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Refined grains

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White rice is an example of a refined grain

Refined grains have been significantly modified from their natural composition, in contrast to whole grains. The modification process generally involves the mechanical removal of bran and germ, either through grinding or selective sifting.

Overview

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A refined grain is defined as having undergone a process that removes the bran, germ and husk of the grain and leaves the endosperm, or starchy interior.[1] Examples of refined grains include white bread, white flour, corn grits and white rice.[2] Refined grains are milled which gives a finer texture and improved shelf life.[3] Because the outer parts of the grain are removed and used for animal feed and non-food use, refined grains have been described as less sustainable than whole grains.[4]

After refinement of grains became prevalent in the early 20th-century, nutritional deficiencies (iron, thiamin, riboflavin and niacin) became more common in the United States.[5][6] To correct this, the Congress passed the U.S. Enrichment Act of 1942 which requires that iron, niacin, thiamin and riboflavin have to be added to all refined grain products before they are sold. Folate (folic acid) was added in 1996.[5]

Refining grain includes mixing, bleaching, and brominating; additionally, folate, thiamin, riboflavin, niacin, and iron are added back in to nutritionally enrich the product.[6] Enriched grains are refined grains that have been fortified with additional nutrients. Whole grains contain more dietary fiber than refined grains. After processing, fiber is not added back to enriched grains.[6] Enriched grains are nutritionally comparable to whole grains but only in regard to their added nutrients.[5] Whole grains contain higher amounts of minerals including chromium, magnesium, selenium, and zinc and vitamins such as Vitamin B6 and Vitamin E.[5][6] Whole grains also provide phytochemicals which enriched grains lack.[5]

In the case of maize, the process of nixtamalization (a chemical form of refinement) yields a considerable improvement in the bioavailability of niacin, thereby preventing pellagra in diets consisting largely of maize products.[7] Similar to whole grains, refined grains are a good source of starch, including resistant starch.[8]

Research

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The dietary guidance of many countries is to replace refined grains with whole grains.[9][10] The Dietary Guidelines for Americans (2020–2025) advises people to limit their intake of refined grains to be no more than half of total daily grain consumption.[11]

Cardiovascular disease

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The American Medical Association have advised people to consume whole grains instead of refined grains to improve cardiovascular risk factors.[12]

A 2020 review of controlled trials that used the GRADE approach found that although whole grains have been shown to improve low-density lipoprotein and total cholesterol there is insufficient evidence to recommend "whole grains as opposed to refined grains for the prevention and treatment of CVD".[13]

Obesity

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There is no strong scientific evidence associating refined grains with obesity.[14][15]

Nutrition

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Nutritional effects of refining or enriching wheat and rice[16]
Wheat Rice
Whole Refined Enriched Whole Refined Enriched
Food energy 100% 107% 107% 100% 99% 99%
Carbohydrates 100% 105% 105% 100% 104% 104%
Fiber 100% 22% 22% 100% 37% 37%
Protein 100% 75% 75% 100% 90% 90%
Thiamin (B1) 100% 27% 176% 100% 17% 144%
Riboflavin (B2) 100% 19% 230% 100% 53% 53%
Niacin (B3) 100% 20% 93% 100% 31% 82%
Pantothenic Acid (B5) 100% 43% 43% 100% 68% 68%
Pyridoxine (B6) 100% 13% 13% 100% 32% 32%
Folate (B9) 100% 59% 350% 100% 40% 1155%
Vitamin E 100% 5% 5% 100% 18% 18%
Calcium 100% 44% 44% 100% 100% 100%
Iron 100% 30% 120% 100% 54% 293%
Magnesium 100% 16% 16% 100% 17% 17%
Phosphorus 100% 31% 31% 100% 35% 35%
Potassium 100% 26% 26% 100% 52% 52%
Sodium 100% 40% 40% 100% 71% 71%
Zinc 100% 24% 24% 100% 29% 29%
Copper 100% 38% 38% 100% 79% 79%
Manganese 100% 18% 18% 100% 29% 29%
Selenium 100% 48% 48% 100% 65% 65%

