Supplements Reviewed Jul 5, 2026

Optimum Nutrition

The Gold Standard whey brand — owned by Glanbia; its Serious Mass was flagged for arsenic.

Safety Finding · 2025

Consumer Reports arsenic finding (Serious Mass)

In Consumer Reports' October 2025 test, Optimum Nutrition Serious Mass showed inorganic arsenic at roughly 200% of the safe daily limit (CR advised limiting it to a few servings a week). Note: CR rated ON's Gold Standard 100% Whey among the safer products tested.

Source →

Our take

Why It’s on Our Radar

We don't recommend it as a clean pick on ownership — it's owned by the public company Glanbia. Its flagship whey tested relatively well, but its Serious Mass gainer was flagged for arsenic. Here as a rated cautionary reference.

What's inside

Ingredients & Safety

Its Gold Standard whey tested among the safer products in Consumer Reports (Oct 2025), but its Serious Mass gainer showed inorganic arsenic at ~2× the safe daily limit — and the mass gainer is maltodextrin-based.

A couple to know — 1 ingredient we flag:

Maltodextrin — sometimes listed as Dextrin

A refined-starch filler with a glycemic index higher than table sugar that may also disrupt gut bacteria.

Ingredient List Reviewed

Safe Watch Caution
  • Maltodextrin also listed as Dextrin, Modified Food Starch Watch
  • Whey Protein Blend
  • Creatine

Formula scope: the disclosed ingredient list captured for this review. Formulas can differ by product, scent, country, and date; compare the current package with this list before deciding.

Want another top-tier option? Nordic Naturals in Supplements & Protein currently meets our top criteria. Review its formula scope and cited records before deciding.

Who owns it

Ownership & Independence

A wholly-owned subsidiary of Glanbia plc (public), acquired in 2008 (~$315M); not independent.

Where to buy

Key Products

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