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Processing changes the food we eat – here’s what that means for health

To understand how healthy a food is, we generally look at its components – carbohydrates, fats and proteins, or the vitamins, minerals and other substances it may contain. But this purely “nutritional” vision overlooks one property that’s a key part of a food’s health potential – its structure.

For example, serving a child a breakfast cereal made up of whole wheat or rice may seem like a good idea, but research shows that processing can significantly impact its nutritive qualities.

Extrusion-cooking or puffing can transform wheat and rice into primarily a source of sugars that the child’s body rapidly absorbs, and many of the nutritive values of the original grains are lost.

The “matrix” of a food

Too long ignored by nutritionists, the concept of a food’s structural matrix is crucial to correctly assess its health potential, especially at a time when ultra-processed products have flooded supermarket shelves.

The term matrix (from the Latin “mater” meaning mother) refers to an element that “provides support or structure, and serves to surround, reproduce or construct”. In the case of food, it is a kind of three-dimensional structure. Within this matrix, the elements that compose a food interact with each other, conferring particular properties.

Take an almond: it is hard, brown and fibrous. If an almond is ground, its matrix changes: it’s now in the form of powder. But if the composition of ground almonds is theoretically identical to that of whole ones, their effects in the body are not the same. In particular, the nutrients are digested differently, altering the body’s physiological and metabolic responses.

The matrix effect of food implies that “two foods of identical composition but with different structures do not have the same effects on health”.

Put differently, for the body, a calorie of food A is not the same as a calorie of food B. What is crucial is the matrix environment of the calorie, the structure within which it is contained. In short, all calories are not interchangeable.

The parts and the whole

The “matrix” effect is not just about whole foods, but also about food ingredients, and even the nutrients themselves.

Take food carbohydrates (also known as starches): if you hydrolyse them to create a glucose syrup and then a glucose-fructose syrup, the composition – or at least the calorie content – remains the same. Fructose has the same composition as glucose, but a different structure.

However, the effects on the human body are no longer the same, because the glycemic indexes – the intensity with which a food boosts blood-sugar levels – differ. Moreover, despite a low glycemic index, excessive consumption of fructose has been associated with fatty liver disease or non-alcoholic fatty liver disease.

Consequently, understanding the “matrix” effect of foods, ingredients and nutrients is essential to correctly assessing their effects on human health.

Three physiological effects

Because of the range of impacts they can have, the matrix of foods play a fundamental role in our diet:

  • Our sense of satiety. The form of a food – hard, soft, friable, liquid and more – affects how much we must chew, and the more we do, the higher our sense of satisfaction and fullness.
  • The rate of release of nutrients in the digestive tract, and therefore their availability and subsequent use by the body.
  • How quickly food moves through the digestive tract.

If we again take the example of almonds, whole ones have a solid matrix and must be chewed, making them more satisfying. Compared to ground almonds, solid ones also release less fat in the blood and do so more slowly. All three effects are essential mechanisms for long-term health.

Similar differences exist for whole apples (solid matrix), apple sauces (semi-solid matrix) and apple juice (liquid matrix), and this holds true for all foods. Consequently, we should always favour a food in its solid form if it is regularly consumed.

From processing to ultra-processing

Modification of a food’s matrix is sometimes desirable because it makes it more digestible. However, transformations that completely disrupt its matrix to isolate its ingredients and then recombine them in artificial matrices can pose health problems.

One of the main characteristics of many ultra-processed foods is not only the loss of the “matrix” effect by cracking/fractionation, but also by extraction, purification, hydrolysis or chemical modifications.

Such foods are both “hyper-palatable” (which leads to over-consumption), yet they’re crumbly, soft, viscous or liquid and are thus little chewed (and therefore don’t satiate us). These two qualities are the essence of “junk food”, addictive yet empty of almost everything but calories.

The example of dietary fibre is also interesting. Industrial food companies often add fibre to products that have been over-refined. However, fibres naturally present in food matrices are associated with phytonutrients, including antioxidants.

By passing through the blood, these molecules potentially protect against the oxidation of low-density lipoprotein (LDL). Known as “bad cholesterol”, these oxidized LDLs can form atheromatous plaques in blood vessels, a cardiovascular risk factor.

The antioxidants associated with the natural food fibres also help fight free radicals produced by colonic bacteria. With added dietary fibre, however, these positive effects are lost.

Public health recommendations

The explosion of chronic disease in the world may be due more to the loss of the “matrix” effect of food than to its composition.

Indeed, research indicates that the degradation or artificial modification of a food’s original matrix is one of the key drivers of excess calorie intake. The over-consumption of saturated fats, salt, sugars and additives is simply a symptom of this modification.

Based on the scientific evidence, it is essential that nutritional recommendations begin to take into account the “matrix” effect of foods.

For researchers, this opens up a whole range of scientific exploration in the field of processes and formulations.

For us as consumers, solutions are often within arm’s reach: when given the choice between whole, complex natural foods and ultra-processed products derived from them, go for the ones that are closest to their natural state.

The Conversation, authored by Anthony Fardet, Researcher, UMR 1019 – Unit of Human Nutrition, University of Clermont-Auvergne, INRA; and Edmond Rock, Director of Research, INRA. This article was originally published in French.

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