Given at a dose of 3.2 g/d, CLA produces a modest loss in body fat in humans.

The Deltatrac Metabolic Monitor (DTC), one of the most popular indirect calorimetry systems for measuring resting metabolic rate (RMR) in human subjects, is no longer being manufactured. This study compared five different gas analysis systems to the DTC. Resting metabolic rate was measured by the DTC and at least one other instrument at three study sites for a total of 38 participants. The five indirect calorimetry systems included: MedGraphics CPX Ultima, MedGem, Vmax Encore 29 System, TrueOne 2400, and Korr ReeVue. Validity was assessed using paired t-tests to compare means while reliability was assessed by using both paired t-tests and root mean square calculations with F tests for significance. Within-subject comparisons for validity of RMR revealed a significant difference between the DTC and Ultima. Bland-Altman plot analysis showed significant bias with increasing RMR values for the Korr and MedGem. Respiratory exchange ratio (RER) analysis showed a significant difference between the DTC and the Ultima and a trend for a difference with the Vmax (p = 0.09). Reliability assessment for RMR revealed that all instruments had a significantly larger coefficient of variation (CV) (ranging from 4.8% to 10.9%) for RMR compared to the 3.0 % CV for the DTC. Reliability assessment for RER data showed none of the instrument CV's were significantly larger than the DTC CV. The results were quite disappointing, with none of the instruments equaling the within person reliability of the DTC. The TrueOne and Vmax were the most valid instruments in comparison with the DTC for both RMR and RER assessment. Further testing is needed to identify an instrument with the reliability and validity of the DTC.Correspondence and request for reprints: Dr. Dale Schoeller,

Objective: The incidence of obesity and overweight in the US has increased considerably during the past two decades and currently affects 65% of the adult population. Research has indicated that small, yet irreversible, gains during the holiday season contribute to increases in weight during adulthood. Conjugated linoleic acid (CLA), a naturally occurring dietary fatty acid, has been found to reduce weight gain and dramatically decrease fat mass in animals. Although research in humans has shown inconsistent results, most studies have been of insufficient duration or have utilized body composition methods that are less accurate than the currently accepted criterion. Design: Randomized, double-blind, placebo-controlled study of 3.2 g/day CLA for 6 months. Subjects: Forty healthy, overweight subjects (age: 18-44 years; body mass index: 25-30 kg/m 2 ). Measurements: Body composition by the four-compartment model, resting metabolic rate (RMR) by indirect calorimetry, selfreported physical activity and dietary intake, and blood chemistries were determined at baseline and after 6 months. Body weight was measured monthly during the pre-holiday season (August-October), holiday season (November-December) and post-holiday season (January-March). Adverse events were assessed monthly. Results: Compared to CLA, the placebo group showed a greater rate of weight gain during the holiday season (P ¼ 0.01). Within the placebo group, holiday weight change was significantly greater compared to the pre-holiday period (August-October) (P ¼ 0.03). Six-month change in body composition was improved with CLA compared to placebo (P ¼ 0.02), and body fat was significantly reduced within the CLA group (À1.072.2 kg, P ¼ 0.05). CLA had no effect on RMR, physical activity or dietary intake. The rate of reported negative emotions decreased significantly with CLA, although there was no difference in any other category of adverse event. In comparison to the placebo, CLA did not affect insulin resistance, blood lipids and markers of liver function or markers of inflammation, with the exception of a significant decrease in a biomarker of endothelial dysfunction. Conclusion: CLA supplementation among overweight adults significantly reduced body fat over 6 months and prevented weight gain during the holiday season. Although no adverse effects were seen, additional studies should evaluate the effect of prolonged use of CLA.

CLA supplementation for 7 +/- 0.5 mo decreased body fatness in 6-10-y-old children who were overweight or obese but did not improve plasma lipids or glucose and decreased HDL more than in the placebo group. Long-term investigation of the safety and efficacy of CLA supplementation in children is recommended.

Cooper JA, Watras AC, Shriver T, Adams AK, Schoeller DA. Influence of dietary fatty acid composition and exercise on changes in fat oxidation from a high-fat diet. J Appl Physiol 109: 1011-1018, 2010. First published July 22, 2010; doi:10.1152/japplphysiol.01025.2009.-Acute high-fat (HF) diets can lead to short-term positive fat balances until the body increases fat oxidation to match intake. The purpose of this study was to examine the effects of a HF diet, rich in either monounsaturated or saturated fatty acids (FAs) and exercise, on the rate at which the body adapts to a HF diet. 13 C-labeled oleate and 2 H-labeled palmitate were also given to determine the contribution of exogenous vs. global fat oxidation. Eight healthy men (age of 18 -45 yr; body mass index of 22 Ϯ 3 kg/m 2 ) were randomized in a 2 ϫ 2 crossover design. The four treatments were a high saturated fat diet with exercise (SE) or sedentary (SS) conditions and a high monounsaturated fat diet with exercise (UE) or sedentary (US) conditions. Subjects stayed for 5 days in a metabolic chamber. All meals were provided. On day 1, 30% of energy intake was from fat, whereas days 2-5 had 50% of energy as fat. Subjects exercised on a stationary cycle at 45% of maximal oxygen uptake for 2 h each day. Respiratory gases and urinary nitrogen were collected to calculate fat oxidation. Change from day 1 to day 5 showed both exercise treatments increased fat oxidation (SE: 76 Ϯ 30 g, P ϭ 0.001; UE: 118 Ϯ 31 g, P Ͻ 0.001), whereas neither sedentary condition changed fat oxidation (SS: Ϫ10 Ϯ 33 g, P ϭ not significant; US: 41 Ϯ 14 g, P ϭ 0.07). No differences for dietary FA composition were found. Exercise led to a faster adaptation to a HF diet by increasing fat oxidation and achieving fat balance by day 5. Dietary FA composition did not differentially affect 24-h fat oxidation. saturated fat; mono-unsaturated fat; nonprotein respiratory exchange ratio; stable isotopes THE PREVALENCE OF OBESITY continues to be a leading public health concern in the United States with approximately twothirds of the adult population being classified as overweight or obese (18). The development of obesity is by definition an accumulation of excess body fat due to positive energy balance. This is generally assumed to be caused by periods of positive energy balance resulting in the storage of fat but can also occur from short periods of positive fat balance even under eucaloric feeding conditions if, as hypothesized by Flatt, the weak human leptin system is overpowered by the stronger carbohydrate balance system leading to positive energy balance during the days following the period of positive fat balance (5). We and others have studied conditions that lead to a short-term positive fat balance and have shown that a shift to a high-fat (HF) diet from an average fat diet is not accompanied by an immediate increase in fat oxidation that would match the rate of fat intake even when the diets are eucaloric (6,27,28). The rate of fat oxidation increases only slowly with time, and thus it ca...