Experimental research with rats showed that those able to access occasionally sources of pleasure, such as sweet solution treats or sexually receptive partners, have lower stress levels than those who cannot, even if the same amount of calories was fed directly to stomach.
Full story at Science Daily.
Ref. Yvonne M. Ulrich-Lai et al., Pleasurable behaviors reduce stress via brain reward pathways. PNAS 2010 (pay per view for six months).
This finding (somewhat self-evident, I'd dare say) left me wondering about why so many religious sects repress pleasure and I must conclude that the real reason is to create perpetually stressed adepts. Now, what's the advantage (for the sect) of perpetual stress among its flock? Are perpetually unsatisfied people more easily manipulable? I will presume so even if the exact mechanism eludes me.