Can Eating Fat Stop Cancer in Its Tracks?


Caveman Doctor was recently talking with some health professionals about the benefits of eating grass-fed beef. One of the other people in the conversation said, “Give me just one reason why eating beef is healthy!” Caveman Doctor quickly responded with one word: CLA. Caveman Doctor then explained to them what CLA was and its benefits. Afterwards, the others asked how Caveman Doctor gets more in his diet. Once again, as usual, Caveman Doctor was very confused as to why he would try to get more CLA in his diet. His diet is already naturally full of CLA.


Conjugated Linoleic Acid: Another Reason to Ignore the Food Pyramid and Eat Like a Caveman


Conjugated Linoleic Acid

Conjugated linoleic acid (CLA) is formed from a simple change in the geometric structure of linoleic acid, a common unsaturated fat found in differing amounts in many foods. While CLA has a structure similar to that of linoleic acid, the manner in which each affects our body is strikingly different. CLA is found in the meat and milk fat (cheese, butter, and dairy products) of ruminant animals and turkey.1 If you remember from a previous article, ruminant animals, like cows, are those that have a rumen in their GI tract where grass sits after it is eaten and ferments, with bacteria eating the fermenting leftovers. The cows then end up, for simplicity sake, eating the bacteria and getting nourishment (as noted in the same post, we as humans do not process grass and cellulose in this way and it simply passes through us undigested). The rumen is where CLA is synthesized with the help of the residing bacteria,2 with the highest amount found in beef, lamb, butter, and cream, and lesser amounts in turkey and veal. CLA content in fish is minimal and there are near-negligible amounts in vegetable oils (not that any of us actually eat or cook with vegetable oils…).

CLA and Cancer


It was hard for many to believe that a substance from fried beef could help fight cancer, but the results showed otherwise.

CLA has had an unbreakable connection with cancer from the onset of its discovery. CLA was discovered in an experiment where scientists were studying heterocyclic amines and hydrocarbons, which are substances formed in burnt meat shown to cause cancer in laboratory studies.3,4 Interestingly, as the scientists were frying up the beef, they uncovered a new substance and eventually it was named CLA. Even more interestingly, as they were experimenting with the goal of creating cancerous substances, they found that this new compound from cooked beef actually stopped the conversion of normal cells to cancer (mutagenesis). It was hard for many to believe that a substance from fried beef could help fight cancer, but the results showed otherwise.
Many studies followed. Most gave mice and rats toxic chemicals that resulted in extremely high rates of cancer and attempted to study how successful CLA was at stopping the development of cancer. The animals were given different diet regimens containing CLA at varying time points (before being given toxic chemicals, during, or after). The studies uniformly showed dramatic decreases in cancer incidence. Human cell lines in lab studies have confirmed these results, also showing a decrease in cancer occurrence. Large human trials remain to be done, but hopefully this will change soon as more and more people realize the importance of diet and nutrition in cancer.
For example, in one study, mice were fed different amounts of CLA and then were given a cancer-causing (carcinogenic) chemical that causes breast cancer in most of its victims. After the chemical was given to the mice, 80% of those on a normal diet got breast cancer while only 40% of those consuming CLA were found to have cancer. A 50% reduction in cancer incidence!5
However, not only does CLA work to stop the incidence of cancer, but other studies have shown a massive reduction in the occurrence of cancer spread (metastasis) in mice with prostate cancer. In a different but similarly run study, mice were either given linoleic acid or CLA. Cancer metastases occurred in 80-100% of mice fed the linoleic acid versus only 10% of CLA-fed mice. Once again, a very dramatic difference.6
One study actually compared CLA with other fats, including olive oil and linoleic acid. Olive oil did not stop cancer development in animals exposed to carcinogens while CLA significantly reduced cancer incidence7. Linoleic acid, as you’ll read more on below, did not reduce cancer occurrence.

