• A 20-year-old can get away with 2,000 calories a day; after 50, it's just 1,600.
• Sharon Stone, all 59 years of her, still looks gorgeous in a bikini.
• Cindy Crawford, 51, works out for 75 minutes from 8am three times a week
Ladies, I apologise. The pictures here will be causing a range of feelings, and I'm sure not many are good.
There's Sharon Stone, all 59 years of her, looking gorgeous in a bikini - one of those two-piece affairs you probably owned for a summer or two in the 80s.
Her figure is astonishing. Cut off her head (a bit harsh, but I bet some are tempted) and look at the body, and you couldn't age it. You certainly wouldn't put it above 30.
Then there's Halle Berry. She turned 50 last August, and a month later was pictured posing on the beach in a tiny black number many 20-year-olds may be scared to wear outside a changing room.
There were no lumps, bumps or overhang, and - pass me a 99 with an extra Flake - she had a six-pack.
You could console yourself by remembering Sharon and Halle knew the camera was on them, and had time to pull everything in and check sympathetic sun angles, but then Courteney Cox (aged 52), Cindy Crawford (aged 51) and Paul McCartney's wife Nancy Shevell (aged 57) ruin it all by getting snapped by paparazzi looking beautiful while letting it all hang out - only nothing was hanging out.
Don't get me started on Liz Hurley. Appalling luck with men, but no bad bikini pictures. She'll be 52 in June.
Women my age - I turn 50 in September - will feel sadness and anger looking at these photos. Sad we didn't relish our bikini days while we had them, and angry we let them go.
For surely, we think, looking at these women, it can't be so hard to maintain a bikini-worthy body well into middle-age? If only I wasn't so greedy and lazy I, too, could look this good, couldn't I?
Cue the self-loathing and biscuit tin raids. Wrong. Let no one be fooled: a hellish world of hard work, discipline and hunger goes into those bodies.
Gwyneth Paltrow (not in the 50 club yet, but she'll be welcomed with open arms) at least admits she 'works her butt off' to look as good as she does.
We are working against nature to aspire to a figure like that in our 50s. As we age, our muscle volume decreases, our metabolism slides and our calorie requirement is lower. A 20-year-old can get away with 2,000 calories a day; after 50, it's just 1,600.
Dropping oestrogen levels in menopause cause fat to redistribute around the abdomen. With all the nutritionists and personal trainers in the world, you could try to shift it, but for those of us whose careers are not tied up in our looks, it's nearly impossible.
For what these pictures don't show is the hunger. That debilitating drag in your belly which can be put up with for a couple of weeks at best, before a holiday or wedding - any longer would drive us mad.
Liz Hurley says she 'likes' to go to bed hungry. That's what you'd have to deal with for a body like hers. No ice-cream, no wine, no 'stuffed to the gills' satisfaction.
Still envy Liz Hurley? Don't look at her taut belly, just think of the rumble within and know she'll never enjoy melting chocolate on her tongue, or a bag of hot chips. It will make those pictures easier to look at, believe me.
So how do they do it?
CINDY CRAWFORD: 75-MINUTE WORKOUT FOR BREAKFAST
At 51, her training programme is incredible. Cindy works out for 75 minutes from 8am three times a week.
Her routine includes weights and lots of old-school lunges and squats. To keep her heart rate up, she runs up and down stairs for timed intervals, then finishes by doing abs exercises on a mat.
She says she tries to eat healthily at least 80 per cent of the time.
HALLE BERRY: PROTEIN SHAKES AND PUSH UPS
The 50-year-old diabetic actress is on a super-restricted diet and eats only natural sugars.
She has also cut out bread and drinks lots of water.
On set, she relies on shakes made with vegetable protein to keep going. She exercises for at least half an hour every day 'no matter what'.
Her routine involves planks, press-ups and lots of cardio.
BTS on my last shoot of the summer. A post shared by Halle Berry (@halleberry) on Aug 30, 2016 at 11:55am PDT
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SHARON STONE: LEG LIFTS IN THE BATH
The 59-year-old actress is a self-confessed exercise fiend. 'Every time I exercise, I do something different,' she says.
'Sometimes I do leg lifts and circles in the tub, using the water as resistance.'
She doesn't go to a fancy celebs-only gym, preferring to visit huge U.S. chain 24-Hour Fitness.
She eats lots of red meat - especially steak - but you can forget about a nice glass of red. Alcohol is out.
LIZ HURLEY: GOING TO BED HUNGRY
Perenially gorgeous Liz, 51, swears she never goes to the gym, but admits to never staying still.
'I try to walk or run with the dogs every day,' she has said. To maintain that washboard midriff, she has admitted to drinking mugs of hot water to stave off hunger pangs.
She goes to bed hungry as she likes to eat earlier in the day, so the food doesn't turn to fat. So what does she eat? Not much.
Her diet tends to be confined to wholegrains, vegetables, fish and 'bits of lean meat'.
ELLE MacPHERSON: EXTREME SPORTS AND BAREFOOT BEACH RUNNING
"I make sure I find at least 45 minutes in my day to do an outdoor sport. I love to paddleboard, surf, swim or water-ski."
She says this is "much simpler and gentler" than what she did in her modelling heyday.
She likes to run barefoot on the beach near her home in Miami, doing a few lunges as she goes.
As for food, Elle adheres to the Alkaline Diet, supposed to reduce your body's natural acidity, and drinks three litres of water a day. She tops that off with fruit smoothies.
CHRISTIE BRINKLEY: USES 'TORTURE' RACK
A committed vegan, Christie, 63, says she even does leg lifts while brushing her teeth.
'I also try to get in 100 press-ups every day. It's really easy,' she says.
She's also a fan of the Total Gym home exercise system, which looks a lot like an instrument of torture. 'It is constantly stretching and strengthening,' she said.
When it comes to food, she's all about variety - as long as it's vegan. 'I go for as many colours as possible in a day.'