Jessica feels in control when she says “no” to things that she really wants. Let’s go get some sweets after school, Jess.

No.

Fancy sharing these biscuits in my packed lunch with me, Jessie?

No.

Let’s get an ice cream on our way to the park, ok, Jessica?

No.

It’s not that she’s anti-social or that she doesn’t like having fun. It’s that Jessica is afraid of getting fat. The nine-year-old has watched one girl after another in Year 6 putting on weight and she’s vowed that she’s not going down that podgy road.

She’s been taught in personal and social education lessons that it’s perfectly natural, that it’s what happens to girls before they start their periods. And she can accept that this is the reason that her older friends have plumped out a bit. But she won’t accept that it has to happen to her.

Being fat, in her mind, is the worst thing that can happen. She believes that if she gains weight, her life will be as good as ruined. To be “fat” is to be outside the mainstream. You don’t see tubby models in magazines, you don’t see overweight actresses on the telly or in films. The world that she wants to be a part of is thin, beautiful, lively, glamorous. Weight gain is, in her worldview, failure.

But it’s not just the image problem that puts her off putting on a few pounds. Gaining weight is part of puberty and puberty is part of growing up. And from what Jessie sees of her 13-year-old sister’s existence, growing up isn’t all it’s cracked up to be. In fact, it’s positively horrendous. Anna cries a lot and rows with her mum and has lurid spots on her face. And she constantly goes on about being fat, throwing fits when her mum offers her pudding after supper. When that happens, her mum reacts by getting in a terrible mood and then the whole house is swathed in misery. When you’re young, Jessie’s worked out, it’s easy to be loved. When you’re a teenager, it’s just the opposite.

Even though Jessica’s fixated on her weight, she’s not stupid. She knows about the dangers of anorexia and bulimia, how they can mess you up forever - and how the mere mention of the words can strike fear in the heart of any parent. So she covers things up by saying that she doesn’t want second helpings or pudding because she had a snack after school and she’s full up. She does the same sort of thing at school when birthday cake is passed around, just to make sure the teachers don’t suspect anything.

What she wants, above all else, is to remain a child so that her mum and the world will love her forever. And for that to happen, she has to make sure she stays small, so that her body doesn’t betray her.