Validity of individual portion size estimates in a food frequency questionnaire

BACKGROUND

Dietary surveys often rely upon subjects' ability to estimate their portion sizes instead of weighing them, but information on the validity of such estimates is lacking. This study investigated the validity of estimated portion sizes from a self-administered food frequency questionnaire including photos.

METHODS

Validity was evaluated by comparison with portion sizes from 14-day weighed food records. Eight sets of photos were included in the study (three meat dishes, one fish dish, three vegetables, potatoes), each set with four options. Subjects (59 men, 85 women) were 40-64 years.

RESULTS

The majority of subjects (85-95%) selected the most correct photo or a neighbouring photo. However, regression analyses showed that the relationship between the estimated and the measured portion sizes was relatively weak for most of the foods tested, and correlations were only significant for three of the eight foods. This apparent contradiction was partly due to the pattern of the error: subjects selecting small portions had underestimated their actual portions while subjects selecting large portions had overestimated them. This error pattern could not be explained by the theoretical error resulting from the use of four discrete portion sizes instead of continuous weights, neither was it a simple consequence of the unidirectional errors at the extreme ends. Actual portion sizes varied from day to day, with intra-individual coefficients of variation of 34-40%.

CONCLUSIONS

The photos used in the present study were of limited value for ranking individuals correctly according to their actual portion sizes. Whether this is a common feature of photos used in food frequency questionnaires remains to be answered.

Adipose tissue fatty acids as biomarkers of dietary exposure in Danish men and women

Adipose tissue fatty acids, it has been proposed, reflect dietary intake. Using data from a validation study preceding a prospective study on diet, cancer, and health in Denmark, we were able to compare fatty acid profiles in adipose tissue biopsies from 86 individuals (23 men and 63 women) aged 40-64 y and dietary intake of fatty acids (as percentage of total fat) assessed by two 7-d weighed-diet records or by a semi-quantitative food frequency questionnaire. Correlation coefficients (Pearson r) between fatty acid concentrations in adipose tissue biopsies (as percentage of total peak area) and dietary intake of fatty acid (percentage of total fat), determined from the diet records for men and women, respectively, were as follows: polyunsaturated fatty acids r = 0.74 and r = 0.46; n - 3 fatty acids of marine origin: eicosapentaenoic acid r = 0.15 and r = 0.61, and docosahexaenoic acid r = 0.47 and r = 0.57. Correlation coefficients obtained by using the food frequency questionnaire were slightly lower for most fatty acids.

Oxidative DNA damage estimated by 8-hydroxydeoxyguanosine excretion in humans: influence of smoking, gender and body mass index

Oxidative DNA damage may be implicated in ageing, carcinogenesis and other degenerative diseases. Oxidative DNA damage can be assessed in humans in vivo from the urinary excretion of the DNA-repair product 8-hydroxydeoxyguanosine (8OHdG). We investigated factors influencing the excretion of 8OHdG in 24 h urine from 83 randomly selected healthy subjects (52 women) aged 40-64 years. For 2 weeks prior to urine collection the subjects kept a weighed diet record. 8OHdG was quantified by an automatic three-dimensional HPLC analysis with electrochemical detection. The 8OHdG excretion was 252 +/- 103 (mean +/- SD) pmol kg body weight/24 h with a range from 78 to 527. Multiple regression analysis identified three factors, smoking, body mass index (BMI) and gender, as significant predictors of the 8OHdG excretion. In 30 smokers the 8OHdG excretion was 320 +/- 99 pmol/kg/24 h opposed to 213 +/- 84 pmol/kg/24 h in 53 non-smokers. According to multiple regression analysis smokers excreted 50% (31-69%; 95% confidence interval) more 8OHdG than non-smokers. In 52 women the 8OHdG excretion was 240 +/- 106 pmol/kg/24 h opposed to 271 +/- 96 pmol/kg/24 h in 31 men. According to the multiple regression analysis men excreted 29% (10-48%) more 8OHdG than women. According to multiple regression analysis the 8OHdG excretion decreased with 4% (2-6%) per increment in BMI measured in kg/m2. The dietary distribution of energy demonstrated no important predictive value with respect to 8OHdG excretion. The intake of the antioxidant vitamins C and E and of vitamin A equivalents, including beta-carotene, was not associated with 8OHdG excretion. The results suggest that smoking increases oxidative DNA damage by approximately 50%. This effect implies potential serious health effects adding to the other well-known health hazards of smoking. The higher 8OHdG excretion in men and lean subjects may be related to a higher rate of metabolism with increased availability of reactive oxygen species. The apparent 7-fold individual variation in oxidative DNA damage carries implications regarding the rate of ageing and the risk of cancer and other degenerative diseases. The excretion of 8OHdG into urine offers a valuable tool for testing such hypotheses in humans.

