Retatrutide and Tirzepatide: What the Trials Actually Measured

One extra receptor is the whole story. Tirzepatide works at two — GIP and GLP-1. Retatrutide adds a third, glucagon. Everything worth knowing about the comparison comes out of that single structural difference, and everything below is what the trials themselves reported, with the study attached to each figure.

Your blueprint: 30 kg in 12 months

Dropping excess body fat changes the entire human, inside and out — it is the single greatest lever for healing and vitality. Everything below is the blueprint for pulling it. It is six habits and one number, and the number is the easy part: 0.6 kg a week is 30 kg in a year. Not a heroic January. Not 2 kg a week. Just the same week, repeated fifty-two times.

The maths, so it stops sounding enormous

• 0.6 kg a week — that is the whole target, divided up.
• ~2.5 kg a month, and expect it lumpy: 4 kg one month, 1 kg the next, a fortnight where the scale sulks and your waist shrinks anyway.
• Checkpoints: ~7 kg by month 3, ~15 kg by month 6, ~22 kg by month 9, ~30 kg at twelve.
• Behind at a checkpoint? The answer is nearly always in the tracking, not in the protocol.
• Read it honestly: retatrutide's 12 mg arm averaged −24.2% of body weight at 48 weeks, which at a 125 kg start is about 30 kg and at 90 kg is about 22 kg. The trials reported percentages, not kilograms — so 30 kg is a target to organise a year around, not a number anyone can promise you.

Eat: protein first, at every meal

• Protein every time you eat: chicken breast, white fish, eggs, cottage cheese, lean mince. This is the one to protect — the DXA substudy above is the whole reason the fat-versus-lean distinction matters, and protein plus lifting is what keeps the loss on the fat side of that line.
• Clean carbs, not no carbs: sweet potato, potato, rice, whole fruit. They are what fuels the training below.
• Something fermented daily: sauerkraut, kimchi or plain kefir, for the gut.
• Fat under 30 g a day, and from real food — butter, avocado, olive oil.

Drink: two litres, and count what is in your cup

• Two litres of water a day, more on training days and through a Highveld summer.
• Milk in tea and coffee counts. Four flat whites is a meal nobody logged — include it.
• No alcohol. The reasoning is in the avoid list below.

Track: if it is not logged, it did not happen

• Log everything in FatSecret — the app is free, and the honesty is the point. Milk, oils, sauces and the handful of nuts included.
• Weigh once a week, same morning, same conditions. Daily weight is mostly water, and it will talk you out of a protocol that is working.
• Measure your waist monthly and take a photo. On the weeks the scale sulks, those two are what show you the truth.

Train: lift four to five times a week

• Resistance training, 4–5 sessions a week. Not cardio in its place — lifting is the signal that tells your body to keep the muscle while it gives up the fat.
• Add a little each week: one more rep, one more set, 2.5 kg more on the bar. That is the whole method.
• Walk 8,000–10,000 steps on the days you do not lift, and sleep seven to eight hours — recovery is where the adaptation actually happens.

Supplement: cover the gaps a small appetite leaves

• Take your vitamins daily. Eating less food means eating fewer micronutrients, and that is the first gap to close.
• Magnesium and electrolytes while intake is low — the cramps and the flat afternoons usually trace back here.
• Vitamin D through winter, which for most of us means most of the year spent indoors.

Avoid: three things, and the reason for each

• Alcohol — none. Ethanol is classified a Group 1 carcinogen by the IARC and is a neurotoxin; on top of that it blunts recovery from training, and it is the easiest 500 calories anyone drinks without logging.
• Industrial seed oils. Cook with butter, ghee or olive oil instead. Her reasoning is that they signal for fat cells to expand; the evidence on that is contested rather than settled, so take it as a house position and not as a finding.
• Glyphosate-treated produce where you can avoid it — buy organic, and wash and peel what you cannot. The concern is mineral displacement from bone and tissue; that too is a precautionary stance rather than an established result.

Hold the line

Weight loss takes time, and the trials are the honest picture of how much: 48 weeks for retatrutide's 24.2%, 72 weeks for tirzepatide's fat-mass figure. Nobody in those studies was finished in six weeks. Measure this in months, keep hitting 0.6 kg a week, and let the timescale do the work. None of this is medical advice — it is the habits that decide whether the weight you lose is fat or muscle.

What incretins actually do

Incretins are hormones the gut wall releases in response to food. Four things matter about them:

• Insulin on demand: they amplify insulin release only when glucose is present, rather than driving it constantly.
• Slower gastric emptying: food leaves the stomach more slowly.
• Satiety signalling: they signal fullness centrally.
• Engineered half-life: native GLP-1 is degraded within minutes by the enzyme DPP-4 — the entire class of analogs exists to solve that one problem.

Tirzepatide — the deepest dataset

Tirzepatide (LY3298176) engages GIP and GLP-1 together, and its Phase 3 programme is complete. The part worth reading is the DXA substudy of SURMOUNT-1 (Look et al., Diabetes Obes Metab 2025, n=160), which measured body composition directly instead of inferring it:

• −33.9% total fat mass at 72 weeks, against −8.2% on placebo.
• −21.3% body weight over the same 72 weeks.
• Roughly three quarters of the loss was fat rather than lean mass — which is the figure DXA exists to separate.

Retatrutide — the third receptor

Retatrutide (LY3437943) adds glucagon-receptor agonism. Glucagon moves blood glucose in the opposite direction to insulin, but here it is studied for its contribution to energy expenditure — which is why a triple agonist is not simply “more of the same”. Its principal dataset is Phase 2 (Jastreboff et al., NEJM 2023, n=338), 12 mg arm:

• −17.5% mean body weight at 24 weeks.
• −24.2% at 48 weeks.
• 83% of that arm reached at least a 15% reduction by 48 weeks.

The mistake almost everyone makes

Retatrutide’s headline figure is a body-weight percentage. Tirzepatide’s 33.9% is a body-fat-mass percentage from a DXA substudy. Different quantities, different timeframes — they cannot be set side by side as though they were the same number. Almost every viral comparison of these two compounds gets this wrong, and knowing it is the fastest way to spot who has read the papers.

Where they sit against each other

Tirzepatide has the completed programme and the direct body-composition measurement. Retatrutide is earlier — Phase 2 — with a third receptor arm whose contribution is still being characterised. Neither is a treatment, neither is registered as a medicine in South Africa, and the evidence on the triple agonist in particular is preliminary.

Which vial, and why

• Retatrutide 60 mg: the better price per milligram of the two, and fewer reconstitutions across a longer protocol.
• Retatrutide 30 mg: the single-vial way into the triple agonist.
• Tirzepatide 30 mg: the compound with the deepest completed dataset.
• All three: HPLC-verified with a batch-specific Certificate of Analysis, held in stock in South Africa, and dispatched with tracking.

Every compound referenced here is supplied by Living Water Labs strictly for laboratory research purposes. Research Only Supplier. These are not approved medicines in South Africa, they are not prescribed or dispensed, nothing in this journal is medical advice, and no dosing schedule is given here — the research protocol for your compounds is emailed with your order.