More Surprising Paleo No-No's

One of the most problematic foods on any diet is the potato, but not just because of its starch content.

Potatoes with the peel

They contain resistant starch that feeds probiotic bacteria, rather than fat cells, and if they are boiled and served warm rather than piping hot, they don't have a particularly high glycemic index. The problem is the peel.

The potato peel is high in potassium, but it is also the part of the tuber that makes the toxic alkaloids solanine and chaconine. Even small amounts of green potato peelcan cause burning in the throat, burning in the lower digestive tract, and fever, and large amounts of green potato peel can cause dizziness, fever, hallucinations, miscarriage in pregnant women, and even death.

And never, ever eat any part of the Irish (white) potato plant except the tuber, the spud. Sweet potato leaves, on the other hand, are a nutritious green vegetable.

Root beer

Root beer contains quillaja extract, which also contains the soap-like chemicals known as saponins. In excess, root beer can literally make the contents of the stomach and gut "soapy," and irritate their lining in the same way that washing dishes can cause dish-pan hands. The compound also stimulates a kind of white cell known as a macrophage, which is the white cell that gets trapped in, and increases the mass of, belly fat.

Tomatoes

Devotees of the Perfect Health Diet probably have been told, correctly, that of all the relatively high-sugar "fruits," the tomato has the best ratio of the potassium we all need to the fructose we usually don't. Many people get most of their potassium from tomatoes.

The problem with tomatoes is that they also contain yet another saponin called alpha-tomatine. This compound can literally be used to make soap. 

Read More: The Truth About Paleo Diets

But alpha-tomatine is also one of two compounds (along with lycopene) that makes tomatoes so effect in reducing the risk of prostate cancer. In addition to irritating the lining of the digestive tract, alpha-tomatine protects cells in the prostate gland in men from changes in DNA that can lead to cancerous transformation. The lycopene in tomatoes also protects against prostate cancer and makes sperm better "swimmers" so that men are more likely to become dads after sexual intercourse with their female partners.

So, eat tomatoes with caution. You don't want too much sugar, and you don't want to inflame your digestive tract. Men only need the equivalent of about 2 servings of tomatoes a week for maximum prostate protection, which may not be enough to cause any kind of gastrointestinal distress.