The short answer: nobody has a retatrutide-specific protein target. None of Lilly's 32 registered retatrutide trials lists protein intake as a measure, so any "reta protein number" is borrowed from somewhere else.
The closest guidance is a 2025 joint advisory on GLP-1 drugs from four US medical and nutrition groups. It says 1.2 to 1.6 g/kg a day has been proposed during active weight loss, and that a flat 80 to 120 grams a day may be easier to stick to. It doesn't mention retatrutide.
Status as of November 6, 2026: Retatrutide is investigational and isn't approved by the FDA or any regulator. Lilly plans to file for U.S. approval in Q1 2027. The protein numbers below are general nutrition guidance written for other drugs and other weight-loss settings. Nothing here is medical advice or a dosing guide.
Key takeaways
No reta-specific protein target exists. None of Lilly's 32 registered retatrutide trials lists protein intake as a measure.
The joint GLP-1 advisory reports 1.2 to 1.6 g/kg a day as proposed during active weight loss, or a flat 80 to 120 g a day. Neither was tested on reta.
The 1.0 to 1.5 g/kg figure seen online isn't in the advisory. I couldn't confirm where it comes from.
Collagen has no tryptophan. In two small trials in older adults (22 women, 31 men), it didn't raise longer-term muscle protein synthesis. Whey did.
With chronic kidney disease the guidance flips: KDIGO suggests 0.8 g/kg a day in stages G3 to G5 and says to avoid more than 1.3 g/kg if you're at risk of progression.
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How much protein should you eat on reta?
There's no tested answer, so use the general GLP-1 numbers. On November 6 I pulled every retatrutide record on ClinicalTrials.gov and kept the 32 sponsored by Lilly. None mentions dietary protein (ClinicalTrials.gov registry search, November 6, 2026). The general guidance covers drugs like semaglutide, liraglutide and tirzepatide (Mozaffarian et al., AJCN, 2025).
Number | Where it's from | Meant for | The catch |
|---|---|---|---|
0.8 g/kg a day | US recommended daily allowance | General adults | Under review, per the advisory |
1.2 to 1.6 g/kg a day | Joint advisory, "proposed" | Active weight loss | Unclear which body weight to use |
80 to 120 g a day | Joint advisory | People on GLP-1s | Offered as an alternative that "may enhance adherence" |
1.5 g/kg of lean mass a day | Joint advisory | People with body composition data | Needs a body composition scan |
1.2 to 1.5 g/kg of adjusted weight a day | 2026 scoping review | People on semaglutide or tirzepatide | The authors' suggestion, not a trial result |
Sources: joint advisory, Spreckley et al., 2026.
The advisory also sets edges. Intake "should not fall below 0.4–0.5 g/kg/d," and prolonged intake "at or above 2 g/kg/d should be avoided due to potential adverse health effects."
Body weight matters too. The advisory says "the use of actual weight can significantly overestimate protein requirements" in people with obesity, and that there's no consensus on the best method. Take someone who weighs 220 pounds (100 kg). On actual weight, 1.2 to 1.6 g/kg means 120 to 160 grams. The flat range tops out at 120.
For scale, KDIGO's kidney guideline notes that 100 grams of meat holds only about 25 grams of protein (KDIGO, 2024). So 100 grams of protein is about 400 grams of meat, or about 14 ounces.
Is 1.0 to 1.5 g/kg the right number for reta?
It might be reasonable, but it isn't what the advisory says. I read all four published versions, and that range doesn't appear in any of them. I couldn't open a primary source for it, so I'm not attributing it to anyone. If you see it credited to the joint advisory, that credit is wrong.
Why is it so hard to eat enough protein on reta?
Because low appetite comes with this class of drug. The advisory says adequate protein "may be difficult to achieve due to reduced appetite and/or taste aversions." In TRIUMPH-2, in people with obesity and type 2 diabetes, decreased appetite was reported as a side effect by 17.1% on the 12 mg dose vs 4.5% on placebo (Lilly, Sept 29, 2026). In TRIUMPH-1, nausea hit 42.4% vs 14.8% on placebo at that dose (Lilly, June 6, 2026). The full side effect tables are in is reta safe?
In BHN's October reader survey (38 self-selected readers, not a study), 16 of the 26 who named reta as their main compound reported appetite loss. Appetite can also come back, which is covered in why reta can seem to stop working.
Nobody has published what people on reta actually eat. The nearest data comes from older drugs like semaglutide and tirzepatide. A 69-person food record study of GLP-1 users found an average of 77.3 grams a day, against calculated needs of 74 to 169 grams at 1.2 to 2.0 g/kg (Johnson et al., Frontiers in Nutrition, 2025). All the authors worked for the supplement retailer that funded it.
The advisory's practical ideas for low appetite:
Eat the protein first in a meal.
Try small, frequent meals.
Lean on low-volume foods: fish, eggs, Greek yogurt, cottage cheese, nuts and nut butters.
Use smoothies and protein drinks, which are "often more appealing" than heavier foods.
Set an alarm or other reminder to eat.
One trade-off: the advisory says foods high in protein or fat can slow stomach emptying further and worsen constipation. In TRIUMPH-1, constipation was 26.1% at 12 mg vs 10.9% on placebo.
Are protein shakes OK on reta?
