objectives), and must be methodologically (precision, accuracy,
sensitivity, specificity) and biologically (biological plausibility,
dose-response ratio, consistency) validated.
Moreover, it should be noted that it is not feasible to perform
the direct measurement of the effect of consuming a single food or
a single dietary component as these need to be considered in the
context of the overall diet. In the case of provitamin A carotenoids,
the effects could be due to their conversion to retinol or to their
own biological activities.
3.4 Duration
of the Study
In addition to the concentration of the bioactive compound supplied, it is also important to consider the time during which it is
consumed. Hence, the duration of the study should be sufficient to
allow changes in the primary outcome measured but not longer to
avoid participant noncompliance or withdrawal. Turnover rates of
relevant tissues should also be taken into account.
3.5 Quality, Validity,
and Reliability
of the Measurements
The equipment and procedures used for biomarker analysis and the
training of personnel involved in the study will contribute to the
internal and external validity of the intervention study. This
includes the calibration of instruments, standardization of procedures, training of researchers, dietary interviews, and anthropometric measurements. In this regard, it is important to check the
compliance (adherence to the treatment) of the participants with
the intervention assigned by means of biochemical markers or
evaluations based on dietary assessment through periodic visits
and examinations.
3.6 Data Collection
Interviews of participants, physical examinations (anthropometric
data), laboratory procedures (i.e., biomarkers), and other complementary tests (nutritional status assessment—dietary evaluation)
must be standardized. Special attention should be paid to factors
that could influence the degree of association between intervention
and outcome (confounding or interaction factors). If such factors
are known, they should be distributed evenly among the groups.
Regardless of the intervention study being conducted, it is
always advisable to carry out a dietary assessment in order to
know normal (or past) intake patterns and the present intake of
the subjects [26] (see Note 12). This requires the use of FCT with
individualized carotenoid data (i.e., [11].). When preparing
(or choosing) a questionnaire to assess ingestion, it is important
to define which components of the diet that should be the focus of
attention, the chemical formats in which they are found (i.e., freeform carotenoids, in ester form as total forms or isomers) and what
types of food they are found in. In the case of carotenoids, it is also
useful to know what factors may affect the absorption and metabolism of carotenoids such as, for example: tobacco consumption,
chronic disease, use of medicines or food supplements. In general,
Intervention Studies
369
sensitivity, specificity) and biologically (biological plausibility,
dose-response ratio, consistency) validated.
Moreover, it should be noted that it is not feasible to perform
the direct measurement of the effect of consuming a single food or
a single dietary component as these need to be considered in the
context of the overall diet. In the case of provitamin A carotenoids,
the effects could be due to their conversion to retinol or to their
own biological activities.
3.4 Duration
of the Study
In addition to the concentration of the bioactive compound supplied, it is also important to consider the time during which it is
consumed. Hence, the duration of the study should be sufficient to
allow changes in the primary outcome measured but not longer to
avoid participant noncompliance or withdrawal. Turnover rates of
relevant tissues should also be taken into account.
3.5 Quality, Validity,
and Reliability
of the Measurements
The equipment and procedures used for biomarker analysis and the
training of personnel involved in the study will contribute to the
internal and external validity of the intervention study. This
includes the calibration of instruments, standardization of procedures, training of researchers, dietary interviews, and anthropometric measurements. In this regard, it is important to check the
compliance (adherence to the treatment) of the participants with
the intervention assigned by means of biochemical markers or
evaluations based on dietary assessment through periodic visits
and examinations.
3.6 Data Collection
Interviews of participants, physical examinations (anthropometric
data), laboratory procedures (i.e., biomarkers), and other complementary tests (nutritional status assessment—dietary evaluation)
must be standardized. Special attention should be paid to factors
that could influence the degree of association between intervention
and outcome (confounding or interaction factors). If such factors
are known, they should be distributed evenly among the groups.
Regardless of the intervention study being conducted, it is
always advisable to carry out a dietary assessment in order to
know normal (or past) intake patterns and the present intake of
the subjects [26] (see Note 12). This requires the use of FCT with
individualized carotenoid data (i.e., [11].). When preparing
(or choosing) a questionnaire to assess ingestion, it is important
to define which components of the diet that should be the focus of
attention, the chemical formats in which they are found (i.e., freeform carotenoids, in ester form as total forms or isomers) and what
types of food they are found in. In the case of carotenoids, it is also
useful to know what factors may affect the absorption and metabolism of carotenoids such as, for example: tobacco consumption,
chronic disease, use of medicines or food supplements. In general,
Intervention Studies
369