The Reinvention Issue · Turn the page ∨
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What this is.
A free monthly magazine for women who intend to get better at fifty, not quieter.
One compound taken apart properly. One thing worth putting on your face, explained at the percentage rather than the promise. And the short list of what we are actually buying.
How to read the science in here
Early signal means preliminary, often in cells or small groups. Established means it held up in human trials. Most of what is exciting right now is early signal, and I am not going to blur the two.
In this issue
Contents
The compound everyone is whispering about
Peptide Decoded. The number you were shown is not the number that got published.
That weighted vest everyone suddenly owns
Worth the Hype? The $279 one, the $40 one, and the physics.
Peptide Decoded · The compound of the month
Retatrutide.
Three receptors at once. And the number you have been shown is not the number that got published.
Read this first
Retatrutide is not approved anywhere. It is investigational. Everything below is what the trials reported. There are no doses on this page. I decode. I do not dispense.
Semaglutide hits one receptor. Tirzepatide hits two.
This one hits three. GLP-1, GIP, and glucagon.
The first two reduce what comes in. The glucagon arm is the one nothing else has alongside the other two, and it works the other direction. It raises what goes out.
The part I actually care about
You have seen “up to thirty percent” attached to this molecule. Vendor sites, podcast summaries, under every reel.
The phase 3 trial published in the New England Journal of Medicine reports twenty-five percent at the top dose.
The thirty is real. It is just not from that group of people. It comes from a two-year extension of 532 people out of the original 2,339, drawn from a heavier subgroup who stayed on, and counted the generous way.
Both numbers sit side by side in the sponsor's own published tables. Nothing is hidden. One of them simply travels better, and the one that travels is the one that ends up in your group chat.
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Does the number describe everyone who started, or only the people who finished?
Ask it out loud at dinner and watch what happens.
What gets left out
At the top dose over eighty weeks, nausea in roughly forty-two percent, and about eleven percent stopped because of side effects against five on placebo. That discontinuation rate is exactly why the two ways of counting diverge.
Your resting heart rate is likely to rise, more than on the others in this class, and a rate parked over a hundred is a doctor conversation. Blood pressure can drop. On insulin or a sulfonylurea, doses have to be reviewed.
And the trials were not run on you. The best age- and sex-matched dataset in the programme has a mean age of fifty-five and is forty-eight percent women, and even that one is not broken out by menopausal status. Unstudied is not the same as ineffective. It means nobody knows yet, and anyone telling you otherwise is selling.
The mechanism, the honest side-effect table, and what a low-dose protocol actually looks like.
Educational content only. Retatrutide is investigational and not approved by any regulator. Nothing here is a dosing recommendation.
A question
Peptide curious?
Most women start by asking a friend of a friend, and end up with a vial from an Instagram account that was called something different last month.
CouturePeptides is a research-use-only supply house, built by people who got tired of not being able to see the supply chain.
Code HOTGIRL takes 15% off.
Skin Deep
The $117 cream and the $49 one.
The number on the back of the jar decides whether any of it works. Almost nobody prints it.
You have almost certainly already bought this molecule.
Small heavy bottle, the counter called it “copper peptide,” and nobody told you what it actually was.
It is GHK-Cu. Three amino acids holding a copper ion. Your body makes it, and makes about sixty percent less of it at sixty than it did at twenty.
It does two jobs at once. It hands the workers their supplies, delivering copper to the enzymes that cross-link collagen and elastin. And it posts the memo, signalling repair genes up and inflammatory ones down.
Materials plus instructions. Once you have that, you never need the counter pitch again.
Here is the part that decides everything
A peptide in a jar is not a yes-or-no question. It is a percentage question.
Topical copper peptide does its work somewhere around one to two percent. Under one percent it is very likely doing nothing at all except appearing on an ingredient list where it looks impressive.
Which is the entire game, and it is why the label matters more than the brand. A great many beautiful jars sit well under one percent, and the way you know is that they will not tell you the number. The ingredient is listed. The percentage is not. That is a choice, and it is not an accident.
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A therapeutic percentage, or a drugstore sprinkle with a luxury price.
