HNE Summary edX
Module 1
Dietary Assessment
Dietary assessment - questionnaires
Many studies rely on special questionnaires called food frequency questionnaires (FFQ). These
questionnaires ask subjects how often they eat certain types of food and in what amounts. These
questionnaires are different for different countries.
Dietary assessment - recall and diary
Another way to asses dietary intake is by asking people to recall the foods they ate over the past 24
hours, this is called a 24h dietary recall. This is usually performed several times to get a decent
estimate of people’s regular food consumption.
Another way of tracking dietary intake is called a food diary or food record. People write
down what they eat in a day, and sometimes even weigh it, for a week or longer. The advantage of
this technique is that they can be accurate if it is done well. The disadvantage is that people tend to
change their food intake when they have to write everything down. This technique is also expensive
and time consuming, people may lose motivation and become sloppy.
From diet to nutrient intake
The next step is to convert the information from the food questionnaires and food records into
nutrient intake, which is done using so-called food composition tables. Food composition tables are
very large tables that contain information on the nutrient content of a great variety of foods
consumed in a certain region or country. The included nutrients are fat, carbohydrates (including
fibre and sugar), protein and many vitamins and minerals. Combining the food eaten with the table
gives information about the nutrient intake a day. Limitation: many foods are not listed in the
table nutrition researchers have to select an alternative food product to calculate nutrient intake.
Advantage: fairly efficient. Disadvantage: people are not always 100% truthful.
Study designs
Ecological studies: a type of observational study in which the units of analysis are not individuals but
populations or groups of people.
Cross-sectional studies: what is special about this is that dietary intake and the outcome are
addressed at the same time. Because this is measured at the same time the result of the exposure
could be the consequence of the outcome instead of the other way around. This is called reverse
causality. If the outcome of the study is a parameter people don’t know about (blood pressure etc.)
the direction of the relation is more or less fixed. This study shows an association and cannot say if
the relation is causal. This study is prone to confounding. You could think of this as a snapshot of a
group of people at a given point in time.
Case-control study: retrospective studies, which means you look into the past. The basic design: a
group of patients with a certain disease are collected. A group of subjects that do not have the
disease form the control group. All subjects are asked about their dietary habits using food frequency
questionnaires or other types of dietary assessment tools. The dietary information from the two
groups is compared to see if there are any differences in intake or certain nutrients or types of foods.
Advantage: allow you to study the link between diet and rare diseases. Disadvantage: they are prone
to different types of bias. Selection bias: one group is poor and the other group is rich. Confounding.
Mathematical tools are applied to limit the influence of confounding as much as possible, but some
confounding always remains. The case-control studies suffers from the same concerns as other
observational studies (with respect to food frequency questionnaires).
,Cohort study: most powerful observational study design. People report their dietary habits at the
beginning of the study, allowing estimation of their habitual food intake, and are usually followed for
decades. Every now and then participants answer questions about disease and health-related topics.
Because the collection of information on peoples diet precedes the collection of health and disease
data, there is no concern as to which is caused and which is effect. Disadvantages: cohort studies rely
on food frequency questionnaires. Confounding, this effect can be removed in the analysis of the
data. the adjustment may not be perfect and the residual confounding could lead to questionable
conclusions.
Intervention study: can take many shapes and forms. In a standard intervention study, subjects are
randomly divided over two or more groups. The subjects in the first group receive some sort of
control treatment, whereas subjects in the second group receive the actual treatment. After a while,
parameters that are relevant to the research question are determined. Often the same
measurements are done at the beginning of the study to be able to determine the change in values
over the course of the study. Intervention studies that measure a disease (as opposed to some sort
of risk factor) are logistically difficult and very expensive. Advantage: this type of study can determine
whether a particular dietary treatment causes a change in certain parameters.
Alimentary track
The alimentary track has two functions:
Break down foods into their basic components (=digestion)
, Carry out the absorption of the basic components into the body
Digestion:
Mechanical breakdown: foods into smaller particles via the action of the teeth
Contractions of the muscles along the alimentary tract
Chemical breakdown of macronutrients protein, fat and carbohydrate into their basic
components. Protein amino acids. Carbohydrates mainly into glucose.
When digestion is complete, the basic components are taken up into intestinal cells and are
subsequently distributed throughout the body= absorption.
Chemical breakdown is carried out by digestive enzymes produced by various cells and tissues along
the alimentary track= catalysts. Catalysts increase the rate of reaction via lowering of the activation
energy. All these reactions are called hydrolysis cleavage of chemical bond by addition of water.
Chemical digestion happens in the entire alimentary track except for the large intestine.
The only macronutrient that undergoes significant digestion in the mouth is the starch
(=carbohydrate). The stomach is important in protein digestion and has a minor role in fat digestion.
