What fizzy drinks really do to your body – and the worst ones for your health

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Sugary drinks are a leading cause of tooth decay and Type 2 Diabetes

Coca-Cola contains almost 35g of (added) sugar in a 330ml can – almost nine teaspoons. A 500ml can of Monster Energy Drink weighs in at a tooth-aching 55g of sugar – almost 14 teaspoons. Drinking just one can will take you well over the recommended daily sugar allowance of 30g.

But, although most of us know that fizzy drinks are bad news for our health, the sugar rush remains irresistible. British adults still consume more than one can of soft drink each per week – the kind with sugar, not artificial sweeteners – according to the government’s annual Family Food survey.

Soft drink sales have seen almost continual growth in the last decade, with UK sales reaching almost 3.2 billion in 2023. With Type 2 Diabetes and heart disease being two of the key risk factors for anyone on a high sugar diet, it’s no wonder that nutritionists welcomed the Budget’s hike in the sugar tax.

But which has more sugar, old-fashioned cream soda or a can of Red Bull?

What are the health worries of too many sugary drinks?

Manufacturers load their drinks with sugar because it extends shelf life and is a cheap and easy ingredient to use in processing. They also know it appeals to our taste for sweet things, which has grown alongside our intake of ultra-processed food and drink; even savoury products are often loaded with sugar. “We know that the amount of sugar, as well as salt, in foods has increased in recent years and our palates have got used to it,” says Beth Bradshaw, a public health nutritionist with Food Active, a healthy weight programme that runs the GULP (Giving Up Loving Pop) campaign.

Consumed in excess, all free sugar can potentially damage our health, but sugary drinks are particularly problematic. “They don’t fill you up, they’re absorbed very quickly, and they have no nutritional value,” Bradshaw says. “They just provide a big bang of sugar.”

What do sugary drinks do to your body?

Weight gain

It’s not just the calories in sugar-sweetened soft drinks, but the way the body processes the sugar that leads to weight gain, says nutritional therapist Jeannette Hyde.

“When you have a sugary drink a lot of sugar is released into your body very quickly, and the hormone insulin is released, which carries the sugar to your cells,” she explains. “Insulin is a fat storage hormone, so it will make you gain weight.”

As well, the rise and subsequent fall in blood sugar that occurs when you consume sugary drinks makes you feel hungry again quickly. “So, you’ll seek out more sugar and the cycle will start again,” Hyde says. She stresses that this applies to sugary drinks and fruit juice, not foods naturally containing sugar like fruit and whole grains, which are absorbed slowly.

Type 2 diabetes

A study by Harvard University in 2010 found that people who drink one can or more per day of sugar-sweetened drinks have a 26% increased risk of developing Type 2 diabetes. The drinks cause spikes in blood sugar levels, which can lead to insulin resistance, a condition that occurs when the body’s ability to respond to insulin decreases.

“It gets to the point where the cells in your body have had so much insulin coming at them that they become disordered and can’t cope anymore,” Hyde says. Type 2 diabetes can develop when the body becomes less effective at storing and managing blood sugar.

Heart and liver disease

Emerging evidence suggests drinking lots of sugary drinks can increase your risk of heart disease because they lower levels of “good” cholesterol and increase triglycerides, a type of fat that can thicken the arteries.

High sugar intake, particularly from sugary beverages, can lead to fat accumulation in the liver, non-alcoholic fatty liver disease and – potentially, according to some research – a higher risk of liver cancer.

Why fizzy drinks are so bad for children

As well as being linked to rising obesity levels in children, sugary drinks are also in the frame for more cases of Type 2 diabetes. “We’re seeing a worrying number of younger children starting to be diagnosed,” Bradshaw says. “There’s no single cause, it’s usually a multitude of factors, but sugary drinks can have a real impact.”

Also concerning is the “staggering” number of children starting school who already have experience of dental decay. This is now the number one reason for hospital admissions among young children, with over 42,000 tooth extractions taking place in NHS hospitals in England last year on patients aged 0-19. “Sugary drinks have had a major role to play in that,” Bradshaw says.

But sugar is not the only problem. Various acids found in sugary and artificially sweetened drinks – citric acid, phosphoric acid, and carbonic acid – are destroying the enamel on children’s teeth. “It can weaken the surface of the teeth, which can become very sensitive as well,” she says.

Sugar-sweetened energy drinks, popular among young people, pose the additional problem of containing caffeine. Caffeine can interfere with the absorption of calcium, raise blood pressure and cause sleep disturbances, headaches and stomach aches among adolescents, according to the British Dietetic Association.

Are low-sugar drinks better?

Many manufacturers have now replaced some or all of the sugar in their drinks with artificial sweeteners. But experts are divided about this. Bradshaw echoes NHS advice that artificial sweeteners are rigorously tested and safe. “They’re a great first step for somebody who wants to reduce their sugar intake,” she says.

But Hyde is not convinced. Animal studies suggest that artificial sweeteners disrupt the balance of healthy bacteria in the gut. “And when the gut microbiome is in this state of dysbiosis, people get more sugar cravings,” she says.

Recent studies have found that the artificial sweeteners used in soft drinks, such as aspartame and sucralose, may also prompt insulin resistance over time.