CLA (Conjugated Linoleic Acid) for Insulin Sensitivity

CLA is sometimes marketed as improving insulin sensitivity, but adult trials don't support it. A 6-month clamp study in overweight adults found no change, and 12 weeks of the trans-10,cis-12 isomer made insulin sensitivity worse in abdominally obese men. In people with type 2 diabetes, a standard 50:50 blend raised fasting glucose by 6.3% in 8 weeks.

A 2023 meta-analysis of 13 trials in people at cardiovascular risk found CLA raised fasting glucose by 4.49 mg/dL, with no change in HOMA-IR or HbA1c. Two findings point the other way: a clamp trial in children with obesity and a meta-analysis of CLA added to exercise. On balance, CLA is not a supplement to take for blood sugar; see insulin sensitivity for options with better evidence.

In a 12-week trial in 60 men with metabolic syndrome, trans-10,cis-12 CLA raised urinary 8-iso-PGF2alpha, a marker of lipid oxidation, by 578% and C-reactive protein by 110% versus placebo. The rise in oxidative stress was independently related to worsening insulin resistance.

In a related trial in 57 abdominally obese men, the same isomer raised proinsulin, the proinsulin:insulin ratio and C-peptide. The rise in proinsulin tracked impaired insulin sensitivity (r = -0.58), a pattern that predicts diabetes and cardiovascular disease.

These are surrogate markers in short trials of men, mostly with a purified isomer that is not sold on its own. A mixed-isomer product over 6 months did not change clamp-measured insulin sensitivity. Animal studies show CLA causing insulin resistance and fatty liver in mice, but mouse effects are far larger than human ones, so the size of the human risk is uncertain.

The adult trials used about 3-3.4 g of CLA a day for 8 weeks to 6 months, either as the trans-10,cis-12 isomer alone or as the common 50:50 mix. No dose has been shown to improve insulin sensitivity in adults, so there is no dose to recommend for this goal.

A 6-month trial in overweight and obese adults measured insulin sensitivity with euglycaemic clamps in 41 completers and found no change with mixed CLA. An 8-week crossover trial in 27 overweight men found no change in insulin sensitivity or other safety markers. A one-year trial in 180 overweight adults found fasting glucose unchanged.

In 32 people with diet-controlled type 2 diabetes, 3 g a day of a 50:50 blend for 8 weeks raised fasting glucose by 6.3% and lowered insulin sensitivity on three indices (P = 0.05), although HDL rose 8%. A 2023 meta-analysis of 13 trials found a 4.49 mg/dL rise in fasting glucose and no change in HOMA-IR or HbA1c.

In children with obesity in a lifestyle programme, CLA improved clamp-measured insulin sensitivity compared with placebo (6.53 vs 5.05 mg/kg/min, P = 0.035), but the abstract does not give the sample size or dose. A separate 7-month trial in overweight children found no change in glucose or insulin. A 2023 meta-analysis of CLA added to exercise found a small fall in insulin resistance (SMD -0.25) compared with exercise alone.

No trial has tested whether CLA changes diabetes risk or long-term glucose control, and the clearest harm signals come from small 8-12-week trials, backed by a small pooled rise in fasting glucose. The isomer question also matters: the clearest harm came from trans-10,cis-12 on its own, which makes up about half of typical supplements.

The insulin-sensitivity findings are themselves the main safety issue. Alongside them, one meta-analysis of 11 trials found CLA raised C-reactive protein by 0.89 mg/L (a 2023 meta-analysis found no change), and the trans-10,cis-12 isomer raised it by 110% in men with metabolic syndrome. Rare liver-injury cases have also been reported with CLA weight-loss products.

CLA has not been studied formally with diabetes medicines. Because it raised fasting glucose in type 2 diabetes, it could work against them.