We are a society programmed to end our meals with something sweet. From “Sugar in the morning, sugar in the evening, sugar at suppertime...” to sugar-free craze, sweet-toothed dieters can't seem to escape the cravings. No surprise - humans naturally have an appetite for sugary foods. It's part of our biological make up. One simple reason for the notorious sugar cravings can be found in our brain's drive to get a boost.

Why does our brain need carbohydrates?

To warm up your mind, answer one simple question - Which cells govern and rely on the most efficient communication? If you answered “brain cells,” then you are not going crazy which is not hard to do when you hear another dogma about carbohydrates.

The brain lives on a sharp blade of metabolic knife and is especially sensitive to sugars and requires carbohydrates to operate. Roughly 150 grams of glucose per day is burned by the brain. From all the body tissues, it gobbles more than two thirds of the circulating carbohydrates in the bloodstream whether you sit, walk, work out, sleep, eat, etc. At rest, the metabolism of the brain accounts for 15 per cent the total metabolism of the body even though the brain weights roughly 2 per cent the mass of the body. This means that brain metabolism is about 7.5 times higher than the average for the rest of the body.

At any one time, you have only about 5 grams of sugar in the blood, enough to supply the brain for less than one hour. What happens when these five grams are burned? Your liver and muscle tissues should have additional supply, around 100 grams of a polymerised from of sugars called glycogen. This should keep your body functioning for only about half a day provided you are sitting most of the time.

The brain uses a disproportionately large amount of energy for its weight. The moment the brain is not fed properly could cause it to deteriorate and cause what is commonly known as 'brain dead' situation. If the level of glucose in the blood falls from its normal range, the brain begins to malfunction. Just 50 percent cut in blood glucose levels can lead to dizziness, nausea and eventually loss of consciousness. When your blood sugar levels fall to a quarter of its normal level, the brain goes into coma with some potential irreversible damage. Cut off the supply of glucose in the blood and the brain will survive for less than 2 minutes.

What if you don't eat? Will you go into coma?

Well, no. But you will feel angry, fatigued, irritated and unable to concentrate until the brain gets what it needs - sugars. Not only does a diet lacking in carbohydrates cut off the brain's main energy supply, a scarcity of glucose can impede the synthesis of several neurotransmitters, namely acetylcholine, dopamine, serotonin to name a few out of thousands.

In simple words, each neurotransmitter is a chemical messenger released from one nerve cell which finds its way to another nerve cell where it influences a particular chemical reaction to occur. Neurotransmitters control major body functions including movement, emotional response, our physical ability to experience pleasure and pain. These invisible alarms set in motion specific functions within our body and our nervous system and can create and control a range of feelings, moods and even thoughts - everything from depression, anxiety and addiction, to feelings of self-confidence, to high or low self-esteem, the competitive spirit and can even affect our deep sleep.

Cut your carbs short, and you are running a high risk of setting your brain neurochmicals our of balance. If you don't supply your brain with the needed nutrients, it's easy to imagine what could happen - any miscommunication or slowdown could cause major mental and emotional problems.

When you are under stress, or engage in the activity which requires a lot of mental work or thinking, and especially when your emotions go through roller-coaster rides, your brain need even more glucose. Not only is the thought process effected, your moods, concentration, attention, even motivation and balance get out of hand.

Why does sugar make us feel so good?

As far as your feelings are concerned, foods are drugs. They work exactly the same way – being foreign substances, foods come into your body and switch around various natural chemical processes going about their own business. Sugars and other carbohydrates are perfect examples.

If the sugar level is off, your mood changes. You eat sugar, which makes you feel sky-high. Usually people with a low blood sugar level will be very irritable, feel blue or even exhausted. An enormous percentage of us crave sugar, carbohydrates, or alcohol. In most cases, these food cravings are not true eating disorders, but instead are signs of hormonal imbalance caused by a lack of healthy nutrition and low blood sugar levels. When everything is functioning well and everything is being nourished properly, there is no problem. But if hormones are disrupted, we don't feel good. This shouldn't be surprise as many mood-related hormones also depend on carbohydrates. Food cravings mean that the body has its signals mixed up.

