Hi, We're Retainix.
Preserve The Strength, Lose The Rest
Our mission
Preserve The Strength, Lose The Rest
Retainix exists to protect what GLP-1 medications quietly take alongside the fat: muscle, bone density, and steady energy. We build one credible daily habit that lets men win the weight loss fight without losing the strength that made it worth fighting for.
Built After Watching A Father Shrink
Retainix started with a founder watching his father drop forty pounds on a GLP-1 medication and feel proud, then start feeling frail. Clothes fit looser, but he seemed smaller in every direction, tired in a way that worried the whole family. Digging into the research revealed a pattern nobody had explained to him: rapid GLP-1 loss can take real muscle and quietly drain nutrients like vitamin K2. There was no product built specifically for that gap, only whey tubs and gated clinics. So the team built one.
Shop HOLDFASTThe People Behind HOLDFAST
A small team of formulators, researchers, and product builders who take GLP-1 physiology seriously. We exist because nobody else was building specifically for what these medications take from a man's body.
Marcus Whitfield
Founder. Marcus spent twenty years formulating everyday supplement products before a family member's experience on a GLP-1 medication reframed his focus entirely. He leads Retainix with a bias toward precision over hype, insisting every claim trace back to a measurable physiological loss the product is built to defend.
David Renner
Head of Research. David translates the physiology of GLP-1 weight loss into formula decisions, tracking dosing thresholds for creatine, HMB, and vitamin K2 against what the body is actually losing. He's spent his career in nutrient formulation and insists every gram in HOLDFAST earn its place.
Elena Kowalski
Quality & Formulation. Elena oversees ingredient sourcing and manufacturing standards, verifying creatine purity, protein isolate specs, and MK-7 isomer content batch to batch. She came from pharmaceutical-grade supply chains and treats consumer nutrition with the same rigor.
Thomas Brandt
Product Education. Thomas builds the plain-language explanations that help men understand what's happening in their bodies on GLP-1 medications and why each ingredient in HOLDFAST is there. He writes to respect the reader's intelligence, never to alarm or oversell.
Rachel Sorensen
Customer Experience. Rachel runs the team that helps men fit HOLDFAST into their existing daily routine, from mixing questions to timing it with a GLP-1 shot. She's focused on making the habit feel effortless, never like another clinical task.
Marcus Whitfield
Founder. Marcus spent twenty years formulating everyday supplement products before a family member's experience on a GLP-1 medication reframed his focus entirely. He leads Retainix with a bias toward precision over hype, insisting every claim trace back to a measurable physiological loss the product is built to defend.
David Renner
Head of Research. David translates the physiology of GLP-1 weight loss into formula decisions, tracking dosing thresholds for creatine, HMB, and vitamin K2 against what the body is actually losing. He's spent his career in nutrient formulation and insists every gram in HOLDFAST earn its place.
Elena Kowalski
Quality & Formulation. Elena oversees ingredient sourcing and manufacturing standards, verifying creatine purity, protein isolate specs, and MK-7 isomer content batch to batch. She came from pharmaceutical-grade supply chains and treats consumer nutrition with the same rigor.
Thomas Brandt
Product Education. Thomas builds the plain-language explanations that help men understand what's happening in their bodies on GLP-1 medications and why each ingredient in HOLDFAST is there. He writes to respect the reader's intelligence, never to alarm or oversell.
Rachel Sorensen
Customer Experience. Rachel runs the team that helps men fit HOLDFAST into their existing daily routine, from mixing questions to timing it with a GLP-1 shot. She's focused on making the habit feel effortless, never like another clinical task.