Background: Conjugated linoleic acid (CLA) has been shown to be an effective supplement for reducing fat mass in animals, whereas results in humans have been inconsistent. Objective: This is a meta-analysis of human studies in which CLA was provided as a dietary supplement to test its efficacy in reducing fat mass. Design: We searched the PubMed database (National Library of Medicine, Bethesda, MD) and references from the resulting search to identify studies in which CLA was provided to humans in randomized, double-blinded, placebo-controlled trials and in which body composition was assessed by using a validated technique. Results: We identified 18 eligible studies. Of these, 3 were single-isomer studies, and results comparing CLA isomers were inconclusive. We compared the length of treatment by using studies in which a mixture of purified isomers were used and those in which purified trans-10,cis-12 isomers were used. This comparison indicated that the effect of CLA was linear for up to 6 mo and then slowly approached an asymptote at 2 y. An analysis of the dose effect indicated that fat loss compared with placebo was −0.024 kg · g CLA⁻¹ · wk⁻¹ (P = 0.03). After adjustment to the median dose of 3.2 g CLA/d, CLA was effective and produced a reduction in fat mass for the CLA group alone (0.05 ± 0.05 kg/wk; P < 0.001) and for the CLA group compared with placebo (0.09 ± 0.08 kg/wk; P < 0.001) Conclusion: Given at a dose of 3.2 g/d, CLA produces a modest loss in body fat in humans.

Although obesity has multiple etiologies, an overlooked possibility is an infectious origin. We previously identified two viruses, SMAM-1, an avian adenovirus (Ad), and Ad-36, a human adenovirus, that produce a syndrome of visceral obesity, with paradoxically decreased serum cholesterol and triglycerides in chickens and mice. In the two studies presented in this paper, we used nonhuman primates to investigate the adiposity-promoting potential of Ad-36. In study 1, we observed spontaneously occurring Ad-36 antibodies in 15 male rhesus monkeys, and a significant longitudinal association of positive antibody status with weight gain and plasma cholesterol lowering during the 18 mo after viral antibody appearance. In study 2, which was a randomized controlled experiment, three male marmosets inoculated with Ad-36 had a threefold body weight gain, a greater fat gain and lower serum cholesterol relative to baseline (P <0.05) than three uninfected controls at 28 wk postinoculation. These studies illustrate that the adiposity-promoting effect of Ad-36 occurs in two nonhuman primate species and demonstrates the usefulness of nonhuman primates for further evaluation of Ad-36–induced adiposity.

Objective biomarkers are needed to assess adherence to vegetable and fruit intervention trials. Blood carotenoids are considered the best biomarker of vegetable and fruit intake, but collecting blood is invasive and the analyses are relatively expensive for population studies. Resonance Raman spectroscopy (RRS) is an innovative method for assessing carotenoids in skin noninvasively. Our objective was to compare blood carotenoid concentrations with skin carotenoid assessments by RRS during a controlled feeding intervention. Twenty-nine participants consumed low-carotenoid diets (6 wk, phases 1 and 3), a provided diet containing 6-cup equivalents (1046 g/d) of vegetables and fruit (8 wk, phase 2), and usual diet (final 8 wk, phase 4). At baseline, skin and plasma total carotenoid values were correlated (r = 0.61, P < 0.001). Skin and plasma carotenoid values decreased (P < 0.001) 36% and 30%, respectively, from baseline to the end of phase 1 and then increased (P < 0.001) by >200% at the end of phase 2. Plasma carotenoids returned to baseline concentrations by the middle of phase 3 and skin carotenoid concentrations by the middle of phase 4. Skin carotenoid status predicted plasma values by using a mixed linear model including all time points (r = 0.72, P < 0.001), which indicates that changes in skin carotenoid status closely follow changes in plasma across a broad range of intakes. At the individual level, skin carotenoids predicted plasma values (r = 0.70, P < 0.001) over all time points. Skin carotenoid status assessed by resonance Raman spectroscopy is a noninvasive, objective biomarker of changes in vegetable and fruit intake.