How much does sugar affect brain performance?

Dick is stupid for the brain

Very few people want to be fat, but more and more people are getting fat. Two thirds of men and half of women in Germany carry too much body fat with them, a quarter of all adults even so much that they are considered obese. Worldwide, the number of fat men has tripled since the 1970s and that of women has doubled.

So much fat is not good for the brain, that's for sure. Fat people are more likely to get diabetes, a disease the incidence of which has also doubled worldwide in the last 20 years and which shrinks the brain and increases the risk of stroke and dementia. And even those who are only fat and do not (yet) have diabetes must expect a reduced brain volume and cognitive limitations.

Why is it? The long-term relationships between eating, obesity, and the brain are notoriously difficult to study. We consume complex mixtures of nutrients that change on a daily basis and that are neither easy to document precisely nor are they easy to control over the long term. Their effects on the body build up over decades and can be influenced by many other aspects of lifestyle.

The different modes of action of different sugars and fats on the body as well as the hormones that it uses to maintain its energy balance play a central role. Carbohydrates consist of various simple sugars, including grape sugar (glucose), which is made up of starch molecules, and fruit sugar (fructose), which together with glucose forms white table sugar (sucrose). Glucose is an important fuel for the body and especially for the brain. However, too much of it in the blood can also be harmful, especially because excess proteins accumulate. The resulting glycoproteins form deposits and contribute to local inflammatory processes that damage cells and vessels, be it in the context of diabetes complications or degenerative diseases of the nervous system.

When the level of glucose in the blood rises, the pancreas secretes the hormone insulin, which allows cells to absorb glucose and remove it from the blood. Cells can either use glucose directly as an energy source or store it after biochemical conversion - in muscle cells and liver in the form of the polysaccharide glycogen, in fat cells as fatty acids. If little or no dextrose gets into the blood for a long time, other hormones stimulate it - such as B. glucagon, which is also produced in the pancreas - opposing processes to meet the body's energy needs: glycogen stores are broken down; Fat cells release their stores and the liver uses protein breakdown products to produce glucose itself if necessary.

A controversy begins at this heart of energy metabolism: if a constant rush of sugar in the blood promotes fat storage thanks to increased insulin secretion, eating with fewer carbohydrates should make it easier to access body fat reserves and thus keep your appetite in check and your figure slim, say proponents low-carbohydrate diet. Man is also prepared for this, since carbohydrate bombs have only become possible through modern agriculture. The opposite position sees the problem with the overall excess of food, which leads to excessive eating pleasure in modern industrial societies regardless of the carbohydrate content. The premise is that if you constantly eat more than you consume, you will get fat.

The opponents agree that the insulin metabolism should remain in equilibrium. If that doesn't work, there is a risk of insulin resistance, a condition in which body cells become insensitive to insulin and which increases the risk of diabetes and other diseases [see insulin resistance box]. The fact that too much sugar is unhealthy is at least now accepted. Since 2015, the World Health Organization has advised reducing the consumption of added sugar to below 10 percent of your daily energy intake, and possibly even to below 5 percent. This is also due to the fact that sweet things usually contain not only glucose, but also roughly the same amount of fructose thanks to the composition of the most popular types of sugar.

This particularly sweet-tasting simple sugar does not trigger any insulin release. For many years, fructose has therefore been recommended as a healthy alternative to table sugar, especially for diabetics, and has been added to many foods. However, fructose is now considered to be much more unhealthy than glucose. Because fructose is mainly metabolized in the liver - where it is mainly converted into fat. This sugar goes straight to the hips - and also stimulates the fat storage from other components of the food. In addition, fructose reacts even more strongly than glucose with proteins and can increase insulin resistance, especially in the liver.

Whether the regular consumption of carbohydrate-rich food has a negative effect on the metabolism regardless of a high sugar content remains a matter of dispute. Proponents of a high-carbohydrate mixed diet argue that many carbohydrates are unproblematic as long as unprocessed foods such as whole grain products are consumed, which do not increase the blood sugar level as suddenly as e.g. B. white flour products or sweet drinks.

The role of dietary fats is also controversial. The German Nutrition Society, for example, advises in its guidelines to eat little fat, since fat leads to the consumption of too many calories and thus to obesity due to its high energy density.

