Whey protein

What it is

Whey is the liquid left over when milk is made into cheese. It is dried into a powder and sold as a protein supplement. It contains all essential amino acids and is especially rich in leucine, which signals muscle building.

It is a food, not a drug. For most people it is simply a convenient way to add protein to a day, particularly around training, or for older adults who struggle to eat enough.

Whey comes from milk, so it contains lactose and milk allergens.

How it works

Whey is digested quickly, giving a fast rise in blood amino acids. Leucine in particular helps trigger muscle protein synthesis. Combined with resistance training, adequate total protein over the day supports muscle repair and growth.

What the evidence says

• Strong Meeting daily protein targets conveniently
  It is an efficient protein source, but whole foods can do the same job.
• Strong Gaining muscle with resistance training
  Helps in people whose protein intake is otherwise short; effect is small once overall protein is adequate.
• Moderate Preserving muscle in older adults
  Extra protein plus resistance exercise can help, especially when appetite is low.
• Limited Fat loss and appetite
  Protein can increase fullness, but whey itself has no special fat-burning effect.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• A typical serving is 20-40 g of powder, giving roughly 20-30 g of protein depending on the product.
• Many people aim for roughly 1.2-2.0 g of protein per kg of body weight a day if training hard; check current guidance for your circumstances.
• Timing matters less than total daily protein.
• People with kidney disease should check with a clinician before raising protein intake.

Forms and what to look for

• Concentrate (WPC) is cheapest, typically 70-80% protein with some lactose and fat.
• Isolate (WPI) is about 90% protein or more, with little lactose; useful if you are lactose-sensitive.
• Hydrolysate (WPH) is pre-digested for faster absorption and a bitter taste; it is pricier and the extra benefit is small.
• Check the protein per serving, not just serving size, and watch for added sugar or sweeteners.

What to expect, and when

• Effects on muscle need consistent training and diet over weeks to months.
• You won't feel anything immediate from a shake.
• Satiety effects are felt within a couple of hours.

Side effects

• Bloating, gas or diarrhoea, especially with concentrate and lactose intolerance.
• Acne has been reported by some users.
• Stomach upset with large servings.
• Allergic reactions in people with milk allergy.

Interactions

• Few direct drug interactions.
• May affect absorption of some medicines if taken at the same time; separate from levothyroxine and certain antibiotics.
• Protein can interfere with levodopa absorption in Parkinson's disease.
• Sweeteners or added ingredients may interact with some conditions; check the label.

Who should avoid it

• Anyone with a milk protein allergy.
• People with severe lactose intolerance should avoid concentrate or choose isolate.
• People with kidney disease should get advice before high protein intake.
• People on Parkinson's medicines, who may need guidance on protein timing.

Risks and safety

• Some products have been found to contain heavy metals or contamination; quality varies.
• Some budget products are "spiked" with cheap amino acids to inflate protein figures on tests.
• Mislabelling and banned-substance contamination can be a problem in sport.
• Excess calories can accompany shakes if added to an already adequate diet.

Buying well: quality and testing

• Informed Sport or NSF Certified for Sport gives the best reassurance for contamination.
• Look for protein per 100 g close to what the product claims.
• Short ingredient lists without large amounts of added sugar are preferable.
• Be wary of "proprietary blend" proteins and amino-spiking.

Bottom line

Whey is a food, not magic. It suits people who struggle to eat enough protein, train regularly or want a quick, portable option. If you already eat enough protein from regular meals, whey adds little. Pick one with testing and low added sugar.