Intra- and inter-individual variations in diets of the middle-aged and the elderly]

This study was conducted to examine intra- and inter-individual variations in diets of the middle-aged and the elderly (40 years or older, 46 men and 42 women). The coefficients of variations for intakes of nutrients and food groups were computed from four 4-day weighed dietary records performed at 3-month intervals from June 1996. The results were as follows: a) The highest intra-individual variation (%) for nutrient intake was observed in retinol (men 293.5, women 283.8) and the lowest in carbohydrate (men 17.7, women 22.1). b) The highest inter-individual variation (%) was found in retinol (58.2) in men, and in carotene (56.7) in women. The lowest inter-individual variation (%) was observed in magnesium (17.0) in men, and in carbohydrate (14.4) in women. c) Nuts and seeds showed the highest intra-individual variation (%) for food group intake (men 291.5, women 391.8), while rice presented the lowest (men 30.5, women 38.9). d) The highest inter-individual variation for food group intake (%) was seen in milk and dairy products (111.7) in men and in alcoholic beverages (162.3) in women. The lowest inter-individual variation was observed in potatoes and starches (20.7) in men and in pulses (26.0) in women. e) The number of days necessary to estimate true average nutrient intake was much longer for such vitamins as retinol and carotene (over 50 days) than for macronutrients (3-5 days) except for fat. More than one year was required to estimate intake of nuts and seeds in both sexes and alcoholic beverages or seaweeds in women, whereas only 9-15 days for intake of rice. In conclusion, energy, protein and carbohydrate can be estimated by short-period dietary recalls or records, since their intra-individual variations were relatively small. On the other hand, many days, were found to be required to estimate usual dietary intake of such vitamins as retinol or carotene and that of each food group except for rice. It would therefore be very difficult to estimate usual intake of these nutrients and food groups by short-period dietary recalls or records.     

A minimum of six days of diet recording is needed to assess usual vitamin K intake among older adults

There is a growing interest in the role of vitamin K in health, especially in aging populations. Knowledge of inter- and intra-individual variability of dietary vitamin K intake could be useful to accurately assess usual intake and rank participants in epidemiological studies. Our objectives were to: 1) estimate the variance components of vitamin K intake; 2) investigate whether day of the week, season, and energy intake are factors related to intra-individual variance; and 3) calculate the requisite number of days to achieve desired degrees of accuracy for estimating individual vitamin K intake, ranking individuals and estimating regression coefficient. Vitamin K intake was assessed in 939 older adults (67-84 y) enrolled in the Québec Longitudinal Study on Nutrition and Successful Aging study using 2 sets of 3 nonconsecutive multiple-pass 24-h dietary recalls (24HR) collected 6 mo apart. Each set included 2 weekdays and one weekend day. Intra- to inter-individual variance ratios for vitamin K intake were 3.2 (95% CI = 2.6-3.9) overall, 2.6 (95% CI = 2.1-3.5) for men, and 3.7 (95% CI = 2.9-5.0) for women. Day of the week (weekdays) and season (May to October) were positively and significantly associated with vitamin K intake but explained a negligible part of intra-individual variation (<1%). Adjusting for energy intake explained <7% of variance and did not affect the variance ratio. Six to 13 24HR are required to properly rank individuals according to their usual vitamin K intake and limit attenuation of the regression coefficient. These results should be considered in studies planning to assess vitamin K intakes in older adults.     

Assessment of the association between habitual salt intake and high blood pressure: methodological problems.

Despite the finding in cross-cultural comparisons that habitual sodium intake correlates with levels of blood pressure, similar studies from within population groups have yielded inconsistent results. The data presented in this report indicate that in industrialized societies the high degree of intra-individual variability of sodium intake, compared to much smaller inter-individual differences, may obscure potential biological correlations. A quantitative statistical method is presented to assess and minimize the effect of the large intra-individual variation in daily urinary sodium excretion.     

