Diet products make people eat more, says nutritional toxicologist Peter Dingle.

He said some sweeteners in diet products were linked with stimulating appetite.

"Aspartame, commonly known as the sweetener NutraSweet, is a neuro-stimulant linked with stimulating appetite, so it can make you hungry," Prof Dingle, associate professor in health and the environment at Murdoch University, said.

"Diet stuff doesn't satisfy hunger like conventional food, because hunger is linked to certain texture and taste sensations. If you don't get them, you don't feel satisfied -- you don't have the feeling 'I've had enough, I'm full'."

He said people also ate more because they felt they had "done something healthy" by having diet products.

"Then they tend to consume just as much, if not more, than before," he said.

"There is little research to show that these foods have great benefit for long-term weight control.

"Long-term weight control is about eating good, healthy, nutritious foods, combined with a positive lifestyle, which includes keeping fit."

He said people focused on calories instead of nutrition.

Rather than diet food, people should eat healthier, with fewer processed grains and more "super foods" such as beans, nuts, vegetables and omega-3 oils, Prof Dingle said.

Instead of diet or soft drinks, people should drink water, which was healthier.

"Parents give their kids two cans a night and then they complain they can't sleep," he said.

The Aspartame Information Center website says scientific evidence overwhelmingly shows aspartame is safe and not associated with adverse health effects.