Everyone has either heard of, encountered or are confused by the different types of carbohydrates. However, not all carbohydrates were created equal.
Carbohydrates are manufactured by plants and are a major source of energy in the diet comprising around half the total calories. Carbohydrates are composed of carbon, hydrogen, and oxygen.
Important dietary carbohydrates can be categorized as:
- Monosaccharides do not normally occur as free molecules in nature but as basic components of disaccharides and polysaccharides.
- Examples: glucose, galactose and fructose.
- Disaccharides and oligosaccharides
- Although a wide variety of disaccharides and oligosaccharides exist in nature, the three most important disaccharides in human nutrition are sucrose, lactose, and maltose.
- Sucrose (e.g. table sugar, cane sugar, beet sugar, grape sugar) is formed when glucose and fructose are linked together. Sucrose occurs naturally in many foods and is also an additive in commercially processed items.
- Lactose, or milk sugar, is formed by glucose and galactose and made almost exclusively in the mammary glands of lactating animals; it accounts for 4.5% of the composition of cow’s milk.
- Maltose (malt sugar) formed from two glucose molecules is seldom found naturally in the food supply but is formed by hydrolysis of starch polymers during digestion and is also consumed as an additive in numerous food products.
- Polysaccharides are carbohydrates with more than 10 monosaccharide units. Plants store these carbohydrates as starch granules which are formed by linking glucose in α-1,4 straight chains and branching the straight chains with α-1,6 linkages into a complex granular structure.
All that these very technical terms mean is that all carbohydrates we eat (like starches, fruit, vegetables, dairy products, legumes or sweet foods), even if they don’t taste sweet, are digested in the stomach and intestines and are then absorbed into the bloodstream in the form of glucose. The glucose in the blood then stimulates the pancreasto produce and excrete insulininto the bloodstream. This hormone, insulin, helps the body cells take up glucose from the blood, so that the cells can use the glucose for energy.
Research over the past 20 years has found that not all carbohydrates are digested and absorbed at the same rate. This means that different carbohydrates have different effects on blood glucose and blood insulin levels of diabetics and non-diabetics.
What is the glycaemic index?
The term “glycaemic index” can be explained in the following manner:
- “gly” in medical terms referring to glucose
- “aemic” in medical terms referring to blood
- “index” is an indicator/measure
Thus, the glycaemic index is a “blood glucose indicator”.It provides an indication of the rate at which the food affects blood glucose levels after being eaten.
Carbohydrate foods with GI values nearer to 100 are considered high GI foods and are digested and absorbed faster than those carbohydrate foods with GI values of 55 and below.
- High GI foods, e.g. bread, will therefore cause a huge increase in blood glucose levels followed by a rapid drop thereafter.
- These foods are also referred to as simple carbohydrates – simple as in broken down and absorbed easily.
- Low GI foods, e.g. butter beans, are digested and absorbed slowly, but steadily, and thus only produce small increases in blood glucose levels.
- These foods are referred to as complex carbohydrates – taking longer to break down and absorb.
Therefore, a meal containing butter beans would keep one feeling full for much longer than a meal based on bread. In addition, the body would have to secrete much less insulin to deal with the carbohydrate from the butter beans, than for the large amount of carbohydrate that is dumped into the bloodstream by the bread.
Foods that are mainly sources of protein and fat e.g. meat, fish, chicken, eggs, cheese, nuts, avocado, margarine, peanut butter etc. do not have GI values, since it is only carbohydrate containing foods that have a GI value, because they have an immediate effect on blood glucose levels.
Based on the GI of each carbohydrate containing food, carbohydrates are now divided into three broad categories:
- LOW GI foods (Frequent and Often foods)
- INTERMEDIATE GI foods (Sometimes foods)
- HIGH GI foods (Exercise foods)
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Not all carbohydrates are created equal and for the best results (such as staying fuller for longer, have long-lasting slow release in energy and prevention of lifestyle diseases) it is best to choose low GI options.