Yes, as far as the guidance goes. The advisory says "some individuals can meet protein targets by supplementing with high-protein shakes, bars, and other fortified products." No study has tested a shake in people on retatrutide.
Whey has direct muscle data behind it. In a trial of 31 men in their 70s, adding 50 grams a day of whey or pea protein raised muscle protein synthesis over a diet at the RDA, while collagen didn't (McKendry et al., AJCN, 2024). So pea looks like a fair dairy-free option, with two caveats: the groups had 10 or 11 men each, and the study was funded by a research contract with a company that makes pea protein.
Does collagen count as protein on reta?
It counts on the label, but don't count it toward your target. Collagen "lacks one indispensable amino acid (tryptophan) and is therefore categorized as an incomplete protein source" (Paul et al., Nutrients, 2019). Scored alone, its protein quality is zero in theory.
That paper also makes the industry's best case: up to 36% of daily protein could come from collagen in a standard American diet and still meet amino acid needs. But one author worked at a collagen manufacturer, another does research services for a supplement maker that sells collagen, and the model relies on the amino acid surplus in a normal diet. My read: someone barely eating has less surplus to lean on. Nobody has tested it.
The muscle data agrees. Besides the trial in men above, 22 older women took 30 grams twice a day for 6 days. Longer-term muscle protein synthesis rose on whey but wasn't significantly above baseline on collagen, even in the exercised leg (Oikawa et al., AJCN, 2020). Both trials are small, short and in older adults, not people on GLP-1 drugs.
Is high protein bad for your kidneys on reta?
With healthy kidneys, the evidence doesn't show harm, but it's short-term. With kidney disease, the guidance is different, so talk to your doctor before raising protein.
Healthy adults. A review of 26 studies found "little or no effect on blood markers of kidney function." All but two cohorts ran under 6 months, all had moderate to high risk of bias, and one author was affiliated with a beef trade group (Van Elswyk et al., Advances in Nutrition, 2018).
Chronic kidney disease. KDIGO suggests 0.8 g/kg a day in stages G3 to G5 and says: "Avoid high protein intake (>1.3 g/kg body weight/d) in adults with CKD at risk of progression" (KDIGO, 2024).
Kidney stones. The advisory says people with a history of stones should be counseled to avoid high-oxalate foods, highly processed foods and animal-source proteins.
On reta itself, a Lilly-funded look back at two phase 2 trials found eGFR unchanged vs placebo in people with diabetes and up at higher doses in people with obesity. It only included people with eGFR of 45 or higher, and the authors call the analyses exploratory (Heerspink et al., Kidney Int Rep, 2025). A 146-person trial in chronic kidney disease has finished, with no results posted (ClinicalTrials.gov). The big heart and kidney outcomes trial runs to 2029 (ClinicalTrials.gov).
The better-documented kidney risk in this class is dehydration. Tirzepatide's label warns of acute kidney injury, mostly in patients with vomiting, diarrhea or nausea that led to dehydration (Zepbound label, Aug 2026). Retatrutide has no label, but it causes the same kinds of stomach side effects.
One lab wrinkle: KDIGO says reading creatinine "requires consideration of dietary intake." If you get a metabolic panel, mention that your protein changed.
Is protein enough to protect muscle on reta?
No. The advisory says "increased protein intake alone is likely inadequate to support the preservation of muscle mass in the absence of structured resistance/strength training." It calls for strength training at least 3 times a week plus at least 150 minutes of moderate aerobic exercise. Creatine is a separate question, covered in creatine and reta.
The only retatrutide body composition paper I could find is a phase 2 substudy in type 2 diabetes. Of 189 people enrolled, 103 finished with both scans at 36 weeks. The authors said the share of weight lost as lean mass "was similar to other obesity treatments" (Coskun et al., Lancet Diabetes Endocrinol, 2025). Lilly funded it, and the abstract doesn't report what those people ate. What the scans show, and the gap in the data, is in does reta cause muscle loss?
Protein is barely tested on any drug in this class. A 2026 review of 12 studies found that "no randomized trial monitored habitual nutrient intake" (Spreckley et al., 2026). One trial is now testing it directly: 232 adults on semaglutide or tirzepatide, randomized to resistance exercise, protein at 1.6 g/kg a day, both, or neither (LEAN-PREP, BMJ Open, 2026).
If Lilly publishes phase 3 body composition data, I'll update this post. Get the update by email.
Protein on reta FAQ
How many grams of protein a day on retatrutide?
There's no retatrutide-specific number. Guidance written for other GLP-1 drugs offers a flat 80 to 120 grams a day, and reports 1.2 to 1.6 g/kg as proposed during active weight loss.
Should I base protein on my current weight or my goal weight?
Nobody has settled that. The joint advisory says it's unclear which weight to use, and that actual weight can overestimate needs in people with obesity. The flat 80 to 120 gram range avoids the question.
Can you drink whey protein on reta?
The guidance allows for shakes, and whey raised muscle protein synthesis in small trials of older adults. No study has tested whey in people taking retatrutide. Protein-rich foods can worsen constipation for some people, so watch for that.
Does collagen powder count toward my protein goal?
It adds grams, but it has no tryptophan, so it's an incomplete protein. In two small trials it didn't raise longer-term muscle protein synthesis the way whey did.
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If you're on reta and tracking protein, reply and tell me what works when you don't want to eat: which foods go down and how close you get to your number.