I read that the protein in milk could cause kidney damage and the calcium in milk isn't well absorbed. Is this accurate?
Both statements could be viewed as technically accurate, but most nutritionists would say they are also misleading.
The first statement is true only for people with kidney problems, and it holds for any type of protein. People with pre-existing kidney disease or with just one functioning kidney should work with a dietitian to make sure their dietary protein is low enough to prevent overload on the kidneys. For most people, the protein in milk doesn't pose any such risk.
As for the absorbability of calcium from milk -- well, it's true, but calcium isn't absorbed very well by the body from any source. Typically, nutritionists estimate, most people absorb only between 20 percent and 40 percent of the calcium they consume. Lots of factors help or hinder that absorption, including:
- Your age. As bones develop, infants and young children can absorb 60 percent or more of the calcium from their diets. But as people grow older, their body's absorption of calcium declines.
- Vitamin D, which promotes calcium absorption and helps form and maintain strong bones. Most milk products are fortified with vitamin D.
- Phytic acid and oxalic acid. These substances, found in some plant foods, bind to calcium and reduce the absorption rate. Spinach, collard greens, sweet potatoes, rhubarb and beans are high in oxalic acid. Soybeans are high in phytic acid, but studies indicate that calcium from soybeans is still partially absorbed. Fiber, particularly from wheat bran, contains phytate (phytic acid salt) that may inhibit calcium absorption.
- High protein and high sodium. Both can increase calcium loss through urine, but increasing potassium could help slow the loss, especially in postmenopausal women. Even so, the major factor negatively affecting bone health is low calcium intake.
The bottom line? Most people should try to consume more calcium, and low- and non-fat milk and dairy products are just as good or better than other calcium sources. In fact, consumption up to 2,500 milligrams a day shouldn't cause any problems.
The "Daily Value" for calcium, used on Nutrition Facts labels, is 1,000 milligrams. That's how much calcium adults up to age 50 should consume each day. Older adults should get more -- 1,200 milligrams a day. To track your calcium consumption using Nutrition Facts, add a "0" to the percent listed for calcium. For example, if a label says the food gives you 15 percent of the Daily Value of calcium, it contains 150 milligrams.
Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or email@example.com.
Editor: This column was reviewed by Hugo Melgar-Quinonez, nutrition specialist for Ohio State University Extension and the Ohio Agricultural Research and Development Center, and assistant professor in the Department of Human Nutrition, College of Education and Human Ecology.
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