See also

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References

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  1. ^ Marcus, Jacqueline B. (2013). "Chapter 4 - Carbohydrate Basics: Sugars, Starches and Fibers in Foods and Health: Healthy Carbohydrate Choices, Roles and Applications in Nutrition, Food Science and the Culinary Arts". In Culinary Nutrition: The Science and Practice of Healthy Cooking. pp. 149-187. ISBN 978-0123918826
  2. ^ "Grains". myplate.gov. Retrieved 16 November 2022.
  3. ^ "Whole Grains, Refined Grains, and Dietary Fiber". heart.org. Retrieved 16 November 2022.
  4. ^ Poutanen, Kaisa S; Kårlund, Anna O; Gómez-Gallego, Carlos; Johansson, Daniel P; Scheers, Nathalie M; Marklinder, Ingela M; Eriksen, Anne K; Silventoinen, Pia C; Nordlund, Emilia Nordlund; Sozer, Nesli; Hanhineva, Kati J; Kolehmainen, Marjukka; Landberg, Rikard (2022). "Grains – a major source of sustainable protein for health". Nutrition Reviews. 80 (6): 1648–1663. doi:10.1093/nutrit/nuab084. PMC 9086769. PMID 34741520.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ a b c d e Sizer, Frances; Whitney, Ellie. (2013). Nutrition: Concepts and Controversies. Cengage Learning. pp. 125-126. ISBN 9781285785981
  6. ^ a b c d Edelstein, Sari. (2019). Food Science: An Ecological Approach. Jones & Bartlett Learning. p. 480-482. ISBN 9781284122305
  7. ^ D’Ulivo, L. (2019). "Solution to vitamin B3 mystery challenge". Analytical and Bioanalytical Chemistry. 411 (1): 3. doi:10.1007/s00216-018-1432-9. PMID 30594959. S2CID 58561104.
  8. ^ Slavin, J. L. (2000). "Whole grains, refined grains and fortified refined grains: What's the difference?". Asia Pacific Journal of Clinical Nutrition. 1: S23-7. doi:10.1046/j.1440-6047.2000.00171.x. PMID 24398274.
  9. ^ Korczak, Renee; Slavin, Joanne L. (2020). "Definitions, regulations, and new frontiers for dietary fiber and whole grains". Nutrition Reviews. 78 (1): 6–12. doi:10.1093/nutrit/nuz061. PMID 32728750.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Miller, Kevin Burke (2020). "Review of whole grain and dietary fiber recommendations and intake levels in different countries". Nutrition Reviews. 78 (1): 29–36. doi:10.1093/nutrit/nuz052. PMID 32728749.
  11. ^ "Dietary Guidelines for Americans (2020–2025)". dietaryguidelines.gov. Retrieved 16 November 2022.
  12. ^ Lichtenstein AH, Appel LJ, Vadiveloo M, Hu FB, Kris-Etherton PM, et al. (December 2021). "2021 Dietary Guidance to Improve Cardiovascular Health: A Scientific Statement From the American Heart Association". Circulation (Review). 144 (23): e472–e487. doi:10.1161/CIR.0000000000001031. PMID 34724806. S2CID 240422142.
  13. ^ Marshall S, Petocz P, Duve E, Abbott K, Cassettari T, Blumfield M, Fayet-Moore F. (2020). "The Effect of Replacing Refined Grains with Whole Grains on Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials with GRADE Clinical Recommendation" (PDF). Journal of the Academy of Nutrition and Dietetics. 120 (11): 1859–1883. doi:10.1016/j.jand.2020.06.021. PMID 32933853. S2CID 221746754.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ Williams, Peter G. (2012). "Evaluation of the evidence between consumption of refined grains and health outcomes". Nutrition Reviews. 70 (2): 80–99. doi:10.1111/j.1753-4887.2011.00452.x. PMID 22300595.
  15. ^ Papanikolaou Y, Slavin JL, Clemens R, Brenna JT, Hayes D, Gaesser GA, Fulgoni VL. (2020). "Do Refined Grains Have a Place in a Healthy Dietary Pattern: Perspectives from an Expert Panel Consensus Meeting". Current Developments in Nutrition. 4 (10): nzaa125. doi:10.1093/cdn/nzaa125. PMC 7538308. PMID 33062912.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. ^ USDA Standard Reference 17 Food Nutrient Database
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