Directional-sum test for nonparametric Behrens-Fisher problem with applications to the dietary intervention trial

For a nonparametric Behrens-Fisher problem, a directional-sum test is proposed based on division-combination strategy. A one-layer wild bootstrap procedure is given to calculate its statistical significance. We conduct simulation studies with data generated from lognormal, t and Laplace distributions to show that the proposed test can control the type I error rates properly and is more powerful than the existing rank-sum and maximum-type tests under most of the considered scenarios. Applications to the dietary intervention trial further show the performance of the proposed test.

Achievement of the Targets of the 20-Year Infancy-Onset Dietary Intervention—Association with Metabolic Profile from Childhood to Adulthood

The Special Turku Coronary Risk Factor Intervention Project (STRIP) is a prospective infancy-onset randomized dietary intervention trial targeting dietary fat quality and cholesterol intake, and favoring consumption of vegetables, fruit, and whole-grains. Diet (food records) and circulating metabolites were studied at six time points between the ages of 9–19 years (n = 549–338). Dietary targets for this study were defined as (1) the ratio of saturated fat (SAFA) to monounsaturated and polyunsaturated fatty acids (MUFA + PUFA) < 1:2, (2) intake of SAFA < 10% of total energy intake, (3) fiber intake ≥ 80th age-specific percentile, and (4) sucrose intake ≤ 20th age-specific percentile. Metabolic biomarkers were quantified by high-throughput nuclear magnetic resonance metabolomics. Better adherence to the dietary targets, regardless of study group allocation, was assoiated with higher serum proportion of PUFAs, lower serum proportion of SAFAs, and a higher degree of unsaturation of fatty acids. Achieving ≥ 1 dietary target resulted in higher low-density lipoprotein (LDL) particle size, lower circulating LDL subclass lipid concentrations, and lower circulating lipid concentrations in medium and small high-density lipoprotein subclasses compared to meeting 0 targets. Attaining more dietary targets (≥2) was associated with a tendency to lower lipid concentrations of intermediate-density lipoprotein and very low-density lipoprotein subclasses. Thus, adherence to dietary targets is favorably associated with multiple circulating fatty acids and lipoprotein subclass lipid concentrations, indicative of better cardio-metabolic health.

Best (but oft-forgotten) practices: sample size and power calculation for a dietary intervention trial with episodically consumed foods

ABSTRACT Dietary interventions often target foods that are underconsumed relative to dietary guidelines, such as vegetables, fruits, and whole grains. Because these foods are only consumed episodically for some participants, data from such a study often contains a disproportionally large number of zeros due to study participants who do not consume any of the target foods on the days that dietary intake is assessed, thus generating semicontinuous data. These zeros need to be properly accounted for when calculating sample sizes to ensure that the study is adequately powered to detect a meaningful intervention effect size. Nonetheless, this issue has not been well addressed in the literature. Instead, methods that are common for continuous outcomes are typically used to compute the sample sizes, resulting in a substantially under- or overpowered study. We propose proper approaches to calculating the sample size needed for dietary intervention studies that target episodically consumed foods. Sample size formulae are derived for detecting the mean difference in the amount of intake of an episodically consumed food between an intervention and a control group. Numerical studies are conducted to investigate the accuracy of the sample size formulae as compared with the ad hoc methods. The simulation results show that the proposed formulae are appropriate for estimating the sample sizes needed to achieve the desired power for the study. The proposed method for sample size is recommended for designing dietary intervention studies targeting episodically consumed foods.

