I thought it was common knowledge, but have linked some info here from a scientific site, with sources and quotes from recognised research institutes (www.fi.edu/learn/brain/carbs.html):
basically, carbs are necessary, just chose good carbs (whole grain bread, note coca cola) that release energy slowly. Cutting out carbs drastically affects your brain:
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Nourish - Carbohydrates Fuel Your Brain
Glucose is the form of sugar that travels in your bloodstream to fuel the mitochondrial furnaces responsible for your brain power. Glucose is the only fuel normally used by brain cells. Because neurons cannot store glucose, they depend on the bloodstream to deliver a constant supply of this precious fuel.
This blood sugar is obtained from carbohydrates: the starches and sugars you eat in the form of grains and legumes, fruits and vegetables. (The only animal foods containing a significant amount of carbohydrates are dairy products.)
Too much sugar or refined carbohydrates at one time, however, can actually deprive your brain of glucose ? depleting its energy supply and compromising your brain's power to concentrate, remember, and learn. Mental activity requires a lot of energy.
Your brain cells need two times more energy than the other cells in your body.
Neurons, the cells that communicate with each other, have a high demand for energy because they're always in a state of metabolic activity. Even during sleep, neurons are still at work repairing and rebuilding their worn out structural components.
They are manufacturing enzymes and neurotransmitters that must be transported out to the very ends of their? nerve branches, some that can be several inches, or feet, away.
Most demanding of a neuron's energy, however, are the bioelectric signals responsible for communication throughout the nervous system. This nerve transmission consumes one-half of all the brain's energy (nearly 10% of the whole body's energy).
Complex vs. Simple Carbohydrates
Complex carbohydrates are like time-release capsules of sugar. Simple carbohydrates are more like an injection of sugar.
Complex carbohydrates tend to be in natural foods ? and have long chains of sugar molecules that the liver gradually breaks down into the shorter glucose molecules the brain uses for fuel. In natural foods, the cell walls are made of cellulose fiber that resists digestion, slowing the breakdown and the subsequent release of sugars into the bloodstream, kind of like the way a time-release capsule works.
Simple carbohydrates are found in most processed or refined foods and some natural foods. These carbohydrates have short-chained sugar molecules and, because they break apart quickly, enter the bloodstream quickly. Sugary foodsincluding corn syrup, fruit juices, and honeycontain glucose that is absorbed directly through the stomach wall and rapidly released into the bloodstream, almost as quickly as if delivered by syringe.
Brain Power ? The Energy of Thought and Memory
Most of us have discovered that thinking can be tiring, even exhausting. As the primary source of energy in the human brain, glucose can be rapidly used up during mental activity.
Some interesting research has shown that mental concentration actually drains glucose from a key part of the brain associated with memory and learning ? underscoring just how crucial this blood sugar is for proper brain function.
Too Much Blood Sugar ? Too Little Brain Sugar
A sugary snack or soft drink that quickly raises your blood sugar level gives you a boost (and any caffeine adds to the lift), but it's short-lived. When you eat something with a high sugar content your pancreas starts to secrete insulin. Insulin triggers cells throughout your body to pull the excess glucose out of your bloodstream and store it for later use.
Soon, the glucose available to your brain has dropped. Neurons, unable to store glucose, experience an energy crisis. Hours later, you feel spaced-out, weak, confused, and/or nervous. Your ability to focus and think suffers. The name for this glucose deficiency is hypoglycemia , and it can even lead to unconsciousness.
How to Control Blood Sugar Swings
Frequent blood sugar swings stress the mind and emotions, and chronic stress raises insulin levels ? creating a vicious cycle.
A helpful way to learn how to minimize blood sugar swings is to know which carbohydrates are the slowest time-releasers of sugar. The glycemic index measures how quickly blood sugar increases after eating a particular food.
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sorry for the lecture, it's just that "carb bashing" is a personal bugbear of mine!