Sugar and your health

Free sugars aren't linked to diabetes, heart disease, cancer or hyperactivity in children. However, experts agree that they can play a role in tooth decay. They also provide empty kilojoules, which may lead to weight gain.

Tooth decay

Bacteria in the plaque on your teeth use sugars as food. The bacteria then produce acids that can eat into tooth enamel. So any type of sugar can be a problem under the right conditions, as can starches and starchy foods. How much of a problem depends on how often you eat sugar and starches through the day, and how long they stay in your mouth.

Frequent snacking on sugary or starchy foods, and in particular ones that hang around in your mouth, like sticky, clingy biscuits, cakes and sweets, or foods you sip or suck for some time, can easily result in problems your dentist won't be happy about. Eating these foods as part of a meal is better than having them between meals.

Good oral hygiene is important: regular teeth cleaning with fluoride toothpaste, flossing, and check-ups are all essential to healthy teeth, no matter how much sugar you eat.

Weight gain

Maintaining a healthy weight is pretty straightforward. If you eat more energy than you use, the extra is stored as fat. It doesn't matter where those extra kilojoules come from - fat, protein, or carbohydrates (including sugar). Eat more than you need and you'll get fatter.

A healthy diet isn't just about eating the right amount of kilojoules, though. It's also about getting all the vitamins, minerals and fibre you need. Heavy consumers of sugar, who may eat sugary foods instead of more nutritious ones, could end up missing out on some of the nutrients they need for a healthy diet.

Blood sugar & GI

Eating sugary foods used to be blamed for sending people's blood sugar levels soaring and then plunging - surges which some nutritionists think could have long-term effects on health.

But while some foods can send blood sugar levels bouncing, it seems the answer to which foods do this isn't as simple as just those with the most sugar.

The glycaemic index (GI) of foods is a way of measuring how they affect levels of sugar in the blood, giving each food a comparative score out of 100. It compares the effect of eating an amount of each food that contains 50 grams of carbohydrate with eating the same amount of pure glucose (GI = 100).

Foods with a low GI (55 or less) make blood glucose levels rise and fall more gently, while high-GI foods (70 or more) are broken down more quickly and cause blood sugars to surge and crash. Perhaps surprisingly, table sugar scores a moderate 61.

Syndrome X

It sounds like a pilot for a sci-fi series, but in fact it's a name coined to describe a cluster of abnormalities associated with insulin resistance, high blood pressure, obesity (centred around the stomach), low HDL-cholesterol (that's the good kind) and high blood triglycerides - all of which increase the risk of diabetes and heart disease.

A link has been suggested between syndrome X and large quantities of fructose - a type of sugar used much more extensively in processed foods in the US than here, but which also makes up one half of a molecule of ordinary sugar (sucrose). The science is far from clear. There are animal studies that support the idea, but a very limited number of human studies. Some experts say there's not enough fructose in NZ diets to have any noticeable effect, but it's early days and more research is needed. There's no suggestion that eating fruit (which provides fructose in association with dietary fibre) is a risk.