Best Whey Protein Isolate (2026): 11 Compared

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I am Fred, a marketer, not a doctor or dietitian, and I did not try these products. Whey protein isolate is the filtered, lower-lactose form of whey, and it usually costs more than ordinary whey. This guide compares eleven isolates sold on iHerb, most of them unflavored, on what you can check yourself: grams of protein per scoop, how much of the scoop is protein, sugar, certifications that appear in the certifier's own database, warnings on the product page and the real price of 25 g of protein. AI helps me draft; every number comes from the label or a linked source. Checked on 28 October 2026, US prices.

The short answer

• Best overall: NOW Sports Whey Protein Isolate (5 lb) — unflavored, just isolate and a little sunflower lecithin, Informed Sport certified (confirmed in the database), $1.55 per 25 g of protein in the 5 lb tub.
• Cheapest: California Gold Nutrition Sport Whey Protein Isolate (5 lb) — $105.0 per 25 g, unflavored, iHerb's own brand, but no certification I could find in a certifier's database.
• For drug-tested athletes: Thorne Whey Protein Isolate — NSF Certified for Sport (confirmed), but vanilla with a little added sugar, and its iHerb page carries a Prop 65 lead warning.
• Flavored and certified: Optimum Nutrition Gold Standard 100% Isolate — Informed Choice certified (confirmed), $2.05 per 25 g.
• Most protein per scoop: Nutricost Whey Protein Isolate — 30 g per scoop, $1.92 per 25 g, no certification found.
• Hydrolyzed: Dymatize ISO100 Hydrolyzed — Informed Choice certified (confirmed), the most expensive here at $2.97 per 25 g.

What makes whey isolate different

Whey comes from cheese making. Filtering the liquid whey gives whey protein concentrate, which ranges from 34% to 85% protein; filtering further gives whey protein isolate, with at least 90% protein on a dry basis and very little fat or lactose (USDA technical report on whey, 2015). The full process is explained in how protein powder is made.

In practice that means three things:

• Less lactose. Lactose is a sugar, so it is counted in "Total Sugars" on the label. The unflavored isolates here list 0–1 g of sugar per scoop, so a scoop contains at most about 1 g of lactose. Many people who get bloated from regular whey do fine with isolate; if you cannot have any dairy, choose a plant protein instead (best vegan protein powders).
• More protein per scoop, fewer calories. In the unflavored products here, 86–93% of the scoop weight is protein. Flavored isolates are lower, 75–81%, because cocoa, flavor and sweetener take up room.
• Higher price per gram than concentrate, although large tubs of unflavored isolate can be cheaper than small tubs of flavored blends.

Isolate does not build more muscle than concentrate when you eat the same amount of protein. Both are dairy proteins with high digestibility of their amino acids (Mathai et al., British Journal of Nutrition, 2017). What matters is total protein for the day, roughly 1.4–2.0 g per kg of body weight for people who train, and 20–40 g per serving (ISSN position stand, 2017).

All 11 whey isolates compared

Sorted from cheapest to most expensive per 25 g of protein. "—" means I found no certification for that product in the NSF, Informed Choice or Informed Sport databases; brand claims and iHerb badges are not counted.

Price per 25 g of protein = price ÷ (servings × grams of protein per serving) × 25. Protein share = grams of protein ÷ scoop weight. Prices change daily; check the current price before you buy.

Lead and heavy metals

In October 2025 Consumer Reports tested protein powders and shakes for lead and found that plant-based products averaged about nine times as much lead as dairy-based ones (Consumer Reports, Oct 2025, updated Jan 2026). None of the eleven isolates here was in that test; Consumer Reports tested Optimum Nutrition's regular Gold Standard 100% Whey, not the isolate. Two products here carry a California Prop 65 warning for lead on their iHerb page: ALLMAX ISONatural and Thorne Whey Protein Isolate. A Prop 65 warning means the company chose to warn that a daily serving may exceed California's very low limit; it is not a test result, but it is information the other products do not give you.

The picks, one by one

Best overall: NOW Sports Whey Protein Isolate (5 lb)

24 g protein per 28 g scoop · $1.55 per 25 g of protein · $120.28

Unflavored whey protein isolate with less than 1% sunflower lecithin and nothing else, 0 g of sugar, and an Informed Sport listing I found in the certifier’s own database. Informed Sport tests for substances banned in sport.

What to keep in mind: The small 1.2 lb tub costs much more per gram ($2.83 per 25 g), so the 5 lb tub is where the value is. Informed Sport does not test for heavy metals.

