Hungry again? Think about the last meal you had and it could lessen your hunger, a new study shows.

A British research group showed volunteers either a 300 ml or 500 ml bowl of soup before lunch, and then changed some of the portions without the participants' knowledge.

Immediately after lunch, the volunteers' hunger was based on the actual amount of soup they ate, but a few hours later the volunteers who thought they'd eaten the 500 ml portion of soup reported being less hungry. This continued 24 hours later.

The study states this is only effective when a very recent meal is remembered.

The researchers from the University of Bristol say this is the first time science has shown the impact memory has on how full people feel.

With obesity on the rise, the information could be used to help reduce people's food consumption, the researchers said.