Evaluation of a self-help dietary intervention in a primary care setting.

BACKGROUND. Dietary intervention to reduce fat consumption and increase fiber consumption has been recommended by the National Cancer Institute, but there is little evidence concerning the effectiveness of self-help materials. The purpose of this study was to evaluate such self-help materials, introduced by a nurse in a primary care setting. METHODS. A randomized controlled trial involving 242 subjects was conducted in two primary care clinics in Chapel Hill, NC, in 1987. Changes in fat and fiber consumption in the intervention and control groups during the 3-month interval between interviews were compared using analysis of covariance. RESULTS. The estimated reduction in fat was 3.8g larger for the intervention group than for the control group, but the confidence interval included zero. For those individuals who had some responsibility for meal preparation there was a larger difference (-6.9g) in favor of the intervention group, although the difference using calorie-adjusted values was -3.8g with a 95% confidence interval (-7.1, -0.4). The differences for fiber change were smaller. CONCLUSIONS. We found significant small but consistent differential changes associated with a minimal self-help intervention, but we cannot rule out the possibility of some response bias. Nonetheless, this study demonstrates that the use of self-help materials for dietary change is feasible, and may be effective.     

Validity of reported energy expenditure and reported intake of energy, protein, sodium and potassium in rheumatoid arthritis patients in a dietary intervention study

OBJECTIVES: The aim of the study was to validate a diet history interview (DHI) method and a 3-day activity registration (AR) with biological markers. SUBJECTS AND STUDY DESIGN: The reported dietary intake of 33 rheumatoid arthritis patients (17 patients on a Mediterranean-type diet and 16 patients on a control diet) participating in a dietary intervention study was assessed using the DHI method. The total energy expenditure (TEE), estimated by a 3-day AR, was used to validate the energy intake (EI). For nine subjects the activity registration was also validated by means of the doubly labelled water (DLW) method. The excretion of nitrogen, sodium and potassium in 24-h urine samples was used to validate the intake of protein, sodium and potassium. RESULTS: There was no significant difference between the EI and the TEE estimated by the activity registration or between the intake of protein, sodium and potassium and their respective biological markers. However, in general, the AR underestimated the TEE compared to the DLW method. No significant differences were found between the subjects in the Mediterranean diet group and the control diet group regarding the relationship between the reported intakes and the biological markers. CONCLUSION: The DHI could capture the dietary intake fairly well, and the dietary assessment was not biased by the dietary intervention. The AR showed a bias towards underestimation when compared to the DLW method. This illustrates the importance of valid biological markers.     

Analysing repeated measurements data: a practical comparison of methods.

A variety of methods are available for analysing repeated measurements data where the outcome is continuous. However, there is little information on how established methods, such as summary statistics and repeated measures analysis of variance (RMAOV), compare in practice with methods that have become available to applied statisticians more recently, such as marginal models (based on generalized estimating equation methodology) and multilevel models (that is, hierarchical random effects models). The aim of this paper is to exemplify the use of these methods, and directly compare their results by application to a clinical trial data set. The focus is on practical aspects rather than technical issues. The data considered were taken from a clinical trial of treatments for asthma in 240 children, in which a baseline and four post-randomization measurements of outcomes were taken. The simplicity of the method of summary statistics using the post-randomization mean of observations provided a useful initial analysis. However, fixed time effects or treatment-time interactions cannot be included in such an analysis, and choice of appropriate weighting when there is substantial missing data is problematic. RMAOV, marginal models and multilevel models generally provided similar estimates and standard errors for the treatment effects, although in one example with a relatively complex variance structure the marginal model produced less efficient estimates. Two advantages of multilevel models are that they provide direct estimates of variance components which are often of interest in their own right, and that they can be naturally extended to handle multivariate outcomes.     

