Best Protein Powders At Costco (I Tried Every One)

Costco offers six whey protein powders, including its own Kirkland brand.

I tested each one over several months, evaluating factors like taste, mixability, price, protein content, artificial ingredients, third-party testing, and any adverse effects like stomach upset.  

The truth is that there are some excellent protein powders available at Costco, and you can get them for cheaper than buying them anywhere else–in some cases, 50% cheaper. 

That said, before I share my results with you, there is one downside when buying protein at Costco, no matter what brand you buy.  

You will be limited by flavor selection.  

If you’re shopping at Costco or even off the Costco website, you’ll likely only have one flavor available, two at most.  However, if you buy the same protein from the brand’s website, you’ll sometimes have 10+ flavors.

One more thing to note…  

I’m only covering whey protein powders on this list, not other types like ready-made protein drinks or collagen protein, which should not be compared with the same standards as your traditional whey protein powder.

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1. Isopure – Highest Protein Percentage

Key Features

• Price Per Serving: $1.30
• Calories: Contains 100–110 calories per scoop, depending on the flavor.
• Protein: 25g
• Carbs: 1g
• Fat: 0.5g
• Sugar: 0g
• Sweeteners: Sucralose
• Third Party Tested: No

Isopure definitely stands out for a few key reasons. First, the Dutch Chocolate flavor was a big win. It had a rich, genuine chocolate taste, even when mixed with water. 

I didn’t need a shaker either—it mixed smoothly with just a spoon and water without any clumps, which is always a plus.

There was a slight grittiness, but it was minimal and didn’t bother me. For those who are more texture-sensitive, mixing it with milk or using a blender solves the issue easily.

Isopure’s added vitamin and mineral blend is a nice touch, offering more than 20 nutrients, including electrolytes, which go beyond what most protein powders deliver. It’s not something I’d use as a replacement for multivitamins or nutrient-rich foods, but it’s a convenient way to supplement your daily intake. 

What really grabbed my attention was Isopure’s protein percentage. 

The scoop contains 25g of protein, with only 100-110 calories, depending on the flavor, making it one of the highest protein percentages I’ve found. 

Some flavors, like Banana Cream and Vanilla Salted Caramel, offer up to 100% protein per scoop, which is rare in the supplement world (note: these flavors are not available at Costco). This does come at a cost, though, as Isopure is the most expensive protein powder at Costco, coming in at $1.30 per serving.  

One important thing to note about the 100% protein content claim: there is no 3rd party testing for this protein powder, which does raise a red flag for me. 

While I trust Isopure as a brand with a long-standing reputation, I prefer seeing third-party certifications to confirm the exact protein content, especially when some competitors, like Transparent Labs, are fully transparent about their independent lab results.

Another potential drawback for those who avoid artificial sweeteners is that Isopure is sweetened with sucralose. There’s actually only one protein powder from Costco that doesn’t use artificial sweeteners, which I’ll cover later.

Overall, I’d recommend Isopure to anyone looking for a high-quality whey protein with added vitamins and minerals. While it’s a bit pricier, the quality, protein content, and added nutrients may justify the cost. 

Read my in depth review of Isopure here.

2. Dymatize ISO 100 – Ideal For Post-Workout

Key Features

• Price Per Serving: $1.26
• Calories: 110 to 120
• Protein: 25g
• Carbs: 1-3g
• Fat: 0-1g
• Sugar: ≤1g
• Sweeteners: Sucralose
• Third Party Tested: Yes

The impressive mixability and taste were the first things that caught my attention with Dymatize ISO 100. 

I tried several flavors, including Cocoa Pebble, Fruity Pebbles, Cookies and Cream, all of which were delicious and left no unpleasant aftertaste. The Fruity Pebbles is the only one available at Costco.  

The sweetness level was just right for me, though some may find it a bit too sweet, depending on personal preferences.

Mixing it with water, milk, and even adding it to oatmeal or protein balls worked great. It blended smoothly in all scenarios without needing a blender or whisk, which made it super convenient.

It’s a fast-digesting whey hydrolysate and isolate, so it’s best for quick digestion after exercise, not as a meal replacement.

Just like Isopure, what really impressed me about Dymatize is the high protein content. 

With 25g of protein per serving and only 110-120 calories, it’s one of the leaner options, with a protein percentage ranging from 83-91%, depending on the flavor. The only flavor available at Costco (when publishing this) is Fruity Pebbles, which has 91% protein.  Unlike Isopure, though, Dymatize ISO 100 is third-party tested, so we can independently verify that the protein content and the rest of the ingredient label are accurate.

Dymatize ISO 100 also contains 5.5g of BCAAs and 2.6g of leucine, which according to the International Journal of Sports Nutrition Exercise, is the amount needed to optimize muscle protein synthesis, making it a solid choice for anyone serious about post-workout recovery.

On the downside, Dymatize uses sucralose as a sweetener. While I didn’t personally experience any digestive issues, some people sensitive to artificial sweeteners might want to be cautious. 