Most of the chemical digestion takes place in the small intestines via the action of enzymes produced
by either the pancreas (alvleesklier) or by the intestinal cells that line the alimentary track.
The large intestine is a major site of digestion of undigested foods, mainly in the form of dietary fibre,
via the activity of large numbers of bacteria that reside there.
Different parts of the alimentary track
Mouth: moisturizes by addition of saliva produced by the salivary glands. Our teeth are responsible
for breaking down the food so that it can be swallowed, this process is called mastication. Teeth are
firmly rooted into the underlying bone and covered with a hard substance called enamel (composed
of calcium and phosphate). Saliva is 99% water, with the remainder consisting of salts, mucus,
enzymes (mainly amylase) and anti-bacterial compounds. Produced by the salivary glands located
underneath the tongue (sublingual gland), beneath the floor (submandibular gland, primary
producer) of the mouth and around the ears (parotid gland). The primary role of saliva is lubricating
the food for easy passage through the esophagus. It initiates chemical digestion of food, has anti-
microbial function and is important for tasting.
The esophagus is a hollow tube that transports the food bolus from the mouth to the
stomach. The walls of the esophagus consists of muscles that propel downwards via a motion called
peristalsis. The esophagus is surrounded by an upper sphincter, a muscular ring that closes the
esophagus when no food is being swallowed. At the bottom the esophagus is bordered by a lower
sphincter, which prevents reflux of food from the stomach. When food is being swallowed a leaf-
shaped epiglottis covers the voice box (/larynx).
The stomach is a hollow bag with a very muscular wall that is situated between the esophagus
and the duodenum. The wall of the stomach produces hydrochloric acid that accounts for a unique
feature of the interior of the stomach. The layer of the stomach is composed of four main types of
cells:
Chief cells: responsible for the production of pepsinogen, one of the three most important
enzymes in the alimentary track involved in protein breakdown. Pepsinogen is a pro-enzyme
that is self-activated into the functional enzyme pepsin.
Parietal cells produce the hydrochloric acid which accounts for the high acidity of the
stomach.
Goblet cells are spread around the entire intestinal wall and produce mucus. In the stomach
they are also called foveolar cells. The mucus protects the interior lining of the cell.
Endocrine-paracrine cells are responsible for the production of a variety of hormones such as
ghrelin and gastrin.
Module 1
Dietary Assessment
Dietary assessment - questionnaires
Many studies rely on special questionnaires called food frequency questionnaires (FFQ). These
questionnaires ask subjects how often they eat certain types of food and in what amounts. These
questionnaires are different for different countries.
Dietary assessment - recall and diary
Another way to asses dietary intake is by asking people to recall the foods they ate over the past 24
hours, this is called a 24h dietary recall. This is usually performed several times to get a decent
estimate of people’s regular food consumption.
Another way of tracking dietary intake is called a food diary or food record. People write
down what they eat in a day, and sometimes even weigh it, for a week or longer. The advantage of
this technique is that they can be accurate if it is done well. The disadvantage is that people tend to
change their food intake when they have to write everything down. This technique is also expensive
and time consuming, people may lose motivation and become sloppy.
From diet to nutrient intake
The next step is to convert the information from the food questionnaires and food records into
nutrient intake, which is done using so-called food composition tables. Food composition tables are
very large tables that contain information on the nutrient content of a great variety of foods
consumed in a certain region or country. The included nutrients are fat, carbohydrates (including
fibre and sugar), protein and many vitamins and minerals. Combining the food eaten with the table
gives information about the nutrient intake a day. Limitation: many foods are not listed in the
table nutrition researchers have to select an alternative food product to calculate nutrient intake.
Advantage: fairly efficient. Disadvantage: people are not always 100% truthful.
Study designs
Ecological studies: a type of observational study in which the units of analysis are not individuals but
populations or groups of people.
Cross-sectional studies: what is special about this is that dietary intake and the outcome are
addressed at the same time. Because this is measured at the same time the result of the exposure
could be the consequence of the outcome instead of the other way around. This is called reverse
causality. If the outcome of the study is a parameter people don’t know about (blood pressure etc.)
the direction of the relation is more or less fixed. This study shows an association and cannot say if
the relation is causal. This study is prone to confounding. You could think of this as a snapshot of a
group of people at a given point in time.
Case-control study: retrospective studies, which means you look into the past. The basic design: a
group of patients with a certain disease are collected. A group of subjects that do not have the
disease form the control group. All subjects are asked about their dietary habits using food frequency
questionnaires or other types of dietary assessment tools. The dietary information from the two
groups is compared to see if there are any differences in intake or certain nutrients or types of foods.
