Food shopping is not as easy or clear-cut as you might think.

Often, nutrient claims like 'calorie-free' do not mean that the product contains zero calories - trace amounts may still be present but are considered minimal enough to allow for such a claim.

Also, fat-free food may not necessarily be healthy as it may contain lots of sugar instead.

Here are the important facts and figures that you should know about.

Sugar-free

No more than 0.5g of sugar per serving.

Note, however, that some sugar-free foods may contain substantial amounts of fat, said Ms Nehal Kamdar, a dietitian at Raffles Hospital.

No added sugar/salt

Even though sugar or compounds with sodium were not added, the food may still contain its own natural sugar or salt.

Some examples are honey and fruit juice which have naturally-occurring sugar.

Hence, do look under the carbohydrate content or energy levels in the nutrition information panel for more details.

Carbohydrate-modified

Usually, this means that sugar alternatives such as sorbitol or mannitol are used, said Ms Kamdar.

'These are best avoided as they may have the same energy as sugar,' she added.

Fat-free

No more than 0.5g of fat per serving. For liquids, less than 0.15g of fat per 100ml.

As for low-fat food, these should contain no more than 3g of fat per serving.

Ms Kamdar warned that some fat-free or low-fat food may have large amounts of sugar instead, to substitute for flavour or texture.

Trans-fat free

Less than 0.5g of trans-fat per serving.

According to Ms Jeannie Tay, a dietitian at Alexandra Hospital, food manufacturers do not have to report the amount of trans-fat if they occur naturally - such as in some meat and dairy products.

There is currently no evidence stating that this type of trans-fat is linked to heart diseases, she added.

The Health Promotion Board says Singaporeans should limit their daily intake of trans-fat to no more than 2g per day.

Cholesterol-free

Less than 5mg of cholesterol and less than 1.5g of saturated fat per 100g. This is because cholesterol is believed to be found only in foods of animal origin.

However, products that are labelled cholesterol-free may still be high in total or saturated fat, Ms Kamdar said.

Calorie-free

This label refers to food that is fewer than five calories per serving or no more than one calorie per 100g.

'Low-calorie' food should contain no more than 40 calories per serving.

High-fibre

At least 4g of fibre per serving, or at least 6g per 100g.

Wholegrains

Wholegrains contain all three components of the natural grain - bran, germ and endosperm.

When grains are refined or processed, one or more of these parts may be removed, said Ms Tay.

Food made of more than 50percent wholegrain are considered good sources of wholegrains.

Usually, you can identify wholegrain food easily as flecks of grains are visible in the food, she added.

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

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