Costco vs. Sam's Club: Which Has the Cleanest Protein Powder? (2026)
Quick Take: It's Closer to a Tie Than You'd Think
✅ Both clubs sell the same top-verified national brands — Optimum Nutrition Gold Standard and OWYN Pro Elite are on the shelf at both.
🏷️ Sam's Club has an edge with Dymatize 100% Whey Isolate and a full Premier Protein RTD lineup.
🏷️ Costco has an edge with MuscleTech's CR-#1 undetectable-lead mass gainer and Levels Whey (187 warehouses).
⚠️ Neither club's house brand — Kirkland Signature Whey or Member's Mark Protein Shake — has ever been independently tested for heavy metals.
Costco and Sam's Club run the same playbook: bulk sizes, membership fees, and protein powder tubs the size of a small dog. What neither store tells you on the shelf tag is which brands have actually been checked for lead, cadmium, and arsenic.
We pulled independent testing data (Consumer Reports, Clean Label Project) and cross-referenced it against what's actually stocked at each retailer as of 2026. Here's how they compare.
Important: Warehouse club inventory varies by region and changes over time. This article focuses on brands with published independent heavy metal testing that are commonly stocked at each retailer. Always confirm the exact product and flavor against current data before buying.
📋 Table of Contents
What "Clean" Means in This Comparison
When we say a protein powder is clean, we mean something specific — not marketing language like "natural" or "premium." For this guide, a product is considered clean for regular use if it meets all of these:
- Lead: At or below California Prop 65 safe-harbor (0.5 µg/day), ideally <0.1 µg per serving or non-detect.
- Other metals: Cadmium, arsenic, and mercury either not detected or well below health-based limits in third-party testing.
- Independent testing: Data from Consumer Reports, Clean Label Project, or published COAs — not just a "we test everything" claim on the label.
Whey-based proteins consistently test cleaner than plant-based blends because cows filter metals before milk is produced, while plants absorb them directly from soil.
Head-to-Head: Verified Brands Sold at Both Clubs
These two brands are the real headline — both are sold at Costco and Sam's Club, and both have real independent test results.
Disclosure: Some links below are affiliate links. If you buy through them, CleanProteinList may earn a commission at no extra cost to you. We only recommend products with independent safety data.
| Product | Costco | Sam's Club | Heavy Metal Status |
|---|---|---|---|
| Optimum Nutrition Gold Standard | ✅ Yes | ✅ Yes | CR #5 — 56% of level of concern, Clean Label certified |
| OWYN Pro Elite | ✅ Yes | ✅ Yes | CR #7 — only plant protein CR rated clean for daily use |
Optimum Nutrition Gold Standard
Why it's the safe bet at either club: Consumer Reports #5 (lead 56% of CR's level of concern) plus Clean Label Project Purity Award — dual-verified at roughly $0.75/serving. It's the strongest verification stack sold at either warehouse club.
- ~120 calories, 24g protein per serving
- Dual independent verification
- Confirmed sold at both Costco and Sam's Club
OWYN Pro Elite
Why it's the vegan pick at either club: In the same testing round where most plant proteins failed, OWYN Pro Elite was the only plant-based option Consumer Reports cleared for daily use. If you're vegan and shopping at either warehouse club, this is the benchmark.
- ~180 calories, 35g plant protein
- Third-party sports certification
- Confirmed sold at both Costco and Sam's Club
Costco-Exclusive Picks
A few verified-safe brands are specifically associated with Costco's shelves and warehouse network.
MuscleTech 100% Mass Gainer
Why it's a Costco standout: In Consumer Reports' 2025 testing, MuscleTech's mass gainer was the only protein powder where lead was completely undetectable.
- ~1,300–1,400 calories per serving
- ~80g protein (whey-based)
- Verified "lead not detected" in independent lab testing
Dymatize Super Mass Gainer
Why it's a safe Costco pick: Hydrolyzed whey with lead 25% of CR's level of concern. Ranked #2 by Consumer Reports — a strong option for fast-absorbing, clean protein in bulk.
- ~110–120 calories per serving
- ~25g protein
- Low heavy metals, great mixability
Levels Whey Protein Concentrate
Why it's worth knowing: Levels holds an active Clean Label Project Purity Award and is stocked in 187+ Costco warehouses across 13 states — grass-fed whey with a short ingredient list, competitive with ON Gold Standard on price.
- ~$0.75/serving
- Clean Label Purity Award — not yet CR tested
- Read the full Levels analysis →
Sam's Club-Exclusive Picks
Sam's Club carries a couple of verified options that round out the picture — including its own take on ready-to-drink shakes.
Dymatize 100% Whey Isolate (ISO-100)
Why it's a Sam's Club standout: Clean Label Project Purity Award — non-detectable heavy metals. Confirmed sold at Sam's Club in multiple flavors, including vanilla and chocolate.
- ~120 calories per serving
- Hydrolyzed whey isolate, fast absorption
- Read the full Dymatize ISO-100 analysis →
Premier Protein RTD Shakes
Why it's the RTD pick at Sam's Club: Consumer Reports tested Premier Protein at 0.59 µg lead — ranked #6 of 28 products, cleared for daily use. Sam's Club stocks the full flavor lineup in 15-packs.
- 30g protein per bottle
- Consumer Reports #6 (Jan 2026 round)
- Read the full Premier Protein analysis →
House Brand Showdown: Kirkland Signature vs. Member's Mark
If you're standing in either aisle, the obvious question is whether the store's own brand is any good. Here's the honest answer for both.