Comparison of dietary assessment methods in a low-fat dietary intervention program

The food frequency questionnaire (FFQ) is commonly utilized for assessment of dietary fat intake, but its validity among individuals following a low-fat diet is unclear. We evaluated the agreement of nutrient estimates derived from FFQ, 24-h recall, and 3-day food records obtained from 104 participants in a randomized trial of a low-fat dietary intervention for women at elevated breast cancer risk. Comparisons were made for total calories, percent calories from fat, and total fat after 1 yr. Correlation was assessed using standard methods based on a null hypothesis of no agreement between instruments as well as by a methodology based on a null hypothesis that the instruments should be in agreement. With the use of standard methods, FFQ estimates for women on the low-fat diet were significantly correlated to records only for percent calories from fat (r = 0.39), whereas recall and record estimates were significantly correlated for all three dietary variables. Using the new method, we found no significant correlation between FFQ and either recalls or records for women following a low-fat diet but significant correlation between recall and record estimates for total calories (r = 0.67). Traditional correlation testing may overestimate the extent of agreement in dietary instruments among women on a low-fat diet. We found empirical support for the nontraditional method.     

Maintenance of a low-sodium, high-carotene and -vitamin C diet after a 1-year dietary intervention: the Hiraka dietary intervention follow-up study

BACKGROUND: The importance of dietary modification for disease prevention is widely accepted. The difficulty of implementing and sustaining long-term changes is also well documented. Nevertheless, a few studies have attempted to achieve significant dietary change for extended periods. METHODS: The Hiraka Dietary Intervention Study was a community-based randomized cross-over trial designed to develop an effective dietary modification tool and system in an area with high mortality for stomach cancer and stroke in 1998-2000. The main study subjects were 550 healthy volunteers, who were randomized into two groups and given tailored dietary education aimed at decreasing the intake of sodium and increasing that of carotene and vitamin C in either the first or second year. Four (first intervention group) and three (second intervention group) years after the intervention ended, 308 subjects were selected for this follow-up dietary survey. RESULTS: The low-sodium, high-vitamin C and -carotene diet was maintained with only a small, nonsignificant reversal from post-intervention to follow-up (P = 0.082-0.824). Significant changes from pre-intervention to follow-up were also maintained (P < 0.01). CONCLUSION: This dietary intervention program was maintained well over 4 years after the termination of the intervention sessions.     

Measurement characteristics of 2 different self-monitoring tools used in a dietary intervention study

OBJECTIVE: To examine the measurement characteristics of 2 self-monitoring tools, a food diary and fat scan, used in the dietary intervention of the Women's Health Trial: Feasibility in Minority Populations study. DESIGN: Comparison of fat intake reported on the self-monitoring tools to a criterion measure of fat intake, specifically the mean of a food frequency questionnaire and a 4-day food record. The main outcome measures were differences in fat grams and correlations between each of the self-monitoring tools and the criterion measure. SUBJECTS/SETTING: Six-month postrandomization data from 313 women aged 50 to 79 years who participated in the intervention group of the Women's Health Trial: Feasibility in Minority Populations study. RESULTS: Both self-monitoring tools underestimated fat intake compared to the criterion measure, the food diary by 9 g and the fat scan by 6 g. The self-monitoring instruments were better than chance at detecting a low-fat dietary pattern, however, and did not differ from each other in their ability to do so. APPLICATIONS/CONCLUSIONS: The self-monitoring tools were modestly precise as measures of fat intake, but neither was sufficiently accurate to be reliable as a sole assessment of dietary adherence. Dietetics professionals are encouraged to assess the measurement properties of self-monitoring tools to use them appropriately in supporting dietary changes.     

Occupational styrene exposure and hearing loss: a cohort study with repeated measurements

Objective

Associations between occupational styrene exposure and impairment of hearing function were investigated, guided by three questions: are there hearing losses concerning high frequency and standard audiometric test? Are there dose–response relationships and measurable thresholds of effects? Are there signs of reversibility of possible effects if the workers are examined during times of improvement from their work?

Methods

A group of workers from a boat building plant, some of whom were laminators, were examined in subgroups of current low (n = 99, mean mandelic acid MA + phenylglyoxylic acid PGA = 51 mg/g creatinine), medium (n = 118, mean 229 mg/g creat.) and high (n = 31, mean 970 mg/g creat.) exposure to styrene. In addition, subgroups chronically exposed to high-long (n = 17) and low-short (n = 34) styrene levels were analysed. The examinations were carried out during normal work days and during the company holidays. Hearing thresholds and transient evoked otoacoustic emissions (TEOAE) were measured. Statistics included multiple co-variance analyses with repeated measures, linear regressions, and logistic regressions.