Linoleic Acid

Linoleic acid is a fatty acid found in large proportions in vegetable oils, walnut, sesame, and canola oil, with chicken fat containing about 20%8 and egg yolks 15%. It is also found in minimal amounts in butter, macadamia oil, and coconut oil. Unlike CLA, it has been shown to enhance the occurrence of cancer in animal studies with carcinogens9. Corn oil, heavy in linoleic acid, was given to animals, resulting in high levels of cancer. However, we already know about the issues of grains like corn (here, here, here, and here) and accordingly, eating corn oil is just as unhealthy as eating corn. While linoleic acid was shown to stimulate cancer development, CLA was actually able to overcome this effect and still limit cancer formation.5

Can Eating More Beef Help Fight Breast Cancer?

CLA appears to have an important relationship with all cancers; however, breast cancer appears to be the most important thus far. While CLA has been shown to decrease skin, liver, and colon cancer in animal studies, results with breast cancer have been the most remarkable in revealing this fat compound as a cancer-fighting powerhouse. Much like the studies above with mice were fed CLA, it was successful in stopping chemically-induced breast cancer. Amazingly, when animals were fed CLA, it was actually incorporated into their breast tissue. In other words, in response to eating a substance that may protect us from cancer, the body stores it in its fat tissue, basically keeping this cancer-fighting substance around in outposts to fight cancer.. In oncology, we are constantly experimenting with methods to localize breast cancer treatment, yet it appears that our bodies may do this naturally, by placing a cancer-fighting substance directly in the breasts. Also, studies show that in animals with established breast cancer, the cancer cells also took up CLA from the diet, resulting in decreased tumor rates.5
Since CLA has been shown to fight cancer in animal studies, its placement in breast tissue would lead us to conclude that this would decrease the risk of breast cancer, and population studies show just this. A recent study in Finnish patients looked at the dietary intake of CLA, as well as serum levels of CLA in a group of women with breast cancer and a matched group of women without breast cancer. It was found that the more CLA that the women consumed, the significantly less chance they had of being diagnosed with breast cancer and the authors concluded that CLA may in fact protect against breast cancer.10 As a side note, while CLA has been shown to be incorporated into breast tissue, it is also incorporated into the brain and liver as well and may serve to protect us in these locations.

 Is CLA an Antioxidant?

One of the large opinions on this site is that attempts to reduce inflammation on the body potentially reduce the risk of cancer.11 On a daily basis our bodies receive insults from free radicals, stress, and trauma, resulting in inflammation, oxidation, and cell damage. This damage may come from areas where it is near-impossible to avoid, such as chemicals in the air and water, or even from hefty doses (or even low doses12) of radiation, shown to cause cancer, compliments of TSA with each trip through security at the airport13,14 (always refuse to get scanned!). Regardless of the source, our body is getting bombarded constantly. While it is difficult to say what independently causes cancer, especially since it is likely a combination of many factors,15 the insults are nearly impossible to stop. As a result, we must constantly attempt to build up our arsenal to help fight this bombardment. Antioxidants play a large part in this. They help fight and fix the oxidation that occurs when a free-radical, or for simplicity sake, an active oxygen molecule, attacks our body. Thus the term anti-oxidant.
Similarly, fats and oils that we consume can be oxidized from cooking and even sitting on the shelf, and this oxidation causes damage to our body. As you may remember from a past article, oxidized fat is what is likely responsible for atherosclerosis and clogged arteries (not fat alone). While we are on the topic, remember those rabbits whose arteries were clogged by cholesterol (and more so by oxidized cholesterol)?  Well, giving their friends CLA with a heavy fat and cholesterol diet actually reversed their atherosclerosis by as much as 50%,16 another one of the many instances where eating fat (CLA) actually results in less atherosclerosis. In this study, rabbits were given large amounts of cholesterol and CLA, and serum cholesterol levels remained unchanged (yet atherosclerosis decreased). While tangential, this also further questions the rather weak hypothesis that fat or cholesterol alone clogs arteries and our serum cholesterol affects atherosclerosis. CLA has also been shown to stop the peroxidation (attachment of free-radical oxygen) to unsaturated fatty acids.

