| Food and Nutrition Q&A: | |
by Chelsy Leslie, from the January 2003 newsletter
Q: I heard that too much protein in our diet can cause calcium to be
pulled from our bones! Is this true? Does that mean that vegetarians need less
calcium because they eat less protein?
A: It is no secret that calcium is essential for building strong bones and minimizing bone loss. The Dietary Reference Intake (DRI) for calcium for both men and women is 1300 mg for age 18 and younger, 1000 mg for ages 19-50, and 1200 mg for age 51 and up. These levels are considered adequate for the majority of the US population. However, individual calcium needs vary depending on many factors including diet, lifestyle and genetics.
Protein is one dietary component that affects calcium balance in the body. Low and excess protein can both be detrimental to bone health. Protein is required for building, repairing, and keeping bones healthy and strong.
Excess dietary protein may be bad for bone by causing calcium loss. When protein is broken down in the body, acid is produced. The body compensates by buffering the acid through a complex process that involves the release of calcium from the bone. The calcium is then excreted in the urine. The higher the protein intake, the more calcium is lost. Protein-containing foods vary in the amount of acid they generate. Although animal proteins are commonly assumed to produce more acid, this is not always true. Fish, meat, poultry, cheese, and many grain products have a high potential renal acid load (PRAL), a measure of acid production. Milk and yogurt have a low PRAL. Fruits and vegetables have a negative PRAL, meaning they supply alkali that can help buffer acid.
Based on protein's effect on calcium balance, a diet lower in protein may have lower calcium requirements than a high protein diet. Although vegetarians tend to consume less protein than meat-eaters, most still eat above the amount considered adequate-especially if dairy and/or eggs are included in the diet. The standard recommendations for calcium are most likely suitable for vegetarians as they usually eat plenty of protein.
Rather than ask, "Do vegetarians need less calcium?" the question should be, "Should people with high protein diets consume more calcium than is recommended?" The answer to that question is, "Yes." To offset the loss of calcium in the urine caused by processing protein, a high calcium intake can protect bone health. However, too much calcium can also be detrimental and intake should not exceed 2500 mg per day.
It is important to keep in mind that protein is only one part of the picture. Other dietary components affect calcium as well. For example, a high sodium intake can also cause calcium to be excreted in the urine. In addition, while a vegan diet may be lower in protein, it is usually high in oxalates and phytates. These compounds are present in some plant foods and they bind calcium so it cannot be absorbed. Foods high in potassium, such as fruits and vegetables, help to buffer acid that is produced and reduce the amount of calcium lost in the urine.
To protect your bones, consume a diet adequate in protein (0.36-0.45 grams of protein per pound of body weight), high in fruits and vegetables, moderate in sodium, and high in calcium. Good sources of calcium include milk, yogurt, fortified soy or rice milk, tofu processed with calcium sulfate, calcium-fortified orange juice, collard greens, kale, mustard greens and blackstrap molasses. In addition to eating well, physical activity in your daily routine can help to strengthen bones.
Have a food or nutrition question? Please send an email.
Chelsy Leslie, RD is a registered dietitian interested in public health and disease prevention.
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