Advantage: allow you to study the link between diet and rare diseases. Disadvantage: they are prone
to different types of bias. Selection bias: one group is poor and the other group is rich. Confounding.
Mathematical tools are applied to limit the influence of confounding as much as possible, but some
confounding always remains. The case-control studies suffers from the same concerns as other
observational studies (with respect to food frequency questionnaires).
,Cohort study: most powerful observational study design. People report their dietary habits at the
beginning of the study, allowing estimation of their habitual food intake, and are usually followed for
decades. Every now and then participants answer questions about disease and health-related topics.
Because the collection of information on peoples diet precedes the collection of health and disease
data, there is no concern as to which is caused and which is effect. Disadvantages: cohort studies rely
on food frequency questionnaires. Confounding, this effect can be removed in the analysis of the
data. the adjustment may not be perfect and the residual confounding could lead to questionable
conclusions.
Intervention study: can take many shapes and forms. In a standard intervention study, subjects are
randomly divided over two or more groups. The subjects in the first group receive some sort of
control treatment, whereas subjects in the second group receive the actual treatment. After a while,
parameters that are relevant to the research question are determined. Often the same
measurements are done at the beginning of the study to be able to determine the change in values
over the course of the study. Intervention studies that measure a disease (as opposed to some sort
of risk factor) are logistically difficult and very expensive. Advantage: this type of study can determine
whether a particular dietary treatment causes a change in certain parameters.
Alimentary track
The alimentary track has two functions:
Break down foods into their basic components (=digestion)
, Carry out the absorption of the basic components into the body
Digestion:
Mechanical breakdown: foods into smaller particles via the action of the teeth
Contractions of the muscles along the alimentary tract
Chemical breakdown of macronutrients protein, fat and carbohydrate into their basic
components. Protein amino acids. Carbohydrates mainly into glucose.
When digestion is complete, the basic components are taken up into intestinal cells and are
subsequently distributed throughout the body= absorption.
Chemical breakdown is carried out by digestive enzymes produced by various cells and tissues along
the alimentary track= catalysts. Catalysts increase the rate of reaction via lowering of the activation
energy. All these reactions are called hydrolysis cleavage of chemical bond by addition of water.
Chemical digestion happens in the entire alimentary track except for the large intestine.
The only macronutrient that undergoes significant digestion in the mouth is the starch
(=carbohydrate). The stomach is important in protein digestion and has a minor role in fat digestion.
Most of the chemical digestion takes place in the small intestines via the action of enzymes produced
by either the pancreas (alvleesklier) or by the intestinal cells that line the alimentary track.
The large intestine is a major site of digestion of undigested foods, mainly in the form of dietary fibre,
via the activity of large numbers of bacteria that reside there.
Different parts of the alimentary track
Mouth: moisturizes by addition of saliva produced by the salivary glands. Our teeth are responsible
for breaking down the food so that it can be swallowed, this process is called mastication. Teeth are
firmly rooted into the underlying bone and covered with a hard substance called enamel (composed
of calcium and phosphate). Saliva is 99% water, with the remainder consisting of salts, mucus,
enzymes (mainly amylase) and anti-bacterial compounds. Produced by the salivary glands located
underneath the tongue (sublingual gland), beneath the floor (submandibular gland, primary
producer) of the mouth and around the ears (parotid gland). The primary role of saliva is lubricating
the food for easy passage through the esophagus. It initiates chemical digestion of food, has anti-
microbial function and is important for tasting.
The esophagus is a hollow tube that transports the food bolus from the mouth to the
stomach. The walls of the esophagus consists of muscles that propel downwards via a motion called
peristalsis. The esophagus is surrounded by an upper sphincter, a muscular ring that closes the
esophagus when no food is being swallowed. At the bottom the esophagus is bordered by a lower
sphincter, which prevents reflux of food from the stomach. When food is being swallowed a leaf-
shaped epiglottis covers the voice box (/larynx).
The stomach is a hollow bag with a very muscular wall that is situated between the esophagus
and the duodenum. The wall of the stomach produces hydrochloric acid that accounts for a unique
feature of the interior of the stomach. The layer of the stomach is composed of four main types of
cells:
Chief cells: responsible for the production of pepsinogen, one of the three most important
enzymes in the alimentary track involved in protein breakdown. Pepsinogen is a pro-enzyme
that is self-activated into the functional enzyme pepsin.
Parietal cells produce the hydrochloric acid which accounts for the high acidity of the
stomach.
Goblet cells are spread around the entire intestinal wall and produce mucus. In the stomach
they are also called foveolar cells. The mucus protects the interior lining of the cell.
Endocrine-paracrine cells are responsible for the production of a variety of hormones such as
ghrelin and gastrin.