Improved Glucose Tolerance, Weight Loss, and Increased Lean Mass from CLA

In animal studies, CLA reduced levels of harmful omega-6 fatty acids in rat tissue (which cause inflammation) and increased levels of healthy omega-3 fatty acids. CLA also improved glucose tolerance and lowered insulin levels (!) in animals and humans.17 In several studies, CLA has been shown to result in increased lean muscle mass and decreased body fat in animals and humans.18 However, while CLA has shown an increase in energy exertion and fat loss, results are mixed.19

 How to Get CLA in Your Diet

One common criticism of animal studies is the large amounts of a substance often needed to fight cancer. However, the amounts of CLA were not exceedingly high in these studies and it was often given over short periods of time. One study lasted four months, yet only five weeks of consuming CLA was enough to fight cancer induction. Another study showed only three weeks of CLA consumption to be sufficient enough to fight cancer.20 While we may be consuming less with our diet, if this is done on a daily basis over long periods of time (entire lives), it may afford us similar cancer protection.
A person on a typical western diet consumes about 1g per day,21 though some data points toward Americans consuming a paltry 150 mg per day.22 While there are not great data on the caveman diet, personally, by lunch I usually eat well over the total daily amount of CLA in a Western diet. Below is a list of foods containing CLA, compiled from several sources.1,3 Keep in mind this is not considering the feed and grazing patterns of the cattle (which is important, as you will see below).

Food CLA (g/kg fat) Linoleic Acid (g/kg fat)


Butter 4.7 23
Milk 5.5 22
Yogurt 4.8 20
Cheddar 3.6 17
Cottage 4.5 22
Parmesan 3 11
Ricotta 5.6 24
Romano 2.9 11


Ground Beef 4.3 24
Chicken 0.9 179
Lamb 5.6 58
Pork 0.6 79
Turkey 2.5 218
Veal 2.7 53
Salmon 0.3 102
Shrimp 0.6 16
Trout 0.5 26

Vegetable Oils

Maize 0.2 58
Olive 0.2 79
Peanut 0.2 32
Safflower 0.7 74

The other obvious way to get more CLA in your diet is to follow the premise of a caveman diet. Of note, several studies look at CLA supplements comprised of different configurations23 and the data is mixed, with some CLA types beneficial and others as detrimental.24,25 As if often the case with nutrition, there is no silver bullet in pill-form and it’s likely better to simply eat the real thing. Unfortunately, in our poly-pharmacy society, most of the newer studies look at supplements made from CLA derivatives. Looking at the list of foods in my fridge and freezer, it contains nearly all of those above that are high in CLA, and they are eaten on a daily basis. On my schedule, morning eggs are cooked in grass-fed butter, my coffee contains pure grass-fed cream (both non-caveman parts of my diet), broccoli with my dinner is often cooked in grass-fed butter, and grass-fed beef is consumed often for dinner (with leftovers for lunch the next day).
Keep in mind CLA is found in the fat from dairy, hence CLA is not a reason to drink milk regularly, with it’s nearly 20 grams of sugar per serving. Skim milk is worse yet, as the valuable nutrition in the fat is removed, leaving some protein and a hefty amount of sugar (lactose). This is one thought as to why whole milk, but not skim, was associated with a decreased risk of prostate cancer in a Norwegian study.26 Also, I am well aware of the fact that cavemen did not consume dairy. Dairy fat, especially if it is one of your few non-caveman foods with its healthy CLA and minimal carbohydrates, remains a good non-caveman food and one way of many where we can mimic the lifestyle of a caveman under modern-day living.
However, when consulting lists (including the one above), note that not all beef, chicken, or any animal meat is the same. In fact, over 30 years of research has shown that meat from cattle fed all-grass diets as opposed to grain-fed cattle meat has significantly more CLA, vaccenic acid (the precursor to CLA), and antioxidants.27 Also, remembering that grass and other foods consumed by cows remain in their rumen and ferment, it is important to note that grain consumption causes an unnatural acidic environment in the rumen. Grass consumption leads to a much more favorable environment for bacteria to grow in the rumen and ferment more grass in the future, resulting in greater synthesis of CLA. Interestingly, the damage of grains toward CLA synthesis can likely be applied to humans as well, as we also synthesize CLA within our body. In fact, studies show that grass-fed cows have 2-3 times more CLA in their meat than grain-fed counterparts.27,28

Two conclusions can be made from this data:


1. Don’t eat animals that are fed grains, instead eat animals that freely roam the pasture, eating grass and food they were meant to eat.