There are two neurochemicals released in the brain when you eat carbohydrates - Serotonin and Dopamine. They are known as 'feel-good hormones' and work as natural anti-depressants in the body. Serotonin and dopamine are the fun houses of your brain. They are released when we exercise, have sex, or feel satisfaction from a heart-warming experience of, say, being praised. When these chemicals run low in the system, you start feeling uncomfortable, tense, hostile, restless, even unusually hungry.

Many people turn to drugs or alcohol to get a quick brain fix, which most times turns out to be the opposite – the brain gets disturbed. Consider the alternative - eating carbohydrates. These non-essential nutrtients naturally stimulate the production of serotonin and dopamine which reduce levels of the stress hormone cortisol in your system while giving you immediate energy boost at the same time. Once you eat and replace your blood sugars, your mood will dramatically improve and you will feel like a new happy, calm and satisfied person.

Can the brain live without sugar?

Muscles and liver can store sugars and use them later on for energy when they need it. They can even burn fat when there’s no other fuel around. Unfortunately, neurons cannot store glucose and can recognize only about five per cent of all required calories from ketones. These oxygen-dependant hard working tissues count on the bloodstream to deliver a constant supply of precious carbohydrates.

When the sugar that is needed to run the body drops below a critical level, the body starts breaking down muscle tissues first, and then turns to fat reserves. The proteins and fats are converted to ketones and used to do the work carbohydrates normally do.

I've heard that when you don't eat carbohydrates, your body can use fat stored in my body for energy. Is this true?

Strictly chemically-speaking, the principal source of energy for brain and neurons is not glucose, but acetic acid and carboxylic acids which are fatty acids converted to ketones.

What are ketones?

Ketones or ketone bodies are the by-products of fat and protein metabolism and are an alternative source of energy. Like other fats, ketones provide twice as much energy as carbohydrates, 9 vs 4 calories per gram respectively. But unlike normal fats, ketone energy can be released rapidly and without blood sugar fluctuations you get from sugars.

In contrast to fatty acids, ketones can pass the blood-brain barrier to deliver energy to this organ. Nevertheless, there appears to be an obligatory reliance on glucose to sustain normal function of brain as a whole. Your heart, muscles, digestive organs have the ability to survive on ketones and use these as an excellent low-carb fuel, but your body has other cells and tissues which depends solely on carbohydrates. Red and white blood cells, testes, inner parts of the kidneys, and the retina, lens and cornea in the eyes need glucose at all times. The brain and central nervous system may be a particular case.

The problem here is that it requires a meaningful amount of glucose because neurons cannot normally survive without the support of glial cells. These run on glucose only and ketones from fat tissues are not enough to meet the demand. When fully engaged, ketones may produce almost half of the energy the brain requires, but the remainder should be still coming from glucose. In such case, protein becomes the ultimate raw material used by the body to produce glucose for the brain. In essence, in order to feed this glucose hog, the body is cannibalising mostly muscles and turning them into something you can actually eat - carbohydrates. Obviously, if this continues you would lose strength, tone, co-ordination, heart muscle and the proteins in organs like liver and kidney.

No-one knows why the brain cannot use fat as energy source like the rest of the body. If it could, then we wouldn't have to worry about eating since most of us have fifty to one hundred times as many fat calories stored as glucose calories – anywhere around 10-20 kilograms of fat, and only 400 grams of sugars. So, there may be plenty of energy, calories and capacity to perform some physical action, but if brain has exhausted its supply of glucose, it becomes tired or falls asleep.

What happens when ketones are the only brain fuel?

Lets look back at how human metabolism evolved. Bouts of starvation may have been the normal state of our hunter-gatherer ancestors who were used to run their bodies on low-glycogen supply. Ketones may have probably been the only other available alternative to glucose for supplying energy to the brain and ketosis was the natural state of our predecessors. Ketones may be the secret to why humans could survive starving for about 2 months instead of 2-3 weeks.