Results

The analyses of all participants demonstrated no clear exposure effects. Particularly no sufficient proof of dose–response relationship measured against parameters of current exposure (MA + PGA, styrene/blood) and of chronic exposure (cumulative and average life time exposure resp.) was found. The analyses of groups exposed to high levels show elevated thresholds at frequencies up to 1,500 Hz among the subgroup exposed to high styrene levels (e.g. 40–50 ppm as average) for a longer period of time (e.g. more than 10 years). These participants also demonstrated signs of “improvement” at frequencies above 2,000 Hz during work holidays, when they were not exposed to styrene. A significantly elevated odds ratio for cases of hearing loss (more than 25 dB (A) in one ear, 3,000–6,000 Hz) was found among the group exposed to high levels (above 30 ppm as average) for a longer period of time (more than 10–26 years). The measurements of TEOAE did not exhibit significant results related to exposure.

Conclusion

This study found, that chronic and intensive styrene exposure increases the hearing thresholds. At levels of about 30–50 ppm as an average inhaled styrene per work day over a period of about 15 years with higher exposure levels above 50 ppm in the past, an elevated risk for impaired hearing thresholds can be expected. The formerly published results on ototoxic effects below 20 ppm could not be confirmed. With few exceptions (at frequencies of 1,000 and 1,500 Hz) no dose–response relationship between threshold and exposure data was found. Improvements of hearing thresholds during work- and exposure-free period are possible.     

Occupational styrene exposure and neurobehavioural functions: a cohort study with repeated measurements

Objective  Associations between occupational styrene exposure and cognitive as well as psychomotor functions were investigated with a view to answering three questions: (1) are the published results for neurobehavioural impairment reproducible, (2) if such effects exist, are they related to current or to chronic exposure and (3) if effects exist, are there reductions in the effects during an exposure-free period. Methods  Workers from a boat-building plant, some of whom were laminators, were investigated in groups of low (n = 83, mean mandelic acid MA + phenylglyoxylic acid PGA = 53 mg/g creatinine), medium (n = 101, 230 mg/g creat.) and high (n = 29, 928 mg/g creat.) levels of exposure to styrene. The mean job tenure was about 6 years. In addition, subgroups chronically exposed to low-short (n = 30, lifetime weighted average exposure mean 184 mg/g creat. for 6 years) and high-long (n = 16, 693 mg/g creat., 15 years) styrene levels were analyzed. The examinations were carried out during normal working days and during the company holidays. A symptom questionnaire and the tests Benton visual retention, symbol digit substitution and digit span for cognitive functions as well as choice reaction, aiming, peg board, tapping, and steadiness for psychomotor functions were administered. Co-variance analyzes with repeated measurements and linear regressions were used for statistical analysis. Co-factors were education, age, job tenure, long-term alcohol consumption, and German as mother tongue. In some cases also the activity as a laminator was considered. Results  Symptoms were not related to exposure. The tests for cognitive functions generally revealed (all variance analyses) no exposure-related associations. Only the linear regressions of Benton test results showed significant correlation with parameters of chronic exposure which was still evident as a tendency in the work-free and exposure-free period. Most tests for psychomotor functions also revealed no relationships with exposure. However, the peg board test results showed significant correlations with chronic exposure which disappeared during holidays. The activity as a laminator––considered in addition to exposure parameters––was significant as a factor to explain the variability of psychomotor variables. Conclusion  Acute exposures to up to 40 ppm styrene and long-term exposures to about 27 ppm averaged over a period of 15 years were not identified as being associated with an elevated risk of developing impaired cognitive and psychomotor functions or increased symptom levels with the tests applied. This statement must be qualified by two exceptions: performances in the Benton test and in a finger dexterity test were associated with parameters of long-term exposure as a dose-response relationship, but not with current exposure.     

