ASSESSMENT OF THE ADEQUACY OF INDIVIDUAL NUTRIENT INTAKE IN WOMEN IN THE WAITING LINE
FOR BARIATRIC SURGERY IN RELATION TO THOSE WHOSE SURGERY WAS MORE THAN TWO YEARS
AGO
Noa PP Souza1, Patrícia FS Novais2, Irineu Rasera Jr3, Claudia RP Detregiach4, Deborah de Oliveira5, Maria RM Oliveira4
1
Doutoranda. Universidade Estadual Paulista, Araraquara, Brasil, [email protected]
Clinica Bariátrica de Piracicaba / Universidade Estadual Paulista, Piracicaba, Brasil, [email protected]
3
Clinica Bariátrica de Piracicaba e FMB/UNESP, Brasil. [email protected]
4Centro de Estudos e Práticas em Nutrição/ IBE -UNESP, Botucatu, Brasil, [email protected]
5
Graduanda do Curso de Nutrição da Universidade Estadual Paulista, Botucatu, Brasil, [email protected]
2
Abstract: Of the set of American and Canadian references,
the Estimated Average Requirement (EAR), which
represents the median intake of a reference population, was
taken as the cut-off point for the assessment of the adequacy
of individual nutrient intake in women who have undergone
or will undergo obesity surgery.
Keywords:
population
dietary
assessment,
obesity,
environment), assuming a normal distribution of the data
under the curve (or normalized by statistical methods).
reference
1. INTRODUCTION
The Dietary Reference Intakes (DRI) are defined as
the set of American and Canadian reference values that
correspond to quantitative estimates of nutrient intake,
established to be used in the dietary planning and
assessment of healthy individuals and groups, according to
their life stage and gender. The DRI cover and differentiate
the
concepts
of
nutritional
requirements
and
recommendations [1]. The Nutritional Requirements are
defined as the amount of nutrients and energy available in
foods that a healthy individual should ingest to meet his or
her normal physiological requirements and prevent
deficiency symptoms (means for similar population groups).
Meanwhile, the Nutritional Recommendations are the intake
values of essential nutrients that, based on scientific
knowledge, are considered adequate to meet the specific
nutrient requirements of nearly all healthy individuals
(mean + safety margin).
The DRI proposition took into account the energy
and nutrient balance and metabolism of different age groups
and genders, the reduction of risks for non-communicable
chronic diseases, the bioavailability of the nutrients and the
errors associated with the assessment methods [1]. The DRI
consist of the EAR (Estimated Average Requirement), RDA
(recommended dietary allowances), AI (Adequate Intake)
and UL (Tolerable Upper Intakes Levels). These values
were established from the estimated intakes of a reference
population (intake by healthy individuals living in a suitable
Figure 1 - Dietary Reference Intakes [1]
In the distribution curve of the reference population
(Figure 1), the EAR is the mean, which corresponds to 50%
of the area under the curve. The EAR is the smallest value
that meets the requirement of the group [1]. Thus, an
individual who habitually ingests an amount of nutrients
corresponding to the EAR has a 50% chance of ingesting an
adequate amount during the reference period. The RDA
corresponds to 97-98% of the area under the curve, meeting
the requirements of almost all individuals of a given age
group. The AI area in the distribution curve of the reference
population is not accurate because it is a value that has been
arbitrarily established when the EAR cannot be established.
Meanwhile the UL refers to the upper level of daily nutrient
intake that does not offer a risk of side effects for almost all
individuals of the general population [1]. It is also an
arbitrary value that has not been determined for all
nutrients.
To assess the adequacy of food intake by an
individual, it is first necessary to establish his or her
habitual nutrient intake and confront it with his or her
Proceedings of the 9th Brazilian Conference on Dynamics Control and their Applications
Serra Negra, SP - ISSN 2178-3667
1113
requirements. This would require one to know the food
intake during a long period of time, taking into account the
great intra-individual intake variation. This makes it
impossible to assess an individual’s actual intake.
Therefore, in practice, the apparent intake is assessed using
food questionnaires on three non-consecutive days.
