Are you absorbing the nutrients you eat?

An introduction to understanding the bioavailability of micronutrients.

The term bioavailability refers to the proportion or fraction of a nutrient, consumed in the diet, that is absorbed and utilized by the body. According to a micronutrient lecture by Dr. Suzanne Cole at the University of Michigan, bioavailability is influenced by several factors including diet, nutrient concentration, nutritional status, health, and life-stage. Diet-related factors affecting foods include the structure of food, the chemical form of a particular nutrient, interactions between various nutrients and foods, and the processing or treatment of a particular food.

What does this mean?

One example of food structure influencing bioavailability or the utilization of nutrients is with plant foods. The rigid cell wall of plant cells can make the nutrients in plants less bioavailable or usable when eaten. Health or life-stage similarly affect bioavailability because individuals absorb and use nutrients differently depending on their age, general health status and if they have any acute or chronic health conditions. Eating certain foods together can also influence how the body absorbs various micronutrients because some components of foods interact with other foods, leading to less absorption than expected.

How does this affect nutrient absorption?

Structure of food

Nutrients from plant foods or other foods that take longer to digest such as corn or meat are less bioavailable than nutrients in foods with less complex tissue structures. Foods of this type must be broken down or cooked in order for certain micronutrients to be available for absorption.

Health or life-stage

There is a normal decline in gastric acid as we age, so younger individuals can have a higher bioavailability of micronutrients than older individuals. This means our ability to absorb micronutrients is reduced as we age.

Chemical form

Heme iron is more readily available for absorption than non-heme iron. Heme iron is found in foods like meat, fish or poultry and non-heme iron is found in plants. Recommendations for iron intake for vegetarians are higher than for those who eat meat because the non-heme iron in plants is less bioavailable.

Interactions with compounds in foods

Antioxidants like phytates or polyphenols can bind with certain micronutrients in the gastrointestinal tract and prevent absorption into the body. Phytates are found in the outer layer of plants and can bind with minerals like zinc, calcium or iron, which prevents their absorption in the intestines. Polyphenols are a compound found in plants that can also interfere with mineral absorption in the intestines.

What can we do?

  • To increase the bioavailability of nutrients in foods with rigid tissue structures, chop or mince the food before consumption. For example, in order to get the most folate (a water-soluble B vitamin) from spinach, mince or chop the leaves.
  • If you are a vegan or vegetarian and not consuming foods with heme iron (fish, meat, poultry), increase your consumption of foods that are good sources of non-heme iron like nuts, beans, vegetables, and fortified grain products.
  • Antioxidants like phytates and polyphenols are reduced in the processing or treatment of foods. Examples include pounding grains to remove the bran, soaking grains in water and discarding the water (phytate is water-soluble), or cooking foods like beans to reduce polyphenols. While antioxidants are important dietary components, consider balancing consumption of both raw and cooked foods to ensure maximum micronutrient absorption.
  • Consume foods that work together to increase absorption of certain micronutrients. Eating citrus foods or foods high in vitamin C with foods high in iron increases the absorption of both heme and non-heme iron. This also prevents minerals from binding with phytate or polyphenols in the gastrointestinal tract.

The field of nutrition and related topics can seem complex so Michigan State University Extension has a number of resources for further reading. Contact your local MSU Extension county office for information about programs near you. For individual concerns related to nutrient absorption, see your primary care provider and a registered dietitian.

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