There is no third option, and only one of them prints the number.
The honest part, which costs me money
I sell a cream built on this molecule, so hear it from me rather than from somebody who would rather you did not know.
The entire randomised human evidence base for GHK-Cu on its own is two trials. Two. One of them, in eighty-six people, found it performed the same as inert placebo.
Three separate systematic reviews published this year land in the same place. Unproven. Not disproven. The preclinical case is genuinely strong. What does not exist is the human trial base the price tags imply.
I still use it every night. I am just not going to tell you there is a randomised trial behind my jar, because there is not one behind anybody's.
So: $117, or $49.30
OneSkin's OS-01 is $117. It is built on their own peptide, not this one, and it has company-funded published work behind it. A serious product. I am not pretending otherwise.
Copper Glow is $49.30. One percent Copper Tripeptide-1, which is GHK-Cu, plus nought point two percent SNAP-8. Printed on the front of the jar, where you can read it without a decoder ring.
And here is the part that makes that comparison exact rather than rhetorical. Both jars are fifty millilitres. Same size, same shelf, same six weeks of use. One of them is $117 and one of them is $49.30.
I did not invent copper peptides. I went looking for a jar that printed its actives at percentages that clear the floor, and when I could not find one at a sane price, I stocked the one I wanted to buy.
Face
Copper Glow Firming Cream
$49.30. 50 ml, morning and night. 1% Copper Tripeptide-1 + 0.2% SNAP-8. Firmer-looking skin, softer-looking expression lines.
Body
CU+ Silk Body Cream
$42.00. 100 ml. The same thinking for everywhere that is not your face, which is most of you. The OneSkin body cream is $105.
Code HOTGIRL takes 15% off.
Cosmetic products. Appearance claims only: firmer-looking, smoother-looking. Nothing here diagnoses, treats or prevents any condition.
The Hot List
Nine things, and why.
Copper Glow Firming Cream
1% GHK-Cu and 0.2% SNAP-8, printed on the front. The whole argument above.
Shop Skin by Couture →
CU+ Silk Body Cream
Inner arms, chest, the backs of the hands. All the places that tell on us first.
Shop Skin by Couture →
Wavytalk IPL Hair Removal
A category full of devices that are a torch with a price tag. This one has a precision roller and does the whole body.
See it on Amazon →
The Hatch circadian machine
Sleep is the one input no compound replaces, which is why a device working on light timing rather than sedation is interesting at all.
See it on Amazon →
Cool Girl Cropped Track Jacket
The shape everybody is paying four times as much for. Nobody can tell from across a room.
See it on Amazon →
Natrelax modal henley + pants
The dupe for the expensive whipped one, and the reason I sleep in something other than a t-shirt now.
See it on Amazon →
The weighted vest, and the bands
Verdict below. Buy weight, not branding. The forty-dollar one is doing the same physics as the $279 one.
See it on Amazon →
The Mireya Top
Pale pink, and the one thing on this list linked purely because I want it.
See it on Revolve →
The eye patches
Coming to Skin by Couture, so I am not sending you elsewhere for them. Next issue.
Code HOTGIRL takes 15% off at Skin by Couture.
Worth the Hype? · The verdict
That weighted vest everyone suddenly owns.
Every January there is a device. This year it arrived early, and it is a vest.
The mechanism is real, and it is load. Bone responds to being asked to carry things. So does muscle. It is the oldest idea in training wearing a nicer jacket.
What is oversold is the vest becoming the intervention. A vest does not have a metabolism. You do. Most of the benefit anyone reports is the walking.
Early signal
Weighted-vest research in postmenopausal women is small, mixed and mostly short. The bone-loading rationale is sound. A specific commercial vest producing a specific result is not something I can show you a trial for.
What the compression is actually for
The expensive one is neoprene, and the brand talks about compression and heat capture. Worth being precise about what that does and does not mean.
Compression here is a fit feature, not a muscle feature. The neoprene conforms to your shape and holds it, so the weight sits still instead of shifting and slapping while you walk. That is the honest reason to pay for one: a vest that moves around is a vest you stop wearing by week three.