However, these data do not allow one to correctly assess the
intrapersonal intake variation, so the use of pre-established
variability values of a reference population is
recommended. Hence, in order to calculate the intake
adequacy of a given nutrient, one needs to take into account
the estimated requirement given by the EAR of the nutrient,
the variation coefficient of this nutrient and the
intrapersonal variation. With this information, it is possible
to estimate a confidence interval in which the nutrient
intake meets the individual’s requirement. Thus, the
probability that the intake of a nutrient is adequate is given
by a z score [2,3].
The micronutrient requirements of obese
individuals are theoretically the same as those of the general
population. Meanwhile, the requirements of individuals who
undergo obesity surgery are greater since these surgical
procedures limit nutrient intake and/or absorption, so it is
important to assess the adequacy of micronutrient intake of
this population.
2. OBJECTIVE
The objective of this study was to discuss the
adequacy of individual intakes of vitamin C, vitamin A,
riboflavin, niacin, pyridoxine, phosphorus, magnesium, iron
and zinc in women who underwent obesity surgery more
than two years ago and in those who will undergo obesity
surgery.
3. METHOD
A total of 70 women aged 21 to 67 years
participated in the study. Of these, 35 had already
undergone bariatric surgery (banded or not Roux-en-Y
gastric bypass (RYGB)) two or more years ago and the
other 35 women were waiting for surgery. The study was
approved by the Research Ethics Committee of the School
of Pharmaceutical Sciences of UNESP in Araraquara,
protocol CEP/FCF/CAr. nº 16/2006, opinion nº 8/2007.
Food intake during three non-consecutive days
was investigated with a 24-hour recall. The women were
asked about the kind of meals, foods and beverages they
had had in the previous 24 hours, expressed in cooking
units, which were then converted to grams (g). The nutrient
composition was estimated with the software NutWin® 1.5,
version 2002. The nutrient supplementations prescribed to
patients who had already undergone surgery were not taken
into account.
Assessment of the adequacy of individual intake
was done by subtracting the median requirement from the
intake, as follows:
D = Mi − EAR
Where:
D = difference
Mi = mean intake.
EAR = median requirement
(1)
Z = D/Dpo =
(2)
Where:
Mi = mean intake of the nutrient in “n” days by the
individual
EAR = the best estimate of the individual’s requirement for
the nutrient
V req = requirement variance
V int = intrapersonal variance
The requirement variation coefficient assumed for
all nutrients was 10%. The intrapersonal variation was
calculated by considering the standard deviation of North
American population studies [4].
The calculations were done in a spreadsheet
created specifically for estimating the adequacy of nutrient
intake, based on Excel®’s dynamic spreadsheets which
allow the calculation of Z and the estimate of the probability
of judging the intake adequacy correctly.
In order to calculate the magnitude of the
difference in terms of the probability of judging the intake
adequacy of a particular nutrient correctly (Chart 1) the
standard deviation of the difference was considered by
calculating Z, corrected for requirement and intake
variances.
Chart 1 - Values for the ratio D/SDo (Z) and the corresponding
probability of judging correctly if the habitual intake is adequate
Criterion
D/SDo
(Z)
> 2.00
> 1.65
> 1.5
>1.00
> 0.50
>0.00
< -0.50
< -1.00
< -1.50
< -1.65
< -2.00
Judgment regarding
habitual intake
Adequate
Adequate
Adequate
Adequate
Adequate
Adequate / Inadequate
Inadequate
Inadequate
Inadequate
Inadequate
Inadequate
Probability of
judging correctly
0.98
0.95
0.93
0.85
0.70
0.50
0.70
0.85
0.93
0.95
0.98
Source: Snedecor; Cochran, 1980. In: [4].
Considering that the percentage of adequacy in
relation to the RDA was an assessment approach used until
the 1990’s and still used by some professionals in their
Proceedings of the 9th Brazilian Conference on Dynamics Control and their Applications
Serra Negra, SP - ISSN 2178-3667
1114
practice, for comparison the individual intake (mean of
three days) was expressed in percentile of the RDA, setting
the cut-off point at 85% (coefficient of variation=15%).
