12. Meat

Definition of red meat

• Meat that is red when you buy it

• Unprocessed mammalian muscle meat: beef, veal, pork, lamb, mutton, horse and goat

Definition processed mea

Meats transformed through salting, curing, fermentation, smoking or other processes to enhance flavor or improve preservation

What is the relative risk increase for colorectal cancer per 100 grams of red meat consumption per day?

17% increased risk

What is the relative risk increase for colorectal cancer per 50 grams of processed meat consumption per day?

18% - in otherword 1 out of 20 individuals in UK/NL gets colorectal cancer

Group 1 carcinogens

Causes cancer

• Processed meats

• Alcohol

• Cigarette smoking

Risk of cancer in smoking vs processed and red meat

• Smoking is a significantly larger problem

two studies with same RR but different interpretations on red meat

Cancer risk among vegetarians vs non-vegetarians

• Showed that risk was lower

• However, VERY confounding as these are very different groups of people: different BMI, different lifestyles, different education, more often women are vegetarian.

• Difficult to compare.

Why is it not perse advised to be vegetarian/vegan?

Because meat also has good nutrients

• Vitamin B3

• Vitamin B12

• Vitamin B6

• Iron

• Zinc

• Selenium

Are meat replacements always healthy?

No, often contain high salt.

Dietary recommendations all over the world

Possible mechanism (overall unhealthy diet)

• Due to heterocyclic amines that are formed when cooking or heating meat

• Potent carcinogens in rodents (animal studies)

• Also present in poultry

Possible mechanism II (PAH)

Polycyclic aromatic hydrocarbons

• Formed when fat drips on fire

• Smoke contains PAHs

• Also found in cigarette smoke

Possible mechanism III (N-nitrosocompounds)

• N-nitrosocompounds (NOC’s) => preservatives

• Nitrite and Nitrate => nitric oxides

• Endogenously formed (caricongenic)

• Exact structure and role in color poorly understood

Possible mechanism IV (dietary heme)

• Heme-iron is colouring pigments of red meat

• Poorly absorbed in small intestine

• Toxic metabolite during digestion

Experiment with mice and dietary heme

• Two groups of mice, one was given additional heme equivalent to 160g of red meat a day.

• Colon was tested, by testing cytotoxicity

• Overtime, the mice who consumed additional heme had greater cytotoxocitiy

• Group with additional heme also had more proliferation

Gene expression and dietary heme

• Feedback mechanisms for proliferation inhibited

• Tumor supressor gene TP53 was expressed less

  • = less apoptosis

Mice vs humans (stomach bacteria)