Carbohydrates The Basics

Carbohydrates are stored energy. They are primarily synthesised by plants from water and carbon dioxide and when used up by us they release back to us the carbon dioxide, water and 4 calories per gram in energy.

What Carbohydrates should I be eating?

As part of a diet designed to maintain energy levels and not gain weight, eat complex and less refined carbohydrates regularly, and only simple, high GI carbohydrates during and directly after strenuous activity.

The Details

Carbohydrates can take on various chemical compositions ranging from simple to complex. Glucose is the simplest form of carbohydrate and falls into the sugars category. The body is able to readily break down these simple sugars to gain their energy. The sugars are the sweetest of the natural food carbohydrates and fructose is the sweetest of these to the palate.

Other types of carbohydrates are Oligosaccharides and polysaccharides. Starch is a polysaccharide. Different types of carbohydrates behave quite differently in the human body so having some understanding of the differences between simple and complex carbohydrates is useful in making better nutritional choices. The body breaks all carbohydrates down into sugars before use, so the additional steps required by the body to break the complex carbohydrates down often slows their digestion and absorption.

Carbohydrate is the most common type of food consumed in the world and makes up most worldwide caloric intake. Yet, unlike certain essential oils and essential amino acids, (proteins) carbohydrate is not essential for a human to survive.

Different terminology is often used when describing whether a carbohydrate is simple or complex and it is not the case that simple carbohydrates are bad and complex ones are good. Different carbohydrates will behave differently in the digestion and absorption process depending on how they are prepared and processed. So a complex carbohydrate may absorb quickly because it has been heavily processed and refined. Rice crackers are an example of this.

What's all the fuss about?

When any carbohydrate is digested it releases sugars into the blood stream. The rate of this rise in blood sugars will be indicative of how fast the body has digested the food consumed. When there is too much blood sugar the body releases insulin which causes cells in the liver, muscle and fat tissue to absorb glucose from the blood and store it. These sugars will then be absorbed and stored as fat.

In simple terms, if you regularly consume and digest more carbohydrates than your body can burn then they will make you fat.

The Glycemic Index

In the early 1980's Doctors developed the concept of the Glycemic Index as a way of measuring the effect of carbohydrates on blood sugar levels. Originally this was to assist diabetics whose ability to control their blood sugar through insulin release was compromised.

The advantage of the glycemic index is that it takes the simple vs complex carbohydrate debate and provides a real measure for what effect these carbohydrates actually have on the human body.

The index itself works by creating an arbitrary value of 100 for a specific food's effect (often pure glucose) and ranking other products compared to that. Low GI foods have an index of 55 or less, medium rank between 56-69 and high GI foods are 70 or above.

In general low GI foods will release their energy more slowly making them suitable for maintaining energy levels and blood sugar levels during normal consumption. High GI foods will be more suitable during or directly after strenuous exercise for recovery as they will release their energy quickly to replenish glucose levels for muscles which have been depleted either by aerobic or anaerobic exercise (citric acid or lactic acid cycles respectively).

It is worth keeping in mind that the rate of absorption of a carbohydrate will depend also on what else is consumed. The consumption of proteins, fats and soluble fibre will slow down the absorption of the carbohydrate, thereby smoothing out the increase in blood sugars that would otherwise occur. For example, having a slice of cheese with the rice cracker will slow the body's absorption of the energy from the rice cracker.

Similarly, although fruit may contain large percentages of the simple carbohydrate fructose, it is bound up in the cellular structure of the whole fruit (including fibre) and will be slower to absorb than sugars in a fruit juice or lolly (even the so called natural lollies...). Fructose itself is metabolised to glucose by the liver, slowing it's absorption again. Many popular fruits therefore taste sweet but have a relatively low GI and provide a more steady flow of energy to the body that may be thought.

The GI has been criticised as being an artificial tool which doesn't take into account all the different ways in which food is prepared and consumed. The Index itself creates a value based on an individual who has been fasting overnight and measures blood sugar levels two hours afterwards. As described above, foods will have greatly different effects on individuals and some people are of the view that the GI is more confusing than it is useful.

For more information on the Glycemic Index and a handy calculator, click here.

Carbohydrates also play an important part in making us feel full and regulating our dietary intake.

The Bottom Line

Carbohydrates are not essential to human functioning but form an important part of human diet worldwide because they provide a reliable and flexible source of energy.

Different carbs metabolise differently. In broad terms, complex whole food carbohydrates are likely to be lower on the Glycemic Index and are likely to be better for you for regular consumption. Simple carbs will be higher on the GI and are ideal for during and after strenuous activity but less suitable at other times.

Sources:
Essentials of Human Nutrition, Third Edition, Oxford University Press
http://en.wikipedia.org/wiki/Carbohydrate
Arnold Schwarzenegger, The New Encyclopedia of Bodybuilding
http://www.glycemicindex.com/
http://www.merckmanuals.com/home/disorders_of_nutrition/overview_of_nutrition/carbohydrates_proteins_and_fats.html
http://www.ausport.gov.au/ais/nutrition/factsheets/basics/carbohydrate__how_much
http://www.bodyscoop.com.au/food-weight-loss/carbohydrates.asp