What does bioavailability mean?

The word “bioavailability” or “biological availability” is frequently used in the field of nutrition. However, most people do not immediately understand what it specifically means. Essentially, it refers to the body's ability to absorb certain macronutrients (carbohydrates, proteins, fats) as well as micronutrients (vitamins, minerals, trace elements, and secondary plant compounds) and use them for metabolism. What exactly does that mean?

The Definition

Scientifically, biological availability is defined as the efficiency with which a food component is systematically utilized through normal metabolic pathways. It is expressed as a percentage of intake and corresponds to the amount absorbed that is actually incorporated into and used in metabolism. The degree of usability depends on many nutritional and environmental influences as well as individual factors. The importance of nutrient bioavailability can be explained by the necessity of food for the organism. After all, we not only need to eat and drink regularly to survive but also need to provide the body with all necessary nutrients in sufficient quantities. How much of which foods we need to eat depends on the bioavailability of the nutrients in the food and the combination of different foods and their ingredients. What good is a nutrient if it cannot be absorbed and used by the body? For example, a high phytate content in the diet can impair zinc absorption, and good vitamin D supply, which can be achieved, among other things, with the help of a vitamin D3-rich oil, promotes the absorption of calcium from the intestine. More on that later.

How is bioavailability measured?

Classically, the bioavailability of a nutrient is determined using the so-called pharmacological method, which is also applied to pharmaceuticals. In this method, the concentration of the active ingredient in the blood is measured at specific time points after it is ingested orally. Plotting these concentrations over time results in a graph showing the course of nutrient absorption into the blood. The area under the curve (AUC) is used to calculate absolute bioavailability. To determine this, the same nutrient is administered intravenously at the same dose, and the resulting AUC is compared with that of the orally administered nutrient. The maximum concentration of the active ingredient is reached at the peak of the graph when the amount absorbed equals the amount metabolized. For most nutrients, however, this method is not suitable for determining their bioavailability, as many minerals and trace elements are regulated by the body to maintain constant blood levels, known as homeostasis. In the field of nutrition, the “balance method” is often used instead. In this method, a specific amount of a nutrient is ingested orally, and after a certain period of time, the amount excreted in the stool is measured. The difference represents the amount retained in the body, which is considered bioavailable. However, this approach does not fully match the scientific definition of bioavailability, as it measures potential absorption rather than actual metabolism of the nutrient. Furthermore, many nutrients are broken down and transformed by bacteria in the colon, which could skew the measurement of bioavailability. For minerals and trace elements, these processes play a lesser role, making the “balance method” more suitable for determining their bioavailability. The concentration of a nutrient can also be measured in the urine following ingestion. There are additional methods to measure bioavailability, which we will not cover in this article.

Interim Conclusion

At this point, we can conclude that bioavailability is a very complex process influenced by many factors. As a result, determining bioavailability is not always straightforward. Ideally, all possible influencing factors should be considered when measuring and calculating nutrient availability. However, this is almost impossible, as individual factors such as organ function or the composition of our gut flora also play crucial roles in the metabolism and excretion of nutrients. Additionally, bioavailability is often equated with absorption (as hinted above with the “balance method”), which makes it difficult to distinguish between the two. Ultimately, the question remains as to how accurate and useful a generalized bioavailability statement can be, as it does not apply equally to all individuals and is highly variable due to numerous influencing factors.

Excursion: What is the food matrix?
In nutritional science, the food matrix refers to the structure and composition of a food. The ingredients are not randomly distributed but arranged in specific structures, such as being inside or outside a cell, bound to another substance, or in free form. These structures, which are characteristic of each food, determine the availability and effect of individual nutrients.

Factors influencing bioavailability

Other components of food, the digestive performance of our gastrointestinal tract, the composition of gut flora, individual characteristics of a person, the processing and preparation of food—all these are factors that can influence the bioavailability of nutrients. Additionally, the food matrix (see box) plays a crucial role in the availability of a nutrient. For example, when nutrients are embedded in a complex structure, they must first be released by digestive enzymes before our body can absorb them. Furthermore, many compounds in animal and plant-based foods are present in different chemical forms. For instance, iron in meat and sausage products is present in a more bioavailable form (heme iron), absorbed at about 15 to 35 percent. Plant-based foods, however, contain non-heme iron, absorbed at only about 5 percent. Combining animal and plant-based foods can almost double the bioavailability of plant-based iron. Additionally, the simultaneous intake of vitamin C, as found in our organic acerola, can significantly improve the absorption rate of iron by converting poorly soluble non-heme iron into the more soluble heme iron form. So, don’t forget a piece of fruit with your oatmeal! On the other hand, some food components hinder the absorption of other nutrients, forming poorly soluble complexes known as antinutritional substances. This group includes phytates, tannins, and oxalates found in grains, legumes, and vegetables, which are important components of a healthy diet. In the context of a balanced mixed diet, these substances are not a cause for concern. Chemical and physical characteristics also play a role in nutrient availability. Fat-soluble vitamins (vitamins A, E, D, and K), as their name suggests, should be taken with fats or oils for optimal absorption. The same applies to the curcumin contained in our curcumin capsules. Thorough chewing ensures that food components are released from the food matrix in the mouth, making them more accessible to digestive enzymes. This can save your gastrointestinal tract a lot of work. Not all nutrients are equally resistant to environmental factors. Heat-sensitive vitamins like vitamin B1 and pantothenic acid are destroyed at high temperatures, while minerals like calcium and magnesium, found in Sango coral, are very stable against light, heat, and oxygen. The rule “more is better” may apply in many cases, but it is not always appropriate when it comes to nutrient intake. For instance, excess water-soluble vitamins like vitamin C cannot be stored, as the excess is simply excreted in the urine, and extremely high dosages that are not medically justified should be avoided.

The bioactive form

As you know, the components and nutrients in our food exist in different chemical forms. When referring to the bioactive form of a nutrient, it means the form that can be directly incorporated into the body's metabolic processes and used. Essentially, all substances are bioactive that trigger a reaction in our body. However, most nutrients exist in forms that must first be converted into another form before they can be part of a reaction. For example, beta-carotene from carrots, as a provitamin, is a precursor to “eye vitamin” A, which is only formed in the body.

Natural foods vs. supplements

Whole foods, as natural sources of proteins, fats, carbohydrates, fiber, vitamins, minerals, trace elements, and secondary plant compounds, form the basis of a balanced diet. In certain situations, dietary supplements can also be a helpful way to ensure daily nutrient supply, compensate for increased needs or deficiencies, and support specific requirements. According to current knowledge, most opinions suggest that individual nutrients and vital substances should not be considered in isolation but rather in the overall context of nutrition. Many indications suggest that the complex interplay of naturally occurring substances and their interactions with other compounds provide their actual health benefits. If you want to enhance your diet with specific nutrients, you should prefer natural products and make use of the synergistic effects of beneficial nutrient and food combinations.