Table 2. Comparison of the assessment of adequacy by Z1 and by
RDA2.
Before surgery
AD
PA = (Mi / RDA) * 100
Vitamin C:
Where:
PA = Percentage of adequacy
Mi = Mean intake of the nutrient during “n” days by the
individual
RDA = Recommended Dietary Allowances [4]
The data were input in Excel® spreadsheets and
processed or transferred to the BioEstat 3.0 software [5] for
the statistical analyses. The comparison between
proportions of adequacy and inadequacy was done by the
chi-square test (χ2) or Fisher’s exact test for expected values
smaller than 5 or null. The Adequate/Inadequate category
was merged with Inadequate to allow comparison with the
PA of the RDA. The significance level was set at 5%.
26
9
10
13
22
18
Z
Median (min-max)
19
16
7
28
p=0.002; χ2=8.811
Riboflavin:
Z
RDA
30
5
25
10
p=0.145; χ2=2.121
Niacin:
26
8
27
p=0.780; χ2=0.078
15
20
21
14
p=0.151; χ2=2.059
16
6
25
10
23
Z
17
18
18
17
p=0.811; χ2=0.057
31
4
7
28
p=0.000; χ2=33.158
31
4
19
28
7
11
p=0.324; χ =0.971
RDA
24
p=0.053; χ =3.733
15
20
0
3
32
1
35
34
p=1.000
Z
32
3
0
33
RDA
0
35
1
34
p=0.000; χ2=58.947
Zinc:
16
2
p=0.001; χ2=10.769
Iron:
12
p=0.000; χ =17.014
Z
Z
29
2
RDA
2
Magnesium:
9
19
p=0.137; χ =2.202
Phosphorus:
p=0.051; χ =3.809
Z
2
17
2
RDA
RDA
Table 1 – Age and anthropometric data of women before and 2 years
after bariatric surgery, Piracicaba, 2008.
Pre-surgery group
Post-surgery group
P-value*
(n=35)
(n=35)
25
Z
RDA
RDA
4. RESULTS
Table 2 lists the results of two assessment
approaches: corrected Z according to the requirement and
intake variances (EAR) and percentage of the RDA. Of the
9 nutrients investigated, Z assessment indicates that 5
nutrients have a greater proportion of adequacy in women in
the waiting line for obesity surgery. On the other hand, the
proportion of adequacy among women who had already
undergone surgery was significantly greater in the
percentage of RDA-based assessment.
IN
p=0.001; χ =9.785
Pyridoxine:
Ages and anthropometric characteristics of the
women who participated in the study are listed in Table 1.
Note that the age range of women who are waiting for
bariatric surgery is greater.
AD
2
Vitamin A:
After surgery
IN3
p=1.000
Z
29
6
3
32
RDA
19
16
11
24
p=0.010; χ2=6.629
p=0.017; χ2=5.714
Z of the median requirement corrected by the requirement and intake
variance; RDA = percentage of the Recommended Dietary Allowances.
3
(AD/IN+IN)
1
Median (min-max)
Age (years)
37 (21 – 67)
46 (26 - 61)
0.009
Height (m)
1.6 (1.4 – 1.8)
1.6 (1.4 – 1.7)
0.638
Weight (kg)
114.5 (93.6 – 155.6)
76.8 (58.9 – 121.7)
0.000
BMI (kg/m2)
45.3 (36.1 – 60.0)
31.4 (22.8 – 48.8)
*= Mann-Whitney test; BMI = body mass index
0.000
Figure 2 shows the intakes of the two groups
according to the proportion of adequacy, classified by Z
after correction for EAR variances and intra-individual
intake. The comparison of the proportions of nutrient intake
adequacy between the groups showed that all nutrients
differed (Figure 2). Inadequacy prevailed among women
who had already undergone obesity surgery: the proportion
of inadequate + adequate/inadequate exceeded 50% for all
nutrients except phosphorus.
Proceedings of the 9th Brazilian Conference on Dynamics Control and their Applications
Serra Negra, SP - ISSN 2178-3667
1115
whose mean intake is below the EAR is probably
consuming an inadequate amount. How about individuals
whose intake is between the EAR and the RDA?
