Conjugated linoleic acid supplementation for twelve weeks increases lean body mass in obese humans.

Randomized, placebo-controlled, 12-week trial in healthy obese adults aged 18 to 50 years with BMI 30 to 35 kg/m^2, who were nonsmokers and had no chronic disease. Active intervention arms included 16 participants randomized to 3.2 g/day CLA and 16 randomized to 6.4 g/day CLA.

Two oral conjugated linoleic acid (CLA) regimens were tested: 3.2 g/day and 6.4 g/day, using Tonalin capsules containing cis-9, trans-11 and trans-10, cis-12 isomers in a 50:50 ratio. Capsules were taken four times daily for 12 weeks, with placebo as the comparator.

Overall, CLA did not reduce body weight or body fat mass, but the 6.4 g/day dose increased lean body mass. Lean body mass changed by 0.64 kg with 6.4 g/day (P < 0.05) and by 0.65 kg with 3.2 g/day (P = 0.18), while resting energy expenditure and respiratory quotient did not change in any group. The higher dose also increased inflammatory markers, including C-reactive protein (P = 0.03), IL-6 (P = 0.04), and white blood cells (P = 0.005), and altered several laboratory values. Adverse events were reported by 13 participants (27%) overall.

The active arms were small (n = 16 each), the intervention lasted only 12 weeks, and the population was limited to otherwise healthy obese adults, which restricts generalizability. The modest body-composition effect was accompanied by short-term inflammatory and laboratory changes at the higher dose, and long-term clinical relevance was not assessed.