September 3, 2020
In the past, nutritional research has tended to focus on the relationships between these individual components of foods and our health, based on a simple list of nutrients.
Now researchers are starting to focus on the idea of a ‘food matrix’ – how the physical and chemical properties of whole foods affect how our bodies break down and use the nutrients locked up inside them – and what this means for our nutrition and health.
Our food contains plenty more compounds than simple nutritional labeling might suggest. There are complex structures built from water, fiber, nutrients, flavor molecules, vitamins, minerals and myriad other molecules that make up the food matrix.
Food matrices, like foods, take many different forms. There are liquids (like orange juice), gels (grape jelly), emulsions (mayo), fibrous materials (fruits and vegetables), crystals (sugar), porous structures (marshmallows) and much more.
Muffins, peanut butter, burgers, cheese – each has its own combination of components mixed together in a unique way.
These properties create the tastes and textures that make foods pleasurable to eat, but they also change the nutritional properties.
For example, eating a bowl of porridge made from coarse-ground grains leads to a lower rise in blood sugar levels as the same amount of finely-ground cereal, yet the simple nutrient list would be identical.
Similarly, there’s a lower rise in blood fat after eating whole almonds compared with eating finely ground almonds containing exactly the same amount of fat.
So simply looking at the nutrient list on a food label won’t tell you the full picture about how your body will respond to it.
The structures in food affect the availability of energy and nutrients, how much of a particular nutrient is released (termed ‘bioaccessibility) as food is digested in our guts, and how well we absorb them. As a result, each food’s particular matrix can make it easier or harder to break down and use the nutrients inside it.
The nutritional information on food packaging is calculated by adding up the basic proportions of fat, carbohydrate, protein and fiber in each of the raw ingredients listed in huge databases, like this one run by the USDA. This system was originally developed by 19th century American biochemist Wilbur Atwater, and it still underpins our nutritional labelling today.
For example, a typical English muffin clocks in at 227 calories per 100 grams, made up of 1.7 grams of fat, 44 grams of carbohydrate and 8.9 grams of protein. 100 grams of ground beef contains 13 grams of fat, zero carbs and 19 grams of protein, adding up to 198 calories, while the same amount of full-fat Greek yogurt has 97 calories, 5 grams of fat, 4 grams of carbohydrate and 9 grams of protein.
But these simple tallies tell us nothing about how much of each nutrient we can digest and absorb from these foods or how each of them will affect our blood sugar or fat levels.
The impact of the food matrix was neatly shown in a study from USDA scientists, published in 2012, who investigated exactly how much energy people extracted from eating almonds, compared with the standard nutritional information that would be listed on a package of nuts.
How did they do it? By feeding people different amounts of almonds and then measuring the energy content (fats, carbohydrates and proteins) in their urine and poop, all in the name of science.
According to conventional nutritional labelling, almonds should contain around 170 calories per 28 gram serving. But the researchers found that people typically extracted only around 129 calories per serving - nearly a quarter fewer calories than would be expected just from looking at the label.
As another example, different food matrices in dairy products such as milk or cheese seem to affect how well we can absorb the protein and fat from different dairy foods, even if their labels list exactly the same amounts of each nutrient. For example, in calcium-rich dairy foods like cheese, fat droplets are encased in membranes that reduce how much fat gets absorbed in the gut, compared with eating a portion of butter containing exactly the same amount of fat.
These matrix effects mean that some foods affect our health in ways that might not be predicted by simply looking at the label on the pack. For example, full-fat dairy foods such as cheese and butter don’t increase the risk of heart disease, even though they contain relatively high amounts of saturated fat.
When you eat whole foods like fruit, vegetables and grains, your body has to work to release nutrients by breaking up the structures inside them, such as cell walls.
This means that nutrients are released more slowly or to a lesser degree - as is the case for whole almonds coarse-grain oatmeal - helping you to feel satisfied for longer, controlling blood sugar, reducing overall calorie intake and keeping your gut healthy.
The more we process our food before eating it, the more we mess up the matrix. Chewing, cooking and other types of food processing all change the composition of our foods, altering how our bodies digest, absorb and respond to them.
In some cases this is essential. We would struggle to get enough nourishment (or enjoyment!) from a cupful of dry rice, so we need to soak and cook it before eating. And many types of raw beans contain a toxic chemical called phytohaemagglutinin, which can only be inactivated by cooking.
But lots of processing also makes nutrients more digestible, so larger amounts of fat and sugar are taken up into our blood than would be accessible from less processed food with the same nutritional composition.
A good example of this happens when fruits are blended or pureed. Their internal structures and cells are disrupted, breaking down the food matrix and releasing sugars more rapidly into our blood when we eat them.
This was first shown in a classic research study from 1977 comparing the effects of eating the same amount of carbohydrates in whole or pureed apples, or in apple juice.
Although everyone’s blood sugar rose to the same level after each of the different foods, it fell much faster after drinking the juice, a bit more slowly with the puree and slowest of all after eating whole apples.
So when we drink a smoothie, we will experience a larger spike in blood sugar and a faster crash - and feel hungrier sooner - than if we had eaten the same amount of whole fruit.
Many nutritional scientists are now focusing their attention on investigating how the matrix in different foods affects how they are broken down and used, seeing how this relates to the simple list of nutrients on the label and how it impacts on health.
But there’s an extra twist to this story.
The amount of nutrition you get from a particular meal depends not only on the physical and chemical makeup of the foods you eat, but also on your body.
Our research has shown how variable our responses to foods are and that there really is no one “right” way to eat. It’s only by understanding your unique biology that you can find the right foods for you.