“It’s quite simple,” she says. “We’re all a product of how much food we eat and how often we exercise. Super-skinny stars only look that way because they’ve either been hitting the gym or sticking to a strict diet – and I can tell which within seconds.”

Monica’s experience means she can size up celebs just by looking at their body shape, and she’s lucky enough to have seen many A-listers in the flesh.

“I’ve met many of these stars here or in the States, and some of them have asked my advice informally at parties,” she reveals.

“They’re not clients of mine, but I know their body insecurities. And even if they haven’t confessed to me, I can tell what they are doing to their bodies from how they look.”

Here’s Monica’s verdict on who’s working out and who’s going without…

VICTORIA BECKHAM, 34

She says: “I’ve got so much saggy skin on my stomach and I haven’t the time or the energy for the gym. I look really awful naked.”

Monica says: “Victoria has worked on her size 4 body for some time. Her legs are sculpted and her shoulders are defined. I’ve stood next to her and she’s not skeletal – just petite and fat-free. Unless she wears an industrial-strength corset, she’s worked on her abs, although I suspect Pilates as well as sit-ups.”

Verdict: Workout

SARAH JESSICA PARKER, 43

She says: “I eat everything. I’m just an eater. My stay-slim secret is anxiety!”

Monica says: “When you’re stressed, hormones make your heart beat faster, which burns calories – so no wonder recent rumours that her husband had an affair have led size 4 SJP to lose weight. But even when she’s calm, she doesn’t eat much. I was in the same restaurant as her, and eating ‘everything’ meant three mouthfuls of lamb and veg!”

Verdict: Go Without

JENNIFER ANISTON, 39

She says: “Staying fit has always been important to me. I take a short jog before yoga.”

Monica says: “I think Jen’s given up the gym for now. She’s always looked great and had good legs, thanks to running, but her muscles aren’t as defined lately. I think being loved-up with John Mayer meant size 6 Jen skipped jogging and went off her food, both of which would make the pounds fall off. Now they’ve split up, I predict she’ll hit the gym again to get over her heartbreak.”

Verdict: Go Without

AMY WINEHOUSE, 24

She says: “I’m fussy about food. There aren’t many things I’ll eat.”

Monica says: “Despite her skeletal frame, size 4 Amy isn’t underfed – those late-night trips to pick up chocolate and ice lollies keep her calorie intake up. But her pot belly suggests she could be lacking in protein and starving her body of vital nutrients.”

Verdict: Go Without

ASHLEY JENSEN, 39

She says: “I just refuse to starve to a size zero. Being healthy is more important.”

Monica says: “The size 8 Ugly Betty star has lost at least 2st. Looking at her sleek and slender body, I’d say she’s been running and cycling to burn fat.”

Verdict: Workout

TARA PALMER-TOMKINSON,36

She says: “I hate my muscles and I’m conscious of my boyish frame. I’m a size 6 but it’s due to a fast metabolism.”

Monica says: “Tara’s muscles aren’t terribly big, they’re just not covered with fat. People who don’t eat much usually claim a fast metabolism, but metabolism is higher the heavier you are. I’d say that Tara simply doesn’t eat much.”

Verdict: Go Without

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