Processed foods affect your microbiome and your risk of getting obese

In 2012 researchers did a study that had a puzzling outcome. Two of the groups of mice in the study were given a diet that had the same composition of fat, protein and carbohydrates, and other ingredients. Despite these similarities, the effects of the diets on body weight were very different. One group got obese and had other adverse effects, and the other group did not.

These findings may be hard to explain if all one considers when assessing different diets is the nutrient content of meals, and if one does not take the microbiome into consideration. Because, food is more than nutrients. How the food is processed, the rapidity of how a meal is eaten and the frequency of the meals in a given diet, are some other factors that may play a role in how foods affect us. We’ll get back to the mice and why they got obese shortly, but let’s first take a closer look at the food we eat from the view of what we do to the food after it has been harvested.

It is time to shift from a nutrient to a structure centered view of our food

In terms of post-harvest changes, or in other words, processing of foods, there are several factors that could change the health impact of foods, both in terms of structure and in terms of food stuffs added or subtracted to the food product. These include emulsifiers (common additives that are added to improve the consistency of foods), sweeteners and taste enhancers, milling and extrusion of grains, mincing of meat, and extraction of sugars, starches and oils. These factors have received little attention as a separate entity in nutrition research. The focus has instead mainly been on the nutrient content. Thus, there is a chance of “receiving a stronger signal” when investigating how processing affects health, rather than looking at for instance processed foods such as milled grains and table sugar solely as separate entities. That is, milled grains and sugar share some physical properties that non-milled grains don’t share with sugar. In other words, as a simple hypothetical example, just as it would lead to less clear results to leave out, for instance, half of the sources of sugar for participants in a study analyzing their habitual diet and health outcomes, the same goes for physical properties of foods. If it is the physical properties of sugar that foremost make sugar bad, then other foods that share the same properties should be grouped together to find out if it is a certain kind of processing that leads to adverse health outcomes.

We eat more of easily accessible nutrients

Let’s jump back many years in time to see what changes in the human diet may tell us about the effect of food processing on markers of health. A paper titled Sequencing ancient calcified dental plaque shows changes in oral microbiota with dietary shifts of the Neolithic and Industrial revolutions found that at shifts in the degree of processing of foods, in particular the advent of agriculture, and – during the Industrial revolution - a sharp increase in the use of refined (table) sugar and refined grains, the oral microbiome changed from a composition that is associated with good health to a one that is associated with poorer health. Now, there may be several factors that could explain these changes, but one factor that did change during these times was the accessibility of nutrients, meaning that through milling and other processing, more nutrients were released from plant cells before these plants/grains were consumed.

Well, this is the situation that one could imagine that a bacterium in your mouth and gut would be in when you ingest either sugar or regular bread as opposed to either, say, an apple or non-milled grains. When faced with easily accessible sugars or starches this could signal increased opportunities for survival and make the bacteria metabolically hyperactive. This increased nutrient availability may be related to increased virulence (bad behavior of microbes) as shown in a recent study, and perhaps "territory expansion" that interferes with how the body regulates fat mass. (It is known that increased amounts of bacterial products that enter the blood stream (a form of "territory expansion"?) can influence body weight regulation.)

Compared to what was the case throughout the larger part of our evolutionary history, the average diet in the Western World is vastly different in terms of easily accessible nutrients, or, using a more scientific term: acellular nutrients. Think of how much more pasta, bread (whole-meal, white bread, croissants – doesn’t matter – they are all mostly acellular products), crackers, tortilla chips, pizza, chocolate, candy, waffles, donuts, cookies and sodas you consume compared to your distant relative from the African savannas?

Only future studies can tell us if this is of large significance in terms of developing obesity and other lifestyle diseases, but at least one study points to the amount of acellular nutrients being a significant factor. In this study, a so-called (healthy) Mediterranean diet (including flour-based foods, rice and dairy products) was compared to a so-called Paleolithic diet (or in other words, an unprocessed diet). In short, the ones on the Paleolithic diet fared better in terms of obesity-related factors than the ones on the Mediterranean diet. Furthermore, the more rice the individuals in the Mediterranean diet chose to eat, the better their health markers were at the end. Rice is a cellular food. That is, the nutrients are not as easily accessible as in flour-based foods.

A food item is seldom negative for health in itself.
It’s the processing that turns healthy foods into unhealthy ones.

So, back to the puzzling mice study. The only difference in the two groups’ diet was the consistency of the diets. The group that had worse health outcomes were given food that had a soft consistency and the other group ate the same food as hard pellets. What does this have to do with microbes and nutrient accessibility? Well, the connection is not obvious, but it could be argued that decreased nutrient accessibility for the microbes is a more likely place to search for the reason for the effects than how the diets affect the mice’ body directly (did the pellets remain partly in “a pellet state” upon entering into the small intestine?) .

At least, the new knowledge of the microbiome gives us a chance of being better able to explain some issues in nutrition related research that before seemed puzzling or contradictory.

For more on how mincing of meats, chopped vegetables and other foods, and that are stored for a while, may affect health see this. For more on how emulsifiers and several other processed food factors may affect health see this article by the author.