Modern humans rarely have to starve, unless for some therapeutic, economical or worse yet, fat-losing purpose. And it is a good thing because this enables us to be inventive, creative, progress in life and actually develop our brains. There is a theory that one of the reasons for our intellectual growth is sufficient supply of carbohydrates. Simply, the cognitive ability of the brain is related to the blood glucose concentration. Thinking and mental concentration can be tiring, even exhausting. It rapidly drains tonnes of the primary source of energy, glucose from the part of the brain associated with memory and learning.

Except under conditions of starvation, it was thought that the brain always had an ample supply of glucose, but the new findings suggest that glucose is not always present in ample amounts to optimally support learning and memory functions. Glucose enhances learning and memory, which researchers have clearly seen when they provided regular carbohydrate-rich foods for schoolchildren. Carbohydrates showed to have the most beneficial cognitive effects that enhance learning in well-nourished kids. Eating carbohydrate foods can improve memory within an hour after ingestion in healthy elderly people with relatively poor memories.

Have you ever noticed that a high carbohydrate lunch can make you feel sluggish?

If you eat too many carbohydrates at once, these may spark your brain for the next few minutes, but later on these can make you feel tired. Carbohydrates act as stimulants which carry out the release of insulin, a hormone necessary for the better performance of the brain. Too much of this substance causes the brain to overly sedated and reduces mental performance because it increases the brain's level of the amino acid tryptophan. This building block of protein in turn spurs the brain to make the calming neurotransmitter serotonin which is important for normal sleep patterns, learning, blood pressure and appetite, among many other functions.

Now you can see that it is all about balance. Having too little carbs as well as too much of these can make you feel tired.

Can low-carbohydrate diets change our metabolism?

Proponents of low-carb diets argue that the brain can use ketones very well, in fact so well, that these metabolic 'wastes' can actually change the brain chemistry. In fact, trying to survive on ketones may mess up brain function. At the same time, the brain itself is made of fat. A fascinating arrangement, I have to say.

It is true that brain pathways are changed when carbohydrates become scarce. Some say that the fear of ketosis may be exaggerated, as milder forms of it occur under other circumstances, and may have therapeutic potential. Prominent veteran biochemists agree on the potential therapeutic uses of ketosis. In fact, the ability of the brain to use ketones was only once exploited for therapeutic purposes. In the early 20th century, French neurologists proposed fasting as a treatment for epilepsy on grounds that it was the result of ‘intestinal intoxication’. A Wisconsin osteopath, Hugh Conklin, subsequently successfully treated some epileptic children with a diet of only water for 30 days.

We have seen the beneficial effects of high-fat low-carbohydrate diets, also known as the "ketogenic diets" (high-fat, with carbohydrate energy supplying only less than 10% of calories, and fat being the prime fuel for the body, which makes up 80% of total calories). These are used to treat various mental disorders, such as epilepsy, Alzheimer’s and Parkinson’s diseases.

In one form of epilepsy resulting from a genetic decrease in GLUT1, the major glucose transporter across the blood/brain barrier, ketones provide an alternative energy substrate, compensating for the decreased glucose transport, and hence ketosis therapy has been used.

In one study, 150 severely epileptic children, averaging 400 seizures per month, on a mean of 6.2 antiepileptic medications were placed on a ketogenic diet consisting of 4 parts fat to 1 part protein, with almost no carbohydrate. Thirty percent of the children had a greater than 90% decrease in seizures and 3 became free of seizures.

However, two problems arise in such fat-cut low-carb ketosis therapy.

First, eating even small amounts of carbohydrate causes the release of insulin and an immediate drop in ketone levels. While in healthy people it may be pronounced in moods disturbances and energy highs and lows, those with already poor brain function can have it as bad as seizures. Second, low-carbohydrate high-fat diets increase blood cholesterol (with a decrease in high density lipoprotein, an increase in low density lipoprotein and elevation of total triglycerides). This puts the dieters at a greater risk of atherosclerosis. Third, your other tissues, especially muscles and lean supporting ligaments and tendons, as well as smooth muscles in the digestive tract may be effected. These don't function on ketones as well as they do on carbohydrates.

