Numerous studies have established that CLA is an effective fat-fighter, at least in animals. Experimental mice, pigs and hamsters that were fed a diet supplemented with CLA all lost significant amounts of body fat compared with their matched controls. Mice appear to be the most responsive to CLA, with treated animals losing 60 per cent of their body fat overall (Am J Clin Nutr, 2007; 85: 1203-11).
CLA also appears to increase lean body mass, which refers to all body tissues (mostly muscle) minus the fat. In one study, mice given CLA not only lost body fat, but also showed a statistically significant increase in lean body mass-up to 14 per cent-compared with the control animals (Lipids, 1997; 32: 853-8).
But would such benefits be seen in people, too? More than 30 clinical trials have attempted to answer this question, but the results have been mixed.
In one randomized, double-blind study, researchers in Norway studied 60 overweight or obese men and women who were given either olive oil (placebo) or one of four doses of CLA (1.7 g/day, 3.4 g/day, 5.1 g/day or 6.8 g/day) for 12 weeks. Compared with the controls, all of those taking CLA-regardless of dosage-showed a reduction in body fat, although the results were most significant for the subjects taking 3.4 g/day or more (J Nutr, 2000; 130: 2943-8).
More recently, supplementation with CLA was tested against safflower oil in a group of obese postmenopausal women with type 2 diabetes. With no other changes to either their diet or exercise habits, the women taking the CLA were able to achieve significant reductions in their total body fat as well as their body mass index (BMI) scores, thus suggesting that CLA may be a useful supplement for encouraging weight loss (Am J Clin Nutr, 2009; 90: 468-76).
CLA has also been tested in athletes and regular exercisers-and showed promising results. In a study of 20 normal-weight adults who exercised for 90 minutes three times a week, those taking CLA (1.8 g/day) lost significantly more body fat (but not body weight) than those taking a placebo (J Int Med Res, 2001; 29: 392-6).
In yet another trial, Canadian researchers reported that CLA supplementation (5 g/day) during resistance training resulted in small, but statistically significant, increases in lean body mass and greater losses of fat mass after seven weeks compared with those taking a placebo (Med Sci Sports Exerc, 2006; 38: 339-48).
Nevertheless, despite these positive reports, other studies have failed to demonstrate any signifi-cant benefit with CLA supplemen-tation. One US study reported no changes in either body fat or lean body mass in women who had taken 3 g/day of CLA for two months (Lipids, 2000; 35: 777-82). Another concluded that CLA had no effect on body mass composition when taken by experienced resistance-trained athletes (J Strength Cond Res, 2002; 16: 325-34).
Only modest effects
This lack of consistency across studies has been blamed on study design differences, such as the dosages used, the duration of the studies, and the age and gender of the participants (Nutr Rev, 2008; 66: 415-21). However, when a recent meta-analysis pooled the results of 18 validated, 'gold-standard', CLA studies-in other words, they were randomized, double-blind and placebo-controlled-to address these confounding variables, the researchers came to the conclusion that CLA does appear to have a beneficial effect on human body composition, with a dose of around 3 g/day resulting in fat loss of about 0.09 kg/week.
Although such an effect seems "modest", it can be important when it accumulates over time, especially in the West where continual and gradual weight gain is the norm (Am J Clin Nutr, 2007; 85: 1203-11).
Nevertheless, whether CLA works or not, there are some concerns that the use of such supplements by overweight people could cause or aggravate insulin resistance, which might then increase the risk of developing diabetes (Am J Clin Nutr, 2007; 85: 1203-11; Circulation, 2002; 106: 1925-9). Other research suggests that CLA might lower levels of 'good' (HDL) cholesterol, while contributing to inflammation and oxidative stress (Crit Rev Food Sci Nutr, 2006; 46: 479-88). However, as with the efficacy studies, the evidence is similarly conflicting. There's no doubt that more research is needed to determine whether CLA supple-mentation is safe, particularly over the long term.
Be that as it may, the US Food and Drug Administration (FDA) has recently approved CLA for its 'Generally Recognized as Safe' category, which means that it can now be used in various foods and beverages (Eur J Nutr, 2009; 48: 409-18).
The bottom line
Although CLA appears to have some impact on body fat, it doesn't appear to pack much of a punch. In addition, considering the cost of supplements-and the questions that still surround their long-term safety-we're all probably better off finding another way to fight fat.
WDDTY VOL 21 NO 1