Published in the Journal of the American Geriatrics Society, the study had focused on 749 adults aged 65 years or older over a 10-year period and said it had found that regular diet soda drinkers added up to three inches to their waistlines, compared with non-regular drinkers.
While people who did not drink sodas regularly had an average of 0.80 inches added to their waistlines, people who drank an average of one can of diet soda every day, put on an extra three inches, it said.
However, St George’s Hospital NHS Trust principal dietitian Catherine Collins said the devil was in the study’s “missing detail”. As a dietitian, she said she was cynical of the study as it “carefully” avoided some points such as the main reason why middle aged or older people preferred low calorie soft drinks was because they may already be overweight and were trying to control their weight.
The study did not confirm that ‘diet drinks make you fat’, but simply confused correlation with causation, she said. She said that the authors justified their statement based on 10 year follow-up of only half of the original subject group (375 of 749) who were "able to provide information at follow up on diet, lifestyle and body weight and shape".
But when it came to body weight and storage of surplus calories, all foods (and drinks) count - “not necessarily that diet drinks were playing weird games with their metabolism to keep them fatter than they need to be, as the public may infer from the headline grabbing statement”.
Dr Nita Forouhi of the University of Cambridge also said further research was needed and that the study was not ready for translation into a public health message.
“This study does not establish that diet soda leads to accumulation of abdominal fat, due to current study limitations. Though the authors speculate that the higher waist girth is likely to represent the metabolically active deep visceral fat more so than the superficially located subcutaneous fat, they did not directly measure these, so it is unclear what type of “belly fat” would be associated with diet soda intakes,” she said.
British Soft Drinks Association director general Gavin Partington also said that the study did not establish causation. “In fact the authors look at people over 65 who are already at risk of weight gain and cardiovascular disease so there’s no basis to attribute their waistline to diet soft drinks.
“Indeed the body of evidence accords with common sense, that diet soft drinks can help to reduce calorie intake.”
Mounting concerns over harmful health effects of sugar consumption over the past 30 years may have led to an increased intake of “non-nutritive sweeteners”, but “the prevalence of obesity has increased dramatically over this time”, the study said.
It added that its results were consistent with findings from other studies in which frequent consumption of diet soda was associated with heath concerns such as “greater incidence of overweight and obesity, diabetes and cardiovascular events”.
“In a striking dose-response relationship, increasing diet soda intake was associated with escalating abdominal obesity, a potential pathway for cardiometabolic risk in this ageing population,” it added.