2. Don’t eat grains, because if they result in unhealthier fat and less healthy CLA in the tissues of animals that eat them, it will do the same to you.

Also, this is yet another reason why most of the population based studies looking at fat in the diet are fatally flawed; clearly all fats and fat sources cannot be lumped together as they are very different in their actions on our body.
Recommendations have included eating 3 g per day to get the health benefits of CLA,22 though others say that eating over 6 g per day for men and over 4 g for women is necessary for cancer prevention.21 One thing’s for sure: if we want to get more CLA in our diet, we are going to have to replace the harmful grains and simple sugars with healthy fat from animal sources.

In summary, potential benefits of CLA include:


  1. Decreased risk of cancer
  2. Suppressed cancer progression/promotion29
  3. Decreased body fat
  4. Increased muscle mass
  5. Decreased atherosclerosis
  6. Lower insulin levels
  7. Improved glucose tolerance

The results are in and the potential for CLA to help us fight cancer, while providing many other benefits, appear plentiful. However, CLA is only found in fat and the animal-sources we have been told to avoid for the past 30 years – similar to those that the caveman used to hunt and eat. In one of the many great papers by Kritchevsky3 on nutrition and cancer, his final comment sums it up quite well:

“Animal fat, which has been maligned for so long, may actually contribute a potent therapeutic component to our diet.”

Hopefully more people will attempt to increase their intake of CLA. For those of us on a caveman diet, we have been doing this all along. Once again, nature made it easy for the caveman and easy for us.