And what about your muscle glycogen and overall nutrition for the exercising body? How long do you think your muscles can run on sub-par ketones?

For your body to adjust to low-carb ketone supply, you need at least two weeks. Your brain needs more time to get the 'new feeling' right – about two-three months time. This is why most low-carbohydrate, or ketogenic diets recommend only short-term use, typically 14 days.

Should I avoid eating carbohydrates at night?

The brain, like the heart, never rests, whether you are sleeping, watching television, working out, reading an easy novel or solving a complicated puzzle. The difference in how brain operates may be subject to the way your most important and most metabolically active organ uses its chemicals. A steady stream of fuel is crucial because neurons in the brain are constantly repairing and rebuilding, as well as connecting themselves to other neurons. These energy-intensive bioelectric signals sent through the nervous system directly depend on sustained carbohydrate supply.

Your brain demands glucose even when you are not physically active or are asleep. This is one extremely important difference between choosing where the night-time calories come from – carbohydrates, proteins or fats. Just because you are resting doesn't mean your brain is not working hard. In fact, your brain consumes as much or even more energy when you are asleep as during your waking hours. We know optimal sleep translates into optimal performance, and part of this is due to well-rested brain.

During sleep, your brain releases some of the most important hormones and neuro-chemicals involved in keeping your body healthy and well, boosting your immunity and restoring energy within each body part. Our livers become depleted of glucose overnight because we are not eating. So, when you wake up in the morning, you may feel a bit groggy and hungry, which is a signal of your brain for replenishment.

Unlike other endocrine hormones, there is no direct signal from the brain's pituitary that alerts the pancreas to start making insulin. But this doesn't mean that insulin is not subject to some indirect control by the brain centre hypothalamus, which is responsible for the production of various hormones and neurotransmitters. Specifically, the two chemicals, serotonin and dopamine associated with sense of relaxation and alertness respectively, have a significant impact on insulin secretion. As serotonin levels rise, insulin levels go up as well.

On the other hand, when dopamine levels rise, insulin goes down. Serotonin is mainly released at night or when you are relaxed, such as after a meal. This means that the later you eat a large meal, the more insulin will be secreted. If your dinner is late and large, that is double trouble – elevated serotonin and extra calories will sky-rocket insulin levels and those late-night calories will be stored as fat. Dopamine is highest during the day when you are awake and in the process of going through all your activities – workouts, daily hussles, etc. This is probably the best time to eat most of your food because not only you will burn off calories almost immediately, you don't need too much insulin either – your blood sugar levels will stay even as you keep burning the food for energy. Dopamine will make sure that there is no fat-storing going on.

What are the best carbohydrates for the brain?

To feed your brain, the eternally hungry smart glucose hog, you need carbohydrates all the time. Being selective, it craves and prefers a nice steady supply of sugar for fuel and not all carbohydrates will do. Some carbohydrates calm behavior, others excite it. One formula for avoiding blood sugar spikes while feeding your brain with carbohydrates is to eat complex starches and combine them with foods which are abundant in protein and healthy fats.

The best way to eat for alertness is to have meals that contain protein, are low in fat, and have carbohydrates that won't drag you down. These include whole grains with bran and germ, legumes, pasta, bread, potatoes, cereal, fruit and milk. The molecules in these complex carbs are long, so it takes longer for the intestines to break them down into the simple sugars the body can use. Thus, they provide a time-release source of steady energy rather than a sudden surge followed by a sudden drop.

There may be times when you need a quick brain boost. Here simple sugars work best. Still, when choosing sources of carbs, be sure to pick healthy, least processed fiber-rich starches such as whole-grain breads and pastas, natural oatmeal, and wheat ger