This article is part of a special report on Red Meat. To see the other articles in this series, click here.

Trans fats are one of the few food components that are widely accepted as being unhealthy, and for good reason. Industrial trans fats are created by pumping hydrogen molecules into liquid vegetable oil, changing the chemical structure and causing the oil to become a solid fat.

Trans fats are generally considered to be especially harmful because they raise total cholesterol while lowering HDL cholesterol. However, as usual with conventional nutrition advice, there is far more danger to trans fats than simply the effect they have on cholesterol ratios.

Mark Sisson has written a helpful explanation as to why trans fats are best to be avoided.

However, it may surprise you to learn that many of the foods recommended on a Paleo or whole foods diet contain trans fats as well. Dairy fat and meats from grass eating “ruminant” animals contain significant amounts of trans fatty acids, and grass-fed animals actually have higher levels of these trans fats than grain fed animals. (1) In fact, your grass-fed steak contains about 0.5g-1.4g of trans fat per ounce (28.3g) of total fat. (2)

Does this mean we should avoid all grass-fed animal products, cut out red meat, and only eat fat-free dairy if we want to reduce our risk of heart disease? Not at all! These naturally occurring trans fats in ruminant animal products are not at all harmful to our health, and may actually reduce the development of many different chronic diseases.

Are you eating enough healthy trans fat?

CLA: How is it different than industrial trans fats?

Naturally occurring trans fats are formed when rumen bacteria in the stomachs of ruminant animals (cows, sheep, etc.) digest the grass the animal has eaten and form trans-rumenic and trans-vaccenic acid via biohydrogenation of polyunsaturated fats in the grass. Conjugated linoleic acid, or CLA, is a trans-rumenic acid that is found abundantly in grass-fed meat and dairy products, and to a lesser degree in grain-fed products. It is also produced in our bodies from the conversion of trans-vaccenic acid (VA) from those same animal products.

Industrial trans fats have slightly different chemical structures than those trans fats found in beef and butter (specifically, the location of the double bond). CLA also has contains both cis- and trans- bonds, whereas most industrial trans fats have only trans bonds. But these minor differences in structure lead to majorly different effects in the body, as has been shown in many clinical and epidemiological studies. (3)

While industrial trans fats are shown to increase the risk of heart disease, cancer, and obesity, CLA and other trans fats found naturally in animal products are actually thought to decrease the risk of those diseases.

Health benefits of CLA

The major difference between CLA and industrial trans fats is the effect they have on heart disease and atherosclerosis. Several clinical and epidemiological studies have been performed, and meta-analysis of these studies suggests that natural trans fats from animal products are not associated with any increased risk of heart disease. (4) These studies have generally have shown either an inverse or no association between natural trans fat intake and heart disease across multiple geographical locations. (5)

While there have been very few highly controlled clinical trials studying the effects of CLA and VA on heart disease and atherosclerosis, the few that exist also support the conclusion that these natural trans fats may actually reduce the risk of heart disease. In animal studies, CLA has demonstrated potent anti-atherogenic effects, preventing fatty streak and plaque formation in the arteries of rodents by changing macrophage lipid metabolism. (6, 7) While more research in humans is needed, it seems that grass-fed dairy and meat products, high in both CLA and vitamin K2, are some of the best foods you can eat if you’re looking to prevent a heart attack.

CLA may also be helpful in preventing the development and improving the management of type II diabetes.

In rats, CLA has been shown to improve glucose tolerance and skeletal muscle insulin action. (8) Research has also demonstrated that CLA may reduce hyperinsulinemia by increasing the production of adiponectin, a hormone that can lead to enhanced insulin action and improve insulin sensitivity. (9) Epidemiological evidence suggests that there is an inverse association between CLA levels in adipose tissue and diabetes risk, further supporting the hypothesis that CLA may be involved in healthy insulin regulation. (10)

CLA has even been shown to reduce the risk of cancer, in both experimental and case control studies. (11) It appears to work primarily by blocking the growth and metastatic spread of tumors, controlling the cell cycle, and by reducing inflammation. (12) CLA is able to interrupt the omega-6 PUFA metabolic pathway for the synthesis of eicosanoids, preventing the inflammatory processes that promote cancer development. This may be one reason why dairy consumption has been shown to be inversely associated with certain cancers like breast and colorectal cancer. (13, 14, 15, 16, 17) Based on these animal and human studies, it’s possible that CLA plays a role in cancer prevention.

You may have seen CLA supplements advertised as a weight loss promoter. Some research suggests that CLA can help reduce body fat and promote weight loss in overweight and obese individuals. (18) In a few studies, dietary supplementation of CLA has been shown to increase lean body mass, reduce body fat mass, and improve overall body composition in overweight individuals. (19, 20, 21) It is thought that CLA may promote improvements in body composition by increasing the breakdown and reducing the storage of body fat. That said, this reduction in body fat is small, so CLA may not cause significant weight loss in the way that supplement advertisers would suggest. But it certainly wouldn’t hurt in your weight loss efforts to increase your dietary CLA.

These studies certainly provide interesting food for thought about CLA’s possible health benefits. That said, I think we need more high quality human research before we can be certain about CLA’s role in human health and disease.

The good news is that all of the foods CLA is present in are beneficial in other ways, so you’ll get enough CLA simply by emphasizing grass-fed meat and dairy products (assuming you tolerate dairy).

Dietary Sources of CLA

So now that you know some of the incredible benefits of natural trans fats like conjugated linoleic acid (CLA) and vaccenic acid (VA), how can you increase them in your diet?

As I mentioned earlier, grass-fed dairy and meat are the best sources of CLA and VA. In fact, 100% grass-fed animal products contain from three to five times more CLA than products from animals fed grain. (22) And since CLA is in the fat, the best sources will be fattier cuts of meat, bone marrow, high-fat dairy products like butter and whole milk, and full fat cheeses. Eatwild.com has some great information about CLA in food products, and even has a product directory that allows you to search locally for food made from animals raised on fresh pasture.

Some people may believe that supplementing CLA has the same potential benefits as eating a diet rich in CLA. I disagree, and believe that these supplements could be potentially harmful. Most CLA supplements are derived from linoleic acid in safflower oil, and some studies have shown that CLA supplementation in humans can cause fatty liver, inflammation, dyslipidemia, and insulin resistance. Furthermore, CLA supplements have not demonstrated the beneficial effects seen from dietary intake of CLA in human trials. This may be due to the composition of synthetic CLA supplements; 50% of the product is an unnamed isomer, and is an entirely different fatty acid than the CLA and VA found in meat and dairy products. (23)

It’s always better to get nutrients from food rather than supplements whenever possible, and CLA is no exception. So if you’re looking for a heart-healthy, cancer-preventing diet, be sure to include plenty of grass-fed beef, butter, and cheese. (And don’t worry if your doctor thinks you’re crazy!)