What role does sugar play in our microbiome?
If you follow current dietary recommendations, you might get the impression that man's worst enemy is sugar. Like the demon Balrog of Morgoth, who dragged Gandalf into the abyss in the mines of Moria, any sugar structure appears as a deadly monster. Fueled by the classic, black-and-white headlines in the media, consumers either avoid eating sugar or simply ignore all warnings. But surely it should be possible to view sugar in a completely neutral light?
Sugar is essential for life
First of all: sugar is important for our survival. By breaking down sugar molecules, we gain vital energy in the form of ATP. This energy carrier is our body's currency. We gain energy in one place in the body and thanks to ATP we can use it again in another place. It is comparable with the sale of bread rolls by the baker. He gets money and can use it to pay for his house to be repaired. This way of storing energy has proven itself in evolution and is the reason why it is the same in all life forms, whether humans, animals, plants, bacteria or archae.
There are different forms of sugar: sugar molecules with a very simple structure (single or double sugars), which can be metabolized quickly, and complex sugars, so-called polysaccharides, which can only be broken down with the help of special enzymes.
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The main diets
However, since sugar consumption has increased dramatically in recent decades, it is the main target of every diet. But has sugar consumption really climbed so dramatically? A look at the statistics shows that in Germany, annual per capita consumption has risen from 28.1 kg in 1950 to 33.8 kg in 2020. This is less than one would expect, but of course definitely more than Stone Age man consumed. For him, consuming sugar was a luxury, since he couldn't buy a candy bar at every kiosk. However, more crucial than the amount of sugar is the type of carbohydrates. But let's first focus on the types of diets.
Most diets are based on the following mechanisms:
Diet 1: Complete elimination of sugar - the keto diet.
As soon as the body is no longer supplied with sugar, it switches into an alarm mode. Without sugar it would die, so it first attacks its sugar stores, glycogen, and then it must try to produce the most important intermediate compound, Acetyl-CoA, which is necessary for the production of ATP (our energy currency), in a different way. To do this, it switches to fat metabolism, in which Acetyl-CoA is extracted from fat. This happens in the liver.
We remember that Acetyl-CoA is needed throughout the body for the production of ATP, our energy store. Now the fact that we have a lot of Acetyl-CoA in the liver when we stop consuming sugar is nice, but the body would still die because all other places in the body lack Acetyl-CoA. Therefore, in the liver, the Acetyl-CoA is converted to ketone bodies.
These ketone bodies serve as transporters for the Acetyl-CoA and can transport it to where it is needed. However, once the ketone bodies have arrived in the muscle and brain, our two largest sugar utilizers, they must first be converted back to Acetyl-CoA. This is done by special enzymes, but these have yet to be produced. The Acetyl-CoA that is then released again can be used for urgently needed energy production.
It feels like you are getting sick
Therefore, there is a "time window" in the keto diet in that the body must adapt to utilize the fat and produce the required enzymes.This usually takes 2-3 days. This usually takes 2-3 days. During this time, you feel flabby, tired, and often have headaches and aches in your limbs. It feels like you are getting sick. In fact, only the whole body adjusts. This may also cause bad breath, which is caused due to one of the ketone bodies formed, acetone.
This diet is popular because, first, it completely eliminates sugar, and second, it then stimulates fat breakdown, which the body needs to survive. A short keto diet of 1-2 weeks can definitely help combat a non-alcoholic fatty liver. It is important that sufficient proteins and especially electrolytes, which are lost due to the high water loss, are consumed.
The keto diet should not be practiced for longer
However, the keto diet should not be practiced for longer, even though many people swear by it. The elimination of sugar triggers stress in the body. We must not forget that the formation of ketone bodies is a mechanism that arose during evolution to allow humans to survive in times of crisis.
During the keto diet, a whole range of harmful substances are released.These do not matter when a person is struggling for bare survival and when they are formed only for a short time. But if the release is continuous, it can lead to serious diseases.
Diet 2: Reduction of sugar
The so-called low-carb diet focuses on reducing the amount of sugar. In principle, reducing carbohydrates is a good idea, because we eat far too much sugar due to the industrialization of food. But eating less sugar than necessary also causes stress.
Basically, humans should form one third of their energy turnover from carbohydrates, and the other two thirds in equal parts via fats and proteins. Based on a woman's basal metabolic rate of 1,500 calories, for example, 500 calories should be formed via carbohydrates, 500 calories via proteins and 500 calories via fat.
However, if the consumption of carbohydrates is below the recommended third, this again means a deviation from the norm and thus stress for the body. Especially since the missing calories are often compensated by the intake of fats.
Diet 3: Focus on sugary foods, with a low glycemic index.
