The battle continues between eating whole foods and ultra-processed foods. NOVA classifies foods and their ingredients into four categories from unprocessed to culinary ingredients to processed to ultra-processed. As we go up the scale from unprocessed to ultra-processed, foods become unhealthier. The difference is so stark that it is recommended we only eat processed foods occasionally and ultra-processed ones not at all. The question becomes why does ultra-processing make food so unhealthy? The food matrix provides one explanation.

How the food matrix explains the dangers of ultra-processed foods. When we examine the label of a packaged product we see a list of nutrients and their relation to their % daily value. What the label doesn’t do is provide context. Each food is made up of numerous chemicals arranged within a structure called its matrix. This matrix affects how we perceive a food’s appearance, its flavor, and its texture contributing to its acceptability in our minds. Researchers tell us that the matrix also affects the nutritional properties of a food as well. Bioaccessibility to our bodies of each nutrient is affected by how tightly it is bound to other components in the matrix. Minerals and vitamins can interact more readily if they are confined within a single matrix. Sugars, salt, fats, vitamins and minerals can be released more slowly during digestion if confined in a matrix. The idea is that whole foods have a more complex structure than ultra-processed ones and that we overconsume the latter and not the former.

A primary advocate for relating the food matrix to human nutrition is Anthony Fardet. Much like Colin Campbell, Fardet takes a holistic rather than a reductionistic approach. He says that an emphasis on amounts of fat, salt, and sugar content of ultra-processed foods is missing the mark. It is all about the matrix as “calorie quality matters more than calorie quantity.” [1] Free sugars metabolize differently from sugars in the matrix. Variables associated with the matrix include the extent of chewing, time spent during digestion, the feeling of fullness, nutrient bioavailability, secretion of hormones and interaction of bioactive compounds.

Eating whole foods allow the matrix to connect the mouth with the digestive tract, and the brain network receiving signals from the lining of the stomach. Fardet also notes that blood sugar levels do not spike with whole foods like they do with ultra-processed ones. In addition to modulation of nutrient absorption by dietary fiber, the authors suggest that protein digestion also affect the feeling of fullness helping prevent overeating. Synergy between antioxidants in whole foods helps to protect our cells from uncontrolled oxidation. He notes that more than seventy studies have implicated ultra-processed foods in development of chronic disease.

A food science perspective on the food matrix. José Aguilera provides a somewhat different view of the food matrix[2]. He describes the matrix in terms of its microstructure or a food’s physical and spatial domain. It is affected by food and oral processing as well as digestion. A food’s microstructure affects flavor perception, mouthfeel, and the feeling of fullness. It has implications in nutrition, sensory perception, food allergies and food intolerances. In nutrition, the matrix affects both bioaccessability and bioavailability. While Fardet [1] focuses primarily on cell structure of fruits and vegetables, Aguilera [2] notes that ultra-processed foods have a matrix as well. Bread, for example has a spongy matrix. A food matrix may be fluid such as milk, a sauce, or a cracked egg. Other forms include emulsions, exocellular, gels, and viscoelastic. Artificial matrices can improve palatability of food products as well as nutrient delivery during digestion.

A note of caution on the food matrix. The food matrix, as described by Fardet [1], provides the best explanation of weight changes in the NIH study [3] led by Kevin Hall. A diet of unprocessed foods is high in the cellular matrix of whole fruits and vegetables. In contrast, investigators observed weight gain linked to the diet containing ultra-processed products. Here we have a difference between foods with a natural food matrix and commercial products with an artificial food matrix. We might imagine a discussion between two researchers trying to explain the difference:

Holist: Well Kevin Hall showed us that whole, unprocessed foods keep us from gaining weight, unlike ultra-processed ones.

Reductionist: Yes, but the unprocessed foods caused the participants to lose weight. I thought weight maintenance was the goal for healthy people.

H: It’s all about the food matrix. Whole foods from plants slow the digestive process and the release of fat and sugar.

R: Yes, my friend, but Hall observed that participants on the unprocessed diet ate 500 calories a day less than those in the ultra-processed diet. It’s all about the calories!

