CLA and Weight Loss

Of all the potential health benefits claimed for conjugated linoleic acid (CLA), none get close to the attention commanded by CLA for weight loss.

Indeed, most studies conducted on CLA have focused on its ability to facilitate weight loss, and the vast majority of CLA supplements are purchased by individuals looking to lose weight.

CLA Effects on Body Composition

And yet it is not quite accurate to say that CLA promotes weight loss. Even the studies with the most encouraging results do not demonstrate a significant discrepancy in weight loss between test subjects and the control group. Instead, they show test subjects losing substantial amounts of body fat without losing much weight.

What CLA appears to do is induce changes in body composition, as subjects lose body fat and gain lean mass. Such changes in body composition can have a profound effect on the individual's resting metabolic rate (RMR), which, in turn, can ultimately result in overall weight loss.

In one study, mice received 0.5% of their diet as CLA. The supplement administered consisted of approximately equal amounts of the c9,t11-CLA and t10,c12-CLA isomers. Over a four week period, the test subjects experienced 57% to 60% reductions in body fat and 5% to 14% increases in lean body mass compared to the control group. However, there were no significant changes in body weight between test and control groups.

Abdominal fat appears to be particularly sensitive to CLA supplementation. Several human studies have shown reductions in abdominal fat and waist measurements, even though no weight loss occurred.

How CLA Promotes Fat Loss

While the mechanism by which CLA produces these changes in body composition is not entirely known, there is evidence to suggest that the t10,c12-CLA isomer reduces lipid uptake into fat cells by inhibiting lipoprotein lipase and stearoyl-CoA desaturase activity in these cells.

Stearoyl-CoA desaturase (also known as delta-9-desaturase) and lipoprotein lipase are enzymes that play a key role in fatty acid metabolism. When fat cell levels of these enzymes are reduced, fewer fats are broken down into useable fatty acids and glycerol; hence overall fat uptake is decreased.

The t10,c12-CLA isomer has also been shown to significantly inhibit preadipocyte proliferation. Preadipocytes are cells that can develop into fat cells. Additionally, it appears that CLA may enhance fatty acid oxidation in both fat and muscle cells as well as boosting energy production in cellular mitochondria.

Virtually all activity related to body composition and fat reduction seems to derive from the trans-10, cis-12 isomer. As you may recall, this isomer is present only in very small amounts in CLA rich foods such as red meat and dairy products. Therefore supplementation is necessary to experience CLA's potential fat reduction benefits.

CLA Weight Loss Caveats

The possibility of reducing body fat while simultaneously increasing lean body mass may make you want to go out and purchase CLA supplements not just for your dog, but for yourself. Not so fast.

There are a few things to keep in mind when evaluating CLA's potential for generating weight loss, or fat loss as it were.

First, the studies with the most promising results were done on rodents, not dogs or humans. Body fat reductions between 22% and 70% during 4-8 week studies have been demonstrated in mice, rats, and chicks. Canine and human fat loss as a result of CLA supplementation tends to be much more moderate, when it occurs at all.

Researchers are not quite certain why this is the case, but speculate that rodents are more sensitive to the CLA-induced reduction in fat deposits due to their greater dependence on fat combustion for fuel. A faster metabolic rate may also play a role.

The second point to keep in mind when considering CLA supplementation for weight loss in dogs is that in the vast majority of animal studies, body fat reductions resulted primarily from decreases in new fat formation as opposed to reductions of already existing fat stores.

This is not surprising considering the primary mechanism by which CLA is thought to produce body fat reductions. Therefore CLA would likely be more useful to prevent the regaining of fat following a reduced calorie diet than to facilitate weight loss while on the diet.

Most human and canine CLA studies, however, have focused on trying to achieve reductions in existing fat stores. The results have been decidedly mixed.

Canine Weight Loss and CLA

At this point, only a few studies have examined CLA's potential for promoting weight loss in dogs and the results have not been too encouraging.

A 2006 study conducted by Hills found that "the addition of CLA did not significantly affect food intake, energy intake, final lean body percent, change in lean body percent, or final fat percent."

Another study set out to compare high protein/low carbohydrate diets to traditional high carbohydrate/moderate protein diets, with and without the addition of CLA.

Overweight dogs of similar size, weight, and body composition were divided into four groups (see the box).

All four diets were low in fat, and energy intake was reduced to 85% of maintenance calories for all dogs.

