As pervasive as aspartame, sucralose, stevia, and other low-calorie sweeteners have become, understanding of their health effects is relatively basic. Not to be scary about it; most signs point to no serious concerns, and eating too much sugar does point to serious concerns, and life demands sweetness. But the scale on which low-calorie sweeteners been introduced to our diets in recent decades is massive, and they are evolutionarily novel, so it's good to keep an eye on the latest research on what these chemicals are doing to us, which is this.
The September issue of The American Journal of Clinical Nutrition just published a meta-analysis of the existing research on artificial sweeteners and weight gain. The conclusion lands in support of artificial sweeteners in the right context, specifically when they are substituted for sugar. People tend to see "modest weight loss," suggesting that low-calorie sweeteners (LCSs) indeed "may be a useful dietary tool to improve compliance with weight-loss or weight-maintenance plans."
That might seem obvious, but several studies have suggested that eating/drinking these nutritive sweeteners actually leads to weight gain. That has to do with satiety signals, effects on insulin levels, changes in the body's fluid balances, and other not-immediately-apparent downstream factors.