Determination of intra-/inter-individual variability and its effect on the number of days required to assess the usual intake of a school children population

The inaccuracy with which individuals' usual intake of nutrients influences the assessment of the relation between nutrients as independent variables and outcome as dependent variables. Intra- and inter-individual variability are used to assess such inaccuracy but data for the pediatric population are scant. Intra- and inter-individual variability was therefore investigated in a pediatric population attending the primary school. A seven-day weighted food record was completed twice by the mothers of 110 children over a six-month period. The total variance of each nutrient was subdivided into intra- and inter-individual components by analysis of variance for repeated measure and the coefficients of variability within (CV_intra) and between (CV_inter) individuals were calculated along with the number of days required to describe the individual's usual intake. The nutrients were considered both as raw intake and nutrient density (nutrient expressed in proportion to energy). Many nutrients displayed an intra-/inter-individual variability ratio >1, not amenable to be altered by adjustment for total caloric intake. A calorie 10% error margin or less should be expected by using a 20-day time frame. On the other hand most nutrients present a 10% error over thirty-day studies. For many nutrients, bracketing the error within the 10% margin would require an unrealistic time frame. The adjustment for calorie intake reduced the number of days required for the dietary record. In conclusion, in school children, within a 7-day study design the intake of most nutrients could be calculated with an error margin as wide as 30% and for some nutrients the margin is even wider.     

Determination of intra- and inter-individual variability and its effect on the number of days required to assess the usual intake of a 1-year-old infant population

Summary. Diet variability influences the accuracy of the assessment of the relationship between nutrient intake and disease. The present study investigates intra- and inter-individual variability in an infant population at 12 months. The mothers of 79 infants completed a 7-day weighted food record. No significant difference in nutrient intake was observed between males and females. For some nutrients an intra-/inter-individual variability ratio < 1 was found. Adjustment for total calorie intake slightly altered the intra-/inter-individual variability ratio of many nutrients. An error margin of 10% or less for calories can be expected within an 18-day study. Most nutrients however would need to be studied for over 30 days to give an error margin ≤10%. For dietary cholesterol, vitamins A, B6, C, and E, bracketing the error within the 10% margin would require an unrealistic time frame. Adjustments for calorie intake reduced the number of days in the dietary record for some nutrients. A lower intra/inter-individual variability ratio was seen when data for adults and older infants were compared.     

Variability in transepidermal water loss of the skin: evaluation of a method to assess susceptibility to contact dermatitis in epidemiological studies

Summary Transepidermal water loss (TEWL) has been suggested to be a measure which can be used to identify subjects at risk for the development of contact dermatitis. Transepidermal water loss is high when the barrier function of the skin is impaired. It is assumed that subjects with a high TEWL have skin which is more permeable to substances causing contact dermatitis. The inter-individual and intra-individual variability of simultaneous TEWL measurements and TEWL measurements over a period of three weeks were estimated in healthy individuals. The intra-individual coefficient of variation (CV) of simultaneous measurements was 13.5%. The intra-individual coefficient of variation of the measurements on consecutive days was somewhat higher (15.1%). The intra-individual coefficients of variation were low compared to the inter-individual coefficients of variation. The results indicate that transepidermal water loss is a stable personal characteristic, which can be studied as a risk factor in epidemiologie studies on contact dermatitis.     

Minimizing random error in dietary intakes assessed by 24-h recall, in overweight and obese adults

