Introduction to Human Nutrition

13

Nutrition Research Methodology

J Alfredo Martínez and Miguel A Martínez-González

Key messages

• This chapter identifi es critical aspects and factors involved in
  nutritionally orientated investigations as well as the measure-
  ment qualities concerning research procedures.


• It describes how to select methods and techniques as well as
  animal models to assess nutrient utilization and functions.

© 2009 JA Martínez and MA Martínez-González.

• It defi nes indicators and markers of dietary intake and metabo-
  lism in human studies.


• It helps to choose methods to investigate the causal relationships
  between diet and disease.

13.1 Introduction

Research is a meticulous process to discover new, or
collate old, facts by the scientifi c study of a subject or
through a critical investigation. In this context, nutri-
tion research involves advances in knowledge con-
cerning not only nutrient functions and the short- or
long-term infl uences of food and nutrient consump-
tion on health, but also studies on food composition,
dietary intake, and food and nutrient utilization by
the organism.
The design of any investigation involves the selec-
tion of the research topic accompanied by the formu-
lation of both the hypotheses and the aims, the
preparation of a research protocol with appropriate
and detailed methods and, eventually, the execution
of the study under controlled conditions and the
analysis of the fi ndings leading to a further hypothe-
sis. These stages of a typical research program are
commonly followed by the interpretation of the
results and subsequent theory formulation. Other
important aspects concerning the study design are the
selection of statistical analyses as well as the defi nition
of the ethical commitments.
This chapter begins with a review of some of the
important issues in statistical analysis and experi-
mental design. The ensuing sections look at in vitro
techniques, animal models, and fi nally human studies.

The primary purpose is to provide a primer in nutri-

tion research methods early in a student’s career to

allow a more critical review of the many studies that,

from time to time, a student will need to consider in

the course of their study.

13.2 Statistical analysis and

experimental design

In all areas of research, statistical analysis of results

and data plays a pivotal role. This section is intended

to give students some of the very basic concepts of

statistics as it relates to research methodology.

Validity

Validity describes the degree to which the inference

drawn from a study is warranted when account is

taken of the study methods, the representativeness of

the study sample and the nature of its source popula-

tion. Validity can be divided into internal validity and

external validity. Internal validity refers to the subjects

actually sampled. External validity refers to the exten-

sion of the fi ndings from the sample to a target

population.

Accuracy

Accuracy is a term used to describe the extent to

which a measurement is close to the true value, and