How Much Nutrition Do You Absorb from Food?
You could be absorbing anywhere from 10 to 90 percent of the nutrients in a given food. Find out which factors affect nutrient absorption.
Monica Reinagel, MS, LD/N, CNS
Listen
How Much Nutrition Do You Absorb from Food?
Nutrition Diva listener Andrew writes:
“We can measure the amount of vitamins and minerals in a food, but how do we know how much of that our bodies actually absorb? If a banana contains 422 mg of potassium, for example, do our bodies take in 100% of that? What factors determine how much (or how little) nutrition we get from our food?”
There are, in fact, lots of things that influence what percentage of vitamins and minerals are absorbed, such as the other foods you eat at the same meal, how they are prepared, drugs or supplements you may be taking, even your age and the time of day. Taking all of these into account, you might absorb anywhere from 10 to 90% of a given nutrient from a given food!
Before I get into some specific examples, however, I want to clear up a common misunderstanding about the nutrient content of foods.;
The Nutrient Content of Foods Varies…a Lot
The USDA maintains a huge database of the nutritional composition of thousands of foods. If you look up “banana” in the National Nutrient database, you will see that a medium banana contains 422 mg of potassium. But that is just an average—in this case, based on 14 different samples. In fact, the amount of potassium in these 14 samples ranged from 364 mg to 502 mg per medium banana.
See also: Nutrition Diva’s Potassium Cheat Sheet
The amount of vitamins and minerals in a raw food depends on the variety, growing conditions, weather, timing of harvest, and storage conditions, not to mention natural variation. Although the variables are fewer, even dietary supplements may contain slightly more or less than the amount shown on the label.
So, even if there were a way to predict exactly what percentage of a nutrient your body will absorb (which there isn’t), we’d still be starting with an approximate figure.
With that in mind, let’s take a look at some of the many things that influence nutrient absorption.
Factors That Affect Nutrient Absorption
Which Foods You Eat. Studies show that eating vegetables together with healthy fats, such as avocados or olive oil, can greatly enhance absorption of carotenoids, for example. On the other hand, oxalates in spinach and tea can inhibit the absorption of calcium and iron from foods you eat at the same meal. Phytic acid in grains and legumes can also impair absorption of minerals. However, as I discussed in a previous show, mineral deficiencies caused by phytic acid are unusual, except in cases where people have extremely limited diets and are relying on a single food for most of their calories.
See also: The Other Side of Phytates
How Foods Are Prepared. Cooking can decrease the amount of vitamins in a food, but certain nutrients, such as the lycopene in tomatoes, are rendered more absorbable when they are cooked. And, as I discussed in another recent episode, blending and juicing fruits and vegetables makes some nutrients more absorbable.
See also: Does Blending Destroy Fiber?
The Form of a Nutrient. The chemical form of the nutrient can also be a factor. The non-heme iron found in vegetables is considerably less bioavailable than the heme iron found in animal foods, for example. Calcium phosphate is much more absorbable than calcium chloride, and so on.
The Amount of a Nutrient. The body also adjusts its absorption efforts in response to how much a nutrient is present—and how much is needed. When a meal is rich in calcium, for example, it is not as efficiently absorbed. Conversely, if the diet is low in calcium, the body gets more efficient at extracting and absorbing calcium from foods.
See also: Diet for Healthy Bones
Other Nutrients. Sometimes, nutrients help each other out. Foods high in vitamin C can boost your absorption of iron, especially from plant-based foods, for example. Other nutrients get in the way of each other by competing for the same metabolic pathways. Taking in too much zinc, for example, can reduce your absorption of copper. And in a recent episode on Vitamin E, I mentioned that taking in too much of one form (alpha-tocopherol) can reduce absorption of some of the other forms. These competitive pathway problems, by the way, are almost always the result of taking supplements.
See also: Can You Get Too Many Vitamins?
Time of Day. Some nutrients are also affected by circadian rhythms. Calcium absorption, for example, is governed in part by parathyroid hormone, which reaches a peak during the night. For this reason, many people advise taking calcium supplements right before bed. I’d prefer that you skip the calcium supplements, and get your calcium from foods throughout the day, which is another way to boost absorption.
See also: Should You Stop Taking Your Calcium Supplement?
Medical Conditions. There are medical conditions, such as Crohn’s disease or pernicious anemia, that can gravely impact nutrient absorption. Nutrient absorption also tends to decline as we age. Your doctor can advise you on any special nutrition needs or risks, based on your specific situation.
Drugs. Certain drugs can affect nutrient absorption as well. The most common example of this is acid-blocking drugs. Some nutrients, such as B-12, calcium, and iron, depend on the high acidity of your gastric juices to release them from foods. Those who habitually take acid-blocking drugs often have impaired nutrient absorption and—as a result—can actually develop nutrient deficiencies.
See also: How to Avoid Acid Reflux
Why None of This Matters as Much as You Think
By now, you’re probably wondering how you’ve managed to survive this long and how you can possibly keep track of all of these factors! Relax. There’s no need to.
For one thing, the dietary guidelines and recommended intakes for nutrients take into account that you’re going to absorb only a portion of the nutrients in your food. The recommendations represent the amounts you need to take in order to get enough, despite this. And when you make it a priority to get the lion’s share of your nutrients from foods instead of supplements, you’ll avoid the most common imbalances.
Finally, although the ways in which foods and nutrients interact can get very complex, when you eat a good variety of nutritious foods, all of the factors that enhance or inhibit absorption of nutrients tend to balance one another out.
See also: How Important is a Varied Diet?
Additional Reading
Nutrient Bioavailability: Getting the Most Out of Food
Photos of Sandwich Detective, Avocado and Seeds, and Juggling Foods courtesy of Shutterstock.
About the Author
Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes’ most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation’s leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.