In the assessment of individual intake adequacy,
intake is considered adequate according to the DRI if the
probability of judging its adequacy correctly is greater than
70% (Chart 1), which is very different from 85% of the
RDA. It is not enough to locate the mean intake in a
particular point of the population distribution curve and
infer, from that point, that the intake is adequate or not,
since there is a built-in variation coefficient of 10 to 15% in
the EAR and a great variation in the intra-individual intake,
which is proportionally different from nutrient to nutrient
[4]. This leads to the approach proposed by the DRI which
takes into account these elements when calculating Z, which
in turn corresponds to the probability of judging the
adequacy correctly.
In this approach, a percentage of adequacy greater
than 100% of the RDA can also represent, although poorly,
the probability of inadequacy. Thus, the DRI confer the
concept of adequacy reliability to the assessment, and
consider the values below 70% (Probability of judging
correctly) or Z<0.5 critical.
Figure 2 – Adequacy of nutrient intake in women before (A) and 2
years after (B) bariatric surgery. Piracicaba, 2008. (p<0.005 for all
comparisons done with the χ2 test or Fisher’s exact test). IN=
inadequate. AD/IN= adequate/inadequate. AD= adequate.
5. DISCUSSION
The DRI provide a series of references for the
assessment
of
intake
adequacy
and
nutrient
recommendation [4]. In the present study, the methodology
proposed by this American and Canadian reference was
used to assess the adequacy of individual intake. It is known
that the micronutrient status of an individual can only be
accurately assessed through biochemical tests of the body
reserves, but in clinical practice food intake data are used as
indicators of this status and for dietary prescription. In this
sense, micronutrient intake data can supply valuable
information for the prevention of future deficiencies or even
for pointing out the need of more thorough assessments.
Until the end of the 1990’s, the only reference for
assessing micronutrient intake was the RDA and adequacy
assessment was done in terms of percentage of the RDA, as
illustrated by the present study (Table 2). But the cut-off
point where the percentage of intake adequacy was
considered inadequate was never very clear and this
approach did not take the requirement and intake variances
into account. Since the RDA meet the requirements of
almost 100% of the population, this approach did not result
in proportions of adequacy smaller than those referenced in
the variances.
It is fact that an individual with a mean intake
equal to or greater than the RDA is probably consuming an
adequate amount of nutrients. Likewise, an individual
Some groups within the population require more
intense nutritional monitoring, especially because they
consume smaller amounts of energy and consequently,
micronutrients. It is the case of the individuals who have
undergone bariatric surgery to control obesity. Some time
after surgery, these individuals regain some of their past
eating habits, but to what extent do the dietary nutrient
intakes meet their requirements? Should supplementation be
prescribed prophylactically and indiscriminately?
The modification of the gastrointestinal tract by
bariatric surgery implies in changes in the dietary patterns
since the individual needs to adjust to the new conditions,
such as smaller volume of food intake and characteristics of
the ingested micro- and macronutrient sources [6].
Therefore, it is important to assess the adequacy of the
individual’s intake. Furthermore, the standard meal of this
population is very different from that of the general
population and there is no reference of its intrapersonal
variance.
Regarding the estimated micronutrient intakes that
were assessed by the EAR Z, there were more probabilities
of adequacy among women who were waiting for surgery
than among those who had already had surgery (Figure 2).
Novais [7] used the group assessment proposed by
the DRI [4] to analyze the adequacy of nutrient intake in
women who had had bariatric surgery more than two years
before the study and found high proportions of
micronutrient intake adequacy probabilities; however, this
assessment took into account the regular intake of dietary
supplements by the studied population.
In the DRI document [4], the circumstances in
which the individual approach can be used to infer results
Proceedings of the 9th Brazilian Conference on Dynamics Control and their Applications
Serra Negra, SP - ISSN 2178-3667
1116
for a group of people in terms of proportion of adequacy is
not clear. Other statistical procedures are proposed for
group assessments. This study tried to show that although
generous, the RDA-based assessment can classify an
inadequate intake as adequate and vice-versa, when
compared with the approach that considers variances. For
bariatric patients, this aspect is of great relevance when
dietary assessments are made to provide correct
supplementation prescriptions [8, 9].
