The sweeteners cause a sudden blood insulin and glucose 'rush', which will eventually make the person insulin resistant, and, ultimately, diabetic.
It had been thought that artificial sweeteners had no effect on metabolism, and was a calorie-free way to sweeten a drink. But researchers at the Washington University School of Medicine have discovered that the effect goes much further; receptors in the gastro-intestinal tract and pancreas are almost identical to those in the mouth, and they respond to anything sweet-artificial or natural-by releasing hormones, such as insulin.
They tested the theory on a group of 17 obese people with a body-mass index (BMI) of 42, who were given ordinary water and water sweetened by sucralose, an artificial sweetener marketed as Splenda. After drinking the sweetened water, the participants' insulin levels rose by 20 per cent; although this is a natural and 'good' response, as insulin is the body's way of coping with raised glucose levels, it will eventually lead to insulin resistance if the person regularly drinks diet drinks and colas.
(Source: Diabetes Care, 2013; doi: 10.2337/dc12-2221).