. Schatzkin A, Mouw T, Park Y, et al. Dietary fiber and whole-grain consumption in relation to colorectal cancer in the NIH-AARP Diet and Health Study. Am J Clin Nutr. 2007;85:1353-60.
  15. Strayer L, Jacobs DR, Jr., Schairer C, Schatzkin A, Flood A. Dietary carbohydrate, glycemic index, and glycemic load and the risk of colorectal cancer in the BCDDP cohort. Cancer Causes Control. 2007;18:853-63.
  16. Aune D, Chan DS, Lau R, et al. Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies. BMJ. 2011;343:d6617.
  17. Strate LL, Keeley BR, Cao Y, Wu K, Giovannucci EL, Chan AT. Western Dietary Pattern Increases, and Prudent Dietary Pattern Decreases, Risk of Incident Diverticulitis in a Prospective Cohort Study. Gastroenterology. 2017;152:1023-30 e2.
  18. Ananthakrishnan AN, Khalili H, Konijeti GG, et al. A prospective study of long-term intake of dietary fiber and risk of Crohn’s disease and ulcerative colitis. Gastroenterology. 2013;145:970-7.

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