That article should be taken with a grain of salt. It's theoretical that proteins cause kidney problems, but in a diet relatively low in sugars and starches, it has been shown that there is no cause for concern. Body building advice should always be taken with a grain of salt as they all have their own agenda and myths and misinformation is spread freely, if not encouraged by competing theories, gurus, and products.
What is more of a concern is the recent findings in the US (I think it was in Consumer Reports) that all concentrated supplements may have high levels of heavy metals. This would mean things like Slimfast and Atkins shakes would probably of a concern as well.
One theory for the heavy metal levels is that it's usually very concentrated forms of the protein, so it has concentrated amounts of any contaminant that source might have.
ETA:
http://www.charlespoliquin.com/ArticlesMultimedia/Articles/article.aspx?ID=253At least this guy sites studies. "Ketosis of the liver"? ? ? First of all,
ketosis is not something anyone has to worry about unless they go under a certain amount of carbs a day. And ketosis is also nothing to worry about if you go into ketosis. Ketones are the by product of an alternative form of producing energy for your body where proteins are converted into sugars.
Ketoacidosis is something different, and most people, including diabetics if they are monitoring their diabetes properly, don't have to worry about it either.
BTW, I am sitting here in ketosis at the moment, and I've spent a good portion of the past 3 years in it.
Although this is mainly about low carb, ketogenic diets rather than just a high protein one, the myth about bone loss was busted a long time ago:
http://lowcarbdiets.about.com/od/faq/f/lowcarbboneloss.htmOur bones are made of protein. We might excrete more calcium on a low carb or high protein diet, but it doesn't appear to lead to bone loss.