The problem of repeated measurements. Longitudinal analysis in epidemiology

In longitudinal analyses subjects are repeatedly measured along time. They are mixed designs, characterised for their simultaneous consideration of two or more dimensions of analysis, in which time is one of the dimensions.Longitudinal analyses have important advantages with respect other designs. The most important is that they are more efficient, since they allow to distinguish between-individual and within-individual variation.Longitudinal analyses can be approached marginal and conditionally. Whereas the former allows to draw poblational, or average, inferences, the latter permits to draw individual inferences.The statistical models to use depend on the type of response variable. If the dependent variable is normally distributed one will use linear mixed models. When the response is a count one will use mixed Poisson regressions. Mixed binomial or multinomial logistic regressions should be used when the response would be categorical.     

Dietary changes among husbands of participants in a low-fat dietary intervention.

A dietary intervention delivered to one family member with a beneficial impact on other members could provide a cost-effective approach to public health dietary intervention programs. The Women's Health Trial (WHT) was a study in which women were randomized to be trained in adopting a low-fat diet or to continue their normal diet. The intervention women consumed 21% of total calories from fat versus 38% for control women at six months postrandomization. Husbands of women in the Seattle Clinical Center of the WHT were surveyed between 1985 and 1988 to determine whether and to what extent the husbands' diets changed at six months. Ninety-one intervention men and 162 control men, 79% of those eligible, participated. Intervention men reported an average weight loss of 2.4 pounds, compared to an average 0.7-lb loss among controls (P = .03). Based on self-reported change of specific foods, we found that intervention men more often reduced butter, margarine, eggs, and red meat over the six months than did control men (P less than .001). Based on nutrient consumption estimated by a food frequency questionnaire, intervention husbands consumed 34% of total calories from fat versus 36% for controls (P = 0.04). The number of meals shared with wives per week modified the effect of the intervention: among the intervention group, for every three meals shared, an accompanying one percentage point reduction in percentage of calories from fat occurred in the husband's diet. Thus, we suggest that dietary intervention programs attended by one spouse appear to exert a small beneficial effect on the other spouse.     

Sample size requirement for repeated measurements in continuous data.

In this paper we extend Bloch's discussion on the usefulness and the limitations in the application of repeated measurements per subject in study designs. We derive general sample size formulae for any finite number of comparison groups to calculate the required number of subjects with repeated measurements, that do not have to be conditionally independent. For fixed total cost, we discuss the optimal sample allocation for repeated measurements needed to maximize the power and the underestimation when using Bloch's sample size formula if in the hypothesis testing procedure the variance parameters are unknown. We have also included a quantitative investigation of the effectiveness of taking repeated measurements per subjects to reduced the required number of subjects for a given power at a given alpha-level.     

Validity of 24-hour dietary recalls by adolescent females.

The validity of 24-hour dietary recalls was tested by comparing the recalled intake of adolescent girls to their actual intake during a metabolic study. Diet recalls were a valid bases of estimating the dietary intake of energy, protein, calcium, and zinc by this group of adolescents. However, the majority of the subjects were unable to recall their food intake with enough accuracy so that their intake of vitamins A and C, thiamin, riboflavin, niacin, and iron could be calculated within the range of two-thirds to four-thirds of their actual intake.     

A randomised,controlled study of dietary intervention in autistic syndromes

Impaired social interaction, communication and imaginative skills characterize autistic syndromes. In these syndromes urinary peptide abnormalities, derived from gluten, gliadin, and casein, are reported. They reflect processes with opioid effect. The aim of this single blind study was to evaluate effect of gluten and casein-free diet for children with autistic syndromes and urinary peptide abnormalities. A randomly selected diet and control group with 10 children in each group participated. Observations and tests were done before and after a period of 1 year. The development for the group of children on diet was significantly better than for the controls.     

