Influence of dietary fatty acid composition and exercise on changes in fat oxidation from a high-fat diet.

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 mono-unsaturated 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 ± 3 kg/m(2)) were randomized in a 2 × 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 ± 30 g, P = 0.001; UE: 118 ± 31 g, P < 0.001), whereas neither sedentary condition changed fat oxidation (SS: -10 ± 33 g, P = not significant; US: 41 ± 14 g, P = 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.

Use of an automated chromium reduction system for hydrogen isotope ratio analysis of physiological fluids applied to doubly labeled water analysis.

The doubly labeled water method is commonly used to measure total energy expenditure in free-living subjects. The method, however, requires accurate and precise deuterium abundance determinations, which can be laborious. The aim of this study was to evaluate a fully automated, high-throughput, chromium reduction technique for the measurement of deuterium abundances in physiological fluids. The chromium technique was compared with an off-line zinc bomb reduction technique and also subjected to test-retest analysis. Analysis of international water standards demonstrated that the chromium technique was accurate and had a within-day precision of <1 per thousand. Addition of organic matter to water samples demonstrated that the technique was sensitive to interference at levels between 2 and 5 g l(-1). Physiological samples could be analyzed without this interference, plasma by 10000 Da exclusion filtration, saliva by sedimentation and urine by decolorizing with carbon black. Chromium reduction of urine specimens from doubly labeled water studies indicated no bias relative to zinc reduction with a mean difference in calculated energy expenditure of -0.2 +/- 3.9%. Blinded reanalysis of urine specimens from a second doubly labeled water study demonstrated a test-retest coefficient of variation of 4%. The chromium reduction method was found to be a rapid, accurate and precise method for the analysis of urine specimens from doubly labeled water.

No safe haven: a study of violence exposure in an urban community.

OBJECTIVE: To examine levels of violence exposure and reports of feeling unsafe in relation to psychological and behavioral characteristics for a general population sample of youths from an urban setting. METHOD: A comprehensive survey of high-risk behaviors, attitudes, indicators of adaptive behavior, and daily involvements was administered to a sample of 2,248 students in the 6th, 8th, and 10th grades in an urban public school system. RESULTS: More than 40% of the youths surveyed reported exposure to a shooting or stabbing in the past year, and 74% reported feeling unsafe in one or more common environmental contexts. Multiple regression analyses indicated significant relationships between violence exposure/feeling unsafe and a set of indicators of psychological and behavioral adaptation and expressed attitudes. CONCLUSIONS: These results attest to the picture of violence as a common fact of inner-city life and to the demand that is placed on urban youths to accommodate in their psychological development to chronic threat and lack of safety.

Involvement in multiple problem behaviors of young urban adolescents.

This paper examines four areas of "problem behavior" (i.e., delinquency, high-risk sexual behavior, school failure, and substance abuse) in a sample of urban sixth and seventh grade students. We report descriptive statistics regarding rates of problem behaviors in each of the four categories and examine their interrelationships. The results suggest that the prevalence of problem behaviors in this sample is substantial. Data show a high degree of co-occurrence among problem behaviors in different areas, although many individuals also exhibit more limited involvement. These results underscore the importance of studying younger adolescents in poor, urban communities who may have different patterns and rates of problem behavior involvement than older youth from other contexts. The data also suggest that efforts to prevent high-risk involvements for youth in poor, urban communities should be broad-ranging and be implemented prior to middle school.