{"id":1015,"date":"2017-10-27T16:41:54","date_gmt":"2017-10-27T16:41:54","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-nutrition\/?post_type=chapter&p=1015"},"modified":"2017-11-14T17:40:46","modified_gmt":"2017-11-14T17:40:46","slug":"12-71-iron-uptake-absorption","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-herkimer-nutritionflex\/chapter\/12-71-iron-uptake-absorption\/","title":{"raw":"12.71 Iron Uptake & Absorption","rendered":"12.71 Iron Uptake & Absorption"},"content":{"raw":"
\r\n\r\nThere are 2 transporters for iron, one for heme iron and one for non-heme iron. The non-heme transporter is the divalent mineral transporter 1 (DMT1), which transports Fe2+ into the enterocyte. Heme iron is taken up through heme carrier protein 1 (HCP-1), and then metabolized to Fe2+. Fe2+ may be used by enzymes and other proteins or stored in the enterocyte bound to ferritin, the iron storage protein. To reach circulation, iron is transported through ferroportin1,2<\/sup>. This process is summarized in the figure below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"970\"]\"\" Figure 12.711 Iron uptake into the enterocyte[\/caption]\r\n\r\n<\/div>\r\nSince only the reduced form of non-heme iron (Fe2+) is taken up, Fe3+ must be reduced. There is a reductase enzyme on the brush border, duodenal cytochrome b (Dcytb), that catalyzes the reduction of Fe3+ to Fe2+, as shown below. Vitamin C enhances non-heme iron absorption because it is required by Dcytb for this reaction. Thus, if dietary non-heme iron is consumed with vitamin C, more non-heme iron will be reduced to Fe2+ and taken up into the enterocyte through DMT1<\/sup>.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"512\"]\"\" Figure 12.712 Reduction of non-heme iron by Dcytb[\/caption]\r\n\r\n<\/div>\r\nIn addition to vitamin C, there is an unidentified factor in muscle that enhances non-heme iron absorption if consumed at the same meal3<\/sup>. This unidentified factor is referred to as meat protein factor (MPF). The table shows how MPF can increase non-heme iron absorption.\r\n\r\nTable 12.711 Non-heme iron absorption from chicken or beef muscle fraction3<\/sup>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n
Mean Fe Absorption \u00a0<\/b>\r\n\r\n(% of Dose)<\/b><\/td>\r\nEgg Albumin<\/b><\/td>\r\nWhole Muscle<\/b><\/td>\r\nWhole Muscle Protein<\/b><\/td>\r\nHeme-Free Muscle Protein<\/b><\/td>\r\n<\/tr>\r\n
Chicken<\/td>\r\n8.41<\/td>\r\n16.43<\/td>\r\n26.98<\/td>\r\n36.81<\/td>\r\n<\/tr>\r\n
Beef<\/td>\r\n11.21<\/td>\r\n31.52<\/td>\r\n44.15<\/td>\r\n38.29<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nAlbumin is a protein, so the egg albumin represents a non-meat protein standard for comparison. You can see that absorption is much higher with whole muscle. When only consuming muscle protein, there is a slight increase from muscle itself, and when they look at heme-free muscle iron, absorption is still higher than egg albumin3<\/sup>.\r\n\r\nInhibitors of non-heme iron absorption typically chelate, or bind, the iron to prevent absorption. Phytates (phytic acid), which also inhibit calcium absorption, chelate non-heme iron decreasing its absorption.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"800\"]\"\" Figure 12.713 Structure of phytic acid4[\/caption]\r\n\r\n<\/div>\r\nOther compounds that inhibit absorption are:\r\n\r\nPolyphenols (coffee, tea)1<\/sup>\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"208\"]\"\" Figure 12.714 Structure of gallic acid, a polyphenol5<\/sup>[\/caption]\r\n\r\n<\/div>\r\nOxalate (spinach, rhubarb, sweet potatoes, and dried beans)2<\/sup>\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"304\"]\"\" Figure 12.715 Structure of calcium oxalate6<\/sup>[\/caption]\r\n\r\n<\/div>\r\nCalcium is also believed to inhibit iron uptake.\r\n\r\nReferences & Links<\/b>\r\n\r\n1. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.\r\n\r\n2. Shils ME, Shike M, Ross AC, Caballero B, Cousins RJ, editors. (2006) Modern nutrition in health and disease. Baltimore, MD: Lippincott Williams & Wilkins.\r\n\r\n3. Hurrell R, Reddy M, Juillerat M, Cook J. (2006) Meat protein fractions enhance nonheme iron absorption in humans. J Nutr 136(11): 2808-2812.\r\n\r\n4. http:\/\/en.wikipedia.org\/wiki\/File:Phytic_acid.png\r\n\r\n5. http:\/\/en.wikipedia.org\/wiki\/File:Gallic_acid.svg\r\n\r\n6. http:\/\/en.wikipedia.org\/wiki\/File:Calcium_oxalate.png\r\n\r\n<\/div>","rendered":"
\n

