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| CLA - A muscle specific glucose repartitioner for lean & athletic individuals? |
In their latest article in the scientific journal Nutrition Research scientists from the Universidad Nacional del Litoral report that dietary CLA increases the glucose utilization under basal conditions and prevents the palmitate-induced inhibition of glucose uptake and incorporation that is stimulated by insulin.
Interestingly, Farina et al. also found that the beneficial effects of CLA were significantly more pronounced and without significant side effects in rodents who had been deprived of all omega-6 fatty acids - including CLA - before.
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Unfortunately, the provision of conjugated linoleic acid did also have negative effects on some aspects of glucose control. For example, Farina et al. observed a significant reduction in insulin response capacity that may - in the long run - compromise their ability to handle glucose.
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| Figure 1: CLA increases basal glucose intake and glycogen synthesis - the latter yet only when the rodent diet does not contain any linoleic acid (-LA), if it's not there is also a significant negative effect on insulin stimulated glucose uptake in the soleus muscle of the rodents (Farina. 2014) |
Now, rodent studies are one thing, human studies are - at least according to some experts - something totally different. Against that background you will probably be more interested in the results of a recent study from the
National Taichung University of Education in Korea. The authors, Jung-Piao Tsao, Su-Fen Liao, Mallikarjuna Korivi, Chien-Wen Hou, Chia-Hua Kuo, Hsueh-Fang Wang & I-Shiung Cheng, were able to show that the provision of a standard CLA supplement containing a 50:50 mixture of trans-10 cis-12 and cis-9 trans-11 isomers at a dosage of 3.8 g CLA per day for 8 week lead to significant can enhance the glycogen resynthesis rate in exercised human skeletal muscle.
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| Figure 2: Glycogen levels (a) and differences (b) in vastus lateralis of human skeletal muscle after a single bout of exercise in CLA and placebo trials (Tsao. 2014) |
As you can see in
Figure 2 this advantage was not just statistically significant, but appears to be high enough to be physiologically relevant. What is not clear, though, is whether the increased glycogen uptake of the vastus lateralis is a direct or indirect benefit - after all, previous studies indicate that CLA can decrease the glucose uptake in adipocytes (=fat cells | Perez-Matute. 2007). The increase in glycogen synthesis in the muscle of the 12 male young college students (aged 22.56 ± 0.45 years, body mass index 23.35 ± 0.79 and VO2 max 49.4 ± 1.67 ml/kg/min) who participated in the study may be a simple results of an increased relative glucose availability - or, as a supplement producer would call it to sell their supplements: "Glucose repartitioning"!
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| Figure 3: GLUT4 protein level (a) and P-Akt/Akt ratio (b) in vastus lateralis of human skeletal muscle after a single bout of exercise in CLA and placebo trials (Tsao. 2014). |
A claim that is supported by the data in
Figure 3, which indicate that the increased glucose uptake and subsequent increase in glycogen synthesis is a result of a CLA-induced increase in GLUT-4 glucose transporter expression, of which the data in
Figure 2 also tells us that it occurred before the regular exercise-induced increase in GLUT-3 expression.
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Bottom line: Even if we take into consideration that this "study has limitation with lack of maintenance of the dietary recall or training diary for all participants," the result are an impressive argument in favor of CLA supplementation in athletes in whom the previously mentioned negative effects on insulin response capacity may not be physiologically relevant - if it occurs at all.
And still, Tsao et al. are right: "These findings suggest that CLA could consider as an effective ergogenic aid to improve the muscle glycogen levels and endurance capacity. However, it is necessary to monitor the whole-body glucose homeostasis to avoid possible adverse effects of CLA [..] on glucose metabolism" (Tsao. 2014) |
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References:
- Fariña, Ana C., et al. "Conjugated linoleic acid improves glucose utilization in the soleus muscle of rats fed linoleic acid–enriched and linoleic acid–deprived diets." Nutrition Research (2014).
- Perez-Matute, P., et al. "Conjugated linoleic acid inhibits glucose metabolism, leptin and adiponectin secretion in primary cultured rat adipocytes." Molecular and cellular endocrinology 268.1 (2007): 50-58.
- Ritsche, Kevin, et al. "Acute Exercise-Induced Growth Hormone is Attenuated in Response to Short-Term, High-Intensity Exercise Training." (2014).
- Tsao, Jung-Piao, et al. "Oral conjugated linoleic acid supplementation enhanced glycogen resynthesis in exercised human skeletal muscle." Journal of sports sciences ahead-of-print (2014): 1-9.
