I read it and I believe that they suffer. What I don't believe is their assessment of the reasons for their ills. There is nothing in meat that is even remotely unhealthful for humans. How can we believe that it's the meat that is the problem? Carbohydrate is highly addictive. Cutting them out will inevitably cause us to suffer from the simple withdrawal of them. It can go on for a long time too. This is a problem that causes us to suffer and it's unrelated to meat.

Eating only meat has only a few problems that I can see. The most obvious is taste. Not everybody enjoys the fat. But then taste is merely a habit. Babies don't have any taste to speak of therefore fat would be entirely normal as a food and for a human raised to eat fat from the first, he would thoroughly enjoy eating it as an adult.

Another problem is rabbit starvation. Combine this with the first problem above and it's obvious that anybody raised on a high carb, low fat diet would certainly come across this problem at some point. He would feel ill soon after eating lean meat exclusively for a time. We could see this as a problem of meat but I prefer to see it as a problem of taste since once we get over our aversion to fat, we can eat enough of it to never suffer.

The last problem is cooking. Overcooking will diminish the nutritional potential of meat to such a degree that we can develop diseases of deficiency like scurvy for instance. This is merely another problem of taste.

A problem not immediately related to meat is seasoning with salt and other things. This alone can cause us to suffer. Again another problem of taste.

So yes I believe they suffer but not because they eat meat.