Bioavailability: Everything You Need to Know

Bioavailability refers to the amount that one’s body can absorb and use a nutrient or drug. Before breaking down how our body absorbs specific compounds, let’s talk about broader backdrop subjects; macronutrients and micronutrients. Macronutrients are fats, carbohydrates, and proteins and have a very high bioavailability; meaning that our body readily absorbs macronutrients. On the other hand, micronutrients, essential vitamins and minerals for health, have a low bioavailability. When a micronutrient is taken orally through food or vitamin supplement, there are certain criteria that must be met for its specific contents to actually be absorbed. 

Some examples of micronutrients such as Zinc, Magnesium, and Iron, are inorganic compounds so there are limits to how the body can absorb them. Beyond these three minerals, other well-known micronutrients, like Vitamin C, Iron, Calcium, and Vitamin D, are typically found in multivitamins. But before skipping to taking these micronutrients as supplements, how can we properly absorb these essential minerals through food? 

How a food is cooked can alter its degree of bioavailability. For example, raw vegetables are more bioavailable than cooked vegetables. Also, what a food is paired with can heavily impact its bioavailability. Eating rice and beans on their own is great, but paired together, they provide certain amino acids the other lacks. Since rice has a high level of the amino acid methionine, and beans contain lysine, pairing these ingredients together forms a complete protein. Thus, the chemical form of a nutrient impacts its bioavailability. Eating vegetables raw, or combining certain foods, can strengthen the degree of a food’s bioavailability.

Since it’s not easy to regulate or constantly oversee which micronutrients you absorb through food, it is critical to cover how minerals are absorbed through vitamin supplements. In order to improve a vitamin’s bioavailability, there are certain ways to orally take the vitamin. This brings us to water-soluble vs fat-soluble vitamins. Water-soluble vitamins, such as Vitamins B and C, dissolve in water present in the body. On the other hand, fat-soluble vitamins such as Vitamins A, D, E, and K, can only dissolve in fatty tissues within the body. So, water-soluble vitamins are best absorbed by the body when taken on an empty stomach, while fat-soluble vitamins must be consumed with food.

Beyond the differentiation of water-soluble and fat-soluble vitamins, it is essential to note that only a certain amount of a micronutrient can be absorbed at once. For example, the body can only absorb 500 milligrams of calcium at a time. So, if you want to add more than 500 mg of calcium to your diet per day, you need to engage in dosage splitting. This practice is defined as taking a vitamin, such as calcium, at two separate times of the day so you can absorb its maximum dosage twice. Since calcium is fat-soluble, it must also be taken with food twice a day.

If there’s one piece of advice to give when taking a vitamin as an oral supplement, it’s to look for the chelated version of a mineral. This means that the vitamin is paired with certain minerals and amino acids that enhance the vitamins’ absorption and bioavailability. For example, the chelated forms of iron, zinc, and magnesium are iron bis-glycinate, zinc picolinate, and magnesium glycinate. Beyond the vitamin supplement, though, it’s best to take in micronutrients through food. If there’s one thing to say about taking in micronutrients through food, it’s that I suggest adding a fat source (olive oil, cheese, avocado) to your salad. This is one of the easiest steps to absorbing the fat-soluble vitamins present in vegetables in a salad! Getting a wide variety of vegetables and nutritious foods in your diet is easier than downing multiple vitamins a day! So, whether you’re trying to increase the amount of micronutrients you take in through food or vitamin supplements, it’s clearly not so easy, but I hope that these tips will help!