H: OK, but don’t you think that the whole food matrix provides protection from nutrient destruction and other bad things that can happen during digestion?

R: I think that the complex chemicals in plant cell walls released during chewing and digestion provide a protective effect. I am not so sure that you can credit the food matrix as such.

H: There you go again! The ultra-processed participants had fiber added to their diet too, and it didn’t seem to help them. We eat foods, you, know not nutrients.

R: Hey, the fiber in the ultra-processed diet was not the same as that in the unprocessed diet. The plant fiber in fruits and vegetables might be the most health-promoting factor in these foods! And, by the way, most of us eat meals not just foods except when we snack.

H: So, what does that have to do with anything?

R: The data collected on the protective effect of a food matrix, such as on sugar release (glycemic index) or nutrient interaction is studied on individual foods and not on the mix of many different foods consumed as part of a meal.

H: But the glycemic index is a very good way to studying the release of sugar and the danger it can pose to our health!

R: I am a skeptic. Look at the tables. There is very little difference between brown and white rice. Chocolate foods have a much lower glycemic index than rice. Fat, like dietary fiber, can also slow digestion.

H: It’s always easy to point out exceptions, but the glycemic index is still a great way to separate out healthy foods from unhealthy ones!

R: You are beginning to sound like a reductionist! A more holistic way of thinking would be to develop healthy dietary patterns as opposed to unhealthy ones. That would be a more meaningful approach.

H: So, you don’t think the food matrix plays much of any role in nutrition!

R: I don’t think that we can really tell. The whole food matrix of fruits and vegetables could be exerting a protective effect as you suggest or it could just be the physical properties of the dietary fiber from plant cell walls.

H: How could we tell which is the most important factor?

R: I don’t know, but if you want to visualize what your meal looks like in the stomach, think of the last time you vomited!

H: Oh gross! You really are demented about this, aren’t you?

R: Just offering you a simple mental experiment!

H: But can’t you agree that a natural food matrix is superior to an artificial one?

R: No, I can’t. It is just those ingredients that make an artificial food matrix that classify them as ultra-processed.

H: You are hopeless. You just want to add more chemicals to food!

Take-home lesson. The food matrix is a novel concept that could explain differences we see in whole and ultra-processed foods. Holistic viewpoints clash with reductionistic ones. Is one superior to the other? Or does the answer lie somewhere in between? Both holism and reductionism tend to oversimplify each other’s arguments. Each perspective has its strengths and limitations. Medical scientists have designed artificial matrices to deliver drugs directly to the needed sites in the body. Would food scientists be able to do the same for delivery of a single nutrient or combination of nutrients? Would such a product provide a health benefit, or would it just reproduce the dangers posed by ultra-processed foods? Specific answers to this question probably reflect a confirmation bias based in holism or reductionism.

Thanks to Linn Steward who pointed me to Anthohy Fardet and the Food Matrix.

 Coming soon: Correlation without cause

References:

[1] Fardet, A. and E. Rock, 2022. Chronic diseases are first associated with the degradation and artificialization of food matrices rather than food composition: calorie quality matters more than calorie quantity. European Journal of Nutrition 61:2239–2253 https://doi.org/10.1007/s00394-021-02786-8

[2] Aguilera, J.M. 2018. The food matrix: implications in processing, nutrition and health, Critical Reviews in Food Science and Nutrition 59:3612-3629. https://doi.org/10.1080/10408398.2018.1502743

[3] Hall, K.D., Ayuketah, R. Brychta, H. Cai, T. Cassimitis, K.Y. Chen, S.T. Chung, E. Costa, A. Courville, V. Darcey, L.A. Fletcher, C.C. Forde, A.M. Gharib, J. Guo, R. Howard, P.V. Joseph, S. McGehee, R. Ouwerkerk, K. Raisinger, I. Rozga, M. Stagliano, M. Walter, S. Yang, and M. Zhou, 2019. Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of ad libitum food intake. Cell Metabolism 30(1):67-77. DOI: 10.1016/j.cmet.2019.05.008