The Best Low-Calorie Protein Powder

The best low-calorie protein powder is BulkSupplements Whey Protein Isolate. A scoop has 25 g of protein and 110 calories, with no carbs, fat or sugar. It is unflavored, the lowest cost here at $1.57 per 25 g of protein, and on NSF Certified for Sport.

By Erin Rose Updated October 31, 2026 How we score

Our pick for: Most people

BulkSupplements Whey Protein Isolate (unflavored)

Check price on Amazon Price checked Nov 2

Calories: 110 a scoop25 g of protein, 0 g carbs, 0 g fat
Per 25 g of protein: $1.57At Amazon prices
A tub: $51.97Unflavored, 1 kg, 33 scoops
Testing list: NSF Certified for SportChecks the label and screens for banned drugs
Sweetened with: NothingUnflavored; only sunflower lecithin added

Why we pick it Almost every calorie is protein. It has 110 calories per 25 g of protein, within 10 calories of the lowest here (100), and it adds no sweetener. NSF lists the unflavored tub Amazon sells (listing 1797161). It is also our pick for the best whey isolate.

What you give up It is unflavored, so mix it into something with taste. For a flavored powder with 100 calories, see the flavored pick below.

The best low-calorie protein for your needs

BulkSupplements suits most people. If you want a flavored powder, buy this one instead. It is on a testing list too.

Want it flavored, fewest calories: Optimum Nutrition Gold Standard Isolate

Optimum Nutrition Gold Standard Isolate has 100 calories and 25 g of protein a scoop, the fewest calories per gram of protein here. It is sweetened with sucralose. Informed Choice lists the Gold Standard Isolate line; we could not confirm this exact tub.

Optimum Nutrition Gold Standard 100% Isolate (Rich Vanilla, 2.91 lb)

Optimum Nutrition Gold Standard Isolate
$2.05 per 25 g · $89.99 a tub (Rich Vanilla, 2.91 lb) · 100 calories a scoop

Check price on Amazon

How to choose a low-calorie protein powder

Compare calories for the same protein

A scoop with fewer calories may just be a smaller scoop. Work out the calories in 25 g of protein: label calories times 25, divided by label protein. The table does the math.

Pick whey isolate

Isolate is filtered further than concentrate, so less of each scoop is fat and lactose, and more of it is protein. In the table, the isolates have fewer calories per 25 g of protein than Naked Whey, a concentrate.

Buy one on a testing list

A testing list checks the tub against its label, so the calories and protein you count are the ones you get. See which protein powders are third-party tested.

5 low-calorie protein powders compared

Fewest calories per 25 g of protein first, from each label. Costs are Amazon prices checked November 2, 2026.

Powder	Calories per 25 g of protein	Why it is or is not the pick
Optimum Nutrition Gold Standard Isolate$2.05 per 25 g of protein · Informed Choice	100	Fewest calories per 25 g; sweetened
BulkSupplements Whey Isolate$1.57 per 25 g of protein · NSF Certified for Sport	110	Our pick: no carbs, fat or sweetener; lowest cost
Isopure Low Carb$2.07 per 25 g of protein · Informed Choice	110	Adds vitamins and minerals; sweetened
Momentous Whey Isolate$3.50 per 25 g of protein · NSF Certified for Sport	113	Smaller scoop, so fewer calories a scoop; costs the most
Naked Whey$1.84 per 25 g of protein · Informed Choice	120	A concentrate: more calories, more lactose

The proof for our pick

Here is the NSF listing behind the pick, as we saw it.

NSF Certified for Sport listing 1797161, cropped to the product details: Whey Protein Isolate, Bulk Supplements, United States, powder, unflavored, package sizes 100 g, 250 g, 500 g and 1 kg, serving 4 tbsp (about 30 g), protein 25 g, carbohydrate 0 g, sugar 0 g, fat 0 g, 110 calories, three certified lot numbers. — NSF Certified for Sport lists BulkSupplements Whey Protein Isolate, unflavored, up to the 1 kg bag, with a 30 g serving: 25 g of protein and 110 calories. That is the bag we link. Screenshots taken October 24, 2026; click an image to open the live page.

Questions people ask

Is whey isolate lower in calories than regular whey?

A little. Isolate is filtered further, so it has less fat and lactose. Here, the isolates have 100 to 113 calories per 25 g of protein, against 120 for Naked Whey, a concentrate.

Why compare calories per 25 g of protein?

Scoops differ in size. A small scoop has fewer calories but also less protein. Comparing the calories in the same 25 g of protein shows which powder is leaner.

How we picked

We looked at whey powders sold on Amazon that are on a testing list and read each label. We checked 4 testing lists for 5 products. We ranked on three things, in this order: calories per 25 g of protein, what else is in the scoop, and cost. Want no additives at all? See the best unflavored whey. Or see the best protein powder overall and the protein guide.

Sources

Nutrition labels: BulkSupplements (the panel NSF holds for listing 1797161), Optimum Nutrition Gold Standard Isolate, Rich Vanilla (NIH DSLD 331939), Isopure Low Carb Dutch Chocolate (brand label), Naked Whey (Amazon listing), Momentous (NSF listing 1518123).
NSF Certified for Sport listings, read October 31, 2026: BulkSupplements Whey Protein Isolate (1797161); Momentous Essential Grass Fed-Whey Protein, unflavored (1518123).
Informed Choice certified products list (Optimum Nutrition, Isopure, Naked Whey), read October 31, 2026.
U.S. Dairy Export Council spec sheets: Whey Protein Isolate and Whey Protein Concentrate 80%.