Dietary carbohydrates play a central role in nutrition because they are the body’s primary source of energy and are important for the proper function of everything from muscle contractions to brain activity. Carbohydrates are classified into two basic groups: simple and complex:
As their name suggests simple carbs are just that - typically one-sugar molecules (mono-saccharides) or two-sugar molecules (di-saccharides). This category includes refined carbohydrates, which are rapidly digested and release sugar quickly into the bloodstream. They are good when a quick, readily availble source of energy is required, for instance before or during exercise. However, if eaten too regularly and in large amounts they can leave you feeling unsatisfied and prone to energy highs and lows. Examples include white bread, honey, pastries and biscuits.
These starchy carbs are made up of many simple sugars joined together by bonds - the more bonds, the more complex and the longer the carbs take to break down. Eating complex carbohydrates can reduce the chances of feeling fatigued or hungry between meals. The best examples are those that have undergone the least processing – such wholegrains include jumbo oats, brown rice, spelt, rye and barley.
Ideally complex carbohydrates should make up the bulk of your carbohydrate consumption, as they are the best source of nutrients and fibre.
Some research suggests that excessive consumption of carbohydrates – specifically, simple carbohydrates - can be harmful to blood sugar control, especially if you are insulin resistant, experience reactive hypoglycaemia or are diabetic. Carbohydrate excess, especially consuming too many refined carbohydrates, is sometimes associated with weight gain and increased risk of .
Fruit & vegetables
The natural sugar found in fruit and vegetables is called fructose. While fructose is considered to be a simple sugar, the high fibre content means the body digests whole fruit and veg more slowly than say a biscuit that contains no fibre but high amounts of white sugar. As a result, eating high fibre foods containing simple sugars is thought to have less of a dramatic effect on blood sugar levels.
Low-carb diets and weight loss
The Reference Intake (RI) for a balanced diet is currently 230g of carbohydrates a day. People following a low-carbohydrate diet often try to stick to around 20g a day or less.
Ketosis is often a by-product of a low-carbohydrate diet. Ketones are produced when the body’s glycogen stores have been used up and protein and fat become the primary source of fuel.
Because food choices are limited, low-carbohydrate diets tend to be low in calories yet high in protein and fat. Fruit, bread, grains and starchy vegetables are often limited. The proportion of protein and fat is increased to contribute towards the calories that formerly came from carbohydrate sources.
Jo Lewin holds a degree in nutritional therapy and works as a community health nutritionist and private consultant. She is an accredited member of BANT, covered by the association's code of ethics and practice.
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