Mango Intake Affects Skin Wrinkles in Postmenopausal Women

Objectives To investigate the effects of mango intake on skin wrinkles (SW) and skin carotenoids (C) in postmenopausal women. Methods A randomized, two-arm parallel study was conducted to assess 16 weeks (wk) of mango intake on SW development in the left and right lateral canthus (crow's feet) of healthy postmenopausal women, aged 50 to 70. Participants consumed either 85 g (0.5 cup) or 250 g (1.5 cup) of mangos, 4 times/wk. High-resolution facial images were captured at baseline, 8 wk, and 16 wk. SW were separated into three categories: Average (A), Fine (F), and Emerging (E) with indices of length (L), width (W) and severity (S). F lines were defined as medium contrast wrinkles, while E lines were low contrast wrinkles, both at a minimum length of 2.6 mm. The A SW was the mean contrast of all pixels of a SW. S was calculated as contrast multiplied by L. C values were measured with Raman spectroscopy and participants were separated into low baseline carotenoid (&lt;383 nm; LBC) or high baseline carotenoid (&gt;383 nm; HBC) groups. Participants started the study either in the Fall (Sep 1 – Nov 30) or Winter (Dec 1 – Feb 28) season. SW changes with mango intake were analyzed using One Way ANCOVA with the change in carotenoids, baseline BMI and season as covariates. Results Among women in the LBC group, SW L was differentially affected by mango intake, with an increase in L in the 250 g group compared to decreased L in the 85 g group (left AL: 8wk, P = 0.026 and 16 wk, P = 0.014; left FL: 8 wk, P = 0.009 and 16 wk, P = 0.048). These specific SW were not significantly changed in the HBC group. A positive correlation between C and left FS (r = 0.434, P = 0.027) was seen in 85 g group, while C was positively correlated with SW L and S with 250 g of intake. This includes left AL (r = 0.407, P = 0.039), left FS (r = 0.381, P = 0.054) and right ES (r = 0.479, P = 0.008). After 16 wk, women with LBC had a significant increase in C (P = 0.017) with 250 g compared to 85 g of mango intake. No changes in C were noted for the HBC group (P = 0.909). Conclusions Among women with baseline LBC, reduction in SW were observed with 85 g, but not 250 g, of mango intake. Confirmation of these results in a controlled dietary intervention trial are warranted. Funding Sources National Mango Board.

Associations between the proportion of fat-free mass loss during weight loss, changes in appetite, and subsequent weight change: results from a randomized 2-stage dietary intervention trial

ABSTRACT Background Dynamic changes in body composition which occur during weight loss may have an influential role on subsequent energy balance behaviors and weight. Objectives The aim of this article is to consider the effect of proportionate changes in body composition during weight loss on subsequent changes in appetite and weight outcomes at 26 wk in individuals engaged in a weight loss maintenance intervention. Methods A subgroup of the Diet, Obesity, and Genes (DiOGenes) study (n = 209) was recruited from 3 European countries. Participants underwent an 8-wk low-calorie diet (LCD) resulting in ≥8% body weight loss, during which changes in body composition (by DXA) and appetite (by visual analog scale appetite perceptions in response to a fixed test meal) were measured. Participants were randomly assigned into 5 weight loss maintenance diets based on protein and glycemic index content and followed up for 26 wk. We investigated associations between proportionate fat-free mass (FFM) loss (%FFML) during weight loss and 1) weight outcomes at 26 wk and 2) changes in appetite perceptions. Results During the LCD, participants lost a mean ± SD of 11.2 ± 3.5 kg, of which 30.4% was FFM. After adjustment, there was a tendency for %FFML to predict weight regain in the whole group (β: 0.041; 95% CI: −0.001, 0.08; P = 0.055), which was significant in men (β: 0.09; 95% CI: 0.02, 0.15; P = 0.009) but not women (β: 0.01; 95% CI: −0.04, 0.07; P = 0.69). Associations between %FFML and change in appetite perceptions during weight loss were inconsistent. The strongest observations were in men for hunger (r = 0.69, P = 0.002) and desire to eat (r = 0.61, P = 0.009), with some tendencies in the whole group and no associations in women. Conclusions Our results suggest that composition of weight loss may have functional importance for energy balance regulation, with greater losses of FFM potentially being associated with increased weight regain and appetite. This trial was registered at clinicaltrials.gov as NCT00390637.