After 12 weeks, the two high protein groups lost over 10% of their body weight and experienced a 38% (Group 3) and 36% (Group 4) reduction in fat mass.

There was no statistically significant difference between the high protein group that received CLA supplements and the one that didn't.

The high carb groups saw less than half of the weight loss experienced by the high protein groups: 4.5% (Group 1) and 5% (Group 2). Body fat reduction was also considerably lower than in the high protein groups, but this time there was a difference between the CLA group and the group fed the high carb diet without CLA: 6% (Group 1) vs. 19% (Group 2).

CLA had no effect on weight loss, which is consistent with other studies.

CLA did appear to enhance body fat reduction, but only when a high carbohydrate was fed.

However, the high protein, low carb diet without CLA produced far better results than the high carb diet with CLA, suggesting to researchers that "the macronutrient change from high-carbohydrate to high-protein content has a greater effect on increasing weight loss than does the addition of CLA to a diet."

Can CLA Prevent Regain of Body Fat After Weight Loss?

I'm not aware of any studies involving dogs that examine whether CLA supplementation can reduce regain of body weight or fat following weight loss on a calorie-restricted diet.

Human studies examining this issue have yielded mixed results.

How Much CLA Is Necessary for Weight Loss or Fat Reduction?

Most animal studies examining CLA's effect on weight loss and reduction used a dose of 0.5% to 1% of the diet as CLA. In human CLA and weight loss studies, doses ranged from 0.1% to 1% CLA.

The dose typically recommended to produce fat reduction in humans is 3.4 grams of CLA daily.

Obtaining an amount this high from dietary sources is virtually impossible since it would entail consuming over 5,000 daily calories worth of foods extremely rich in saturated fats.

Consequently CLA supplements are necessary to see the fat reduction benefits of CLA.

In some animal studies, higher CLA dosages sometimes correlated with greater fat reduction, but in human CLA studies amounts up to 6.8 grams daily provided no additional fat loss benefits over the standard 3.4 gram dose.

However, some researchers speculate that significantly higher doses may result in fat reduction levels closer to the ones seen in rodent studies. The difficulty lies in scaling rodent doses to human (or canine) doses.

For instance, a dosage range consisting of 0.1% to 1% of the total diet as CLA correlates with 0.2 to 3 grams of CLA per kilo of body weight in mice, but only 0.015 to 0.1 grams per kilo of body weight in humans. This means that the human equivalent of a mouse fed 0.5% of its diet as CLA for a person weighing 60 kilos would be 90 grams of CLA daily!

Of course the safety of a dose that high has never been evaluated in humans, but even if there were no adverse side effects, most people would find taking that many CLA supplements cost-prohibitive.

How can you scale the standard human dose of 3.4 grams CLA to your dog?

Dogs have a faster metabolism than humans so the typically recommended 0.5% of total diet as CLA is going to be a little higher per kilo of body weight for your dog than for you.

A daily dose between 0.08 and 0.1 grams of CLA per kilo of body weight would be appropriate for most dogs.

The Bottom Line

Several dozen studies have been conducted on CLA and weight loss, and the majority do show a small but statistically significant reduction of body fat (on average, 0.09 kg per week in human subjects taking at least 3.4 grams of mixed CLA isomers daily), sometimes accompanied by weight loss of a few pounds and/or gains in lean body mass.

These changes in body composition have been shown to occur independent of diet or exercise.

Canine studies examining CLA and weight loss have been less positive, but there have only been a couple.

While the level of fat reduction provided by CLA may not sound significant, it's important to keep in mind that, on average, people gain a little fat mass every year. CLA supplementation may has the potential to turn that typical annual increase in body fat into an average fat reduction of two to four kilos a year.

At this point, the overwhelming preponderance of the evidence indicates that CLA provides a modest improvement in body composition, achieved primarily by a reduction in fat mass. As for the CLA studies not showing reductions in body fat, weight loss, or lean mass gains, a review of these studies has determined that most of them were too short, too small (i.e., too few participants), or both to produce statistically significant differences between test subjects and control groups given the average expected 0.09 kg per week discrepancy in fat mass.

That said, CLA supplementation is by no means an indispensable component of successful weight loss or maintenance.

In dogs at least, there is evidence to suggest that a high protein, low carbohydrate diet will have a far more profound effect on weight loss and body fat reduction without loss of lean muscle mass than CLA supplements.

Therefore, I am not using this supplemet in my practice.