⚠️ Neither house brand has been independently tested for lead
Kirkland Signature Whey (Costco, powder) has never appeared in a Consumer Reports testing round — not October 2025, not the January 2026 follow-up — and Costco hasn't published independent data for it.
Member's Mark Protein Shake (Sam's Club, ready-to-drink) is a different format entirely — an ultra-filtered milk shake positioned as a cheaper alternative to Fairlife/Premier Protein — and it has no published independent heavy metal data either.
Neither of these means the products are contaminated. It means nobody has published a result either way, for either brand, and we're not going to invent one. An absence of data is not evidence of a problem — but it isn't evidence of safety either.
✅ The picks that do have a published result
At Costco, that's Optimum Nutrition Gold Standard or MuscleTech 100% Mass Gainer. At Sam's Club, that's ON Gold Standard again, Dymatize ISO-100, or Premier Protein RTD if you want a ready-to-drink option. All four have real, independently published numbers — which is more than either house brand can say.
Which Club Actually Wins?
Honestly? It's a wash on safety. Both clubs sell Optimum Nutrition Gold Standard and OWYN Pro Elite — the two most rigorously verified options in this entire comparison — at essentially the same price. Neither club's private-label protein has been tested, so neither gets credit there either.
Where they actually differ is selection, not safety:
- Bulking or mass-gaining? Costco's MuscleTech and Dymatize Super Mass Gainer options give it the edge.
- Want a whey isolate specifically? Sam's Club's Dymatize ISO-100 is the cleaner, more specific match.
- Want ready-to-drink? Sam's Club's Premier Protein lineup is deeper and CR-verified; skip the untested Member's Mark shake.
- Already have a membership at one? Don't switch clubs for protein powder alone — the verified national brands are the same either way.
The Real Rule
Buy the brand, not the store. Whichever club you already belong to almost certainly carries at least one independently verified option — you don't need to choose a warehouse club based on protein powder safety.
How to Check Any Tub (or Carton) in the Aisle
A quick 30-second workflow for either store:
1. Flip It Around
- Look near the barcode or fine print for a Prop 65 warning.
- If you see it: assume lead/cadmium is above the safe-harbor level and choose a different product.
2. Scan for Certifications
- Good signs: NSF Certified for Sport, Informed Choice, Clean Label Project Purity Award.
- These don't guarantee zero metals, but show the brand invests in external quality checks.
3. Be Extra Cautious With House Brands
- Kirkland Signature and Member's Mark are both untested as of 2026 — treat them as unknowns, not automatic safe bets just because of the retailer's reputation.
4. Use Your Phone
- Google:
[brand + exact product name + "lead test"]. - Or check CleanProteinList.com's lead-free database to see if the brand is listed as safe, mixed, or avoid.
Not Sure Which Option Is Right for You?
Answer a few questions about your goals (bulking, weight loss, vegan, budget) and we'll match you with the best verified-safe options — including warehouse-club friendly picks.
Take the 60-Second Quiz →FAQ: Costco vs. Sam's Club Protein Powder
Is Costco or Sam's Club protein powder safer?
It's effectively a tie. Both warehouse clubs carry the same top-tier, independently verified brands — Optimum Nutrition Gold Standard and OWYN Pro Elite are sold at both. The bigger factor is which specific product and brand you buy, not which club you shop at.
Does Sam's Club sell Optimum Nutrition Gold Standard?
Yes. Sam's Club carries Optimum Nutrition Gold Standard 100% Whey Protein Powder in bulk tubs, the same product line sold at Costco. It's Consumer Reports #5 (56% of CR's level of concern for lead) and Clean Label Project certified.
Has Member's Mark protein shake been tested for lead?
No published independent heavy metal testing exists for Member's Mark's protein shake as of 2026. It hasn't appeared in Consumer Reports or Clean Label Project testing rounds. That doesn't confirm it's unsafe — it means there's no third-party data either way, the same situation as Costco's Kirkland Signature Whey.
Is Kirkland Signature protein powder tested for heavy metals?
No. Kirkland Signature Whey has never been included in Consumer Reports' testing rounds or published Clean Label Project results. Costco has not released independent heavy metal data for it.
What's the safest protein powder to buy at Sam's Club?
Optimum Nutrition Gold Standard (Consumer Reports #5, dual-verified) and Dymatize 100% Whey Isolate (Clean Label Project Purity Award) are the two strongest verified options currently sold at Sam's Club. For a ready-to-drink option, Premier Protein shakes were Consumer Reports #6 in January 2026 testing.
Where can I see a full ranked list of safe brands?
Check out the full database: Lead-Free Protein Brands Ranked (2026). It combines Consumer Reports, Clean Label Project, and other independent testing into one place.
Sources & Testing References
- Consumer Reports (Oct 2025): Independent heavy metal testing of 23 protein powders and mass gainers.
- Consumer Reports (Jan 2026): Follow-up testing of 5 reader-requested protein powders, including Premier Protein.
- Clean Label Project: Protein powder and mass gainer testing programs evaluating lead, cadmium, arsenic, and mercury. Purity Award certifications for Levels and Dymatize ISO-100 confirmed via press releases.
- California OEHHA – Prop 65: Official "safe-harbor" levels for lead (0.5 µg/day for reproductive toxicity) and other heavy metals.
- Retailer product listings (samsclub.com, Costco.com): Used to confirm current product availability at each retailer as of August 2026. Inventory varies by region and time.
Medical Disclaimer: This article is for educational purposes only and is not medical advice. If you're concerned about heavy metal exposure or symptoms, talk with your healthcare provider.