Previously, it was not possible to calculate dietary choline intake in humans, and there are currently no nationally representative estimates of the intake of choline from food or food supplements (7
). This is because the choline content of foods had not been included in major nutrient databases; moreover, until quite recently, extensive food choline data were either lacking or unreliable due to older, imprecise assay procedures.
Using new and recently published data on choline levels in a large number of common foods, we report here that healthy men and women consumed amounts of choline that were at or slightly higher than the current AI level, but some individual subjects, especially women, consumed slightly less. Theses data are of use to nutrition scientists considering the likely validity of the current dietary recommendation. If we had found that healthy individuals consumed significantly less than the recommendations, it would have led to the conclusion that the recommended amounts were likely too high. Our data suggest that the recommended intake is very close to the actual intake of this nutrient, although only 6/16 women met or exceeded this recommended intake of choline.
Betaine intake was substantial in all subjects and may have spared conversion of dietary choline to betaine for methylgroup donation. Vitamin B-12, and methionine + cysteine intakes were well above the current established requirements, and folate intake was adequate in men and women.
We obtained a measurement of dietary intake of choline using in-patient subjects whose total food intake was observed directly for at least 3 d, and we compared these measurements with estimates derived from self-reported intakes during another period. In an earlier study, choline levels calculated from the analysis of individual components of the diet were compared with values obtained from analyses of all foods combined into a single sample (12
). The laboratory analyses of choline and betaine in the whole diet aliquots matched the estimated amounts in the diets that were calculated from the analyses of individual foods. We are thus confident that our calculated estimates of choline intake based on the observed and measured diet phase with ad libitum consumption accurately represent actual choline intakes.
Much debate surrounds the accuracy of current methods to assess dietary intake; 7-d weighed food records were historically considered to be the best for estimating dietary exposure; however, 3- or 4-d records are commonly used in research studies (13
). Validation studies of various dietary assessment instruments, including food records, against doubly labeled water, the most widely accepted biomarker of energy intake, revealed that self-report intake instruments consistently underestimate energy intake (14
). Here we found that self-report in 3-d food records significantly underestimated daily choline intake (as well as betaine, folate, vitamin B12, and methionine + cysteine intakes). There are many possible explanations to account for this discrepancy. Because the amount of choline ingested relative to energy status was similar in the measured and estimated analyses, subjects likely underreported total food intake or serving sizes. Subjects may also have selected a different variety of foods in the hospital-like situation than they would have at home. Although this may be the case, it is difficult to believe that differences of the magnitude that we observed can be explained solely by this factor. Finally, due to the wide variety of foods reported and the limited nature of the database, a number of substitutions had to be made in the analyses. We do not think it is likely that these substitutions contributed to the observed discrepancy because they occurred in both the reported and measured intake analyses. Our data suggest that self-report using 3-d food records should be used with caution when assessing choline or other nutrient intakes.
In summary, we report for the first time the range of ad libitum dietary consumption of choline and betaine in healthy humans. The observed values are similar to the recommended AI for choline.