Artificial sweeteners may be fuelling rather than fighting weight loss
He licked his finger to pick up a piece of paper and noticed a very strong, sweet taste. “I thought that I must have still had some sugar on my hands,” wrote James Schlatter, a chemist working at G.D. Searle, in 1965. But this was no sugar. Schlatter traced the powder to a flask filled with a substance that was supposed to help create a drug for stomach ulcers. He figured this curious chemical, dubbed aspartame, was unlikely to be toxic, so tasted it again.
Today, aspartame is used in more than 6000 types of products and beverages worldwide – including Diet Coke, yoghurt, chewing gum and even baby foods. With almost no calories, it is one of the most widely used “diet” sugar substitutes in the world. But evidence is emerging that aspartame and its “zero calorie” cousins such as sucralose and saccharin are not the helpful dieting substances they claim to be.
“There is no good scientific evidence that artificial sweeteners can help weight loss in the long term,” says Susan Swithers, a professor of behavioural neuroscience at Purdue University in Indiana. In fact, sweeteners are now being linked to weight gain and its related conditions: diabetes, metabolic disorders and heart disease.
The stakes of verifying these links are high. According to the Australian Beverages Council, which represents 95 per cent of Australia’s non-alcohol beverage industry, more than 666 million litres of drinks with sugar substitutes were sold in Australia in 2011. One-third of soft drinks sold are “non-sugar” varieties.
No-calorie, or non-nutritive sweeteners trigger a sweet signal in our brain but cannot be digested and metabolised properly, so they don’t release energy. For decades, lowering calories has been viewed as the cornerstone of losing weight, which is why Australia’s peak body for developing health advice, the National Health and Medical Research Council, still recommends diet soft drinks as alternatives to sugary beverages.
But questions have surrounded the benefit of diet drinks for more than five decades, ever since the low-calorie-diet industry was born. Over three years in the 1950s Mary McCann at Harvard University studied 147 people who attended an obesity clinic. Publishing her results in 1956, she found no connection between the consumption of artificial sweeteners – often based on saccharin then – and whether her subjects lost weight.
More recently, large studies tracking tens of thousands of people for years have found that regular artificial sweetener users gained more weight and had an increased risk of type 2 diabetes than those going for sugary drinks. The most at risk are heavy drinkers of artificial sweeteners. In 2008, a team led by Helen Hazuda at the University of Texas reported that people drinking 21 diet beverages a week were twice as likely to become overweight or obese as those who didn’t drink “diet”. “It raises a troubling question,” wrote the research team in their paper published in Obesity. Are artificial sweeteners “fuelling – rather than fighting – the very epidemic they were designed to block?”
We can’t be sure. As the Texan researchers point out, these studies don’t definitively demonstrate that artificial sweeteners are making us fat. For example, it’s possible that those who start drinking diet soft drinks are already on “weight-gain trajectories”, which might be the reason they switched to diet beverages.
To make a persuasive case, scientists need to unravel how a substance with “no calories” can lead to people gaining weight. One idea is that when people know they are consuming a drink low in energy, they feel justified eating more later. People tend to overindulge in low-fat food, for example, because they overestimate the calories they’ve saved elsewhere. In 1970, a diabetes textbook described this phenomenon as permitting a “deceptive sense of culinary joie de vivre”. But something else is at play here. Lab rats, which don’t consciously acknowledge the energy content of their foods, also overeat when fed non-caloric sweeteners. So what’s going on?
According to Swithers, the long-term use of artificial sweeteners confuses the complex signals between our tongue, brain and gut, ultimately blunting our metabolism and increasing appetite. When we eat foods high in sugar and calories it triggers chemical signals through many parts of our brain and body. The brain’s reward system lights up so we learn to enjoy eating, while hormones flood through the body, preparing the gut to digest calories and regulate appetite.
