Protein powder starts with a whole food source, either animal or plant, that gets processed to strip away most of the fat, carbohydrates, and fiber, leaving behind a concentrated form of protein. The exact ingredients depend on the type you buy, but every tub contains more than just protein. Sweeteners, thickeners, flavorings, and sometimes digestive enzymes round out the formula.
Dairy-Based Powders: Whey and Casein
The most popular protein powders on the market come from cow’s milk. Milk naturally contains two types of protein: whey and casein. They’re separated during cheesemaking, when enzymes cause the milk to coagulate into solid curds (casein) and a leftover liquid (whey). That liquid whey is rich in protein along with B vitamins, minerals, and a small amount of lactose and fat.
From there, the liquid goes through filtration to remove non-protein components. How far that filtration goes determines whether you end up with a concentrate or an isolate. Whey concentrate contains up to 80% protein by weight, with the remaining 20% being mostly carbohydrates (primarily lactose) and fat. Whey isolate undergoes additional processing to push protein content to 90% or higher, which also removes nearly all the lactose. That’s why isolate is often marketed toward people with lactose sensitivity.
Casein powder comes from the solid curd portion of milk. It digests more slowly than whey because it forms a gel-like structure in the stomach, which is why it’s often sold as a “nighttime” protein.
Plant-Based Powders: Pea, Soy, Rice, and Hemp
Plant proteins start with dried legumes, grains, or seeds that are ground into flour. The challenge is separating the protein from the starch and fiber that make up most of the plant. The standard industrial method for pea protein, for example, uses alkaline extraction: the flour is dissolved in a mildly alkaline solution (around pH 8 to 9), which pulls the protein into the liquid and leaves the starch and fiber behind. The pH is then lowered to cause the protein to clump together and settle out, a step called isoelectric precipitation.
A newer, chemical-free approach called dry fractionation uses air classification to sort flour particles by size and density. Protein-rich particles are lighter and smaller than starch granules, so they can be physically separated without any solvents. The tradeoff is a lower protein concentration in the final product.
Soy protein goes through a similar extraction process and has been used in supplements for decades. Rice and hemp proteins tend to have lower overall protein percentages and are often blended together or with pea protein to create a more complete amino acid profile. Pea protein, for its part, contains about 2,100 mg of leucine per serving, which is the amino acid most important for triggering muscle repair. That’s close to whey’s roughly 2,200 mg per serving, making pea one of the stronger plant options for muscle building.
Hydrolyzed Protein: Pre-Digested for Faster Absorption
Some labels say “hydrolyzed” whey or casein. This means the protein has been broken down further using heat, acids, or digestive enzymes. Instead of long, folded protein chains, you get shorter fragments: pairs, triplets, and small clusters of amino acids. Your gut absorbs these smaller pieces faster because they require less digestive work. Hydrolyzed formulas tend to cost more, and whether the speed difference meaningfully improves muscle recovery for the average person is still debated.
Sweeteners and Flavoring
Unflavored protein powder tastes chalky at best and unpleasant at worst, so nearly every flavored product contains sweeteners. The type depends on the brand’s positioning. Conventional powders often use sucralose or acesulfame potassium, both zero-calorie artificial sweeteners. “Natural” or “clean” branded products lean on stevia, monk fruit extract, or erythritol, a sugar alcohol that doesn’t spike blood sugar or insulin.
Flavoring comes from either natural or artificial flavor compounds. Cocoa powder is common in chocolate varieties. Vanilla, cookies and cream, and fruit flavors rely on flavor extracts combined with sweeteners to hit the right taste profile. Some products also add salt to round out the flavor.
Thickeners, Emulsifiers, and Gums
If you’ve ever noticed that some protein shakes mix smoothly while others turn into a clumpy mess, the difference often comes down to a few functional additives. Soy lecithin or sunflower lecithin acts as an emulsifier, helping the powder dissolve in water and improving the texture of the finished shake. Xanthan gum and guar gum serve as thickeners and stabilizers, giving the shake a smoother, slightly creamy consistency instead of a watery feel. These ingredients appear in tiny amounts, typically less than 1% of the formula, but they make a noticeable difference in mixability and mouthfeel.
Digestive Enzymes
Some protein powders include added digestive enzymes to reduce bloating and gas, especially in whey-based products. Protease helps break down protein chains in the stomach, and lactase breaks down lactose, the milk sugar that causes digestive trouble for many people. These additions are particularly common in mass-market whey concentrates, where residual lactose can be an issue. Plant-based powders sometimes include their own enzyme blends to help with the fiber and starches that survive the extraction process.
What About Heavy Metal Contamination
You may have seen headlines about protein powders containing arsenic, lead, cadmium, or mercury. The concern is real but uneven. A large U.S. analysis by the Clean Label Project found that 40% of 130 tested supplements had elevated levels of at least one heavy metal, and roughly 75% had detectable lead, with a third exceeding safe thresholds. A Consumer Reports investigation of 15 products found every single one contained at least one heavy metal above concentration standards.
These contaminants aren’t added intentionally. Plants absorb heavy metals from soil, and animal-derived products can pick them up through feed or processing equipment. Vegan powders tend to have higher aluminum and manganese levels, while dairy-based products aren’t immune either. A study of 26 whey protein samples from Egypt found detectable aluminum in 100% of them and lead in nearly 89%. However, a Hungarian market analysis found all tested products fell within regulatory safety limits, which suggests the problem varies significantly by brand, source region, and manufacturing standards. Third-party testing seals from organizations like NSF or Informed Sport can help you identify products that have been independently verified.