Many "experts" claim that the human body can only digest 30 grams of protein per sitting. I have never found any research to back up this claim. Neither has any one else that I know of:
Lyle Mcdonald, the author of "the Ketogenic Diet" wrote, "My hunch is that this is one of the wonderful bodybuilding myths that has perpetrated itself through the field for years, and is now accepted as fact."
Will Brink, another well respected (and well-studied) nutrition "guru" went as far as to offer a monetary reward to anyone who could show him a recent study that showed that 30 grams of protein was the upper limit anyone could digest, regardless of age, weight, and activity levels. Nobody could produce one.
Nutritional needs are highly variable depending on the individual. That should be obvious. Are the protein needs for a 250-pound bodybuilder the same as a 105-pound ballerina? Are they the same for a 17-year-old football player and a sedentary 70-year-old?
Being that different people have widely varying nutritional needs, you should always look at "absolutes" with caution. By "absolutes," I mean people who say "never" do this or "always" do that. The assertion that the most you can ever digest is 30 grams per meal is one of those "absolutes."
The best way to figure out how much protein you need in one sitting is to first calculate your total daily protein needs (which I covered in detail in my three part article series, "Bodybuilders and Protein.") Then take your daily needs and divide that amount by the number of meals you eat each day (usually five or six).
As a bodybuilder or someone participating in regular strength training, you can't go wrong with the 1 gram per pound of bodyweight guideline as a starting point for daily protein needs. If you weigh 180 pounds and you’re eating six times per day like you should be, then bingo – there's your 30 grams. (180 grams divided by 6 meals)
However, this per meal number can fluctuate greatly depending on age, sex, body size, activity levels and goals. If you’re a 240-pound male bodybuilder, and you eat six times per day, now you’re up to 40 grams per meal.
Many bodybuilders go even higher than 1.0 gram per pound – more like 1.25 to 1.5 grams per pound of bodyweight – especially when they want to gain weight and calorie needs are higher. During pre-contest phases when carbohydrates are restricted, some bodybuilders eat as much as 1.75 – 2.0 grams per pound. That brings the protein up to 50 grams per meal or more.
If you’re a 115 pound female athlete, then 115 grams a day would surely suffice; spread over 5 meals a day, that's 23 grams per meal. On a pre contest bodybuilding diet, many women eat 150-200 grams of protein per day, which, over five meals, is 30-40 grams per meal.
Looking at these examples, you can see that 30-35 grams of protein per meal is pretty close to the average figure. My belief is that this is where the 30-gram "myth" came from. But just because the "average" comes out to around 30 grams per meal, doesn't mean that 30 grams is the most that you can digest. Personally, I eat 40-50 grams of protein per meal.
Diet and nutrition including exact diet plans are covered in detail in my book Burn the Fat, Feed the Muscle (BFFM)