Dr Phil Greipp -
I don't have much knowledge of Capillary Leak Syndrome. Are you asking if an increase in serum protein concentration could be related to a symptom that is caused by the the inability of the capillaries to withstand the osmotic gradient between the serum and the body? Unless there is something targeting the capillaries, which it hasn't sounded to me like there is, chances are that it isn't just one protein, but a variety of proteins in high concentration. It's not just meat, but meat, bread gluten, and milk casein - for example.
At those steak places there isn't just steak, but unlimited bread and butter and cheese and burnt vegetables (maybe it's burnt food!) and those wacky potatoes. And they are all very salty.
A more effective and scientific approach might be to ask people for stories about coming down with symptoms. Were they in or out? On routine or off? What were they eating? What were they doing?