Validation of a semiquantitative food frequency questionnaire developed in Denmark

In 1989, a self-administered food frequency questionnaire, including 92 food items and 40 portion-size photographs, was validated against two times seven days of weighed diet records. A total of 144 subjects, aged 40-64 years, from the general population in Copenhagen were included. Correlations between mean calorie-adjusted intakes from the two-week diet records and the food-frequency questionnaire ranged from 0.27 for vitamin A to 0.71 for calcium. In general, higher correlation coefficients were observed for men than for women. On average, about 70% of subjects were classified in the same (+/- 1) quintile in the food frequency questionnaire and the diet records. Of those subjects belonging to the lowest quintile, estimated from the diet records, 42% fell in the same quintile and 68% into the lowest two quintiles in the food frequency questionnaire. Findings were similar for the upper tail of the distribution. Gross misclassification, observed in the highest and lowest quintile, was found for 4% and 7% of the subjects, respectively. It is concluded that this food frequency questionnaire is a useful instrument for categorizing individuals according to their intake of nutrients and energy.

Development of a semiquantitative food frequency questionnaire to assess food, energy and nutrient intake in Denmark

Foods to be included in a Danish self-administered semiquantitative food frequency questionnaire were identified from food tables developed, together with data collected, for the survey 'Dietary habits in Denmark, 1985'. The questionnaire was to be used in a prospective study on diet, cancer and health, and the aim was to rank individuals with regard to intake of 19 different nutrients considered of prime importance in human carcinogenesis. The questionnaire for the dietary survey included 247 foods and recipes. From stepwise multiple regression analyses with the intake of each of the 19 nutrients as the dependent variable and the intake of the 247 foods and recipes as independent variables, the foods in the models explaining 90% of the between-person variability were considered for the final questionnaire. All relevant analyses were performed for the study group as a whole, for men and women separately, and in each gender for subgroups of energy intake. Taken together, the models explaining 90% of the between-person variability identified a total of 74 foods or recipes, which were important predictors of the intake of one or more of the nutrients considered. A few foods were excluded and a few foods were added to the final questionnaire based on common biological background information, and on information on foods providing important amounts of given nutrients, but which failed to contribute to regression analyses. The 92 foods and recipes, which were included in the final questionnaire provided altogether 81% of the average total supply of the nutrients.(ABSTRACT TRUNCATED AT 250 WORDS)

Low maternal but normal fetal prolactin levels in cigarette smoking pregnant women

In the 36th week of pregnancy, levels of serum prolactin (PRL) (p less than 0.01) and estriol (p less than 0.05) were significantly lower in 101 consecutive women smoking 10 cigarettes or more per day, compared with a control group of 104 non-smoking pregnant women. Cord serum PRL was not related to maternal smoking habits, whereas estriol was significantly (p less than 0.05) lower in the infants of smokers, compared with the control group. The lower PRL levels in cigarette-smoking pregnant women may be due either to a direct effect of nicotine or secondary to lower estrogen levels, and the finding may be of clinical importance in relation to lactation.

Heart ultrastructure in Lepidurus arcticus Pallas (Crustacea, Branchiopoda, Notostraca)

The heart of Lepidurus arcticus consists of an epicardium and a single layer of strongly polarized myocardial cells, 10-50 micron thick, with the myofibrillar part facing the epicardium. The Z-bands are diffuse and some Z-material forms attachment plaques. Relaxed sarcomeres show a hexagonal arrangement of thick filaments and 6 thin filaments in orbit, but filaments often diverge in their orientation. The sarcolemma invaginates from both the epicardial and the endocardial side of the cell, forming clefts and T-tubules. The sarcoplasmic reticulum is loosely reticular, cisternae associate with sarcolemma to form large and typical peripheral and interior couplings. The latter are of the "button-to-button" type and they tend to be located at the A-I level.