OBJECTIVE: To determine the minimum number of days of dietary intake interviews required to reduce the effects of random error (day-to-day variability in dietary intake) when using the multiple-pass, multiple-day, 24-h recall method. DESIGN: Cross-sectional study. SETTING: University research department. SUBJECTS: A total of 50 healthy non-smoking overweight and obese (body mass index=26-40 kg/m2) adult men and women aged 39-45 years completed the study. Participants were randomly selected from volunteers for a larger unrelated study. INTERVENTIONS: Each participant completed 10, multiple-pass, 24-h recall interviews on randomly chosen days over 4 weeks. The minimum number of record days was determined for each macronutrient (carbohydrate, fat, protein) and energy, for each gender, to obtain a 'true' (unobservable) representative intake from reported (observed) dietary intakes. RESULTS: The greatest number of days required to obtain a 'true' representative intake was 8 days. Carbohydrate intakes required the greatest number of days of dietary record among males (7 days), whereas protein required the greatest number of days among females (8 days) in this cohort. Sunday was the day of the week that showed greatest variability in macronutrient intakes. Protein (P<0.05) and fat (P<0.001) intakes were significantly more variable than carbohydrate on Sundays compared with weekdays, for both men and women. CONCLUSION: A logistically achievable 8 days of dietary intake interviews was sufficient to minimize the effect of random error when using the multiple-pass, 24-h recall dietary intake method. Sunday should be included among the dietary interview days to ensure a 'true' representation of macronutrient intakes. This method can be confidently applied to small cohort studies in which dietary intakes from different groups are to be compared or to investigations of associations between nutrient intakes and disease.     

Intra-individual variation in resting metabolic rate during the menstrual cycle

Little information exists on the extent of day-to-day intra-individual variation in resting metabolic rate (RMR) in women. The present study has investigated the intra-individual variation in RMR of women during the menstrual cycle. Nineteen women (naturally cycling non-pill users) were recruited to the study. Anthropometric and RMR measurements were taken at least three times per week for the duration of one complete menstrual cycle; measurements were taken for a second, consecutive cycle in eight of the nineteen subjects. RMR was measured by indirect calorimetry using a ventilated hood system under standardized conditions. The measurements made throughout each complete menstrual cycle were averaged and the levels of inter- and intra-individual variation in RMR were assessed by determining the CV (%). Mean RMR of the group was 5686 (sd 674) kJ/d; inter-individual variation in RMR was 11.8 %. There were wide differences in the intra-individual variation in RMR of women (CV range 1.7-10.4 %). The CV in ten subjects was small (2-4 %), while the CV in nine women was high (5-10 %), indicating a significant variation in RMR during the menstrual cycle in certain subjects. Using statistical models, it has been shown that there was a significant effect on RMR due to a subject-specific level of variability; this was the case even when accounting for a possible training effect. In conclusion, the findings from our present study show that RMR cannot be assumed to be 'stable' in all women. The implications of intra-individual variation in RMR and its impact on energy balance needs further research.     

High intra/interindividual variance ratios for energy and nutrient intakes of pregnant women in rural Malawi show that many days are required to estimate usual intake

Conventional wisdom suggests that because there is less variety in food intake, fewer days may be needed to capture "usual intake" of individuals in developing countries, but it is also known that intakes may vary considerably across seasons. Because few studies have examined the sources of variation in nutrient intake in subsistence communities, where food availability also may limit day-to-day food choices, our objective was to examine intraindividual and interindividual variability in energy and nutrient intakes in pregnant subsistence farmers in Africa. From 1988 through 1991, we collected a total of 1061 diet days (mean = 6; range; 2-12 d/woman), using the direct food weighing method, from 184 pregnant women in a farming community west of Lilongwe City, Malawi. Two or four consecutive days were collected for each of several visits during the 2nd and 3rd trimesters. Variance ratios were calculated as the error variance/variance across individuals. We found major seasonal differences in energy and nutrient intakes with greater intakes in the harvest than in the preharvest seasons. Adjustment for season and stage of pregnancy did not reduce variance ratios. To estimate true individual intakes within an error range of +/- 20% required 8-23 d for energy, protein, carbohydrates and fiber; and 95-213 d for micronutrients. Thus, despite limited dietary diversity, large within-person variation in nutrient intake demonstrated that more, rather than fewer days of dietary intake were required to correctly identify usual intake in subsistence farmers compared with previous reports for urbanized or Western populations.     

