Why does sugar have such an incredible hold on us? Our dietitians explain why our brains love sugar so much.
Sweet is one of the first flavours we learn to love as babies. In fact, breast milk is sweet, so from the very beginning we learn to equate sweet with safe and nutritious foods. For many of us, it’s the start of a lifelong love affair. But sugar is now under fire as the root of all our health troubles. So what actually happens in our bodies when we eat sweet foods? And should we really be worried?
Sugar in our foods
When we hear the word ‘sugar’, most of us think of lollies, soft drinks and the crystals you might put in your cup of tea. These foods contain what we call added sugars, but sugar is also found naturally in food, for example in honey, fruit, dairy and some vegetables. Sugars, whether they are natural or added, are quickly digested, broken down and converted to glucose (the simplest form of sugar) so they can then be used by our bodies for fuel.
What happens when we eat sugar?
Let’s take a high-sugar treat – a jelly snake. When you pop that handful of jelly snakes into your mouth, this is what happens:
In the mouth, we have taste receptors for sweet, and when we chew on the snake, these register pleasure. Then, once we swallow, the sugar travels through the stomach and into the small intestine where it is broken down into fructose and glucose.
Glucose and fructose are absorbed into the bloodstream. When your body senses glucose in the bloodstream, it asks the pancreas to release insulin to help deal with it. Insulin locks onto our cells and acts as a key, allowing glucose to move from the bloodstream into cells, where it is needed for energy. If the sugar (or starch) is digested and absorbed in to your blood quickly, you may get a surge of energy from the new supply of glucose to cells all around your body. This is the origin of the term ‘sugar hit’, which is a misnomer because starchy foods can have exactly the same effect on our bodies and minds.
When glucose hits the brain, you also get a little surge in the production of serotonin, one of our ‘happy hormones’ – you may feel more mentally alert and your mood lifts. Glucose is the preferred fuel for our brain and nervous system (it needs at least 120g a day for optimal functioning).
Continuing on its journey, fructose and any leftover glucose travels into the liver. At this point, the fructose is converted into glucose, too. Any glucose that’s not needed straight away gets packaged up into glycogen (lots of glucose molecules stuck together), for storage in the liver and muscles until it’s needed for energy. Once the storage capacity of our liver and muscles is full, extra glucose can be converted to other fuels like pyruvate and lactate. A very small amount (less than five per cent under normal conditions) can also be stored as fat in your liver.
A few hours after you’ve eaten those snakes, your blood glucose levels start to fall again. It’s now that you feel your energy levels dip, you begin to feel tired and you look for an energy fix and reach for the next handful of snakes to keep you going.
Fast and slow sugars
Sugars are a sub-set of carbohydrates. All carbohydrates undergo a similar digestive process as the sugar in the jelly snakes - they are broken down into glucose and raise blood glucose levels.
How quickly a carbohydrate food raises your blood glucose level is measured by the glycaemic index (GI). High-GI foods cause a faster and greater increase in blood glucose levels and low-GI foods a slower and lower increase.
Carbohydrate foods that are rapidly digested and absorbed (such as white bread) have a higher GI. While foods naturally higher in fibre, that are less refined (such as wholegrain bread), are more slowly absorbed and have a lower GI.
Slowing sugar down
GI can vary depending on the combination of foods eaten. For example, protein eaten with carbohydrates slows digestion, lowering the GI of a meal. It’s worth noting carbohydrate foods containing fat, such as chocolate, also have a lower GI as fat also slows the rate of digestion. Unfortunately, this doesn’t make chocolate a healthy food!
The cooking method and other factors, for example ripeness, also affect GI.
Low-GI health benefits
A lower GI diet compared to a higher GI diet provides better blood glucose control and blood fat profiles (cholesterol and triglyceride levels).
Research shows if our overall diet is lower GI we can maintain better health. And, low-GI diets help people to lose more weight than conventional diets and help to keep weight off for longer.
Is sugar ‘bad’?
Sugar in itself is not bad. There’s also nothing wrong with the occasional glass of soft drink or piece of chocolate. However, eating and drinking too many sugary foods and drinks may lead to some health problems.
Added, refined sugars are widely used in our foods, adding extra kilojoules. It’s easy to overeat these sugary foods because they taste nice, and this overconsumption may lead to weight gain. So sugar has become a contributor to obesity, which is where the health problems may kick in. Recent research commissioned by the World Health Organisation and led by researchers at Otago University in New Zealand, has shown there’s a link between added sugars and weight gain in adults.
An issue of quantity
They also found a link between drinking sugar-sweetened drinks and the risk of being overweight or obese in adults. However, the review also found that added sugars were no worse than added starch. It’s the extra kilojoules that added sugars provide that are the issue. So, sugar is by no means solely responsible for our obesity epidemic, but it is definitely part of the equation.
Balance is best
Food labels don’t separate out sugars that have been added, such as table sugar, from those naturally found in foods, such as in fruit or milk. So, you’ll find them all bunched in together and listed as ‘total sugars’.
There is no need to cut out all sugars, rather it’s best to think about the food as a whole. It’s better to eat a tub of fruit yoghurt, which has a little bit of sugar along with protein, vitamins and minerals, than to eat a sugary lolly that contains no other nutrients at all.
Is going sugar-free a smart solution?
Supporters of sugar-free diets claim fructose, a particular kind of sugar, is responsible for obesity and a whole range of other health issues. Here are some facts to consider:
Sugars are defined by their chemistry – table sugar, for example, is made up of two different kinds of sugar: glucose and fructose.
Fructose is naturally found in fruit and honey, along with vegetables like potatoes and corn.
The scientific evidence against fructose as compared to glucose or other sugars is nowhere near as strong as some people are making out.
When consumed in realistic amounts, fructose does not appear to be any more detrimental to health than any other sugars or starches.
Too much of any added, refined sugar (glucose, fructose, sucrose or starch), or large amounts of high-GI foods in general, is linked with increased weight and insulin resistance – a precursor to type 2 diabetes.
Two serves of fruit per day is strongly recommended as part of a healthy diet, even though fruit contains fructose. Sugar-laden lollies and drinks on the other hand, are best kept for treats.
Does sugar make kids hyperactive?
It’s a common belief that sugary foods can make kids hyperactive, but the science doesn’t support this.
A review of 12 double-blind, placebo-controlled studies failed to find any evidence that consuming sugar affected the behaviour of children, even those diagnosed with ADHD.
When children are at a birthday party or other special event they can get a bit ‘hyper’, in other words, they’re excited. So it could be down to their enthusiasm rather than the sugar!
Also, sugary party foods are often brightly coloured – it’s all part of the fun. But there is some evidence that certain food additives, like colours, can cause hyperactivity in some children.
So, it may be the additives in some sugary foods that can cause hyperactivity in some children, not the sugar: a classic case of mistaken identity.
Parents’ expectations of their children seem to have more to do with the behaviour they report than any sugar their children have or haven’t eaten. In one study, scientists found when parents who believed their children to be sensitive to sugar were told they had eaten sugar when they hadn’t, they reported their children to be much more hyperactive than a control group who received the placebo.