There are 2 transporters for iron, one for heme iron and one for non-heme iron. The non-heme transporter is the divalent mineral transporter 1 (DMT1), which transports Fe2+ into the enterocyte. Heme iron is taken up through heme carrier protein 1 (HCP-1), and then metabolized to Fe2+. Fe2+ may be used by enzymes and other proteins or stored in the enterocyte bound to ferritin, the iron storage protein. To reach circulation, iron is transported through ferroportin1,2<\/sup>. This process is summarized in the figure below.<\/p>\n

\n
\"\"<\/p>\n

Figure 12.711 Iron uptake into the enterocyte<\/p>\n<\/div>\n<\/div>\n

Since only the reduced form of non-heme iron (Fe2+) is taken up, Fe3+ must be reduced. There is a reductase enzyme on the brush border, duodenal cytochrome b (Dcytb), that catalyzes the reduction of Fe3+ to Fe2+, as shown below. Vitamin C enhances non-heme iron absorption because it is required by Dcytb for this reaction. Thus, if dietary non-heme iron is consumed with vitamin C, more non-heme iron will be reduced to Fe2+ and taken up into the enterocyte through DMT1<\/sup>.<\/p>\n

\n
\"\"<\/p>\n

Figure 12.712 Reduction of non-heme iron by Dcytb<\/p>\n<\/div>\n<\/div>\n

In addition to vitamin C, there is an unidentified factor in muscle that enhances non-heme iron absorption if consumed at the same meal3<\/sup>. This unidentified factor is referred to as meat protein factor (MPF). The table shows how MPF can increase non-heme iron absorption.<\/p>\n

Table 12.711 Non-heme iron absorption from chicken or beef muscle fraction3<\/sup><\/p>\n\n\n\n\n\n\n<\/colgroup>\n\n\n\n\n
Mean Fe Absorption \u00a0<\/b><\/p>\n

(% of Dose)<\/b><\/td>\n

Egg Albumin<\/b><\/td>\nWhole Muscle<\/b><\/td>\nWhole Muscle Protein<\/b><\/td>\nHeme-Free Muscle Protein<\/b><\/td>\n<\/tr>\n
Chicken<\/td>\n8.41<\/td>\n16.43<\/td>\n26.98<\/td>\n36.81<\/td>\n<\/tr>\n
Beef<\/td>\n11.21<\/td>\n31.52<\/td>\n44.15<\/td>\n38.29<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Albumin is a protein, so the egg albumin represents a non-meat protein standard for comparison. You can see that absorption is much higher with whole muscle. When only consuming muscle protein, there is a slight increase from muscle itself, and when they look at heme-free muscle iron, absorption is still higher than egg albumin3<\/sup>.<\/p>\n

Inhibitors of non-heme iron absorption typically chelate, or bind, the iron to prevent absorption. Phytates (phytic acid), which also inhibit calcium absorption, chelate non-heme iron decreasing its absorption.<\/p>\n

\n
\"\"<\/p>\n

Figure 12.713 Structure of phytic acid4<\/p>\n<\/div>\n<\/div>\n

Other compounds that inhibit absorption are:<\/p>\n

Polyphenols (coffee, tea)1<\/sup><\/p>\n

\n
\"\"<\/p>\n

Figure 12.714 Structure of gallic acid, a polyphenol5<\/sup><\/p>\n<\/div>\n<\/div>\n

Oxalate (spinach, rhubarb, sweet potatoes, and dried beans)2<\/sup><\/p>\n

\n
\"\"<\/p>\n

Figure 12.715 Structure of calcium oxalate6<\/sup><\/p>\n<\/div>\n<\/div>\n

Calcium is also believed to inhibit iron uptake.<\/p>\n

References & Links<\/b><\/p>\n

1. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.<\/p>\n

2. Shils ME, Shike M, Ross AC, Caballero B, Cousins RJ, editors. (2006) Modern nutrition in health and disease. Baltimore, MD: Lippincott Williams & Wilkins.<\/p>\n

3. Hurrell R, Reddy M, Juillerat M, Cook J. (2006) Meat protein fractions enhance nonheme iron absorption in humans. J Nutr 136(11): 2808-2812.<\/p>\n

4. http:\/\/en.wikipedia.org\/wiki\/File:Phytic_acid.png<\/p>\n

5. http:\/\/en.wikipedia.org\/wiki\/File:Gallic_acid.svg<\/p>\n

6. http:\/\/en.wikipedia.org\/wiki\/File:Calcium_oxalate.png<\/p>\n<\/div>\n\n\t\t\t

\n\t\t\t

Candela Citations<\/h3>\n\t\t\t\t\t
\n\t\t\t\t\t\t
\n\t\t\t\t\t\t\t
CC licensed content, Shared previously<\/div>