The mate selection theory says that women (and men) have developed strategies over time to to monitor potential love rivals. One method is to look at the porportions of the body and assess how attractive they are based on their frames. However, this can actually lead to self-judgement of one's own body and physical appeal. Researchers study if women who are satisified with their own bodies spend more time sizing up other women.
Past research in this area gives mixed results. Some studies say that women who are not satisfied with their own bodies and are vulnerable to eating disorders pay more attention to the bodies of thin women, but other studies say the opposite. Another study says that we do not know much about how much confident and healthy women behave when they look at other women, nor if that attention is influenced by their own body image. Amelia Cundall and Kun Guo from the University of Lincoln conducted an experiment to test these topics. Their results suggest that thinner bodies doesn't exactly mean that one is more attractive. The type of clothing is also a contributing factor. Furthermore, there was no link between one's body image perception and the amount of time they spend looking at models who were considered less attractive.
However, participants who said they were less satisfied with their own bodies were more inclined to compare themselves. And the more they were satisfied with a particular part of their bodies, the less time they spent looking at that region on someone else. Thus it seems that women when assessing females, the factors of clothing, body size, one's body image and satisifaction all plays a role.
Source material from Research Digest