Assessing nutrient intake with an abbreviated dietary interview

There is considerable interest in developing a means of assessing dietary intake of specific nutrients with minimal time and expense in epidemiologic studies. Using data from 1,682 individuals who were interviewed using an extensive food frequency dietary history, the authors examined the question of how many foods might be minimally required in order to estimate specific nutrient intakes for epidemiologic purposes. Nutrient indices were constructed for vitamins A and C, dietary fiber, fat, protein, and total calories based on 128 foods included in the interview. They found that a large fraction of the variability of nutrient intake in this population could be explained by a small number of foods. An abbreviated dietary history ascertaining the intake of as few as 15-20 food items may be all that is required in order to test the association between disease outcome and the intake of a single nutrient.     

Measuring children's diets: evaluation of dietary assessment techniques in infancy and childhood

Epidemiological studies of dietary habits in infancy and childhood face a number of difficulties, which are more or less specific for these ages. In connection with studies on dietary habits of Swedish infants and children an evaluation of different dietary assessment techniques was performed. Breastfeeding data obtained in retrospective interviews at six months had good validity. The reliability of breastfeeding and weaning data decreased over time. Short questions on food frequencies, often used in research and clinical practice, were shown to be a poor screening instrument and suffered from biases when used in groups of four- and eight-year-old children. Group mean estimations of dietary intake of four- and eight-year-old children obtained by 24-hour recalls were close to those of seven-day records from the same individuals. Dietary intake in a 13-year-old group according to 24-hour recall and dietary history differed significantly; the dietary history gave much higher estimations. The reliability of dietary history in a small group of 13-year-old boarding school children was fairly good. The internal validity of food recording was examined by use of chemical analysis of duplicate portions. Generally, there was good agreement between the records and the analysed duplicates. The intake of a number of nutrients varied during the week, often showing a maximum towards the weekend. The intake of vitamin C was higher in winter time, otherwise no seasonal variation was found. The intra-individual variation in dietary intake is illustrated and its consequences for dietary studies are discussed.     

Implications of day-to-day variability on measurements of usual food and nutrient intakes

Day-to-day variability in dietary intake makes it difficult to measure accurately the "usual" intake of foods and nutrients. The objectives of the present study were to estimate within- and between-subject variability for foods and nutrients by adjusted and unadjusted models and to assess the number of days required to assess nutrient and food group intakes accurately by two different methods. Adult men and women aged 18-65 y (n = 1543) in the Food Habits of Canadians Study provided a 24-h recall. A repeat interview was conducted in a subsample to estimate components of variability. Within- and between-subject variability were determined by mixed model procedure (crude and adjusted for age, gender, education, smoking, family size and season). The number of days required to obtain various degrees of accuracy was ascertained by two methods, one that uses the variance ratio for groups and one that considers within-subject variability alone for individuals. Variance ratios were higher using the adjusted compared with the unadjusted method (e.g., for men, energy 1.07 vs. 0.49). More days were required to reflect usual intake with accuracy using the adjusted model (energy 5 vs. 2 d), indicating the need to control for confounders to obtain reliable estimates of intakes.     

Number of days, number of subjects, and sources of variation in longitudinal intervention or crossover feeding trials with multiple days of measurement

Dietary studies are often conducted as longitudinal intervention or crossover trials using multiple days of measurement on each subject during each of several measurement periods, and determining the required numbers of days and subjects is important in designing these studies. Linear mixed statistical models were used to derive equations for precision, statistical power and sample size (number of days and number of subjects) and to obtain estimates of between-subject, period-to-period, and day-to-day variation needed to apply the equations. Two cohorts of an on-going exercise intervention study, and a crossover study of Olestra, each with 14 d of measurement/subject per period, were used to obtain estimates of variability for energy and macronutrient intake. Numerical examples illustrate how the equations for calculating the number of days or number of subjects are applied in typical situations, and sample SAS code is given. It was found that between-subject, period-to-period, and day-to-day variation all contributed significantly to the variation in energy and macronutrient intake. The ratio of period-to-period and day-to-day standard deviations controls the trade-off between the number of days and the number of subjects, and this remained relatively stable across studies and energy and macronutrient intake variables. The greatest gains in precision were seen over the first few measurement days. Greater precision and fewer required days were noted in the study (Olestra) that exerted greater control over the subjects and diets during the feeding protocol.     