Nutritional changes among premenopausal women undertaking a soya based dietary intervention study in Hawaii

BACKGROUND: We conducted a 2-year nutritional intervention among premenopausal women. The goal was to incorporate two daily servings of soya into the regular diet. This report describes the dietary modifications and assesses their nutritional adequacy with regard to major nutrients. METHODS: In this analysis of 100 intervention and 106 control subjects, women completed a validated food-frequency questionnaire at baseline; throughout the study, they participated in at least three unannounced 24-h recalls. RESULTS: At randomization, both groups were similar in age and body weight, reported low soya intake, and did not differ by intake of major nutrients and foods. According to the 24-h recalls, women in the intervention group consumed nearly two servings of soya per day, while the control women remained at 0.2 servings. In comparison with the control group, the intervention group consumed fewer dairy products, primarily milk, but also less meat, nuts and seeds. As a result of the dietary modification, the intervention women consumed less-saturated fat and cholesterol and more protein, dietary fibre, calcium and vitamins than the control group. CONCLUSION: These results suggest that women in the intervention group improved the overall quality of their diet by adding two servings of soya per day.     

Baseline data and design for a randomized intervention study of dietary change in religious organizations

BACKGROUND: Reducing dietary fat has been identified as a potential means of preventing chronic disease. Several studies have identified methods of changing dietary fat consumption in small, intensive intervention settings. Fewer studies have examined how to improve dietary habits of individuals in the general public. METHODS: The Eating for a Healthy Life (EHL) project was a randomized trial [n = 40 religious organizations (ROs) and 2175 individuals, 1099 in intervention]. The study tested an intervention package of self-help books, motivational messages, and social interactions designed to change dietary behaviors (lowering fat, increasing fruit and vegetable consumption) among members of religious organizations aged 18 and over. The primary outcomes are fat- and fruit- or vegetable-related behaviors measured using the Fat and Fiber Behavior (FFB) Questionnaire. RESULTS: Religious organizations and their members participated fully in the initial study activities. CONCLUSIONS: This study will support a rigorous test of the intervention package.     

A latent class model for repeated measurements experiments.

Standard models for the analysis of repeated measurements assume a common response profile for all experimental units within a treatment group. However, in many applications this under-represents the nature of the response. There may be several distinct modes of response within a group (for example, responders versus non-responders to a given treatment), or there may be a set of distinct response profiles which are common to all the treatment groups. In these situations the effect of treatment can be characterized both by the shape of the fitted profiles and by estimating the proportion of cases who exhibit each particular response profile. This paper describes how such experiments may be analysed through the introduction of a latent variable into the standard model. Maximum likelihood estimation is straight-forward using the EM algorithm. Model choice requires some care, but good-fitting models can be identified via inspection of residuals and the use of empirical semi-variogram plots. Once the number of distinct profiles has been determined, treatment effects can be investigated using likelihood-ratio statistics. The approach is illustrated with a re-analysis of a dataset first described by Grizzle and Allen.     

Dietary habits and effects of dietary advice in patients with type 2 diabetes. Results from a one-year intervention study

The diets of 22 patients with type 2 diabetes were evaluated by a dietary-history interview. Sixteen of the patients were also interviewed after a 1-year intervention period, to find out whether continuous contact with a dietitian at a health centre could influence the food habits and thereby improve the metabolic control. In most participants the diabetes was fairly well controlled on entry into the study. Another 24 patients took part in the same intervention programme but did not agree to participate in the dietary-history interview. These subjects had, in general, a poorer metabolic control on admission. According to the study design, the patients were to make four visits to the dietitian during the first 6 months, and one visit at the end of the year. The patients were advised to eat a fat-modified, fibre-enriched diet. Among the patients who completed both the intervention programme and the dietary-history interviews there were significant reductions in mean body weight, haemoglobin A1c and serum triglycerides during the first half of the study. After 12 months, however, only the mean body weight and serum triglycerides remained lower than before the intervention period. A study of the fatty acid composition of the plasma cholesterol esters showed a significant reduction of the content of oleic acid (18:1 n-9). The dietary interviews indicated only minor changes (not significant) in the intake of energy and different nutrients, including dietary fibre, after 1 year. However, the effects of the intervention were better in the patients who did not participate in the dietary interview with significant reductions in the mean body weight, fasting blood glucose, haemoglobin A1c and serum triglycerides also after 1 year.