Ask the Diet Doctor: Bioavailability
Q: Should I be concerned with the bioavailability of nutrients in food?
A: Yes, certain vitamins and minerals can interact with other nutrients in our diet and decrease our bodies' ability to take them in. Here's what you can do to maximize your body's uptake of a few key nutrients.
Vitamin A (Beta-Carotene)
Clinical deficiencies of vitamin A are rare in the U.S., but since only one-third of women eat enough daily servings of fruit and vegetables, many are not reaching optimal levels of beta-carotene. This plant-based precursor to vitamin A is found in many red, yellow, and orange veggies, and also functions as an antioxidant. Increased beta-carotene intake is associated with reduced risk of several cancers, ALS, and eye disease.
To improve your absorption of beta-carotene, pair veggies with fat. For example, research shows that eating avocado with salsa, which is rich in beta-carotene due to the tomatoes, boosts absorption. And rather than fat-free dressing, drizzle your salad olive oil or top with avocado or pieces of cheese.
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This nutrient is extremely important for the transport and distribution of oxygen throughout the body. It's estimated that 9 percent of women have clinical iron deficiencies, with many more falling short of optimal intakes. Iron comes in two forms. The first, heme iron, is found in animal sources like beef and turkey, and is absorbed very well with no known dietary inhibitors. This is not the case with the second kind of iron, non-heme iron, which is found in plant-based sources like spinach, beans, tofu, and fortified cereals.
Calcium inhibits the absorption of non-heme iron, meaning you may want to rethink pouring milk on your iron-fortified cereal. Vitamin C, on the other hand, increases non-heme iron absorption, so adding bell peppers or orange slices will not just make your spinach salad taste better, it will also help you absorb almost three times more iron from the leafy green.
This mineral is used in more than 300 reactions in the human body. Improving magnesium status can lead to better blood sugar control, insulin sensitivity, and reduced risk of heart disease. Dietary sources of magnesium include nuts, green leafy vegetables, and beans. Since magnesium works with calcium and vitamin D to maximize bone health, you can enhance uptake of magnesium by taking a vitamin D supplement-just don't exceed 1,000 to 2,000 IU. This way you reap the added benefit of vitamin D at the same time. (See my previous column for more on D.)