I only looked at one link, so more research is needed, but here is a couple of paragraphs I found about cats and milk and tuna:

Milk can cause digestive upsets in cats. Cats do not have the enzymes to break down the lactose in milk. If you must give your pet milk, it is best to buy the lactose free milk products that are available. You can also use canned milk. Liquid drinks such as Ensure or Baby formulas should not be given to cats because they do not contain enough arginine. Symptoms of lactose intolerance in your cat include skin irritation and diarrhea.

Tuna fish is another food that animal owners may be surprised to find is detrimental to cats. Containing high amounts of mercury, tuna can cause mercury poisoning. Also, canned tuna is extremely high in fat because of the liquid it is packed in. This can lead to steatis, which causes the cats system to lose vitamin E. Symptoms of steatis include impaired mobility, fever and flaking skin.

Here's the whole article:

http://sd.essortment.com/nutritioncats_rnsg.htm