However, different fats have different effects on the metabolism and also on the brain. It is relatively well documented that so-called trans fats, which z. B. arise in industrial fat hardening and frying, baking or deep-frying are not good for the body. They have an unfavorable effect on the blood lipid distribution and inflammation levels and increase the risk of developing cardiovascular diseases and dying from them. Furthermore, based on previous studies, they are at least suspected of contributing to obesity, insulin resistance and diabetes, impairing cognitive performance and promoting depression, aggression and dementia.

In contrast, unsaturated fats, which are liquid at room temperature, have a much better reputation. This is especially true for monounsaturated fatty acids, which z. B. are contained in olives, avocados but also in meat, nuts and dairy products, and polyunsaturated omega-3 fatty acids, which are particularly found in fatty sea fish. They form an important structural component of biological membranes and help keep them flexible and prevent inflammation. The brain particularly likes to build with the omega-3 fatty acid DHA, which is mainly concentrated in the cell membranes of nerve cells. So it is hardly surprising that omega-3 fatty acids are one of the few nutrients that have a demonstrably and consistently positive effect on cognitive development and performance, mental health and resistance to dementia.

However, they can only develop their effect if at the same time too many omega-6 fatty acids, which are contained in many oil seeds, compete for the enzymes that are used in the omega-3 metabolism. If omega-6 fatty acids get out of hand, inflammation levels rise and the associated risks of becoming ill - e.g. B. Alzheimer's dementia. Since many popular edible oils such. B. sunflower or rapeseed oil are rich in omega-6 fatty acids, the ratio between these and omega-3 fatty acids is often unfavorable in industrialized countries. A largely unanimous dietary recommendation is therefore to aim for a more favorable omega ratio by increasing the consumption of oily fish and fats that contain less omega-6.

How saturated fats - which are typically solid at room temperature - affect health is less clear. While assumptions that have been made for decades that they have a fundamentally negative effect on the metabolism have so far hardly been confirmed, the suspicion that they impair cognitive functions and promote dementia remains more persistent. The study situation remains ambiguous for the time being. In any case, it is unlikely that saturated fats are fundamentally bad for the brain metabolism, if only because the body itself stores a large part of its energy reserves in the form of saturated fatty acids. If there is a temporary lack of food, these are released and used. Such phases in no way have a negative effect on the brain. (See box Ketogenic Diet)

The fact that it is so difficult to make simple statements about the advantages and disadvantages of fat, sugar and their individual variants is also due to the fact that nutrients constantly interact with each other and with the respective conditions of the body and can accordingly have different effects. In addition to insulin, a number of other hormones influence the energy metabolism, including leptin, ghrelin and cortisol. Depending on the situation, they are produced by different tissues and can curb or stimulate the appetite. Body fat is one of the most hormonally active and diverse tissues. B. satiety hormones, love handles a substance that promotes insulin sensitivity, and belly fat secretes inflammatory substances.

There is even a type of fat called brown fat, which is particularly high in mitochondria and specializes in converting fat into heat. It used to be thought that only babies who are at risk of cooling down had brown fat, now it has also been discovered in the body of adults. Since brown fat can help you lose weight and have an overall beneficial effect on your metabolism, researchers are intensively looking for ways to stimulate it. This works, for example, with mild cold stimuli.

If you definitely want to do your metabolism good, you don't have to limit yourself to shivering walks without a jacket. As complex as the relationships between macronutrients and human bodies may be, there are foods that make you fat beyond any doubt and can mess up your energy metabolism. This is especially true for treats that combine several suspicious food groups. Industrially processed nibbles, sweets, pastries and ready meals in particular usually contain a lot of fat and lots of carbohydrates. In addition, they are not only available everywhere, but are specifically developed by the food industry in such a way that they have the most enticing effect on the brain's reward system. Also z. B. the salt content, fragrances, flavorings and other additives as well as mechanical properties such as crispness can contribute to the fact that the brain reacts to such food offers with helpless desire.

Some researchers even draw parallels with drug addiction. They argue that the constant supply of junk food and the dopamine release that stimulates its consumption have a long-term effect on the plasticity of the brain in such a way that those affected simply can no longer resist such foods. In fact, many overweight children and adolescents show restricted executive functions - those cognitive abilities that enable us to control our attention and actions in a targeted manner and to defy impulses.

To what extent this is the cause or result of certain nutritional behavior - or both applies - remains open for the time being. But it is worthwhile to find ways to avoid the constant onslaught of junk food: A British study of 14,500 families recently showed that toddlers who were given breast milk and fresh, home-cooked food were later slightly more intelligent, even after checking all other factors than their peers who started life with highly processed, high-fat and high-sugar industrial foods.