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, antioxidanhts, 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.
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 Figure 1. Whole grains

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. 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. 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.

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. [2]

  • 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. [3]
  • 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. [4]

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. [5]
  • 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. [6]

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. [7] 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. [8] 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 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.[9]

Cancer

The data on cancer are mixed, with some studies showing a protective effect of whole grains and others showing none. [10]

  • 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. [11] 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%. [12]

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. [13]

  • 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. [14]

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.

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. 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.
  3. 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.
  4. 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.
  5. 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.
  6. Mellen PB, Walsh TF, Herrington DM. Whole grain intake and cardiovascular disease: a meta-analysis. Nutr Metab Cardiovasc Dis. 2008;18:283-90.
  7. 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. Ẻu J Epidemiol. 2013;28:845-58.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. 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.
  13. 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.
  14. 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.