See it on iHerb

Cheapest: California Gold Nutrition Sport Whey Protein Isolate (5 lb)

27 g protein per 31 g scoop · $105.0 per 25 g of protein · $73.00

The lowest price per gram of protein in this comparison: whey protein isolate from bovine milk plus sunflower lecithin, 27 g of protein per scoop, no sweetener.

What to keep in mind: iHerb shows a "3rd party tested" badge with a certificate on the page, but I found the product in no certifier database, so I do not count it. The 1 lb tub is $30.8 per 25 g.

See it on iHerb

For drug-tested athletes: Thorne Whey Protein Isolate

21 g protein per 27.9 g scoop · $2.58 per 25 g of protein · $65.00

NSF Certified for Sport, the certification most US sports leagues accept, confirmed in the NSF database. Contains bromelain and papain, digestive enzymes.

What to keep in mind: Only 21 g of protein per scoop, 3 g of sugar including 1 g added, and the iHerb page carries a Prop 65 warning for lead. One of the more expensive options per gram.

See it on iHerb

Flavored and certified: Optimum Nutrition Gold Standard 100% Isolate

25 g protein per 31 g scoop · $2.05 per 25 g of protein · $89.99

A chocolate isolate from a large brand, Informed Choice certified (confirmed in the database), and cheaper per gram than Thorne or ISO100.

What to keep in mind: Sweetened with sucralose; contains soy lecithin. The isolate was not part of the Consumer Reports lead test.

See it on iHerb

Most protein per scoop: Nutricost Whey Protein Isolate

30 g protein per 35 g scoop · $1.92 per 25 g of protein · $59.95

30 g of protein in a 35 g scoop, unflavored, with 1 g of sugar. The grass-fed version costs the same.

What to keep in mind: I found no certification in any certifier database. Larger scoop, so a tub has fewer servings than the numbers suggest.

See it on iHerb

Hydrolyzed: Dymatize ISO100 Hydrolyzed

25 g protein per 32 g scoop · $2.97 per 25 g of protein · $59.41

Pre-digested (hydrolyzed) whey isolate, Informed Choice certified (confirmed), with many flavors.

What to keep in mind: The most expensive per gram here. Hydrolysis has no clear muscle advantage for most people; you pay mainly for the brand and flavors. Contains sucralose and soy.

See it on iHerb

Not picked: ALLMAX ISONatural has the highest protein share (93%), but its iHerb page carries a Prop 65 lead warning, and the Informed Choice certification claimed on the page did not show up when I searched the database. EVLution Nutrition 100% Isolate Protein is a clean unflavored isolate at $2.16 per 25 g, but I found no certification.

Unflavored or flavored?

Unflavored isolate tastes faintly milky and mixes into smoothies, oatmeal, coffee or yogurt without changing the flavor much. It is also the cheapest per gram and has no sweeteners. Flavored isolates are easier to drink with just water but add cocoa, flavor and usually sucralose or stevia, and have less protein per scoop. If you are unsure, start with unflavored and add your own cocoa or fruit.

How I chose

• Only products sold on iHerb in the US, picked from iHerb's top results for whey protein isolate and unflavored whey isolate, skipping sponsored listings and products out of stock (NutraBio was out of stock).
• A certification counts only if I found the product in the certifier's own database (NSF Certified for Sport, NSF dietary supplement listings, Informed Choice, Informed Sport).
• Lead data comes only from the Consumer Reports test and the Prop 65 warnings shown on iHerb.
• Price per 25 g of protein, so tubs of different sizes and scoop weights can be compared.
• Taste and mixability are not part of this ranking because I did not try these products.

More comparisons: best protein powder for women, best vegan protein powders.

Frequently asked questions

Is whey isolate lactose-free?

Not completely, but close: the unflavored isolates here have 0–1 g of sugar per scoop, which caps the lactose at about 1 g. People with a milk allergy (not lactose intolerance) should avoid all whey.

Is whey isolate better than whey concentrate?

For muscle, not meaningfully when the protein dose is the same. Isolate has less lactose and fat and more protein per scoop; concentrate is usually cheaper.

How much whey isolate should I take?

One scoop of 20–40 g of protein per serving, as part of about 1.4–2.0 g of protein per kg of body weight a day from all sources if you train (ISSN position stand, 2017).

What is the purest whey isolate?

Look for an unflavored product with whey protein isolate as the only ingredient, apart from a little lecithin, and a certification you can find in the certifier's database. In this comparison that is NOW Sports Whey Protein Isolate (5 lb).