Dear Mark: CLA Supplements

November 3, 2021

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woman taking cla conjugated linoleic acid supplement CLA, or conjugated linoleic acid, is the “good” trans-fat that occurs naturally in meat and dairy, especially from grass-fed animals. In the stomach of ruminants like cows, sheep, or goats, millions upon millions of bacteria help the animal digest its food. They also help convert dietary grass-based linoleic fatty acids into saturated fatty acids. Well, that conversion takes several steps, and one of the steps is the creation of CLA, some of which never gets fully saturated and instead shows up in the animal’s body and milk fat.

Twenty-eight different CLA isomers, or structural arrangements of the molecules, appear in CLA-rich animal fat. It’s very complex and quite different from trans-fat created by partially hydrogenating vegetable oils. Those lab-created trans-fats have definite negative metabolic and health effects, while the panoply of various CLA isomers from grass-fed dairy and meat seem to be beneficial.

What about CLA supplements? Is synthetic CLA just as good for you as naturally-occurring CLA?

What is a CLA Supplement?

Conjugated linoleic acid production is a booming industry with many players. You’ve got the new guys creating the stuff on a massive scale, getting their hands dirty in the lab, converting linoleic acid derived from safflower or sunflower oil into various isomers of CLA. Then there are the stalwarts, those ruminant stomachs filled with microscopic bacterial sweatshops toiling away as they convert unsaturated fats to saturated fats and make various CLA isomers in the process. An isomer called cis-9, trans-11 (or c9, t11) isomer is the primary one. CLA with a trans-10, cis-12 isomer is also evident, but in far scanter quantities. Same type of molecules – different arrangement. In fact, c9, t11 CLA accounts for between 80-95% of the CLA in ruminant and dairy fat, with t10, c12 making up most of the remainder. Supplement makers have the luxury of focusing on other isomers, of course, so they typically produce CLA supplements containing equal amounts c9, t11 and t10, c12.

Are CLA Supplements Healthy?

At first glance, they seem effective in isolated in vitro studies and can help people lose body fat.

T10, c12 can inhibit the growth of human colon cancer cells in vitro (with c9, t11 having no effect).¹
In another in vitro study, this time connective tissues isolated from human body fat, t10, c12 inhibited lipogenesis, or (something analogous to) body fat creation, while c9, t11 did not.²
It also showed promise as a promoter of lean mass versus fat mass in humans.³

However, while the t10,c12 isomer looks to be better at burning body fat, it comes at a cost. In a totally unsurprising twist, results change when you start feeding the stuff to live organisms and paying attention to the full effects (beyond just “does it result in 2% more fat loss?”). Let’s take a look at a few examples.

Healthy humans taking trans-10, cis-12 CLA supplements had increased triglycerides, LDL-HDL ratios, and total cholesterol-HDL ratios when compared to patients taking supplements based on cis-9, trans-11.
In both wild-type and lab mice, the t10, c12 isomer stimulated mammary tumor growth, while c9, t11 isomers had a neutral effect.
T10, c12 CLA supplements worsened metabolic syndrome in men.⁴
T10, c12 CLA supplements increased inflammation and insulin resistance.⁵
CLA loses a head-to-head match with safflower oil. The safflower oil group saw improved insulin sensitivity, higher HDL, and lower inflammation. The CLA was 50% trans-10, cis-12 and 50% cis-9, trans-11. In other words, it wasn’t CLA as you’d get from grass-fed butter or pastured lamb shoulder chops.⁶
In post menopausal women, high t10, c12 CLA supplementation increased inflammatory markers and lipid peroxidation when compared to CLA “supplementation” with milk (containing, remember, mostly c9, t11).
Mice fed t10, c12-enhanced diets experienced reductions in liver fatty acid oxidation and liver detoxification enzymes. In short, t10, c12 CLA gave mice fatty liver and reduced the liver’s ability to burn fat. It had similar effects on hamster livers.
T10, c12 led to dysregulated glucose and lipid metabolism.

To sum up, while t10, c12 supplementation can decrease fat mass, it can also raise LDL, lower HDL, and overall worsen the cholesterol profile, as well as increase insulin resistance, blood glucose levels, and insulin. C9, t11, on the other hand, seems to improve lipid metabolism overall.

Are you noticing a pattern? Again and again, individual CLA isomers appear to be protective or beneficial in isolated studies, usually in vitro, but when you actually feed an animal or a human a CLA supplement with the same isomer ratios, the benefits either disappear or get counterbalanced by a negative effect. You might burn some body fat, but you’ll also become insulin resistant. You may keep off the baby weight, but your breast milk will contain less fat as a consequence.⁷ I’m a big supporter of supplementation, but in my opinion, CLA supplementation simply isn’t worth it.

The right CLA supplement employing the right isomers in grass-fed ruminant-fat proportions could be helpful, but after taking an admittedly brief look at the top CLA supplements results on Amazon, I couldn’t point you toward any that fit that description. They may exist. Heck, they probably do exist, but it’s not obvious. I think you’d be better served simply eating grass-fed animal products: butter, cheese, and meat with fat intact.

In fact, we have good evidence that these “CLA supplements” are the healthiest available and give real benefits.

In one study, sheep cheese “naturally enhanced” with CLA improved lipid markers and reduced the levels of anandamide—an endocannabinoid that increases hunger and food intake—in patients with high cholesterol.⁸ Imagine that: giving high-fat cheese to people with high cholesterols and seeing their numbers improve. Incredible (and totally unsurprising if you know what’s what). Of course, “naturally enhanced” means the sheep ate grass and converted the fatty acids into CLA.
In another, pecorino romano cheese (a proprietary Italian cheese that can only come from grass-fed sheep) “naturally rich in c9, t11 conjugated linoleic acid” improved markers of atherosclerosis in those who ate it. CLA-rich sheep cheese actually reduced the risk of heart attack.⁹

As so often is the case, food is the best way to get your nutrients. Supplements have a place, but only if they emulate the natural form. Supplements with novel forms of nutrients should be viewed with suspicion and confirmed with research.