Alison E. Black

Critical evaluation of energy intake using the Goldberg cut-off for energy intake:basal metabolic rate. A practical guide to its calculation, use and limitations.

OBJECTIVES: To re-state the principles underlying the Goldberg cut-off for identifying under-reporters of energy intake, re-examine the physiological principles and update the values to be substituted into the equation for calculating the cut-off, and to examine its use and limitations.RESULTS: New values are suggested for each element of the Goldberg equation. The physical activity level (PAL) for comparison with energy intake:basal metabolic rate (EI:BMR) should be selected to reflect the population under study; the PAL value of 1.55 x BMR is not necessarily the value of choice. The suggested value for average within-subject variation in energy intake is 23% (unchanged), but other sources of variation are increased in the light of new data. For within-subject variation in measured and estimated BMR, 4% and 8.5% respectively are suggested (previously 2.5% and 8%), and for total between-subject variation in PAL, the suggested value is 15% (previously 12.5%). The effect of these changes is to widen the confidence limits and reduce the sensitivity of the cut-off.CONCLUSIONS: The Goldberg cut-off can be used to evaluate the mean population bias in reported energy intake, but information on the activity or lifestyle of the population is needed to choose a suitable PAL energy requirement for comparison. Sensitivity for identifying under-reporters at the individual level is limited. In epidemiological studies information on home, leisure and occupational activity is essential in order to assign subjects to low, medium or high PAL levels before calculating the cut-offs. In small studies, it is desirable to measure energy expenditure, or to calculate individual energy requirements, and to compare energy intake directly with energy expenditure.

Markers of the Validity of Reported Energy Intake

Energy intake (EI) is the foundation of the diet, because all other nutrients must be provided within the quantity of food needed to fulfill the energy requirement. Thus if total EI is underestimated, it is probable that the intakes of other nutrients are also underestimated. Under conditions of weight stability, EI equals energy expenditure (EE). Because at the group level weight may be regarded as stable in the timescale of a dietary assessment, the validity of reported EI can be evaluated by comparing it with either measured EE or an estimate of the energy requirement of the population. This paper provides the first comprehensive review of studies in which EI was reported and EE was measured using the doubly labeled water technique. These conclusively demonstrate widespread bias to the underestimation of EI. Because energy requirements of populations or individuals can be conveniently expressed as multiples of the basal metabolic rate (BMR), EE:BMR, reported EI may also be expressed as EI:BMR for comparison. Values of EI:BMR falling below the 95% confidence limit of agreement between these two measures signify the presence of underreporting. A formula for calculating the lower 95% confidence limit was proposed by Goldberg et al. (the Goldberg cutoff). It has been used by numerous authors to identify individual underreporters in different dietary databases to explore the variables associated with underreporting. These studies are also comprehensively reviewed. They explore the characteristics of underreporters and the biases in estimating nutrient intake and in describing meal patterns associated with underreporting. This review also examines some of the problems for the interpretation of data introduced by underreporting and particularly by variable underreporting across subjects. Future directions for research are identified.

High levels of energy expenditure in obese women

Total free living energy expenditure was compared in lean and obese women by the new doubly labelled water method and partitioned into basal metabolism and thermogenesis plus activity by whole body calorimetry. Average energy expenditure was significantly higher in the obese group (10.22 versus 7.99 MJ/day (2445 versus 1911 kcal/day); p less than 0.001) resulting from an increase in the energy cost of both basal metabolism and physical activity. Self recorded energy intakes were accurate in the lean subjects but underestimated expenditure by 3.5 MJ/day (837 kcal/day) in the obese group. Basal metabolic rate and energy expenditure on thermogenesis plus activity were identical in the two groups when corrected for differences in fat free mass and total body mass. In the obese women in this series there was no evidence that their obesity was caused by a metabolic or behavioural defect resulting in reduced energy expenditure.

Accuracy of weighed dietary records in studies of diet and health.

OBJECTIVE--To provide an independent evaluation of seven day weighed dietary records, which are currently accepted as the most accurate technique for assessing habitual dietary intake in studies investigating the links between diet and health. DESIGN--Subjects who had previously participated in the Northern Ireland diet and health study were reselected by stratified random sampling to represent the range of energy intakes in the study as assessed by the seven day weighed dietary record. SETTING--Northern Ireland. SUBJECTS--31 Free living adults (16 men and 15 women). MAIN OUTCOME MEASURES--Energy intake as measured by the seven day weighed dietary record and total energy expenditure estimated concurrently by the doubly labelled water technique. RESULTS--Average recorded energy intakes were significantly lower than measured expenditure in the group overall (9.66 MJ/day v 12.15 MJ/day, 95% confidence interval 1.45 to 3.53 MJ/day). Among those in the upper third of energy intakes the mean (SE) ratio of intake to expenditure was close to 1.0, indicating accurate records (men 1.01 (0.11), women 0.96 (0.08]. In the middle and lower thirds the ratios for men were only 0.74 (0.05) and 0.70 (0.07) respectively and for women 0.89 (0.07) and 0.61 (0.07). CONCLUSIONS--These results show a serious bias in reporting habitual energy intake. If substantiated they may have wide implications for the interpretation of many nutritional studies.