Additionally, the price per serving can vary greatly depending on where you buy it. I’ve seen it range from $1.67 to over $3.00 per serving outside of Costco.  However, if you’re buying it at Costco you’ll bring the price down to $1.26 per serving, which is good value, but I’ll be covering cheaper options in just a moment.  

Overall, Dymatize Iso 100 delivers on flavor, mixability, and protein content, making it an excellent option for post-workout use.

Read my in depth review of Dymatize Iso 100 here.

3. Ascent Whey – The Athlete’s Choice

Key Features

• Price Per Serving: $0.88
• Calories: 110-130
• Protein: 25g
• Carbs: 1-5g
• Fat: 0.5-1.5g
• Sugar: 1g (0g added)
• Sweeteners: Stevia extract or monk fruit extract (No Added Sugars or Artificial Sweeteners)
• Third Party Tested: Yes

As someone who follows many Ascent-sponsored athletes, like crossfitter Sydney Wells and weightlifting world record holder CJ Cummings, I was excited to try Ascent Whey Protein.

Ascent stands out for its clean ingredients, making it a great choice for athletes or anyone looking for a simple protein powder.

One of the biggest selling points is that Ascent is sweetened only with stevia or monk fruit extract, so it’s free of artificial sweeteners or refined sugars, which is the only protein powder at Costco to have this feature.  

I really appreciated the light, natural taste. I tried the chocolate flavor, which was simple and not overly sweet, making it enjoyable on its own or when mixed into foods like Greek yogurt or oatmeal. It doesn’t leave an aftertaste, which is a bonus for those who prefer clean, subtle flavors.

Ascent is also third-party verified by Informed Sport, meaning it’s tested for banned substances—perfect for athletes in drug-tested sports or anyone who wants to ensure their supplements are clean. This adds a layer of trust that I found reassuring.

However, one downside is the mixability. While it blended well in a shaker bottle or with a frother, it didn’t mix as easily in coffee or when stirred with a spoon. I also found it didn’t dissolve as well in hot liquids, leaving a few clumps, so it takes a little more effort compared to other proteins I’ve tried.

On the bright side, ascent offers a high protein content, delivering 25g of protein per serving, with a protein percentage of calories of up to 83%, depending on the flavor. You’ll notice this isn’t as high as Isopure or Dymatize ISO 100, but realistically, anything above 80% is still very respectable.

It’s made primarily from native whey isolate, which is filtered to have a higher leucine content, aiding in muscle growth and recovery. Despite the premium quality, the price is competitive and, you can pick it up for $0.88 per serving at Costco. 

Overall, Ascent Whey Protein is a high-quality option that delivers clean ingredients, a light taste, and solid protein content at an excellent price.

Read my in depth review of Ascent Whey here.

4. MyProtein Impact Whey Isolate – Most Affordable

Key Features

• Price Per Serving: $0.79
• Calories: 90
• Protein: 20g
• Carbs: 2g
• Fat: 0g
• Sugar: 2g
• Sweeteners: Natural and Artificial Flavoring, Sucralose, and Acesulfame-Potassium
• Third Party Tested: Yes

If you’re like me and supplement with protein daily, then perhaps you’re on the lookout for a protein that balances quality and affordability.  MyProtein Impact Whey Isolate definitely fits that bill.

Like others on this list, MyProtein Impact Whey has a high protein percentage. At 25g per 110 calories, Impact Whey has 91% protein. It’s also 3rd party lab tested to verify these claims.

What I also really liked about this protein was the flavor. 

The mocha flavor was rich and held up even when mixed with water. It was also versatile enough to blend well with coffee and yogurt, which made it a convenient go-to for quick snacks. That said, it’s quite sweet, so if you prefer a more mild flavor, you might find it a bit overpowering, as I did on some days. 

In terms of price, you really can’t beat it and this is where MyProtein really shines.  

From Costco, you can get it as cheap as $0.79 per serving.  However, if you buy it off the Costco website, there are frequent deals where you can get $15 off, bringing the price down to only $0.62 per serving. This is the cheapest flavored protein you can get while still exceeding 90% protein percent of calories.  

However, some downsides come with the affordable price. 

MyProtein’s packaging, a zipper-sealed bag, wasn’t my favorite. While it’s practical for travel, I found myself being extra cautious to avoid punctures or spills. 

Next, if you want to avoid artificial sweeteners, MyProtein won’t be a good pick since it’s sweetened with sucralose and acesulfame potassium.  

There is one more thing I’ll mention, which isn’t a big deal if you’re buying MyProtein from Costco.  But, multiple YouTube subscribers have pointed out really bad customer service when buying MyProtein from their website – slow shipping, waiting weeks for a response, and receiving the wrong order. 

Overall, MyProtein Impact Whey Isolate is a great value for its protein content, flavor, and mixability. But note the drawbacks and decide whether you’re okay with them.

