Quick Verdict

These are the two highest-scoring protein powders in our rankings, and both carry NSF Certified for Sport certification -- the gold standard for competitive athletes subject to drug testing. The gap between them is narrow but meaningful. Klean Athlete Klean Isolate is the more affordable option at $2.20/serving with pharmaceutical-grade manufacturing pedigree from Atrium Innovations. Momentous Essential edges ahead on heavy metal safety, taste, and protein quality, but costs $2.40/serving. Neither is a wrong choice. The right one depends on whether you optimize for purity credentials and price or for the absolute cleanest safety profile and daily drinkability.

Head-to-Head Comparison

Heavy Metal Safety

Winner: Momentous Essential

This is the most consequential differentiator between these two products. Momentous Essential was ranked the #3 safest protein powder in Consumer Reports' 2025 heavy metal screening -- a rigorous, independent evaluation that tests for lead, arsenic, cadmium, and mercury across dozens of brands. That third-place finish among all protein powders tested (not just whey isolates) is a remarkable result that reflects genuinely low contamination levels.

Klean Athlete scores a strong 9.0 in heavy metal safety, which is well above the category average and reflects Atrium Innovations' pharmaceutical-grade quality control. But Momentous's 9.8 represents a measurably cleaner product by the most objective testing available. For users who consume protein powder daily over years or decades, the cumulative difference in trace heavy metal exposure is not trivial. If heavy metal safety is your primary concern -- and for many health-conscious consumers it should be -- Momentous has the stronger verified track record.

Third-Party Testing and Certification

Winner: Tie

Both products carry NSF Certified for Sport certification, which means every batch is tested for over 270 banned substances, verified for label accuracy, and manufactured in a GMP-compliant facility. This is the certification that matters most for professional and Olympic-level athletes, and both products have it.

Klean Athlete's certification is backed by Atrium Innovations' pharmaceutical manufacturing infrastructure, which applies drug-manufacturing quality standards to supplement production. Momentous partners with NSF and has built relationships with professional sports leagues -- the product is used across MLB, NFL, and NBA organizations. Both companies treat third-party testing as foundational rather than aspirational. At the certification level, these products are indistinguishable. The 9.8 score for both reflects the highest tier of third-party verification available in the supplement industry.

Protein Quality and Nutritional Profile

Winner: Momentous Essential

Both are whey protein isolates, which means both deliver high bioavailability, rapid absorption, and a complete amino acid profile. The difference is in the details. Momentous Essential uses grass-fed whey protein isolate, which carries a modestly improved fatty acid profile (higher omega-3 to omega-6 ratio) compared to conventional whey. Whether this matters in a low-fat isolate is debatable, but it reflects a commitment to sourcing quality that extends beyond the protein fraction itself.

Momentous scores 9.5 on protein quality versus Klean Athlete's 9.0. The gap reflects Momentous's grass-fed sourcing, its partnerships with sports science researchers (including the Huberman Lab), and the consistency of its amino acid profile across batches. Klean Athlete's single-ingredient unflavored option is appealing for purists who want nothing but whey protein isolate -- no flavoring, no sweetener, no additives -- but the protein itself scores slightly below Momentous's on independent quality assessments.

Value and Cost Per Serving

Winner: Klean Athlete

Klean Athlete costs approximately $44 for 20 servings, working out to $2.20 per serving. Momentous Essential costs $60 for 25 servings, or $2.40 per serving. The per-serving difference is $0.20 -- modest on any given day, but it compounds. Over a month of daily use, Klean Athlete saves roughly $6. Over a year, that is about $73.

Neither product is cheap. Both sit firmly in the premium tier, and both cost significantly more than mass-market whey proteins. But within the NSF Certified for Sport segment, Klean Athlete offers the lower cost of entry. It also provides fewer servings per container (20 versus 25), which means a lower upfront purchase price for users who want to try the product before committing to a larger supply. For cost-conscious athletes who need NSF certification, Klean Athlete stretches the budget further.

Taste and Mixability

Winner: Momentous Essential

Momentous Essential scores 8.5 on taste and mixability versus Klean Athlete's 7.0 -- the widest scoring gap between these two products on any criterion. Momentous dissolves cleanly in water or milk with minimal clumping and delivers a flavor profile that is genuinely pleasant to drink daily. The chocolate and vanilla options are well-developed without being overly sweet.

Klean Athlete's unflavored option is a double-edged sword. Purists love it because it adds no taste to smoothies, oatmeal, or other foods. But consumed in water, unflavored whey isolate has a flat, slightly chalky character that many users find difficult to sustain as a daily habit. The flavored versions of Klean Isolate are adequate but not exceptional. If you are mixing protein into smoothies or food, the taste difference is irrelevant. If you are shaking it with water at the gym, Momentous is the more enjoyable experience by a clear margin.

When to Choose Klean Athlete Klean Isolate

Klean Athlete Klean Isolate is the right choice when:

• Pharmaceutical-grade manufacturing pedigree matters to you because Atrium Innovations applies drug-manufacturing quality standards that go beyond typical supplement production, and that level of process rigor provides additional confidence in batch-to-batch consistency
• You want the most affordable NSF Certified for Sport whey isolate because $2.20/serving is the lower price point between these two premium products, and the savings are meaningful over months of daily use
• You prefer an unflavored, single-ingredient protein because you mix it into smoothies, oatmeal, coffee, or recipes where added flavoring would be unwelcome, and you value the simplicity of a product with nothing but whey protein isolate on the label
• You are an Olympic or elite athlete with an existing relationship with Klean Athlete's product line and trust the brand's long track record in competitive sports

When to Choose Momentous Essential Grass-Fed Whey Protein Isolate

Momentous Essential is the right choice when:

• Heavy metal safety is your top priority because a #3 ranking in Consumer Reports' 2025 screening is the strongest independent verification of contaminant safety available, and daily long-term consumption makes this criterion more important than most people realize
• You drink protein shakes mixed with water and need a product that actually tastes good on its own, because Momentous's 8.5 taste score reflects a genuinely enjoyable daily drinking experience that Klean Athlete's 7.0 does not match
• Grass-fed sourcing matters to you for environmental, ethical, or nutritional reasons, as Momentous's grass-fed whey isolate reflects a higher standard of dairy sourcing
• You want the product trusted by professional sports organizations because Momentous's adoption across MLB, NFL, and NBA teams -- along with its Huberman Lab partnership -- reflects a level of institutional vetting that goes beyond certification alone

Final Recommendation

Choose Momentous Essential if you want the highest overall quality in an NSF Certified for Sport whey protein isolate and are willing to pay $0.20 more per serving to get it. Momentous leads on heavy metal safety, protein quality, taste, and transparency. Its Consumer Reports ranking provides independent verification that no marketing claim can replicate. For daily use over months and years, those advantages compound into meaningful differences in safety and adherence.

Choose Klean Athlete Klean Isolate if you want NSF-certified quality at a slightly lower price point, or if the unflavored single-ingredient format fits your usage pattern. Klean Athlete's pharmaceutical manufacturing background is a legitimate differentiator, and the product delivers excellent purity at a cost that is more accessible within the premium tier.

Both products belong in the top tier of protein powders. The gap between them is real but narrow. If you buy either one and use it consistently, you are making a sound decision. The question is whether the marginal advantages of Momentous -- particularly in heavy metal safety and taste -- justify the marginal price premium. For most users who can afford either, they do.