Measurements of total energy expenditure provide insights into the validity of dietary measurements of energy intake

The quantification of errors inherent in methods of measuring dietary intake has been handicapped by the absence of independent markers for testing their validity. The doubly labeled water technique permits a precise measure of energy expenditure in free-living persons. Because energy expenditure must equal energy intake in populations in energy balance, this technique may be used to validate the assessment of energy intake. A series of studies demonstrated good agreement between mean energy intake and mean energy expenditure when food intake was recorded by observers or when it was self-reported by normal-weight, self-selected, highly motivated volunteer subjects using weighed records. However, in randomly recruited men and women, energy intake by weighed records was 82% and 81%, of energy expenditure, respectively, indicating underestimation of habitual intake. Men and women in the lowest third of reported intake recorded energy expenditure of only 69% and 61%, respectively. Reported intake of obese and previously obese women was only 73% and 64% of expenditure, whether measured by weighed record or by diet history, confirming suspicions that these subjects misrepresented their intake. Acceptable weighed records were obtained from 7- and 9-year-olds whereas 15- and 18-year-olds underestimated intake. Diet histories taken from the same children tended to overestimate intake. These studies suggest that, ideally, all dietary studies should include independent measures of validity.

Validation of weighed records and other methods of dietary assessment using the 24 h urine nitrogen technique and other biological markers.

Results from analysis of 24 h urine collections, verified for completeness with para-amino benzoic acid, and blood samples collected over 1 year were compared with 16 d weighed records of all food consumed collected over the year, and with results from 24 h recalls, food-frequency questionnaires and estimated food records in 160 women. Using the weighed records, individuals were sorted into quintiles of the distribution of the urine N excretion:dietary N intake ratio (UN:DN). UN exceeded DN in the top quintile of this ratio; mean ratio UN:DN = 1.13. Individuals in this top quintile were heavier, had significantly greater body mass indices, were reportedly more restrained eaters, had significantly lower energy intake:basal metabolic rate ratios (EI:BMR), and had correlated ratios of UN:DN and EI:BMR (r -0.62). Those in the top quintile reported lower intakes of energy and energy-yielding nutrients, Ca, fats, cakes, breakfast cereals, milk and sugars than individuals in the other quintiles but not lower intakes of non-starch polysaccharides, vitamin C, vegetables, potatoes or meat. Correlations between dietary intake from weighed records and 24 h urine K were 0.74 and 0.82, and between dietary vitamin C and beta-carotene and plasma vitamin C and beta-carotene 0.86 and 0.48. Correlations between dietary N intake from weighed records and 24 h urine excretion were high (0.78-0.87). Those between N from estimated food records and urine N were r 0.60-0.70. Correlations between urine N and 24 h recalls and food-frequency questionnaires were in the order of 0.01 to 0.5. Despite problems of underreporting in overweight individuals in 20% of this sample, weighed records remained the most accurate method of dietary assessment, and only an estimated 7 d diary was able to approach this accuracy.

The sensitivity and specificity of the Goldberg cut-off for EI:BMR for identifying diet reports of poor validity

Objective: To explore the specificity and sensitivity of the Goldberg cut-off for EI:BMR for identifying diet reports of poor validity as compared with the direct comparison of energy intake with energy expenditure measured by doubly-labelled water.Design: Twenty-two studies with measurements of total energy expenditure by doubly-labelled water (EE), basal metabolic rate (BMR) and energy intake (EI) provided the database (n=429). The ratio EI:EE provided the baseline definition of under- (UR), acceptable- (AR) and over-reporters (OR), respectively EI:EE <0.76, 0.76–1.24 and >1.24. Four strategies for identifying under- and over-reporters using the Goldberg cut-off were explored. Sensitivity of the cut-off was calculated as the proportion of UR correctly identified and specificity as the proportion of non-UR correctly identified.Results: UR, AR and OR (by EI:EE) were 34, 62 and 4% respectively of all subjects. When a single Goldberg cut-off for the physical activity level (PAL) of 1.55 was used, for men and women respectively the sensitivity was 0.50 and 0.52 and the specificity 1.00 and 0.99. Using a cut-off for higher PAL traded specificity for sensitivity. Using the cut-off for a PAL of 1.95, sensitivity was 0.76 and 0.85 and the specificity 0.87 and 0.78 for men and women respectively. Using cut-offs for mean age–sex specific PAL did not improve sensitivity. When subjects were assigned to low, medium and high activity levels and cut-offs for three different PALs used, sensitivity improved to 0.74 and 0.67 without loss of specificity (0.97 and 0.98), for men and women respectively. If activity levels for men were applied to the womens’ data, sensitivity improved to 0.72.Conclusion: To identify diet reports of poor validity using the Goldberg cut-off for EI:BMR, information is needed on each subject’s activity level.European Journal of Clinical Nutrition (2000) 54, 395–404