Read my in depth review of MyProtein Impact Whey Isolate here.

5. Gold Standard – Great for “Any Time” of Day

Key Features

• Price Per Serving: $0.87
• Calories: 130
• Protein: 24g
• Carbs: 3g
• Fat: 1.5g
• Sugar: 1g
• Sweeteners: Sucralose
• Third Party Tested: Yes

Optimum Nutrition Gold Standard Whey is one of the most recognizable protein powders on the market. After testing it for several weeks, I can say that while it’s not the best in every category, it’s a solid, versatile option that offers good value, especially for those on a budget.

Gold Standard Whey uses a blend of whey isolate, whey concentrate, and whey peptides. 

This blend makes it suitable for a variety of uses—whether post-workout or as a snack between meals. The whey isolate provides fast-digesting protein, while the whey concentrate adds a bit more satiety, making it a good all-around protein for any time of day. 

It offers 24g of protein per scoop and 130 calories, with 80% of calories coming from protein. While that’s not the highest percentage out there, it’s decent for a protein at this price point.

The flavor variety from Optimum Nutrition is one of its best features. With 18 flavors, there’s likely something for everyone.  That said, if you’re buying it at Costco, you’re only going to find two flavors.  

Personally, I tested the Double Rich Chocolate, and while it wasn’t bad, the flavor was a bit watered down compared to other chocolate proteins on this list (like Isopure). Additionally, the texture was on the thinner side, which works well in smoothies or recipes but left a slightly chalky residue when mixed with water alone.

One downside for me was the inconsistent labeling regarding flavors that include lactase. 

Some flavors, like Vanilla Ice Cream, contain lactase to help with digestibility, while others, like Double Rich Chocolate, do not. As someone with mild dairy sensitivity, I noticed some digestive discomfort after using flavors without lactase, which was disappointing. This is likely because of the whey concentrate in the formula, which isn’t as filtered as a pure whey isolate.

Overall, the product is priced well at $0.87 per serving from Costco, making it a budget-friendly option. Just be mindful of which flavors contain lactase if you have lactose sensitivity, and be prepared for a thinner consistency if that’s not your preference.

Read my in depth review of Gold Standard Whey here.

6. Kirkland – Costco’s Signature Protein Line

Key Features

• Price Per Serving: $0.78
• Calories: 130
• Protein: 25g  
• Carbs: 4g
• Fat: 1.5g
• Sugar: 1g
• Sweeteners: Sucrose and Acesulfame Potassium
• Third Party Tested: No

Kirkland is Costco’s own brand of protein. It definitely offers a solid combination of price, protein content, and taste, but I don’t believe it’s the best protein that you can buy at Costco considering the others on this list.

Kirkland Whey Protein combines whey isolate and concentrate, delivering 25g of protein per 130 calories, which gives it a protein percentage of calories of 76%. This is still okay compared to the broader protein powder market, but compared to others on this list, it’s the lowest protein percentage out of the bunch.  

Still, for its price—$0.78 per serving—it’s a great budget option that fits well with the Costco ethos of good quality at an affordable price.  

One of the standout features of Kirkland Whey Protein was its mixability. 

I’ve tested several budget-friendly protein powders in the past, and many of them tend to clump or leave residue on the shaker. However, Kirkland’s protein mixed smoothly whether I used water, almond milk, or added it to my oatmeal. Even when I used just a spoon to mix it with water, it dissolved much better than expected for its price point. 

In terms of taste, the creamy chocolate flavor really impressed me.

I’m usually skeptical when it comes to budget proteins because they can taste artificial. While Kirkland’s protein is on the sweeter side due to the use of sucralose and acesulfame potassium, it wasn’t overwhelming for me. The flavor reminded me of a richer hot chocolate, which made it enjoyable to drink even just with water. That said, if you prefer a more natural taste or try to avoid artificial sweeteners, this will be a drawback.

Another drawback, Kirkland only offers this whey protein in one flavor—creamy chocolate. It’s not like other protein powders where if you like the brand, you can pick up alternative flavors outside of Costco.  While that limitation is okay for me, I know others might want more variety, and I can see this being a big con for people who like to rotate their flavors. 

The lack of third-party testing is also something to consider. Although I trust Costco’s products, it’s always nice to have the extra assurance, especially if you’re an athlete or someone who prioritizes label accuracy.

Another thing worth mentioning is the use of multiple thickening agents like guar gum and xanthan gum. While this did contribute to the protein’s creamy texture, which I enjoyed, it’s something to consider if you’re looking to avoid additives. Personally, I didn’t experience any digestive discomfort from these ingredients, but some people do.

In summary, when comparing Kirkland with other budget brands like MyProtein, I’d say MyProtein wins.  MyProtein uses 3rd party testing and is a higher percentage of protein per serving. Kirkland isn’t a bad option; it’s just not the better option. 

Read my in depth review of Kirkland Whey Protein here.