Food matrix and nutrient bioavailability overview
- Bioavailability defines proportion of nutrients absorbed and used by body
- Food matrix describes food physical structure composition and nutrient interactions
- Dense matrices trap nutrients while inhibitors like phytate reduce absorption
- Ultra processed foods have pre digested matrices enabling faster nutrient uptake
- Product design must consider matrix effects not just nutrient fortification
The way consumers – well, people in general – absorb nutrients is complex. They cannot simply identify the necessary nutrients and insert them into the body, like inputting code into a computer. Other factors have a role to play.
One of these is bioavailability – the extent to which nutrients can be absorbed. Another is the food matrix, the physical structure of the food in question.
The interaction between these two elements has a significant influence on how nutrients enter the body.
What is bioavailability?
Bioavailability is “the ability of the body to use the nutrients in foods”, explains Marion Nestle, professor of nutrition, food studies and public health at New York University.
“If nutrients are not absorbed across the intestinal wall, they cannot be used and are not bioavailable,” she says.
Essentially, bioavailability refers to the proportion of a nutrient that is absorbed into the body and used for normal body functions.
How bioavailable a nutrient is is not only based on which nutrient it is, but its position within a food. This is due to the food matrix.
What is the food matrix?
The food matrix is, essentially, the physical structure of food. It is not only the composition of the food’s nutrients, bioactive constituents and other compounds, but also their place within the food’s structure.
Therefore, the food matrix reflects how a food is processed, as processing, almost by definition, changes food composition and, by extension, food structure.
Crucially, the food matrix also refers to how these different elements interact. The placement of different elements within food affects how they are digested and metabolised.
How does the food matrix impact nutrient bioavailability?
The bioavailability of food often depends on its food matrix; in particular the ‘tightness’ of its structure.
“If the structure of a food is tight, enzymes in the digestive tract can’t release nutrients,” says Nestle. “Sugars are easy for enzymes to get to; the fats in almonds are not.”
Essentially, in a dense food matrix, a nutrient may be physically trapped and therefore less accessible for the body to absorb.
Nutrients in meat, one study suggests, are more bioavailable than those in plants because certain vitamins in plants are trapped in or bound to the food matrix. For example, niacin, also known as vitamin B3, can be linked to carbohydrates or peptides in grains and not fully released.
Constituents may be present in the food that enhance absorption. For example, iron from meat is more bioavailable than iron from plants. Conversely, nutrients may be bound to an inhibitor, such as phytic acid, that makes absorption more difficult.
Processing often, but not always, affects bioavailability. For example, processing milk does not affect the bioavailability of calcium.
What is the impact of the food matrix on UPFs?
One of the main arguments against the use of the term ‘ultra-processed food’ in discussions around health is that it refers to processing rather than nutrient content. Critics of the concept argue that the food sector should be focused on the latter rather than the former.
However, this framing does not take into account the role of the food matrix in influencing how nutrients are absorbed.
“Ultra-processed foods tend to have an essentially pre-digested matrix,” says New York University’s Nestle.
This means that their structure is taken apart during the production process, before they are consumed. This, according to Nestle, makes it easier for the body to absorb nutrients from them.
One review article proposes that this rapid absorption of nutrients may suppress secretion of satiety-boosting hormones, such as GLP-1.
Is bioavailability different for foods and supplements?
Are nutrients less bioavailable when consumed in the form of supplements than they are when consumed in foods?
“I’m not sure they are,” says Nestle. ”Some foods have components that make nutrients more bioavailable, but others don’t.“
While it is true that, in general, supplements do not produce the same benefits as nutrients in food, this is not necessarily down to bioavailability.
In fact, according to Nestle, the reasons for this are not entirely known. While bioavailability differences are often attributed to the food matrix, Nestle suggests that there could be other reasons for the differences in nutrient absorption between food and supplements.
“One possibility is that foods contain many nutrients that interact to produce benefits; eating isolated nutrients is not as beneficial – although supplements work well for treating vitamin and mineral deficiencies," she says.
One study suggests that supplements and nutrients added to food are at least as bioavailable as those produced in the food endogenously (by the food itself).
What this means for industry
It is important to understand the relationship between a food matrix and nutrient bioavailability. When creating food products, it’s not enough to simply shove in as many nutrients as possible; how the food matrix will affect consumers’ absorption of them must be understood.
This understanding may also shed light on the negative health outcomes that have been linked to ultra-processed foods. The impact of the disrupted food matrix of many GLP-1s on bioavailability is a crucial factor to address in debates around the topic. When industry is trying to address the backlash, it should take the food matrix into account.
Understanding of the food matrix and how it influences bioavailability is still developing, but industry’s approach to food composition should develop with it.
