Ask the Diet Doctor: Nutrient Absorption


Q: A friend recently learned she's not absorbing nutrients from her food effectively. I'm wondering if I am. Is there a test my doctor can run to check this?

A: Some people hold a misled belief that many of us are not absorbing the nutrients we're eating, but there is really no good data to support this assertion. In fact, the obesity epidemic proves just the opposite-we are absorbing calories and nutrients too well!

Your small intestine is the primary site for nutrient absorption in your digestive system. It is designed to absorb and take up all the nutrients in the food that you eat (one of the reasons it is 20 feet long). You should assume that, in general, you are absorbing nutrients very well.

However, optimizing your nutrient status isn't just about absorption. It is possible you aren't getting enough of certain nutrients, or maybe you are getting adequate levels of a particular nutrient, but your individual needs for that nutrient based on your unique metabolism and genetics is more than the average person. Four little-known but important nutrition tests can ensure that your body is getting enough of several key nutrients. [Tweet this tip!] (Talk with your doctor if you are interested in any of them.)

1. Omega-3 index: This test shows what percentage of fats that make up your red blood cell membranes are omega-3 fats EPA and DHA. Research has shown that people with higher omega-3 indices have a reduced risk of heart disease, reduced levels of cognitive impairment with aging, and a slower rate of cellular aging. An optimal omega-3 index is 8 percent, while the average American is at 4 to 5 percent. You can order your own home test at

2. Vitamin D test: Vitamin D is a tricky nutrient. It is very important for bone health, immune function, heart health, brain development, and muscle function. Since your body can produce vitamin D from sunlight, you don't typically need to worry about getting enough. However, many factors such as having darker skin, covering up your skin completely when you go outside, not going outside during the middle of the day, or residing in northern parts of the United States can make for lower D levels. Because of all these different variables, I recommend that clients talk to their doctor about getting a vitamin D blood test. If your levels are low, consider eating more vitamin D-rich foods (i.e. fortified dairy and fish), taking a vitamin D supplement of the appropriate dose (ask your doctor), or getting out more often in the middle of the day.

3. DEXA: It is estimated that nearly 30 percent of postmenopausal women in the U.S. and Europe have osteoporosis. Preventing this problem can't start soon enough (read: in your 20s!). Bone health is extremely important and while we generally attribute this to calcium, there are lots of other nutrients like vitamin D, potassium, vitamin K, and magnesium that all influence the complex building (and breaking down) of your skeleton. Bones are essentially a mineral bank, but unlike a regular bank, your ability to make deposits greatly decreases as you get older. In fact, by the time you hit your early 30s, your ability to bolster your bone density starts to greatly decrease. The best way to determine if your bones are strong and dense enough is a DEXA scan. Armed with this data, you can craft a plan to optimize your intake of key minerals and do resistance training to maintain or re-establish optimal bone density.

4. B12 status: Necessary for the formation of red blood cells, proper functioning of your nervous system, and the cellular metabolism of fats and proteins, vitamin B12 is found in animal products. The liver can also store levels of vitamin B12, enough to last you a couple years, making deficiencies rare. However, if you have been eating a vegan diet (or a vegetarian diet with minimal animal products) for an extended period of time, you run the risk of not having enough vitamin B12 to meet your body's needs. A vitamin B12 blood test is a simple way to determine your status so your physician can figure out the best way for you to obtain more of it if need be (i.e. dietary means, shots, supplements, etc.).

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