What is CLA?
Conjugated linoleic acid refers to a mixture of positional and geometric isomers of linoleic acid (18 carbons) with two double bonds separated by one single bond. Further, each double bond can be in the cis or trans configuration. Therefore, many forms of CLA are possible (Sehat et al., 1999; Yurawecz et al., 1999a, b), but the main form present in foods from ruminant animals is the cis- 9, trans-11 CLA, which was recently given the trivial name rumenic acid (RA; Kramer et al., 1998a). The presence of this fatty acid in ruminant products arises from its formation in the rumen. Conjugated linoleic acid is unique among the naturally occurring anticarcinogens in that it is potent at extremely low levels and present in foods from ruminant animals.
Benefits of CLA Supplementation
“CLA is found to decrease fat mass and increase lean body mass in several animal models. Similar results have also been obtained in some human studies. We hypothesize that supplementing low dietary CLA particularly during midlife or late age will prevent sarcopenia and osteoporosis, thereby decreasing falls and fractures, and preventing both morbidity and mortality in the elderly.”
“Researchers in the College of Agricultural and Life Sciences have been studying CLA since the 1970s. During the past two decades, Michael Pariza, director emeritus of UW–Madison’s Food Research Institute, has discovered a number of health-promoting properties in CLA, including the ability to fight cancer and reduce heart disease. Along with animal sciences professor Mark Cook, Pariza has found that CLA can help reduce body fat.”
“Some pre-clinical studies showed that 10-CLA reduces fat uptake into adipocytes by lowering the activities of lipoprotein lipase and Δ9-desaturase, instead of enhancing lipolysis. Based upon this background, a few clinical investigations were made on the effect of CLA on fat-mass regain after weight loss – with an assumption that CLA could block body fat gain.”
Effect of CLA on exercise
Exercising individuals often add nutritional supplements to their diet to accelerate the increase in muscle mass and strength from heavy resistance-exercise training. Some short- and long-term studies employing high doses of CLA in healthy and obese, sedentary and exercised adults have shown beneficial effects of CLA in reducing fat mass and increasing LBM.
“A daily supplementation of 1.8 mg CLA for 12 wk reduced body fat (measured using near infrared lights); but not body weight in healthy exercising humans of normal body weight, compared to the placebo group who received hydrogel.”
“CLA also gained attention among resistance-trained athletes as agents for reducing catabolism, body fat and improving muscle mass during training, but supplementation of 6 g/d of CLA coupled with 3 g/d of FAs in the formulation (Tonalin®) against 9 g/d olive oil placebo for 28 d showed no significant ergogenic value, as it did not significantly affect changes in total body mass, fat-free mass, fat mass, percent body fat, bone mass, strength, serum substrates, or general markers of catabolism during training.”
Dietary Sources of CLA for Humans
Dairy products are the major dietary source of CLA, but CLA is also found in the meat from ruminants. Of the many different isomers of CLA, 85 to 90% are the biologically active (cis 9, trans 11) anti-carcinogen form. Concentrations of CLA are generally expressed as milligrams (mg) of CLA per gram (g) of fat. Most dairy products contain about 3.5 to 6.0 mg/g fat, or 0.35 to 0.65% of the milk fat (Table 1).
Some of the clinical studies suggested a positive association of the intake of 3.4 to 6.8 g/d isomeric mixture of CLA (mainly 9- and 10-CLA) supplementation for 12 wk for overweight and obese volunteers (BMI, 25 to 35 kg/m2) of either sex in reducing the body fat mass (BFM) significantly.
In another study, supplementation of 4.2 g/d isomeric mixture of 9- and 10-CLAs for 4 wk decreased the sagittal abdominal diameter in obese individuals; but, body weight and BMI remained unaffected.
In a different study comprising 60 overweight or obese volunteers including men and women who received 3.4 g/d CLA for 12 wk showed reduction in the mean weight and mean BMI, and these results indicated that CLA in the given dose was safe in healthy populations with regard to the safety parameters investigated.
It seems that the use of weight-loss supplements containing 9-CLA, 10-CLA or both as mixture is worrying, because most of the clinical studies presented in the previous sections provide mostly neutral or inconclusive results with very few favorable impacts (Table 5). In association with this, a few studies reported some adverse effects such as oxidative stress, insulin resistance, gastrointestinal irritation, etc., but no serious adverse effects were reported at the time of intervention except the relapse of asthma on consumption of 3.4 g/d of CLA. Therefore, most of these side effects could be categorized as ‘mild to moderate’.
Conjugated linoleic acids (CLA) are a family of at least 28 isomers of linoleic acid found mostly in the meat and dairy products derived from ruminants. CLAs can be either cis- or trans-fats and the double bonds of CLAs are conjugated and separated by a single bond between them. CLA is marketed as a dietary supplement on the basis of its supposed health benefits.
Conjugated linoleic acid is both a trans fatty acid and a cis fatty acid. The cis bond causes a lower melting point and ostensibly also the observed beneficial health effects. Unlike other trans fatty acids, it may have beneficial effects on human health. CLA is conjugated, and in the United States, trans linkages in a conjugated system are not counted as trans fats for the purposes of nutritional regulations and labeling. CLA and some trans isomers of oleic acid are produced by microorganisms in the rumens of ruminants. Non-ruminants, including humans, produce certain isomers of CLA from trans isomers of oleic acid, such as vaccenic acid, which is converted to CLA by delta-9-desaturase.
In healthy humans, CLA and the related conjugated linolenic acid (CLNA) isomers are bioconverted from linoleic acid and alpha-linolenic acid, respectively, mainly by Bifidobacterium bacteria strains inhabiting the gastrointestinal tract. However, this bioconversion may not occur at any significant level in those with a digestive disease, gluten sensitivity, and/or dysbiosis.