Animal studies conducted by Swithers and other research groups suggest that consuming sugar substitutes over time dampens this exquisitely intricate response. The brain becomes accustomed to receiving no calories after a sweet burst, she says, so the metabolism is no longer ramped up, even when we ingest sugary food. “Your body doesn’t know what to do,” she says. Meanwhile, the hormones associated with feeling full are not released with the same gusto, which could encourage overeating.
This research is based on animals and will need to be repeated in humans. But already there are a few small studies in people that support Swithers’ work. They show, for example, that artificial sweeteners don’t activate neural pathways in the same way that sugar does.
In July last year, Swithers published an opinion piece on this “counterintuitive” effect of artificial sweeteners. The case isn’t closed, by any means, and there have been reports debunking this line of thinking, too. But their links to the trillion-dollar food and beverage industry invite caution.
Several months after Swithers’ publication, a new study announced no difference between the brain’s response to eating yoghurt containing sugar and to eating yoghurt with artificial sweeteners. One of its authors, Pascalle Weijzen, works for FrieslandCampina in the Netherlands – with a yearly revenue of 11.4 billion euros, it is one of the world’s largest dairy companies.
Industry’s influence on academic research into sugary beverages was confirmed earlier this year. A paper published in The American Journal of Clinical Nutrition reported that industry-funded reviews were more likely to suggest that evidence for a connection between sugar-sweetened beverages and weight gain “was weak”, while independent bodies tended to describe it as “well-founded”. This is yet to be repeated for studies into artificially sweetened beverages, but it is telling that a study published mid-year, funded by the American Beverage Association, reported that artificially sweetened drinks helped people lose more weight than drinking water.
In 2006, Anne de la Hunty, at Ashwell Associates in Britain, analysed “all studies” that asked participants to substitute sugar in their diet with aspartame. Published by Nutrition Bulletin in 2006, she concluded that using the artificial sweetener instead of sucrose significantly reduced body weight. This paper has been cited almost 70 times since its publication, and is used in Coca-Cola’s position statement on non-nutritive sweeteners. It was funded by Ajinomoto, a Japanese manufacturer of aspartame. All five of the nine studies de la Hunty reviewed that found aspartame helped people lose weight had received industry funding.
In 2012, Professor G. Harvey Anderson and colleagues at the University of Toronto published an opinion piece in The Journal of Nutrition claiming there is “no evidence” that low-calorie sweeteners can cause weight gain in adults. Anderson was paid to write the piece by the International Life Sciences Institute, an outfit with a board of trustees including people from Coca-Cola, Nestlé, Ajinomoto and Procter & Gamble, and which is currently licensing one of the newest sweeteners on the market, a derivative of monk fruit. Three of the four authors, including Anderson, received consulting fees from food and beverage companies, while the guest editor accepted funding from the Kellogg Company. The opinion piece was paid for and marked “advertisement”, but it has already been cited elsewhere 15 times.
Swithers, who has turned down industry funding, says the beverage industry “goes after scientists in a tactic borrowed from the tobacco industry”. They seem to cherrypick researchers who might be “sympathetic to their cause”, she says, and slam those who aren’t. The Calorie Control Council, an international outfit representing the low-calorie food and beverage industry, wrote to Swithers’ university instructing it to stop promoting her “biased” papers. The Australian Beverages Council has also criticised her work.
Dr Richard Young at the University of Adelaide, who studies the effects of artificial sweeteners, cautions that industry-funded studies can’t be completely dismissed. “Industry support is important in this day and age, when our funding is strained from government sources,” he says. “But you have to take caution when industry-funded research flies in the face of non-industry-funded research.”
Young agrees the evidence is inconsistent, but says “we haven’t done the perfect study” to show that diet drinks in fact cause weight gain. “We are building the story.”
CORRECTION: In the print edition, the yoghurt study referred to the non-artificial sweetened yoghurt as "plain natural yoghurt".
This article was first published in the print edition of The Saturday Paper on Jul 19, 2014 as "Sweet nothings". Subscribe here.