1. Chin SF, Liu W, Storkson JM, Ha YL, Pariza MW. Dietary sources of conjugated dienoic isomers of linoleic acid, a newly recognized class of anticarcinogens. Journal of Food Composition and Analysis 1992;5:185-197.
2. Dhiman TR, Anand GR, Satter LD, Pariza MW. Conjugated Linoleic Acid Content of Milk from Cows Fed Different Diets1. Journal of dairy science 1999;82:2146-2156.
3. Kritchevsky D. Antimutagenic and some other effects of conjugated linoleic acid. Br J Nutr 2000;83:459-465.
4. Pariza MW, Ashoor SH, Chu FS, Lund DB. Effects of temperature and time on mutagen formation in pan-fried hamburger. Cancer Letters 1979;7:63-69.
5. Ip C, Chin SF, Scimeca JA, Pariza MW. Mammary Cancer Prevention by Conjugated Dienoic Derivative of Linoleic Acid. Cancer Res 1991;51:6118-6124.
6. Cesano A, Visonneau S, Scimeca JA, Kritchevsky D, Santoli D. Opposite effects of linoleic acid and conjugated linoleic acid on human prostatic cancer in SCID mice. Anticancer research 1998;18:1429-1434.
7. Ha YL, Storkson J, Pariza MW. Inhibition of Benzo(a)pyrene-induced Mouse Forestomach Neoplasia by Conjugated Dienoic Derivatives of Linoleic Acid. Cancer Res 1990;50:1097-1101.
8. Nutter M, Lockhart E, Harris R. The chemical composition of depot fats in chickens and turkeys. Journal of the American Oil Chemists’ Society 1943;20:231-234.
9. Welsch CW. Relationship between Dietary Fat and Experimental Mammary Tumorigenesis: A Review and Critique. Cancer Res 1992;52:2040s-2048s.
10. Aro A, Mannisto S, Salminen I, Ovaskainen ML, Kataja V, Uusitupa M. Inverse association between dietary and serum conjugated linoleic acid and risk of breast cancer in postmenopausal women. Nutr Cancer 2000;38:151-157.
11. Rakoff-Nahoum S. Why cancer and inflammation? Yale J Biol Med 2006;79:123-130.
12. Boice JD, Land CE, Shore RE, Norman JE, Tokunaga M. Risk of Breast Cancer Following Low-Dose Radiation Exposure. Radiology 1979;131:589-597.
13. Zanotti-Fregonara P, Hindié E. Radiation Risk from Airport X-ray Backscatter Scanners: Should We Fear the Microsievert? Radiology 2011;261:330-331.
14. Rez P. Uncertainties in the Dose From Full-Body Airport Screening. Arch Intern Med 2011;171:1129-1130.
15. Anand P, Kunnumakkara AB, Sundaram C, Harikumar KB, Tharakan ST, Lai OS, Sung B, Aggarwal BB. Cancer is a preventable disease that requires major lifestyle changes. Pharm Res 2008;25:2097-2116.
16. Kritchevsky D, Tepper S, Wright S, Czarnecki S, Wilson T, Nicolosi R. Conjugated linoleic acid isomer effects in atherosclerosis: Growth and regression of lesions. Lipids 2004;39:611-616.
17. Brown JM, McIntosh MK. Conjugated Linoleic Acid in Humans: Regulation of Adiposity and Insulin Sensitivity. J Nutr 2003;133:3041-3046.
18. Smedman A, Vessby B. Conjugated linoleic acid supplementation in humans–metabolic effects. Lipids 2001;36:773-781.
19. Wang Y, Jones PJ. Dietary conjugated linoleic acid and body composition. Am J Clin Nutr 2004;79:1153S-1158S.
20. Ip C, Scimeca JA, Thompson H. Effect of timing and duration of dietary conjugated linoleic acid on mammary cancer prevention. Nutr Cancer 1995;24:241-247.
21. Ha YL, Grimm NK, Pariza MW. Newly recognized anticarcinogenic fatty acids: identification and quantification in natural and processed cheeses. J Agric Food Chem 1989;37:75-81.
22. Ritzenthaler KL, McGuire MK, Falen R, Shultz TD, Dasgupta N, McGuire MA. Estimation of Conjugated Linoleic Acid Intake by Written Dietary Assessment Methodologies Underestimates Actual Intake Evaluated by Food Duplicate Methodology. J Nutr 2001;131:1548-1554.
23. Kelley NS, Hubbard NE, Erickson KL. Conjugated Linoleic Acid Isomers and Cancer. J Nutr 2007;137:2599-2607.
24. Brown JM, Halvorsen YD, Lea-Currie YR, Geigerman C, McIntosh M. Trans-10, Cis-12, But Not Cis-9, Trans-11, Conjugated Linoleic Acid Attenuates Lipogenesis in Primary Cultures of Stromal Vascular Cells from Human Adipose Tissue. J Nutr 2001;131:2316-2321.
25. Cho HJ, Kim EJ, Lim SS, Kim MK, Sung M-K, Kim J-S, Park JHY. Trans-10,cis-12, Not cis-9,trans-11, Conjugated Linoleic Acid Inhibits G1-S Progression in HT-29 Human Colon Cancer Cells. J Nutr 2006;136:893-898.
26. Veierød MB, Laake P, Thelle DS. Dietary fat intake and risk of prostate cancer: A prospective study of 25,708 Norwegian men. International Journal of Cancer 1997;73:634-638.
27. Daley C, Abbott A, Doyle P, Nader G, Larson S. A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef. Nutrition Journal 2010;9:10.
28. Realini CE, Duckett SK, Brito GW, Dalla Rizza M, De Mattos D. Effect of pasture vs. concentrate feeding with or without antioxidants on carcass characteristics, fatty acid composition, and quality of Uruguayan beef. Meat Science 2004;66:567-577.
29. Ip C, Briggs SP, Haegele AD, Thompson HJ, Storkson J, Scimeca JA. The efficacy of conjugated linoleic acid in mammary cancer prevention is independent of the level or type of fat in the diet. Carcinogenesis 1996;17:1045-1050.
© 2015 CDR Health and Nutrition LLC. All Rights Reserved.