Effects of season and illness on the dietary intake of weanlings during longitudinal studies in rural Bangladesh

Longitudinal, quantitative studies of the dietary intake of 70 weanlings between five and 30 months of age from two Bangladeshi villages have been analyzed to determine the effects of season and illness on dietary intake. During 1014 days of observation, all foods consumed by the children were weighed by a field worker present in the home; 24-hour breast milk intake was estimated from 12-hour test weighings. Inter-individual differences explained 29% to 50% of the variance in consumption of selected nutrients and foods during 632 studies conducted when children were free from diarrhea and fever. Multiple linear regressions controlling for inter-individual differences indicated that 60-day seasonal periods explained a significant proportion of the variation in intake. Average energy consumption (kcal/kg/d) was approximately one-third greater during the post-harvest periods than during the pre-harvest monsoon period. Breast milk intake varied similarly even after controlling for age-related decreases. Consumption of rice and wheat, the major non-breast milk sources of energy and protein, had distinct seasonal patterns, thus limiting the overall seasonal variability in cereal intake. Older children, particularly boys, benefited more from the post-harvest relative abundance of food. The intake of most nutrients was significantly depressed by approximately 10% during febrile illnesses. Minor decreases in intake with other illnesses were not statistically significant.     

Estimating dietary consumption patterns among children: a comparison between cross-sectional and longitudinal study designs

Estimating dietary intake for children is an essential component of conducting pesticide exposure assessments given the fact that children are predominantly exposed to certain pesticides, such as organophosphorus pesticide, through dietary intake. Different study designs and their respective sampling methodology utilized to estimate food consumption patterns can significantly alter the parameter estimates and the variability in the values obtained. This study investigated the impacts of study design on overall estimates of dietary intake by applying the temporal sampling characteristics used in cross-sectional approaches, as in The Continuing Survey of Food for Intakes by Individuals (CSFII), to food consumption data collected in a longitudinal manner via a bootstrap sampling technique. We examined the precision of time-averaged dietary intake estimates under various sampling schemes and explored the contribution of seasonality toward the dietary patterns. A comparison between the estimates of food consumption obtained from the bootstrap replicates and the longitudinal study estimates indicate that variability is significantly decreased when employing a longitudinal study design. Moreover, both between and within-subject variability decreases when individuals are followed over an increasing number of days. Finally, within the longitudinal study cohort, we observed a seasonal component to dietary intake for fruits and grains. Our findings suggest that longitudinal dietary surveys offer substantial improvements for exposure assessment compared to a standard cross-sectional design.     

Wearable Cameras Reveal Large Intra-Individual Variability in Timing of Eating among Young Adults

Studies have shown that young adults follow less structured eating patterns compared with older cohorts. This may have implications for dietary assessment methods which rely on memory and structured meal patterns. Our aim was to describe the intra-individual variation of eating times in young adults aged 18–30 years. Participants (n = 41) wore an Autographer camera that captured first-person perspective images every 30 s for three consecutive days. All images were timestamped and those showing food consumption were used to extract data such as the timing of the first and last eating occasions (EOs), number of EOs per day, and length of eating window. Intra-individual variability was calculated from these data using composite phase deviation (CPD) and coefficient of variation (CV). The number of individuals with high or very high variability was 28 and 18 for timing of first and last EOs, respectively (CPD > 1.70), and 27 and 17 for number of EOs and eating window, respectively (CV > 20%). In this sample of young adults, the lack of regularity in eating patterns should be considered when selecting a dietary assessment method.     

