Despite considerable evidence to the contrary, we are still told by doctors that dietary fats are the major risk factor in colorectal cancer.

The theory was that fats are oxidized into cell-damaging substances that not only damage colon cell DNA, but also stimulate the release of special cancer-causing bile acids. That theory has been disproven.

In fact, multiple studies have shown that fats — especially animal (saturated) fats — play little or no part in colon cancer development.

In one study, researchers fed animals three different fat-containing diets of varying concentrations: 10, 25, and 40 percent fat.

Researchers then analyzed the animals’ feces for the presence of cell damage and precancerous effects from each of the fat concentrations. They found that the percentage of fat in the animals’ diet made no difference in the precancerous changes of the colon cells.

They also found that the presence of bile acids made no difference.

However, when heme iron was added to the animals’ diets, there was a dramatic increase in damage at all three concentrations of fat.

Heme iron is the type that occurs within the blood fraction of meats. The iron is bound within hemoglobin (heme). This iron is highly absorbable and highly reactive in that it triggers intense free radical generation and lipid peroxidation.

Further evidence of the importance of heme iron comes from other carefully conducted studies. In one, researchers fed rats either chicken, beef, or blood sausage. Chicken has very low levels of heme iron, beef a moderate amount, and blood sausage very high levels.

Control animals were fed a diet low in heme iron, but were supplemented with iron citrate.

After 100 days on those diets (about half a rat’s normal lifetime), the researchers found that only the blood sausage diet — which was very high in heme iron — produced significant precancerous changes in the animals’ colons.

Both the chicken and beef diets could produce aberrant crypt foci, but not the more advanced lesions called mucin-depleted foci (MDF). Only the blood sausage diet produced those types of lesions.

In yet another study, researchers looked at the relationship between exposure to heme iron, heterocyclic amine (from seared meats), and N-nitroso compounds (which are found in cured meats and meals containing aspartame).

Surprisingly, they found no carcinogenic effects with heterocyclic amines or N-nitroso compounds, both of which were previously thought to cause cancer.

The most profound tumor-causing effects were seen with a high intake of heme iron.

It should also be appreciated that heme iron promotes the growth, invasion, and metastasis of cancer that already exists in the body.

What this means is that avoiding foods that contain heme iron — especially rare steak — goes a long way toward preventing colon cancer.

Another food that should be avoided is the popular Cajun delicacy boudin, which is made with blood sausage and rice.