Whey protein has the highest bioavailability rating compared to other protein sources which means that you're able to metabolize it significantly faster and so your muscles are able to use the protein to begin repairing and building within 15 minutes which can prevent catabolism and therefore maximize your exercise results.
However, there are a few things you need to consider when buying whey protein:
- Whey Protein Concentrate (WPC) or Whey Protein Isolate (WPI)?
The difference between WPC and WPI is how much the whey has been filtered and the protein percentage. WPC typically has around 80% protein whereas WPI has around 90+% protein. If you're lactose intolerant then look into WPI as more often than not the lactose has been completely filtered out.
- How is it filtered?
A lot of companies use high temperatures and acid to filter the whey which is bad as it denatures (damages) the protein meaning that it isn't as effective as if it's filtered using cold methods such as cross flow micro-filtration (CFM).
- Where does the milk come from?
If the milk comes from factory farmed cows, then your whey protein contains high amounts of antibiotics and if purchased in the US, rBGH bovine growth hormones as well (rBGH is illegal in the EU).
- Are there any added ingredients for flavouring etc?
A lot of the artificial sweeteners used in whey protein are worse for you than sugar, so if you want a flavored/sweetened whey protein powder, then look for one that uses only natural sweeteners (preferably stevia). Another ingredient to avoid is soy lecithin as this is a phytoestrogen which means it can alter your hormone levels and increasing your estrogen when exercising is especially bad as higher estrogen levels tend to mean you're at a higher risk of injury. The world soy crop is also 90% genetically modified and there haven’t yet been any long term studies (that are non-biased) to guarantee their safety and in fact there's evidence that suggests GMOs could potentially be at least in part responsible for the increase of allergies.
Labdoor is a good resource for finding the best protein and supplements.