Thanks for the replies. But I thought you wanted a protein shake to be fast digesting. At times like first thing in the morning or pre/post workout. I like my protein mixed with orange juice. Easy and quick digesting. I'm sorry for sounding like an idiot. Just trying to understand this concept.
Lastly, many people have shakes as a meal during the day. Again, you don't need the fast acting whey and want to slow it down (digestion wise) and provide a longer acting amino source so adding fats would be a plus here as it's not 1st thing am or PWO.
This is also the case for the last meal of the day, i.e. before going to sleep. You want a slow trickle of amino acids for as much of the 8 hour period as possible rather than a large bolus in the first two hours and then nothing after that. This is why casein is also the preferred protein before going to sleep (cottage cheese is rich in casein and it also has some fat so it digests very slowly).
When dieting you don't want the insulin spike that occurs from a fast digesting protein like whey so you add fats to slow the digestion down and prevent the insulin spike. When blood sugar rises the body's ability to burn fat decreases.
When trying to add muscle and following a non-restricted carb style diet then yes, you would not want fats but more than likely a fast digesting carb source. This is so that you would induce an insulin spike to help refill your glycogen stores. Note that there are many different view points here but this is the common belief...at least the belief pushed by the supplement market
Lastly, many people have shakes as a meal during the day. Again, you don't need the fast acting whey and want to slow it down (digestion wise) and provide a longer acting amino source so adding fats would be a plus here as it's not 1st thing am or PWO.