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Optimum Nutrition Gold Standard 100% Casein Protein Powder vs Optimum Nutrition Serious Mass

The published reviews of Optimum Nutrition Gold Standard 100% Casein Protein Powder and Optimum Nutrition Serious Mass, lined up: the five scores, what one serving delivers against the studied dose, the real cost per serving and what each label leaves out. Figures as of 28 September 2026.

The short answer

Optimum Nutrition Gold Standard 100% Casein Protein Powder scores 6.6/10 against Optimum Nutrition Serious Mass's 5.8. The widest gap is dose against the studied amount: 7 for Optimum Nutrition Gold Standard 100% Casein Protein Powder, 6 for Optimum Nutrition Serious Mass.

Pick Optimum Nutrition Gold Standard 100% Casein Protein Powder if…

  • you want a serving that matches the amount used in research
  • you want every amount on the label disclosed
  • you want better value against the plain generic version

Pick Optimum Nutrition Serious Mass if…

It does not lead on any criterion we score. Read its review for the case in its favour.

Criterion by criterion

The five criteria every review is scored on, published on the grading page. The overall score is their average.

Evidence for the marketed claim

How strong the research is for what the product is actually sold to do — not for the ingredient in general.

Optimum Nutrition Gold Standard 100% Casein Protein Powder7/10
Optimum Nutrition Serious Mass7/10

Dose against the studied amount

Whether one serving delivers the amount used in the research behind the claim.

Optimum Nutrition Gold Standard 100% Casein Protein Powder7/10Leads
Optimum Nutrition Serious Mass6/10

Label transparency

Whether the Supplement Facts panel is published in readable text and every active amount is disclosed.

Optimum Nutrition Gold Standard 100% Casein Protein Powder6/10Leads
Optimum Nutrition Serious Mass5/10

Value against the generic equivalent

Cost per gram or per dose of the active ingredient, compared with the plainest version of the same thing.

Optimum Nutrition Gold Standard 100% Casein Protein Powder5/10Leads
Optimum Nutrition Serious Mass4/10

Safety and tolerability

Known risks and interactions, how well characterised they are, and whether the label warns about them.

Optimum Nutrition Gold Standard 100% Casein Protein Powder8/10Leads
Optimum Nutrition Serious Mass7/10

Dose against the studied amount

What one labelled serving delivers, placed against the range on each ingredient’s evidence page. Where a label gives no figure, there is nothing to place, and that is the finding.

Whey protein blendEvidence A

Where muscle protein synthesis maxes out: 20–25 g a dose

  • Optimum Nutrition Gold Standard 100% Casein Protein PowderNot in the formula
  • Optimum Nutrition Serious Mass50 g of protein per servingAbove range

What it actually costs

Price divided by labelled servings, from a dated listing. A serving is whatever the label calls one, which is why the studied-dose row matters more than the headline figure.

  • Optimum Nutrition Gold Standard 100% Casein Protein PowderAbout £36.95–£38.95 for the 924 g tub and £55.79–£64.99 for the 1.8 kg at UK retailers in search listings on 28 September 2026. No per-serving figure: servings not recorded.
  • Optimum Nutrition Serious MassAbout £32.95–£50.00 for the 2.73 kg tub at UK retailers in search listings on 28 September 2026 — roughly £4.12–£6.25 a serving. No per-serving figure: servings not recorded.

Label checks

What each label discloses, and what it leaves out. Read from the reviews, not from the marketing.

Optimum Nutrition Gold Standard 100% Casein Protein Powder

  • Every active ingredient has a stated amount
  • No third-party certification

Optimum Nutrition Serious Mass

  • Every active ingredient has a stated amount
  • No third-party certification
  • Whey protein blend: a serving gives 50 g, above the 20–25 g a dose where muscle protein synthesis maxes out

How this comparison is built

  • Scores are the ones already published in each review. Nothing is re-scored for the comparison, and a product leads a criterion only when it outscores the rest.
  • Doses are read from the label rows in each review and placed against the studied range on the matching ingredient page. A figure that is not printed is never estimated.
  • Costs use a dated retailer price divided by labelled servings. Prices in different currencies are never ranked against each other.
  • Only products in the same category, or ones a review names as an alternative, can be compared. Commission never changes what appears here.

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