Penetrative intercourse only

UK news:

New Scientist magazine reports that Stuart Brody, a psychologist at the University of Paisley, found having sex can help keep stress at bay.

However, only penetrative intercourse did the trick - other forms of sex had no impact on stress levels at all. ...

Dr Brody found that the effect remained even after taking differences in personality and other health-related factors into account.

He told the BBC News website it was possible the calming effect was linked to the stimulation of a wide variety of nerves which takes place during heterosexual intercourse, but not other forms of sex. ...

Professor Brody said it made sense in evolutionary terms for standard heterosexual sexual intercourse to be associated with a wide range of positive effects on behaviour.

He said: "A growing body of research shows that it is specifically intercourse, and not other sexual behaviours, whether alone or with a partner, that is associated with a broad range of psychological and physiological benefits.

I'd be skeptical, like "Dr Peter Bull", but apparently there are other studies with similar results.