By: Janice Tai

Popular low-carbohydrate diets like the Atkins and South Beach may have led some people to believe that carbs are the source of unflattering flabs and bulges.

Such a notion is a dangerous oversimplification.

Nutritionists say carbohydrates are a classic Jekyll and Hyde - they have two faces.

Carbohydrates - easily digested when in the form of white bread, white rice, sugared drinks and other highly processed foods - may indeed affect weight loss and contribute to weight gain.

However, they are also rich in vitamin B and serve not only as a good energy source but are also the least expensive source of energy, said Mrs Magdalin Cheong, the chief dietitian at Changi General Hospital.

Wholegrains, beans, fruits and vegetables promote good health by delivering essential vitamins, minerals, fibre and other important phytonutrients.

Mrs Cheong said carbohydrates should comprise about 55 per cent of the total daily energy intake.

They are found in a wide variety of foods such as pasta, potatoes, cookies and nuts. They also come in different forms like sugars, fibre and starches.

Also, they are grouped in two categories: simple and complex carbohydrates.

Simple carbohydrates, once consumed, are converted into simple sugars which are absorbed quickly by the body, thereby raising sugar levels, said Mrs Cheong.

Complex carbohydrates, on the other hand, take a longer time to digest, thus releasing sugar slowly into the blood stream. This is helpful in, say, controlling blood sugar levels in diabetics, she added.

This traditional classification, however, does not tell us much about what happens to the different kinds of carbohydrates inside the body.

For example, the starch in white bread and potatoes is a complex carbohydrate, yet it is converted to blood sugar nearly as fast as when pure glucose is processed, said a website from the department of nutrition at the Harvard School of Public Health.

A newer classification of carbohydrates is the glycemic index (GI), first formulated in 1994.

With a scale from zero to 100, this index measures the rate at which a carbohydrate breaks down and releases glucose into the bloodstream, said nutritional therapist Pooja Vig of The Nutrition Clinic.

GI has three categories: low (<55), medium (56-69) and high (>70).

Foods with a higher GI like white bread cause rapid spikes in blood sugar while those with a lower GI, like whole oats, are digested more slowly, causing a smaller and less steep change in blood sugar.

Generally, the more processed a food is, the higher its GI.

The GI is a better way of tracking whether your diet is healthy rather than simply counting calories.

'The drawback with calories is that it says nothing about the quality of food you are eating,' said Ms Vig.

'Diets rich in high GI foods have been linked to an increased risk of diabetes, heart disease, obesity and cancer,' she added.

'You don't need to do any sort of mental arithmetic to make sure you are eating a low GI diet. Just make a conscious effort to swop high GI foods for low GI ones,' said MrsCheong.

The GI as a concept is catching on fast. Countries like Australia have already launched a GI symbol programme for food products.

Companies are also beginning to conduct tests for the GI values of food products. Soyjoy, a nutrition snack company, is among those that do this.

Even so, one drawback of using only the GI is that it can be misleading. This is because GI tests are not based on the typical portion sizes of food but based on a standard measure of 50g of carbohydrate.

A more useful measure is the glycemic load (GL), which takes into account both the amount of carbohydrate and the impact it has on blood sugar levels, said Mrs Cheong.

The GL is determined by multiplying the GI by the amount of carbohydrate it contains.

However, the GI and GL should serve only as rough guidelines. A low GI does not mean that a particular food is nutritious. The addition of fat and protein also alters the GI, so it is difficult to apply the GI for the mixed meals we usually have, said Ms Vig.

A 2004 National Nutrition Survey conducted by the Health Promotion Board found that Singaporeans consumed proportionally less fat and more carbohydrates compared to their British counterparts.

However, the carbohydrates Singaporeans consumed were largely refined ones. Such foods contain largely sugar or ingredients made from polished grains such as white wheat or rice flour.

Refined carbohydrate foods are generally rich in starch but are poorer sources of fibre and vitamins than unrefined carbohydrate foods.

A diet that is high in refined carbohydrates can lead to hormonal changes that result in hunger, poor appetite control and overeating.

It is by adding good carbohydrates like wholegrains into one's diet that optimal health is ensured, said Ms Vig.

One useful tip to prevent your blood sugar levels from skyrocketing is not to cram your meals and snacks too close to each other. The body takes at least two hours after a meal to bring the sugar level back to pre-meal level.

Meanwhile, for faithful adherents of a high protein and low carbohydrate diet, you may have to think twice as these diets are usually high in total and saturated fat, which increases the risks of heart disease, she added.

Also, a high protein diet taxes the kidney and the initial rapid weight loss may be due to the loss of water rather than body fat.

This article was first published in Mind Your Body, The Straits Times.