“Are you nuts? You’re not going to be able to do that,” says my friend Anna as we exercise in her living room. It’s been 10 months since we each gave birth to our daughters, and we’re fighting to regain our figures, mainly so we can embrace one of autumn’s hippest trends – high-waisted jeans. It’s a look that’s been sold to us by the fashion bloggers we follow on Instagram. I’ve just told Anna that I plan to embark on a six-month challenge of consuming no new clothing, and her reaction is one of incredulous scepticism.