The brand also claims it builds lean muscle, prevents muscle loss and increases bone density. I am not going to repeat those as findings. They are the manufacturer's marketing, not a trial on this product, and nothing about pressing fabric against your torso builds tissue.
The muscle and bone argument runs entirely through load. You are carrying extra weight, your skeleton notices, and that is true of any vest with the same number of pounds in it.
Verdict: worth it, at the cheap end. AION at $279 earns its price on fit and on being HSA and FSA eligible, which most women do not realise and which is worth roughly thirty percent. The forty-dollar one is doing the same physics. Buy weight, not branding, and spend the difference on anything that gets you outside more often.
Some links are affiliate links and may earn a commission at no extra cost to you. It never changes the verdict.
The Cover Story
Thin, and still in trouble.
There is a name for the fat you cannot pinch, and your jeans will never tell you about it.
Last week I sprinted for ten seconds, six times, with walking in between.
Ten minutes outside. One minute of actual running. I could not get down my own stairs properly for two days.
I am fifty-three. I train. And sixty seconds of moving quickly left me holding the banister like it was my new boyfriend.
There is fat that sits deeper in the abdomen, wrapped around the organs. You cannot grab it in the mirror, your weight does not tell you how much of it you have, and a standard blood panel does not measure that compartment at all.
There is a shorthand. TOFI. Thin outside, fat inside.
Looking smaller and becoming metabolically healthier are two separate achievements. Sometimes they arrive together. Sometimes the photograph improves and every question underneath it sits exactly where it was.
Your jeans are not qualified to give you a clean bill of health. Neither is a compliment at brunch.
One move this month: measure your waist and write the number down with today's date. The scale is a liar with excellent manners. The tape is not.
The muscle finding that changed how I train, and what actually moved it.
Nobody Warned Me
Nobody warned me about the reading glasses.
Three strengths. One pair in the kitchen, one in the car, and the strong pair next to the vial I am drawing up, because I could not read the markings on a 31-gauge syringe and I was not willing to say that out loud to anybody.
Nobody warned me about getting off the floor. Somewhere in here it stops being automatic and starts involving a plan. Furniture gets consulted. I have decided this is the actual fitness test and nobody is administering it.
Nobody warned me the compliments would get a qualifier. “You look amazing.” Pause. “For your age.” The pause is where they do the maths.
And nobody warned me how much I would like it. I know what I am doing now. I know what my labs mean. I have less time and I waste almost none of it.
Apparently that is the trade, and I would not go back.
The Second Act
Two girls in Monterrey, 1995.
Kari got on a plane to Monterrey at twenty, knowing nobody.
Her roommate was from Paris and, over an entire semester, never really spoke to her. And then there was me, down from Colorado. There was no getting-to-know-you period. It was instant and it was total.
She turned fifty-one this year. I called her four times before noon. Once to sing, once about label fonts, once about a shipment, and once about nothing at all, which has always been our best category of phone call.
Between us there are six children, two ended marriages, three companies, and a friendship now old enough to be having its own midlife crisis.
Instead it is having the opposite.
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The second act is not the consolation prize.
It is the part where you already know who you are, which is the biggest advantage anyone has ever had in business, and nobody puts it on the slide.
That company is two shops now. Skin by Couture for what goes on your face, and CouturePeptides for the research-grade supply we could never find anywhere else.
Code HOTGIRL, 15% off either one.
Back cover
You started this to feel like yourself again.
Free, every month. Forward it to the friend who keeps texting you photographs of vials.
Code HOTGIRL takes 15% off at Skin by Couture and CouturePeptides.
The masthead
Substack
The long versions →Skin by Couture
The shop →CouturePeptides
Research use only →Hot Girl Biology is published by the owners of Skin by Couture and CouturePeptides. Some links earn us a commission, including Amazon links. As an Amazon Associate we earn from qualifying purchases. Products appearing here are not claims that they are proven safe or effective for you. Educational content only. Nothing in this magazine diagnoses, treats or prevents any condition, and nothing here replaces guidance from your own clinician.
Hot Girl Biology · Tested, decoded, delivered monthly · Issue No. 01