Assessment of selective under-reporting of food intake by both obese and non-obese women in a metabolic facility

OBJECTIVE: To investigate the degree of bias in under-reporting of food intake in obese and non-obese subjects, hypothesising that under-reporting may be selective for either macronutrient content (carbohydrate (CHO), fat, protein, alcohol), specific food types or eating occasions (meals, snacks).DESIGN: Thirty-three women (18 obese, 15 non-obese) were recruited to a long-stay metabolic facility for 24 h. Ad libitum food intake was covertly measured throughout the study and a reported food intake completed at the end of 24 h.RESULTS: Reported total daily energy intake was significantly lower than measured intake. Whilst meals were accurately reported, energy from snack foods eaten between meals was significantly under-reported. (P<0.001) Reported total carbohydrate and added sugar intakes were significantly lower than measured, whilst reported protein and fat intakes were not significantly different from measured. Reported alcohol intake was also considerably lower than measured, but high variability prevented significance.CONCLUSIONS: In both obese and non-obese women the major cause of under-reporting, as assessed by covert study design in subjects restricted within a metabolic facility, is the failure to report between-meal snack foods. There is some evidence for increased under-reporting in high CHO, but no evidence of a bias in under-reporting towards high fat or high protein foods.

Biased Over- Or Under-Reporting is Characteristic of Individuals Whether Over Time or by Different Assessment Methods

Seven studies with repeated measurements of energy intake and/or nitrogen intake were examined to determine whether misreporting is characteristic of some persons or occurs randomly. Four of the studies were validated by doubly labeled water measurements of energy expenditure. Reporting validity was expressed as the ratio of energy intake to energy expenditure. Ratios were consistently below the expected value of 1.0 for some subjects and consistently above 1.0 for others, indicating characteristic reporting validity within subjects. Two year-long studies provided 4 to 12 measurements and a total number of days sufficient to measure individual habitual intake. Subjects mean energy intake to basal metabolic rate (BMR) ratios were < 1.35 in 45% and 47% and < 1.35 at every measurement in 25% of subjects. This indicated persistent underreporting over time, because 1.35 x BMR is the minimum energy expenditure compatible with a normally active lifestyle. Three of the studies used more than 1 assessment method (validated by doubly labeled water and/or urinary nitrogen excretion). There was a tendency for persons determined to be underreporters by 1 method to be also underreporters when tested by other methods. We conclude that biased over- or underreporting is characteristic of some persons. Thus, repeat measurements do not necessarily provide valid measures of individual intake, extreme intakes may reflect under- and overreporting rather than true low or high intakes, and subjects most prone to reporting bias may be repeatedly misclassified in quantiles of the distribution. This presents a challenge to dietitians nutritionists, and statisticians both for the design of surveys and the handling of flawed data.

Within- and between-subject variation in energy expenditure measured by the doubly-labelled water technique: implications for validating reported dietary energy intake.

Objectives: To estimate the total (CVt), within-subject (CVw) and between-subject (CVb) variation in free-living energy expenditure as measured by the doubly-labelled water (DLW) technique. To examine the limitation of the DLW measurement of energy expenditure for evaluating reported energy intake. To estimate the probable minimum and maximum ‘habitual’ energy expenditures for a sustainable lifestyle.Design: Review and analysis of individual data from 25 studies with repeat DLW measurements of energy expenditure (EE).Results: Pooled mean CVw derived from 21 studies was 11.8% for EE and 12.3% for physical activity level (PAL). Multiple regression analysis of CVw in 25 studies found a positive association with time span between measurements. At zero time CVw for EE was 8.2% rising to 9.6% at 13 weeks and 15.4% at 52 weeks. At the same time points CVw for PAL was 9.1%, 10.0% and 13.4% respectively. Pooled mean CVt was 13.0% for EE and 10.7% for PAL. CVb calculated from pooled mean CVt and CVw was 20.6% for EE and 7.2% for PAL. 95% confidence limits of PAL in 11 age–sex groups averaged 1.2 to 2.2.Conclusions: The analysis supported previous estimates of 8% for within-subject variation in DLW measurements including analytic plus inherent biologic variation. Variation that included changes in weight, season and activity increased with increased time between measurements to about 15% at a time span of 12 months. Confidence limits of agreement between EE and reported energy intake were estimated to range from ±15% to ±32%. Estimates of the range of usual EE for normally active persons ranged from 1.3 to 2.2.European Journal of Clinical Nutrition (2000) 54, 386–394