Iron deficiency and anemia are the most common
nutritional complications of bariatric surgery [10]. The
deficiency of this mineral occurs in 30 to 50% of the
patients two to three years after obesity surgery, especially
in women who menstruate [11]. Iron deficiency in this case
is due to many factors: a) lower ability of the
gastrointestinal tract to reduce dietary iron and increase its
absorption, due to decreased gastric acid; b) duodenum and
jejunum bypass done in bariatric surgery, main locations of
absorption of this nutrient; c) possible competition between
iron and calcium inhibiting iron absorption since calcium is
generously supplemented after bariatric surgery; d) reduced
heme iron intake [10, 11, 12, 13]. In the present study, the
adequacy of iron intake in women who were waiting for
obesity surgery was inversely proportional according to
assessments based on Z and RDA. Almost all the women
presented an adequate intake according to the Z-based
assessment (Table 2). Meanwhile, iron intake among
women who had already had surgery was inadequate
according to all approaches.
It is known that red meat is a good source of heme
iron, zinc and niacin. However, meat is one of the main
foods not tolerated after bariatric surgery. This intolerance is
due to a change in the production of pepsin, responsible for
the digestion of proteins, after resection of much of the
stomach during surgery [14, 15, 16, 17]. Whole grains,
which are rich in magnesium, are foods that are not
consumed very often after surgery but could reduce the
inadequacy of some nutrients [8, 18].
Some authors have found that patients already
present nutritional deficiencies before surgery: 20 to 32% of
the candidates to bariatric surgery do not consume enough
iron. This is due to the fact that despite the high energy
intake of these patients, they do not consume enough
micronutrient-rich foods [10, 23, 24]. In the present study,
intake was considered adequate according to the Z-based
assessment but hardly anyone reached 70% of the RDA.
Thus, one can infer that there is no safety margin in the iron
intake of women in the line for bariatric surgery.
The deficiency of other nutrients after surgery,
such as vitamin A, has been reported [19, 20, 21, 22] and
confirmed by a reduced plasma concentration of vitamin A
in patients subjected to RYGB, reaching a reduction of 10%
after a few years [10]. In the present study, the consumption
of vitamin A among women who had already had surgery
was marginal: it was not possible to state if vitamin A
intake was adequate or inadequate in 18 of the 35 women.
Souza (2007) assessed the adequacy of food intake
in adult women in the waiting line for bariatric surgery. He
found that the intakes of iron, vitamin B12 and vitamin C
were, on average, below the estimated requirements, while
calcium and potassium intakes were, on average, below the
recommended intake values [25].
Generally, in this study, the nutrient intakes that
were most likely to be inadequate were niacin, magnesium,
iron and zinc. Nutrients such as iron, vitamin B12, vitamin
A and thiamine are frequently reported in the literature as
nutrients involved in nutritional deficiencies [19, 20, 21,
22].
In this context, it is necessary to emphasize that the
RYGB surgical technique is a mixed technique, that is, it is
restrictive and malabsorptive. It is not possible to state if the
dietary availability of these nutrients was fully utilized,
because of the physiological changes caused by the surgical
procedure [6,26,27]. Thus, to state that intake is adequate,
serum tests would be necessary. However, this intake
assessment approach should be improved for this group of
patients, maybe considering bioavailability to guide
professionals in their supplementation policies.
6. CONCLUSION
Individual intake adequacy assessments in women
who have undergone bariatric surgery evidenced the need
for prophylactic mineral and multivitamin supplementation
on a permanent basis to avoid nutritional deficiencies after
obesity surgery. This study found that the EAR Z is the
most sensitive way to assess the adequacy of an individual’s
micronutrient intake, but this approach needs adjustments to
be used routinely in the care of bariatric patients.
ACKNOWLEDGMENTS
We thank Fundação de Amparo à Pesquisa do Estado de
São Paulo – FAPESP for sponsoring the study.
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