...if you're a small goby. It's a new take on dieting: small fish turn down food in order to avoid bullying by bigger fish.
These gobies are small ocean fish with a rigid social structure. If small individuals eat too much then they grow and become an apparent threat to the bigger dominant fish. That invites attack, expulsion from the sheltered environment, and probably being eaten. Diet, stay small, and avoid attack. How's that for strong motivation?
These gobies maintain social hierarchies where the dominant fish is 5-10% bigger than the next largest fish, and each fish down the dominance ladder is 5-10% smaller than the fish above. This precise size range is maintained by smaller gobies refusing to eat offered food, in order to stay small and avoid attack. It's an unusual way to promote social order, but it seems to work for gobies.