Is CLA Supplementation Recommended?
No, CLA (Conjugated Linoleic Acid) supplements are not recommended for general use, as there is insufficient evidence of benefit in humans and emerging safety concerns regarding liver function, insulin resistance, and metabolic effects.
Evidence from Clinical Guidelines
The available diabetes and nutrition guidelines do not support the routine use of CLA or similar dietary supplements:
- There is no clear evidence of benefit from vitamin or mineral supplementation in people with diabetes who do not have underlying deficiencies 1
- Routine supplementation with herbal products and micronutrients is not advised due to lack of evidence of efficacy and concern related to long-term safety 1
- The 2024 American Diabetes Association guidelines specifically state that dietary supplementation with vitamins, minerals, herbs, or spices are not recommended for glycemic benefits, and healthcare professionals should inquire about supplement intake and counsel as needed 1
Human Clinical Trial Evidence
Despite widespread marketing claims, the scientific evidence from controlled human trials does not support CLA supplementation:
- Thirteen randomized, controlled trials in humans lasting less than 6 months found little evidence that CLA reduces body weight or promotes repartitioning of body fat and fat-free mass 2
- While CLA appears effective in rodent models for fat loss, these results have not translated to meaningful benefits in human subjects 2, 3
- The effects of CLA on body composition in humans have been "less spectacular" compared to animal studies 4
Safety Concerns
There are documented safety considerations that make CLA supplementation potentially harmful:
- The trans-10, cis-12 CLA isomer may produce liver hypertrophy and insulin resistance via fat redistribution resembling lipodystrophy in both mice and humans 2
- CLA supplementation may adversely affect liver functions, glucose metabolism, and increase oxidative stress 5
- CLA decreases the fat content of both human and bovine milk, which has implications for lactating women 2
- Despite being marketed as natural fatty acids, particular CLA isomers and impurities might induce undesirable side effects 6
Clinical Bottom Line
The evidence clearly indicates that:
- CLA supplements sold as dietary supplements are not effective as weight loss agents in humans and may actually have adverse effects on human health 2
- The limited research available shows no definitive benefit for CLA supplementation in humans, despite extensive animal research 3
- Preparations enriched in specific isomers (c9,t11 and t10,c12) may be preferable to four-isomer preparations if CLA were to be used, though routine use is still not recommended 6
Given the lack of proven efficacy in humans, potential metabolic harms including insulin resistance and liver effects, and the absence of any guideline support for its use, CLA supplementation should be avoided. If patients are currently taking CLA, counsel them to discontinue use and focus instead on evidence-based dietary patterns that emphasize whole foods, as recommended by major diabetes and nutrition guidelines 1.