Thousands of research studies link specific foods to decreased health risks, such as cancer. But few research studies, if any, indicate that some of these same foods, when eaten in excess, can cause nutrient deficiencies.
One concern is that it can take a significant amount of time before a person experiences adverse effects, and many nutrient deficiencies can impact a person’s quality of life and cause other health conditions.
Healthy nutrition involves much more than simply consuming large quantities of “healthy” foods. It’s also important to eat everything in moderation and to eat a varied diet.
Question: What nutrients are commonly affected by consuming them in excess or in the wrong combination with other nutrients?
Answer: Minerals are the most likely nutrients to be negatively affected, but some vitamins are vulnerable as well. Here are three examples.
>> Foods in the brassier family, such as kale, broccoli, Brussels sprouts, collard greens and cabbage, are promoted as healthy foods. Although moderate amounts of brassica vegetables can be beneficial, these foods decrease the thyroid gland’s ability to take up iodine, necessary for producing thyroid hormones. When there is a deficiency of iodine, the thyroid gland adapts by enlarging and can result in a goiter.
Raw brassica vegetables contain the highest concentrations of goitrogens (substances that disrupt the production of thyroid hormones). Be aware that drinking a green smoothie with raw kale several times a week can be hard on the thyroid gland. Include good sources of iodine in the diet, such as iodized salt (not sea salt), to help counter harmful effects of goitrogens.
>> Calcium is essential for numerous biological functions, including bone health, heart health and muscle function. However, calcium inhibits the absorption of iron, zinc and other trace minerals when they are consumed at the same meal. To avoid this problem, eat foods high in iron or zinc (red meats) with meals low in calcium. For example, a burger without cheese or a shake will allow more trace minerals to be absorbed.
Interestingly, some multivitamins and mineral supplements designed for women have high amounts of calcium, iron and zinc in the same pill. In those combinations, calcium will be absorbed, but little of the iron or zinc will be available to the body. To get the most out of supplements, take a separate calcium pill at a different time of day from a pill containing iron and zinc.
>> Oats and other high-fiber foods promote gut health by supporting our microbiome (gut organisms). But like calcium, fiber inhibits the absorption of iron and zinc. Including an enriched white bread source daily could help to provide more iron with less fiber.
Joannie Dobbs, Ph.D., C.N.S. and Alan Titchenal, Ph.D., C.N.S. are retired nutrition faculty from the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa.
