Diet drinks: how much healthier are they?

Irish kids – and adults – are guzzling too many fizzy drinks and leaving themselves open to weight gain, diabetes and cancer, says Dr Donal O'Shea. What should be occasional has become a daily part of our diet.

"Their sugar is nutritionally empty, in that it doesn't provide you with any minerals or vitamins," he says. And it is contributing to obesity. Research he is involved in at Our Lady's Children's Hospital, Crumlin, indicates that obese children are having genes switched on that predispose them to cancer and diabetes.

But what are the options for hard-pressed parents and consumers? Milk and water are best, but diet drinks might seem a straightforward solution.

“They are better than the sugary fizzy drinks alone,” says O’Shea grudgingly. But increasingly he and other scientists are questioning what effect the sweeteners in zero-calorie drinks and in foods are having on our bodies.

Sweeteners include saccharin, acesulfame potassium, neotame, sucralose and aspartame, and can be hundreds of times sweeter than table sugar. Increasingly it seems they don’t have zero impact, however, and may trigger overeating.

Earlier this year, scientists in the US tested overweight people who did not use artificial sweeteners regularly. They found that drinking sucralose caused their body to prime itself for a sugar rush, with blood insulin rising.

“There are taste receptors in your small bowel,” says obesity expert Dr Carel le Roux at UCD, commenting on this report. “Artificial sweeteners can activate these taste receptors. Your body then prepares itself for a meal.”

This quickens the absorption of sugar into your bloodstream, with the expectation of more to come. But as you now have plenty of insulin ready for processing sugar, when it doesn’t arrive you may compensate by eating more, says le Roux. To make matters worse, routinely secreting more insulin can leave you at risk of diabetes.

O’Shea suspects that aspartame, often used together with sucralose to sweeten diet drinks, may also turn the throttle down on our energy burn, thus promoting fat storage. “It appears that some antipsychotic medications switch off your energy burn, leading you to store rather than burn more energy. We are now working on the theory that artificial sweeteners are having a similar impact on your energy burn through an immune mechanism,” he says.

Sweeteners may also throw our taste preferences off kilter. “Artificial sweeteners still promote a taste for sweet and mean you find sour and savoury less palatable. Kids in particular need to taste a variety of foods, and replacing full sugar with artificial sweetener gets rid of the calorie but doesn’t get rid of habituating you to sweet taste and a reluctance to try new flavours,” says O’Shea.

Messaging brain
Scientists know that sugars push the same reward buttons in our brains as, say, cocaine, albeit to a lesser degree, and can induce addictive behaviours. Obese and drug-addicted individuals both suffer damage to the reward pathways of dopamine, the pleasure hormone. Dr Ivan de Araujo at the John B Pierce laboratory in Connecticut is interested in how our brains perceive food, but his results complicate the picture. He believes that, although taste receptors might be hoodwinked by artificial sweeteners, brains are not so easily fooled.

Animals initially like artificial sweeteners but then figure out that they are not gaining energy in consuming them. His findings suggest brain cells, in particular those involved in detecting pleasurable sensations, are sensitive to the energy content of foods. “The brain figures out that there is a lack of energy in them compared to sugar,” says Araujo.

This means it is likely sweeteners are not as addictive as sugars, as they don’t activate the reward centres in the same way. However, it also suggests that consumers might be pushed to act when their brains detect consumption of zero-energy sweeteners – by finding a sugar hit elsewhere.

Not so sweet
Some studies have reported a link between the consumption of diet drinks and weight gain, but cause and effect is difficult to tease out. Research has also found a connection between knowingly drinking aspartame and a rise in energy consumption, pointing to overcompensation.

There is little evidence that consuming artificial sweeteners leads to weight loss, says Dr le Roux. "People eating these sugar replacers think that they are healthier," adds Dr Nora Khaldi, nutrition scientist in UCD. "But there isn't the data to back this up." That's not to say that those who consume gallons of cola won't benefit by switching to diet drinks, but for most of us, it seems switching to diet won't lead to weight loss.

Nonetheless, scientists are certain about one thing: the harm too much sugar causes. "The amount of sugar in these drinks can be really high, and the fizz hides it. [Sugar] should be regulated as an additive, not an ingredient, so that you only add a small amount to give food taste," says Dr Khaldi.


The miky way: Hidden qualities
Dr Nora Khaldi in UCD is searching for molecules in milk that could be added to other foods and drinks to make them healthier.

Adults who consume full-fat milk every day, and have a healthy diet, have a lower risk of high blood pressure than people who don’t drink milk. This is due to health-giving peptides [small parts of proteins].

Khaldi and her team also found molecules in milk that help regulate insulin secretion; these could be used to control blood-sugar levels and thus help with diabetes.

Recently her research on human milk uncovered more than 300 peptides, many of which resembled known antimicrobial or immune-enhancing compounds. Their role may be to protect breastfed infants from infection. Similar peptides are found in cow’s milk.

Her aim is to create new ingredients that can make products healthier and that could be targeted at people with certain conditions, such as diabetes.