HNH32206
Tutorial 1: Study Design and Carbs
Instructor: Sander Kersten
Study design
1. What is the main limitation of an observational study?
Observational studies can establish an association, but if that association is causal, is
unknown.
2. What is the main limitation of a cross-sectional study as compared to a cohort study?
Cross-sectional study: the outcome and the exposure are measured at the same time. So,
you do not know which one happens first. You do not have a temporal relationship.
Cohort study: the measurement takes place before the outcome. The outcome could not
have caused a change in food intake. You measure the food intake first and then you
follow people for a long time and then they develop the disease.
3. Explain why cohort studies are largely unsuitable for rare diseases?
Cohort studies follow a lot of people. But even if there are a lot of people, only a few
people develop this rare disease. So, you cannot really do proper statistics.
4. Do you think it is desirable that public health policy is exclusively based on results of
interventional studies and disregards results from observational studies, including cohort
studies? Describe a particular behavior that is responsible for millions of deaths but for
which the detrimental effects have never been properly investigated in an intervention
study?
Observational can only establish an association and we do not know if the association is
causal. We can tell people to eat more of certain foods/nutrients, but if the relationship
between those foods is with disease is purely based on association, then what does it
really mean?
Smoking is responsible for a lot of deaths, but is not investigated in an intervention study.
Everything we know is based on observational studies. The magnitude of the effect of
smoking is much higher than the effect of diet. Smoking increases the risk of lung cancer
by 10 fold. Because the effect is so huge, it can only be causal.
➔ The size of the effect can help you decide if a relationship is likely to be causal.
5. How would you design a study to investigate the relation between the intake of deep-
fried foods and the development of throat cancer (a relatively rare form of cancer), taking
into account what is practically and ethically feasible. Justify your answer.
,Fried foods will probably increase the risk of throat cancer. It is unethical to experiment
with this. So, we need to do an observational study design. We need to do a case-control
design, because the disease is rare.
We need to collect people who have throat cancer and a group who does not have throat
cancer. Then we ask about their dietary history.
6.
a) Rank the following sentences from low to high in terms of the quality of the scientific
evidence about the relation between coconut oil consumption and heart disease (this is for
illustrative purposes only; none of the statements below are necessarily factually correct)
A. A high intake of coconut oil was accompanied by higher serum levels of cholesterol
among Wageningen University students.
-> cross-sectional study
B. Among a group of 25,000 physiotherapists, those who have a higher intake of coconut
oil have a lower chance of developing heart disease over a 20 year period.
-> cohort study (large group, followed for a longer period of time)
C. When asked about their dietary habits, in a study in Europe people with existing heart
disease indicated a higher habitual consumption of coconut oil as compared to people
without heart disease.
-> case-control study (2 groups: people with heart disease, people without heart disease)
D. Countries characterized by a low per capita consumption of coconut oil have high
rates of heart disease.
-> ecological study (population based study)
Lowest -> highest quality studies:
D-A-C-B
7. How would you design a study to investigate the relation between the intake of
coconut oil and the development of heart disease, taking into account what is practically
and ethically feasible. Justify your answer.
We first need to know some background information. We need to know if there is
evidence that coconut oil protects against heart disease (-> do an interventional study) or
if it promotes heart disease (-> do an observational study – cohort study).
Then we could do a trial. We need to do this study with people who have a higher chance
of having heart diseases and also eat coconut oil in their natural diet -> f.e. older people.
8. Consider the relation between smoking and heart disease. Describe an ecological
study, a cross-sectional study, a cohort study, a case-control study, and an intervention
study investigating the relation between smoking and heart disease.
Ecological study: measure what percentage of the population smokes and look at the rate
of heart disease (not strong evidence).
, Cross-sectional study: you would take a large group of individuals, you ask them if they
have a heart disease and if they smoke. Because they have heart disease they could have
started smoking (not very likely) and it could be that smoking caused heart disease.
Case-control study: ask people with heart disease and people without heart disease if they
smoke (or if they smoked in the past). You compare the cases vs. the controls.
Cohort study: take a large group of people and follow them for a long time. In the
beginning they determine if they smoke or not and how much they smoke. Then you try
to see if the people who smoke more or at all have a higher chance of getting heart
disease than the people who do not smoke.
9. Indicate the study design of each of the following studies:
a) artificial sweeteners and colon cancer
-> cohort study (observational study, about patients)
b) artificial sweeteners and diabetes
-> experimental study (intervention)
c) artificial sweeteners and stroke
-> cohort study (people were followed for a long period of time)
d) artificial sweeteners and blood glucose regulation
-> experimental study (randomized, analyze old intervention studies)
Carbs
1. Carbohydrates are stored in the body as glycogen. What purpose does stored
glycogen serve in skeletal muscle and liver, respectively?
When doing vigorous exercise, you use glycogen in the muscles. You use the glycogen in
the muscles you are using. You break glycogen down to maintain the blood-glucose
level.
2. Why does our body strive to maintain a stable blood sugar level? Where does the
glucose in the bloodstream come from in the morning before breakfast? What about after
24 hours of fasting?
It is important to maintain a stable blood sugar level because the brain needs a lot of
glucose.
The glucose in the bloodstream in the morning before breakfast comes from the liver.
The glucose in the bloodstream after 24 hours of fasting comes from your muscles. The
muscles is been broken down, releasing amino acids, which the liver converts into
glucose.
3. Does an increase in blood glucose concentration lead to an increase in glucose uptake
in brain? Why or why not? How about glucose uptake in muscle?
