The Link Between Animal Food and Cancer
Working with cancer patients I am often asked about animal foods. There are many reputable sources (providers, researchers, books, websites, etc) out there telling patients to avoid all animal food. As an Integrative Dietitian Nutritionist who believes that a high quality omnivorous diet can be optimal I decided to do my own research to get to the bottom of this question.
First I need to say that plant foods are definitely your best ally against cancer. As we've discussed before in my Anti-Cancer Diet post you need a colorful variety of plants (veggies, fruit, legumes, spices, whole grains) every day to optimize your immune system, lower inflammation, and decrease your chances for cancer. That said, do you need to be vegan? Meaning, do you need to avoid ALL animal food to have the best fighting chance.
Types of Animal Food
Let's make sure we're all on the same page as far as what foods I'm referring to when I say "animal food". Here's a list:
- Red Meat: beef, lamb, veal, pork, etc
- Processed Meat: red meats that have been preserved with curing, smoking, salting, drying
- Poultry: chicken, turkey, duck, etc
- Seafood: fish, shellfish
- Dairy: milk, cheese, yogurt, cottage cheese
- Eggs: chicken, duck, quail, etc
After reviewing recent research the risk versus benefit of animal food varies quite a bit depending on the type of animal food and the way it is prepared. Let's look in more detail at some of these concerns.
Cooking and Processing
Cooking methods and the processing of meat cause the biggest concern for cancer risk. Cooking animal foods at high-heat will create carcinogens. The by-products include Heterocyclic Amines (HCAs) and Polycyclic Aromatic Hydrocarbons (PAHs). The reaction which produces these by-products starts to happen at 212 F (100 C) and becomes extremely dangerous by 572 F (300 C). Essentially the hotter and longer a meat is cooked, the more HCAs and PAHs are produced. Direct heat methods like grilling and frying produce more that indirect-heat methods like stewing, steaming, or poaching.
HCAs have been shown to increase occurrence of tumors in the breast, lung, colon, stomach, prostate, pancreas, and esophagus (study). It's important to keep in mind that any animal food, not just meat, can create HCAs if cooked at high heat.
In addition to the concerns with HCAs and PAHs, the processing of meats add chemicals, like nitrites, that generate N-Nitroso Compounds (NOCs); which are another class of carcinogenic compounds.
Another concern is in regards to certain nutrients inherent to animal food. For example, heme iron is particularly high in red meat, liver, and processed meat. Heme iron may be concerning because it is thought to increase production of N-Nitroso Compounds in the digestive tract as well as act as a growth factor for H. Pylori, which can increase the risk for stomach cancer. Another potential concern is with the nutrient choline, which is high in eggs, liver, red meat, and milk. Choline is a necessary nutrient for energy, metabolism, liver function, brain health, and nerve function. But when consumed in high amounts it is converted in the liver to a by-product, which can increase inflammation in the body.
Yet another concern is how the industrialized commercial husbandry practices affect the quality of the animal foods we are eating. Pesticides used on feed plus medications or growth hormones given to the animal can create toxic residues that we then consume in the meat. The quality of the animal's diet is equally important. When animals are fed grain-based diets, rather than grass, we are left with a meat that is very inflammatory. According to a review written in Nutrition Journal in 2010, grass-based diets produce higher contents of omega-3s and CLA in beef as well as higher levels of antioxidants.
You're probably already familiar with the anti-inflammatory benefits of Omega-3s but may be wondering what CLA is. Conjugated Linoleic Acid (CLA) is a naturally occurring fatty acid made from omega-6 essential fatty acids found in meat and dairy. The isomers of CLA have been studied for their potential benefit with immune support and weight loss. Research from the above review suggests that pastured cows produce up to 500% more CLA than grain-fed cows.
If we look at the risk versus benefit of each category of animal food we are left with the following points. Red and Processed Meat seem to provide the most risk while Dairy and Eggs have mixed benefit/risk and Poultry and Fish have the least risk association.
Red and Processed Meats
Out of all your animal food options, processed meat is going to be the biggest problem. It's high in HCAs, PAHs, NOCs, and heme iron. The concern with red meat is going to be greater the hotter you cook it and in regards to the quality of the meat you're purchasing. As discussed above, grass-fed meat is going to not only be less toxic but also less inflammatory.
Dairy and Eggs
Dairy has factors that are both beneficial and possibly concerning. If you're buying dairy from grass-fed or pasture-raised cows then the food will be less inflammatory and have a higher amount of CLA. Dairy is also a good source of calcium and vitamin D as well as probiotics if you're using yogurt or kefir. All of these nutrients can help to lower your risk for cancer. However dairy is also high in IGF-1 and as we discussed in the blog post on Sugar and Cancer this can be problematic by increasing inflammation in the body.
Eggs are often part of a healthier eating pattern however when cooked at high temperatures, as with fried eggs, this will create HCAs and PAHs. Eggs are also a rich source of choline, which may be a contributor of increased inflammation in the body as discussed above. For both eggs and dairy the increased risk seems to be mostly connected with hormonally-related cancers, such as prostate, breast and ovarian.
Poultry and Fish
On the other hand, both poultry and fish in research reviews have shown to decrease risk of cancer. Most of this is likely due to an overall healthier eating pattern but with fish we know there is also some protection from the anti-inflammatory properties of the omega-3s. Be aware though that the benefits of both fish and poultry can be canceled if cooked at high heat; so no frying.
Take Home Guidelines
The over-arching claim to avoid all meat and animal products is not warranted. You do not need to be vegan to lower your risk for cancer, although it's certainly an option if you're so inclined, but you do need to consume a lot of plant food and be mindful of both the quality and type of animal food you are eating.
- Include a large variety of colorful veggies, fruits, and spices.
- Buy the best quality animal food you can afford; 100% grass-fed or pasture-raised is best.
- Rotate through your proteins including plant-based sources of protein with animal protein. Refer to my post on the Benefits of Protein for more instruction on this. Aim to have fish 2 or more times per week; the fattier the better. Poultry, without the skin, would be your next best option. Limit eggs to 1 or 2 times per week; soft and hard boiled will be a better option than scrambled or fried. Consider avoiding eggs completely if you have had a reproductive cancer or are at high-risk for breast, ovarian, or prostate cancer. Limit red meat to once a week or less and avoid cooking at high temperatures.
- Avoid cooking all of your animal foods at high temperatures.
- Keep the heat below 400F (200C)
- Flip the meat often so as to lessen the amount of time the meat is exposed directly to the heat source
- Choose cooking methods that avoid direct heat (poaching, steaming, stewing)
- Add marinades to help offset the damage of HCAs and PAHs when cooking animal food at higher heat.
- Always eat lots of colorful vegetables with your meats as the nutrient content of the veggies may offset the damage caused by heme iron or HCAs and PAHs.
- Avoid charred, fried, and processed meats!
Without making you fearful of animal food I hope this review and the above guidelines provide you with some confidence to include animal food mindfully as part of a healthy diet while still supporting your body's ability to fend off cancer. If you feel like you could use more support in putting together a healthy meal plan for you, please feel free to contact me for customized support.