Nutrition and Brain Function: The Role of Carbohydrates

The brain is the most intriguing and complex part of our bodies. It therefore needs the contributions of a variety of different kinds of food to function properly. Last week we had a look at the way in which proteins are used by the brain. This week our focus will shift to carbohydrates.

The simplest explanation for the role of carbohydrates in the human diet is one word: Fuel! There are three so-called macronutrients from which we can derive energy: They are proteins, fats and carbohydrates. Of the three carbohydrates is the most efficient energy source since it can be easily and efficiently be converted into glucose which can, in turn, be utilised directly by both nerve cells and muscles as an energy source.
Carbohydrates can be divided into two main categories. They are:

Simple Carbohydrates: This is carbohydrates made up of only one kind of sugar (e.g. fructose, glucose, sucrose, lactose or maltose). These sugars are often found in fruits, nuts, certain vegetables, cane sugar and honey. Simple carbohydrates are turned into glucose very rapidly after consumption which means that energy from it can be available very quickly to different parts of the body. However the effects of simple sugars can be compared to that of a small fire that burns intensely before going out just as rapidly as it started. This means that the bloodstream can be flooded with sugars one moment while being energy starved the next. This is the reason why it is very important that we also get sufficient quantities of the other type of carbohydrate namely ‘Complex Carbohydrates’.

Complex Carbohydrates: Complex carbohydrates are composed of several kinds of sugars (They are therefore sometimes called polysaccharides). The body takes a little longer to digest these sugars and release it as glucose into the bloodstream. This means that the energy derived from complex carbohydrates will generally last longer than that gained from simple sugars. One way of measuring the energy release from carbohydrates is the Glycemic Index (GI) which has already been discussed at length in previous articles. Suffice it to say here that GI can be a very valuable indicator of which kinds of carbohydrates will keep brain and body ‘powered up’ for longer.

The link between energy availability and proper brain function is well established. Simply put, nerve cells cannot function properly unless there is a constant stream of energy available. Consider the following:

•    Nerve cells do not store glucose. They can therefore only derive energy from what is available in the blood stream.
•    Neurons (nerve cells responsible for communication) are in a state of constant activity and do not have ‘rest periods’ like the cells in muscles or in the digestive system. Even while you are sleeping your nerve cells are busy with repairs to their structural components and the manufacture of enzymes and neurotransmitters.
•    A core activity of the nervous system is communication (i.e. the sending of ‘messages’ from one part of the brain to another or from the nervous system to another part of the body). This communication takes places through the use of bioelectric signals and is extremely energy intensive.

All of the above leads to the astounding fact that although the brain makes up only about 2% of the body weight of an average person it consumes 20% of the energy in that body. The critical importance of a continuous and reliable energy supply to the brain is further illustrated in the fact that the body will automatically prioritise the brain’s energy needs during periods of extreme trauma.

It is interesting to note that the energy usage of the brain is not on a constant high but that it can range from high to very high. Studies have shown that mentally demanding tasks like solving a puzzle or negotiating a maze actually drain away glucose from the hippocampus, an area of the brain associated with learning and memory. The implications of this fact for the design of school lunches and snacks should be obvious. If clear and intense thinking are going to be required over a long period then it would be very beneficial if the available energy can come from ‘slow release’ carbohydrates. This is where the Glycemic Index can be so very helpful as it allows us to pinpoint the types of carbohydrates that can keep us from ‘running on empty’ very soon after eating.


There are many symptoms associated with ADD-ADHD, but perhaps the most frustrating can be the lack of focus and impulsivity that often comes with the condition. It is possible that these symptoms could be traced back to a brain starved of energy. Asking questions about nutrition and specifically about the kinds of carbohydrates that you are eating should therefore be one of the first steps that you take in taking control of ADD-ADHD. This is such an important topic that it will be further investigated in further articles, please check back regularly!