What are carbohydrates?
Carbohydrates can be divided into two broad groups: complex or starchy carbohydrates and simple carbohydrates or sugars. All carbohydrates are made up from sugars and each gram of carbohydrate provides 3.75 kcalories.
Simple carbohydrates
Simple carbohydrates are made up of single sugars (called monosaccharides) or two sugars joined together (called disaccharides). These sugars are quickly broken down in the mouth and stomach and are absorbed into the blood stream, causing a rapid rise in blood sugar levels. This rapid rise causes the body to produce a sharp rise in insulin levels and results in the sugars being converted into fat - something we want to avoid.
The rapid rise in blood sugar levels is usually followed by a rapid drop. This means that, although we get a "quick lift", the downside is that simple carbohydrates will very quickly leave us feeling more tired than before. These drops in blood sugar levels can cause dizziness and feelings of hunger and weakness. Also, eating a lot of simple sugars can be responsible for tooth decay.
Where are they found?
A good example of a simple sugar is sucrose. This is the type of sugar that we put in tea and coffee. It is also found in many cakes, pastries, biscuits, soft drinks and other confectionery products. It is best to try to keep these to a minimum in our daily diet. An additional problem with some of these foods is that they also contain a lot of fat so they can be major contributors to increases in body weight.
Milk and also some fruit and vegetables contain simple sugars (lactose and fructose respectively). However, in these foods, the sugars are not absorbed rapidly because there are other substances in these foods that prevent this. For example, the sugar in fruit (fructose) forms part of the fruit cell wall and is released slowly when digested.
Complex or starchy carbohydrates
Complex or starchy carbohydrates are molecules that are made up of many sugars joined together. Starchy carbohydrates are an important source of energy. Because the molecules are made up of many sugars, it takes longer for the molecules to be broken down in the stomach. This means that the sugars are released more slowly into the blood stream, avoiding unwanted peaks in blood sugar levels.
Starchy carbohydrates are the body's favourite fuel. This is because starch provides most of the glucose our body needs. Glucose is the preferred energy source for muscles and the other tissues and organs of the body. In fact, glucose is the only energy source the brain will use. Because of this it is vital that we have a regular intake of starch in order to help us meet our glucose needs.
Where are they found?
Good sources of starch are bread, oats, pasta, cereals, potatoes, beans, lentils, noodles, rice and fruit.
Fibre
Many complex carbohydrates cannot be broken down in the stomach into sugars and are known as fibre. Because of this they cannot be digested and turned into energy. However fibre is essential for good health.
How much carbohydrate do we need?
The British Nutrition Foundation states that carbohydrates should supply a minimum of 47 percent of our total daily calories. Most of this (about 40 percent) should come from starch. The rest (up to roughly 10 percent) should come from simple sugars.
In practical terms, this means that if you are eating 2,500 kcalories a day this amounts to a recommended daily intake of at least 313 grams of carbohydrate. If your daily calorie intake is 2,000 kcalories this amounts to at least 250 grams of carbohydrate per day. 1,500 kcalories a day equates to 188 grams of carbohydrate per day. All carbohydrates contain 3.75 kcalories per gram.
References
Department of Health. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. HMSO. 1991.
The British Nutrition Foundation. Carbohydrate.
accessed on 16 September 2002
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