Number of days of food intake records required to estimate individual and group nutrient intakes with defined confidence

The number of days of food intake data needed to estimate the intake of 29 male (n = 13) and female (n = 16) adult subjects, individually and as a group, was determined for food energy and 18 nutrients. The food intake records were collected in a year-long study conducted by the U.S. Department of Agriculture's Beltsville Human Nutrition Research Center. Each individual's average intake of nutrients and standard deviation over the year were assumed to reflect his or her "usual" intake and day-to-day variability. Confidence intervals (P less than 0.05) for each individual's usual intake were constructed, and from these the number of days of dietary records needed for estimated individual and group intake to be within 10% of usual intake was calculated. The results indicated that the number of days of food intake records needed to predict the usual nutrient intake of an individual varied substantially among individuals for the same nutrient and within individuals for different nutrients; e.g., food energy required the fewest days (averaging 31) and vitamin A the most (averaging 433). This was considerably higher than the number of days needed to estimate mean nutrient intake for this group, which ranged from 3 for food energy to 41 for vitamin A. Fewer days would be needed for larger groups.     

The use of computerised 24 h dietary recalls in the French SU.VI.MAX Study: number of recalls required

OBJECTIVE: The 24 h dietary recall is a widely used method to estimate nutritional intakes in epidemiological studies. The objective of the present study was to estimate the number of recalls necessary for an accurate estimation of nutrient intake in French adults followed for 4 y. SUBJECTS AND METHODS: Participants of the SU.VI.MAX study (intervention study on the effects of antioxidant supplementation on chronic diseases) who completed a 24 h dietary recall every 2 months for at least 1 y. Inter- and intra-individual variance ratios (S(w)/S(b)) were calculated by analysis of variance for two time periods: year 1 and 2 (n=4955) and year 3 and 4 (n=1458). The number of recalls necessary was calculated using an accuracy of 0.9. RESULTS: The highest intra-individual/inter-individual variance ratio in the first period was seen for beta-carotene and the lowest for carbohydrate. The number of recalls necessary was five for carbohydrate and calcium intake and 16 for beta-carotene. For proteins, total and saturated fat, fibre, vitamin C and iron eight recalls were required, while nine, 11 and 10 recalls were necessary for mono- and polyunsaturated fat and vitamin E, respectively. The variance ratios in the second period were all lower and fewer recalls were therefore required. The same difference in number of recalls required between the two time periods was observed when only those subjects were included who completed at least 18 recalls (n=727). CONCLUSION: These results indicate that for an accurate estimation of carbohydrate intake only, already five recalls are necessary. Fewer recalls may be needed during long-time follow-up. SPONSORSHIP: The SU.VI.MAX Study has support from public and private sectors: Fruit d'Or Recherche, Candia, Lipton, Kellogg's, Céréal, CERIN, Estée Lauder, L'Oréal, Peugeot, Jet Service, RP Scherer, Sodexho, France Telecom, Santogen, Becton Dickinson, Fould Springer, Boehringer Diagnostic, Seppic Givaudan Lavirotte, Le grand Canal, Danone and Knorr.     

Intake and Factors Associated with Consumption of Pureed Food in Long Term Care: An Analysis of Making the Most of Mealtimes (M3) Project

Residents living in long term care (LTC) who consume a pureed diet tend to have inadequate intake; understanding factors associated with poor intake in this group of residents is not well established. This study examined the adequacy of nutrient intake among LTC residents consuming a pureed diet and the factors associated with this intake (n?=?67). Data was collected as part of a cross-sectional study conducted in 32 LTC homes. Weighed food intake was measured on three non-consecutive days and analyzed using Food Processor software. Intake of nutrients were adjusted for intra-individual variability and compared to the Estimated Average Requirement or Adequate Intake for women only. Consumers of a pureed diet had low micronutrient intakes. Multivariate analysis found that the average number of staff assisting with a meal was associated with energy and protein intake. Overcoming eating challenges, careful menu planning and nutrient-dense options for pureed diets in LTC are recommended.