Side effects of CLA supplement

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CLA may increase oxidative stress in athletes

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Conjugated linoleic acid (CLA) is a popular nutritional supplement among athletes seeking to lose body fat, and there’s also some evidence that it may help maintain lean muscle mass. But new research on mice carried out by Italian scientists suggests that CLA supplementation could be something of a double-edged sword.
In the study, CLA was administered to young, healthy mice to see how it affected body weight and muscle growth following exercise and also the turnover of blood cells associated with oxidative stress (increased oxidative stress indicates increased damage at the cellular level as a result of exercise – a bad thing). The mice were split into three groups; one group underwent six weeks of endurance training (using a treadmill) at gradually increasing durations and speeds. A second group underwent the same training protocol, but were also given 0.425mgs per day of CLA for the entire training period. The third group served as controls – they neither trained nor received CLA. The results were as follows:
Compared to the controls, both groups of trained mice experienced a significant decrease in body weight and a consistent increase in muscle mass;
The trained mice receiving the CLA didn’t lose any more body fat than those receiving no CLA, but they did experience significantly more lean muscle mass gain;

Both groups of trained mice experienced an increased turnover of red blood cells, but the CLA-fed mice also experienced a significant drop in the levels of circulating cells called lymphocytes – an indication of significantly increased oxidative stress in this group.

It’s important to remember that results of animal studies aren’t always mirrored by follow-up studies carried out in humans. However, the authors of this study go on to caution: ‘These findings suggest that CLA may improve the performance of endurance athletes by increasing muscle hypertrophy, and, at the same time, that it may cause oxidative stress damage. Despite the positive increase in muscle size [hypertrophy] claimed by the pharmaceutical companies, we suggest that endurance athletes and those looking to improve their own skeletal muscle mass refrain from CLA supplementation, because it seems to intensify the oxidative stress caused by exhaustive exercise.’
J Strength Cond Res 2007; 21(1):193-198