Tutorial 1: Study Design and Carbs
Instructor: Sander Kersten
Study design
1. What is the main limitation of an observational study?
Observational studies can establish an association, but if that association is causal, is
unknown.
2. What is the main limitation of a cross-sectional study as compared to a cohort study?
Cross-sectional study: the outcome and the exposure are measured at the same time. So,
you do not know which one happens first. You do not have a temporal relationship.
Cohort study: the measurement takes place before the outcome. The outcome could not
have caused a change in food intake. You measure the food intake first and then you
follow people for a long time and then they develop the disease.
3. Explain why cohort studies are largely unsuitable for rare diseases?
Cohort studies follow a lot of people. But even if there are a lot of people, only a few
people develop this rare disease. So, you cannot really do proper statistics.
4. Do you think it is desirable that public health policy is exclusively based on results of
interventional studies and disregards results from observational studies, including cohort
studies? Describe a particular behavior that is responsible for millions of deaths but for
which the detrimental effects have never been properly investigated in an intervention
study?
Observational can only establish an association and we do not know if the association is
causal. We can tell people to eat more of certain foods/nutrients, but if the relationship
between those foods is with disease is purely based on association, then what does it
really mean?
Smoking is responsible for a lot of deaths, but is not investigated in an intervention study.
Everything we know is based on observational studies. The magnitude of the effect of
smoking is much higher than the effect of diet. Smoking increases the risk of lung cancer
by 10 fold. Because the effect is so huge, it can only be causal.
➔ The size of the effect can help you decide if a relationship is likely to be causal.
5. How would you design a study to investigate the relation between the intake of deep-
fried foods and the development of throat cancer (a relatively rare form of cancer), taking
into account what is practically and ethically feasible. Justify your answer.
,Fried foods will probably increase the risk of throat cancer. It is unethical to experiment
with this. So, we need to do an observational study design. We need to do a case-control
design, because the disease is rare.
We need to collect people who have throat cancer and a group who does not have throat
cancer. Then we ask about their dietary history.
6.
a) Rank the following sentences from low to high in terms of the quality of the scientific
evidence about the relation between coconut oil consumption and heart disease (this is for
illustrative purposes only; none of the statements below are necessarily factually correct)
A. A high intake of coconut oil was accompanied by higher serum levels of cholesterol
among Wageningen University students.
-> cross-sectional study
B. Among a group of 25,000 physiotherapists, those who have a higher intake of coconut
oil have a lower chance of developing heart disease over a 20 year period.
-> cohort study (large group, followed for a longer period of time)
C. When asked about their dietary habits, in a study in Europe people with existing heart
disease indicated a higher habitual consumption of coconut oil as compared to people
without heart disease.
-> case-control study (2 groups: people with heart disease, people without heart disease)
D. Countries characterized by a low per capita consumption of coconut oil have high
rates of heart disease.
-> ecological study (population based study)
Lowest -> highest quality studies:
D-A-C-B
7. How would you design a study to investigate the relation between the intake of
coconut oil and the development of heart disease, taking into account what is practically
and ethically feasible. Justify your answer.
We first need to know some background information. We need to know if there is
evidence that coconut oil protects against heart disease (-> do an interventional study) or
if it promotes heart disease (-> do an observational study – cohort study).
Then we could do a trial. We need to do this study with people who have a higher chance
of having heart diseases and also eat coconut oil in their natural diet -> f.e. older people.
8. Consider the relation between smoking and heart disease. Describe an ecological
study, a cross-sectional study, a cohort study, a case-control study, and an intervention
study investigating the relation between smoking and heart disease.
Ecological study: measure what percentage of the population smokes and look at the rate
of heart disease (not strong evidence).
, Cross-sectional study: you would take a large group of individuals, you ask them if they
have a heart disease and if they smoke. Because they have heart disease they could have
started smoking (not very likely) and it could be that smoking caused heart disease.
Case-control study: ask people with heart disease and people without heart disease if they
smoke (or if they smoked in the past). You compare the cases vs. the controls.
Cohort study: take a large group of people and follow them for a long time. In the
beginning they determine if they smoke or not and how much they smoke. Then you try
to see if the people who smoke more or at all have a higher chance of getting heart
disease than the people who do not smoke.
9. Indicate the study design of each of the following studies:
a) artificial sweeteners and colon cancer
-> cohort study (observational study, about patients)
b) artificial sweeteners and diabetes
-> experimental study (intervention)
c) artificial sweeteners and stroke
-> cohort study (people were followed for a long period of time)
d) artificial sweeteners and blood glucose regulation
-> experimental study (randomized, analyze old intervention studies)
Carbs
1. Carbohydrates are stored in the body as glycogen. What purpose does stored
glycogen serve in skeletal muscle and liver, respectively?
When doing vigorous exercise, you use glycogen in the muscles. You use the glycogen in
the muscles you are using. You break glycogen down to maintain the blood-glucose
level.
2. Why does our body strive to maintain a stable blood sugar level? Where does the
glucose in the bloodstream come from in the morning before breakfast? What about after
24 hours of fasting?
It is important to maintain a stable blood sugar level because the brain needs a lot of
glucose.
The glucose in the bloodstream in the morning before breakfast comes from the liver.
The glucose in the bloodstream after 24 hours of fasting comes from your muscles. The
muscles is been broken down, releasing amino acids, which the liver converts into
glucose.
3. Does an increase in blood glucose concentration lead to an increase in glucose uptake
in brain? Why or why not? How about glucose uptake in muscle?