The theory behind the body weight loss strategies known as the Atkinson, Montignac or Glyx diets is as follows: The glycemic index refers to the ability of a food to raise blood sugar levels. Foods with a high glycemic index therefore lead to a high insulin secretion, which in turn leads to the cells absorbing more carbohydrates so that the high blood sugar level soon returns to normal.
At the same time, the release of glucagon, the antagonist of insulin, is inhibited. As a result, the cells absorb more sugar and fat storage is activated. This in turn leads to a lack of blood sugar after 2-4 hours, resulting in a feeling of hunger and increased food intake. This creates a vicious circle that promotes obesity. Additionally, a permanently high insulin secretion can lead to insulin resistance.
Each person reacts differently to food intake
In principle, the idea of eating more foods with a low glycemic index is excellent. However, it often also leads to a conscious or unconscious reduction in sugar intake and an increase in the consumption of animal proteins. In addition, each person reacts differently to food intake, making the calculation of the glycemic index inaccurate.
Sugar and microbiota
But what do diets actually have to do with bacteria? The microbiota, i.e. the totality of all bacteria in our body, needs sugar to survive just as we do. Without it, we cannot survive. So when we mess with our sugar intake, we directly affect the composition of our microbiome (=bacteria in our body + the totality of their genes).
Important bacteria die if our sugar intake is too low, while others gain an advantage from it. Our bacteria live in constant coexistence. They produce substances that other bacteria need to survive. In addition, they keep pathogenic bacteria from taking control in our body.
Conversely, we also shift the stable composition of our microbiota when we consume too much sugar. All of a sudden, bacterial populations have enough energy to prevail over other populations.
Therefore, a balanced diet is important to maintain our stable microbiota and not give pathogens the opportunity to multiply. An important point here is diversity: only a balanced, rich microbiota consisting of many different species can keep harmful bacteria in control.
It’s our choice. We can support our good bacteria!
And this is the essential point: we can influence the composition of our bacterial populations. It’s our choice. We can support our good bacteria! When we reach for the supermarket shelf, when we prepare our food - we are in the active role. If we don't let ourselves be blinded by the advertising promises but look behind the facades, then we can recognize quite quickly what is good for us or not, without necessarily being an expert. Common sense is enough for this.
It is obvious that a brown and sweet cream sandwich has nothing to do with health, even if the advertising promises otherwise. We can decide for ourselves how we start the day. It are the many small micro-decisions in every second of our lives that determine whether or not we will be healthy in a few years.
Experiments have shown that a diet rich in glucose and fructose has a direct effect on the microbiome. Even though the studies were only done on mice, the effects were obvious. As soon as the mice were fed only simple sugars, the diversity of their microbiome decreased. Certain bacterial species died out and other species in turn became dominant. This was accompanied by intestinal inflammation, liver inflammation and an increase in fat.
You can think of it this way: Our small intestine is where most of the nutrients that enter there from the stomach are absorbed. From there, they are distributed throughout the body via the bloodstream. Some nutrients, however, continue on to the connecting large intestine and serve as food for our gut-based microbiome, which is primarily located in the large intestine.
There are also some "bad" bacteria lurking in the intestine
In the gut microbiome, there are "good" and "bad" bacteria. The good bacteria generally only metabolize the sugars that cannot be metabolized by humans, or can only be degraded poorly. They are specialists and have adapted perfectly to the human-bacteria symbiosis over thousands of years.
However, there are also some "bad" bacteria lurking in the intestine. These can break down simple sugars in particular. As soon as we consume larger quantities of them, simple sugars pass from the small intestine into the large intestine, where they lead to an excessive proliferation of the "bad" bacteria.
These microorganisms have the advantage that they can firstly quickly metabolize simple carbohydrates and secondly, generate rapid growth from them. The proportion of these "bad" bacteria thus increases and they displace our "good" bacteria.
This has two effects: Our "good" bacteria become fewer and can no longer support our health to the same extent as before. At the same time, the "bad" bacteria become more and thus have a negative impact on our health.
Mother knows best
Complex carbohydrates are found, among other things, in
vegetables, especially broccoli, zucchini, lettuce, cucumber and cauliflower
Complex carbohydrates are healthy because they do not spike blood sugar levels (low glycemic index) and because they promote our "good" microorganisms. However, for a healthy diet, we should follow the above-mentioned division into thirds (1/3 of the required energy each from carbohydrates, fats and protein.
So when our mother told us to eat more vegetables and whole grain bread, she intuitively knew what was healthy.
Even without knowing the exact details of the glycemic index and the microbiome.
Further literature and references:
Do MH, Lee E, Oh M-J, et al (2018) High-Glucose or -Fructose Diet Cause Changes of the Gut Microbiota and Metabolic Disorders in Mice without Body Weight Change. Nutrients 10:761. https://doi.org/10.3390/nu10060761