To better understand whether consuming artificial sweeteners is associated with negative long-term effects on weight and heart disease, researchers from the University of Manitoba's George & Fay Yee Centre for Healthcare Innovation conducted a systematic review of 37 studies that followed over 400,000 people for an average of 10 years. Only 7 of these studies were randomized controlled trials (the gold standard in clinical research), involving 1003 people followed for 6 months on average.
The trials did not show a consistent effect of artificial sweeteners on weight loss, and the longer observational studies showed a link between consumption of artificial sweeteners and relatively higher risks of weight gain and obesity, high blood pressure, diabetes, heart disease and other health issues.
Source: http://www.cmaj.ca/