Dr. Ed Blonz

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Do veggies prevent mineral absorption?

http://www.NewsAndOpinion.com -- DEAR DR. BLONZ: I am a vegetarian, and I've read about compounds in vegetables that prevent minerals in food from being absorbed. I'm concerned, because my main source of calcium comes from vegetables and grains. -- G.R., Oakland, Calif.

Dear G.R.: Some vegetables contain compounds that bind, or chelate (KEY-late), minerals such as calcium, iron and zinc, preventing their absorption. The two main compounds are phytates, found in oatmeal and other whole-grain cereals, and oxalates, which are present in rhubarb and spinach, among other foods. Spinach, for example, is high in iron and calcium, but it also has a high concentration of oxalates.

Although spinach is a healthful food that contains a number of valuable phytonutrients, its oxalate content prevents it from being a good dietary source for calcium (and magnesium). Usually about 10 percent to 25 percent of calcium in foods can be absorbed, but a study in the American Journal of Clinical Nutrition (April 1988) found that only about 5 percent of the calcium in spinach is absorbed. A second study two years later in the same journal (April 1990) reported that the calcium absorption in a low-oxalate vegetable, such as kale, was comparable to that found with dairy products.

Zinc deficiency was first researched in men on a high-phytate cereal grain diet. The phytates in whole grains are not a problem, it turns out, if present in yeast-leavened bread. This is because yeast contains an enzyme that breaks the bond between the phytate and the mineral. This enzyme isn't effective in foods such as pita bread, where the short fermentation and baking time isn't long enough to break the metal-phytate bond. Zinc deficiency tends to be prevalent in parts of the Middle East where pita bread accounts for about 85-percent of the calories.

Because vegetables and grains are the core of your diet, make sure you include a wide variety of different food sources. Fruit and vegetable sources of calcium without significant quantities of chelators include broccoli, turnip greens, collards, kale, mustard, figs and almonds.

DEAR DR. BLONZ: I just turned 80, and my husband and I try to watch what we eat. After dinner, while we read or watch television, we enjoy a dish of ice cream. Is there anything wrong with this? We put it in a sauce dish. - H.L., Pleasanton, Calif.

Dear H.L.: It is tough to provide specific dietary advice when I don't know much about the rest of your diet or about your health history. I would say that, assuming good health and a good lifestyle, there is absolutely nothing wrong with eating ice cream. The key is the sum of what we eat throughout the day. With few exceptions, it doesn't pay to get all worked up about single foods. You are in the eighth decade of life, so you must be doing something right. I encourage you to enjoy each other and enjoy your lives.

DEAR DR. BLONZ: You responded recently to a reader who questioned whether it is OK to take calcium with vitamin C. I wonder if your writer didn't confuse his or her information. As you said, there isn't a problem with calcium and vitamin C (note that calcium is now added to many citrus drinks), but there is a problem with the body's ability to absorb iron and calcium simultaneously. I discovered this fact by accident after I was diagnosed as anemic and began taking a prescribed iron supplement. I chose to take the iron pill with a glass of calcium-fortified orange juice.

The vitamin C should have been a catalyst for iron absorption, but the added calcium blocked it, and my body did not absorb the iron. My anemia continued, and I was so fatigued that I suspected I might have mononucleosis. By changing to regular orange juice (NOT the calcium-fortified blend), my anemia symptoms and fatigue disappeared. I think you should alert your readers to this. Many may not be aware that adding a seemingly benign supplement like calcium to orange juice can wreak havoc on one's health in so short a time. - H.H., Baltimore, Md.

Dear H.H.: I had considered that the questioner might have meant calcium and iron, but it was unclear whether this was the case. Good job on your detective work. Thanks for bringing this information to our attention.

JWR contributor Ed Blonz, Ph.D., is a nutrition scientist and author of Power Nutrition and the "Your Personal Nutritionist" book series. Send questions to him by clicking here.