Isopure vs Optimum Nutrition Gold Standard (2026): Which to Buy

Better value

Gold Standard

10.0/10

Cost

$1.86 per 25 g protein

Testing

Informed Choice

Check price

 

Isopure Low Carb

9.0/10

Cost

$2.31 per 25 g protein

Testing

Informed Choice

Check price

The price test: Gold Standard costs about 20% less per gram of protein

Gold Standard’s 5.05 lb tub costs $131.99 on Optimum Nutrition’s store and holds 1,776 g of protein (74 scoops of 24 g). That is $1.86 per 25 g. Isopure Low Carb’s 4.51 lb tub costs $143.49 on Isopure’s store and holds 1,550 g (62 scoops of 25 g). That is $2.31 per 25 g.

So the Gold Standard tub costs less and holds more protein. Isopure’s biggest tub, 7.5 lb, brings its price down to $2.16 per 25 g, which is still more than Gold Standard’s 5 lb tub. Gold Standard’s own biggest tub, 10.18 lb, costs $1.61 per 25 g. Prices are each brand’s regular price, read October 1, 2026 and October 3, 2026. Other stores set their own prices; to check a tub you see, use the grams above and our cost per 25 g check.

Price is also why the scores differ: both get full marks on everything else, and Isopure loses one point for costing more per gram.

Some reviews pick Isopure because a scoop has more protein. It does, by 1 g (25 g against 24 g). But the scoop is bigger too, and you pay more for each gram.

Per scoop: Isopure has fewer carbs and less fat, Gold Standard has less sodium

Both scoops give you about the same protein. The difference is what comes with it. Isopure uses only whey isolate. Gold Standard is a blend of isolate, concentrate and whey peptides.

Isopure has 30 mg less cholesterol, 2 g fewer carbs and no sugar a scoop. Gold Standard has less sodium: 55 mg on its label against 210 mg. If you watch your sodium, Gold Standard is the better fit.

Isopure also adds a vitamin and mineral blend. Its label lists 23 vitamins and minerals, including vitamin B12 at 100%, copper at 70% and chromium at 90% of the Daily Value a scoop. If you also take a multivitamin, add the two labels together, especially if you have more than one scoop a day.

For muscle, neither label gives a reason to expect a different result if you get the same protein. How much you need a day: protein dosage guide.

See both labels

Gold Standard’s image is the label NSF keeps, from a 10 lb tub; the 5 lb tub has the same 24 g of protein a scoop. Isopure’s is the brand’s own label for the 4.5 lb Dutch Chocolate tub.

If lactose bothers you, look at the kind of whey. Whey isolate has much less lactose than whey concentrate. Typical isolate is about 0.5 to 1% lactose, and typical 80% concentrate is about 4 to 8%, according to the U.S. Dairy Export Council’s spec sheets (isolate, concentrate). Those are typical values, not the amount in these tubs. Gold Standard adds lactase, the enzyme that breaks down lactose. Both labels list milk and soy, so neither is safe for a milk allergy.

Both are on the Informed Choice testing list

Informed Choice screens store-bought products for banned substances, at least monthly. It lists a product line, not a tub size or flavor: Gold Standard as “ON Gold Standard 100% Whey” and Isopure as “LOW CARB”.

Neither 5 lb Gold Standard nor any Isopure tub is on NSF Certified for Sport. NSF lists Gold Standard only in its 10 lb tubs. If your sport requires NSF, see which Gold Standard tubs and flavors NSF lists.

Both on the Informed Choice list

Gold Standard on Informed Choice

Isopure Low Carb on Informed Choice

Isopure Zero Carb vs Low Carb: only Low Carb is on a testing list

Isopure sells two whey isolates, and many comparisons mix them up. Zero Carb has 0 g of carbs a scoop; Low Carb has 1 g. Both have 25 g of protein. At Isopure’s store, a tub with the same number of scoops costs the same for either one.

The real difference is testing. Informed Choice lists Isopure Low Carb. We did not find Zero Carb on any of the 5 lists we search, so we do not link it. If you want Isopure and care about testing, buy Low Carb; the gap is 1 g of carbs a scoop.

Who should buy which

• You want the most protein for your moneyGold Standard

  $1.86 per 25 g of protein in the 5 lb tub, against $2.31 for Isopure Low Carb.

• You count carbs, or want less fat and cholesterolIsopure Low Carb

  All isolate: 1 g of carbs, 1 g of fat and 5 mg of cholesterol a scoop.

• Lactose bothers youIsopure Low Carb

  All its protein is isolate, which typically has less lactose than concentrate.

• You watch your sodiumGold Standard

  55 mg a scoop, against 210 mg.

• You are drug-testedEither

  Both are on Informed Choice. Check that your sport accepts it. If it requires NSF, only Gold Standard’s 10 lb tubs are listed.

• You already have a tub, or you would rather get protein from mealsBuy nothing

  Finish the tub you have; switching changes the price, not the result. Powder is a convenient option, not a requirement; food can cover your protein (ISSN 2017).

More comparisons: Gold Standard vs Dymatize ISO100, Transparent Labs vs Gold Standard, and every protein powder we price.

Sources

1. Labels: Gold Standard 100% Whey, Double Rich Chocolate, the label NSF keeps with its Certified for Sport listing (10 lb tub); and Isopure’s own Low Carb Dutch Chocolate label (4.5 lb tub), read October 3, 2026.
2. Testing: Informed Choice certified products (both powders) and NSF Certified for Sport (Gold Standard).
3. Prices: optimumnutrition.com (October 1, 2026) and theisopurecompany.com (October 3, 2026), regular price for every size. We print no Amazon prices; Amazon is only where the buy links go.
4. U.S. Dairy Export Council spec sheets: Whey Protein Isolate and Whey Protein Concentrate 80% (typical lactose content).
5. Jäger R, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. PubMed 28642676