  1. Diane and Tom

    How important do you consider C-reactive protein levels 1. in general and 2. in relation to cancer?
    Can you list brand names or stores that carry grass fed meats & dairy? (Yes, I know you are in Philly, but so is my son & his family. We live in Michigan.) Thanks!

    1. CavemanDoctor (Post author)

      Wow I am literally writing an article on stress, CRP, and cancer right now so stay tuned. This has been the best site I have seen: and I think you guys are in good hands up there in Michigan. I actually have looked on here and found some farms I like and I drive out there with a big cooler and buy several pounds of meat. I also live by an indoor market and get my coffee cream and grass-fed butter there, so I am spoiled in that regard. Kerry gold and some other grass-fed butters are at Whole Foods, and I have seen them at run of the mill grocery stores too (same with grass-fed beef, though not as many). PS: grass-fed beef tastes better (in my opinion) but does cook faster so if you like it rare you literally only need to cook eat side for 2 mins of so for a rare to medium rare steak. Also, it is more expensive, but is leaner so you aren’t cutting as much fat of like with grain-fed beef.

      I hope this helps,

      1. Diane and Tom

        Thanks, CD! Interesting site that you pointed out. We’ll be checking out your market in Philly this weekend. It’s a regular stop when we visit.
        It’s very impressive how quickly you can put an article together complete w/ references.

        1. CavemanDoctor (Post author)

          Thanks! Enjoy philly. I’m off to phoenix to present at a conference and then sedona for some hiking. I hope they have some good grassfed beef…

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    1. cavemandoctor (Post author)


      Thanks for the article. Interesting stuff here and no surprise, unfortunately. As the links between cancer and diet strengthen, and we continue to eat more unhealthy foods and become more obese as a society, we very well may experience a continuation of these numbers.

      The infection aspect is interesting because not everyone infected gets cancer. It’s likely those able to fight the infections with a stronger immune system and healthier body (via diet, exercise, etc.) will be more apt to avoid cancer.

      Hopefully people will push more for stopping disease before it starts.


      1. JK

        hey look at the bright side caveman cancer doc will never be out of the job!

        1. cavemandoctor (Post author)

          Well, in this case I would love to be out of a job! Then maybe I could concentrate on nutrition and excercise…

      2. JK

        I have this funny feeling that Caveman Doc rather be a nutritionist than a Cancer Specialist! Hmmm….I’m glad you started this website and help lots people out there!

        1. cavemandoctor (Post author)

          Haha, perhaps…

          Thanks JK!

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  11. Edward

    Hi Colin,

    I came across a reference in “The Art and Science of Low Carb Performance” where Dr. Phinney and Jeff Volek mentioned a study in which obese patients were fasted long enough to elevate their ketones to levels up to 8 mmoles/liter. They then gave the patients a bolus of insulin that dropped the patients to blood glucose levels as low as 9 mg/dl. The whole point of this was to determine if this level of ketosis would alleviate or prevent the symptoms of glucopenia, and indeed it did, the patients were completely asymptomatic. This was in 1971, believe it or not! Just try to do something like that now. However, in a clinical setting…

    Where I’m going with this is wondering if dietary ketosis to an extent that would make this possible might be a route to starving cancer cells, at least those that exhibit the Warburg effect. A ketotic patient could be put on a carefully titrated insulin infusion to get his blood glucose down to a level that would be too low even for cancer cells that have a knack for stealing enough glucose, not to get sufficient nutrition. He could be held at that level for a period of time sufficient to kill the cancer cells or for the duration of radiation therapy or simultaneous administration of chemo.

    Anyway, here’s a link to the study:



    1. cavemandoctor (Post author)

      Thanks for the article Edward, very interesting. It is a good thought as well, and I wouldn’t be surprised if more attempts like this happen in the future.

      There is actually a publication that I have somewhere, where a psychiatrist describes two depressed patients who undergo hypoglycemia-induced comas. This was an actual treatment for depression. During the severe hypoglycemia, these patients experienced a clinical complete response and their advanced cancer went into remission. They have tried this treatment recently (I think in Mexico) without success, but pretty interesting nonetheless. Once cancer cells stop getting their sugar, positive things happen…

      Take care,

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