Nov 29 (Nutritional Epi)

Question 1

What is a diet?

Answer 1

• kind of food that a person, animal, or community habitually eats
• vegetarian (source of foods), organic (conditions of harvest), paleo (overall pattern), low carb (nutrient specific), gluten free (ingredient specific)

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Question 2

What are potential components of diet?

Answer 2

• essential nutrients (vitamins)
• major energy sources (carbs, fat)
• additives (colours)
• microbial toxins (botulin)
• contaminants (lead)
• chemicals formed during cooking (acrylamide)
• natural toxins
• other compounds (caffeine)

Question 3

What things affect pathway from diet to disease?

Answer 3

• body size which is influenced by physical activity
• genetic factors
• cooking method
• metabolic differences
• other dietary components

Question 4

What is nutrient based approach?

Answer 4

• take apart food and see what nutrients are contained in it
• then can make specific recommendations
• not very intuitive for everyday people

Question 5

What is good about nutrients?

Answer 5

• directly relate to our knowledge of biology
• allow for synthesis of supplements
• incorporates all food and supplement sources of nutrient of interest

Question 6

What is uncertain about nutrients?

Answer 6

• premature focus on specific nutrient may lead to erroneous hypotheses (eg vitamin E and lung cancer)
• foods not represented fully by nutrient composition (eg. milk and yogurt have same composition but processed differently)

Question 7

What is the food-based approach?

Answer 7

• healthy or unhealthy foods- default to specific nutrients when thinking about why things are healthy or unhealthy
• instead of talking about specific nutrients, suggests eat lots of fruit/veg, limit sugary drinks, etc.
• be mindful of eating, cook, enjoy food, etc.

Question 8

What does Canada’s food guide provide?

Answer 8

• policy and educational tool
• helps people make food choices to meet nutrient needs, improve their health, and reduce their risk of nutrient-related chronic diseases and conditions
• interprets complex nutritional info in practical way

Question 9

What is good about food-based approach?

Answer 9

• resonates better
• analyses based on foods are more in line with dietary guidelines (eg. green leafy vegetables)
• useful to hypothesize about diet-disease relationships when exact compounds responsible are not yet known

Question 10

What is uncertain about food-based approach?

Answer 10

• complex relationships exist between foods, and between nutrients within foods
• measuring food intake does not always account fully for how the food is consumed

Question 11

What is nutrition?

Answer 11

-process of providing or obtaining the food necessary for health and growth

Question 12

What is nutritional epidemiology? What is the objective?

Answer 12

• study of how the food a population eats influences the health of the population consuming it
• to provide personal and policy choices to promote human health and well being

Question 13

What are the goals of nutritional epidemiology?

Answer 13

• monitor food consumption, nutrient intake, and nutrition status of a population (eg. vitamin D deficiency)
• generate hypotheses about long term diet and disease
• provides evidence to support or refute existing hypotheses (eg. use of vit D supplements and multi vitamins)
• quantify the strength and direction of diet-disease associations (red meat consumption and diabetes)
• prevent disease and enhance public health

Question 14

What is the focus of public health?

Answer 14

• all organized measures (public or private) to prevent disease, promote health, and prolong life among the population as a whole
• might not meed everyone’s needs but looking at population as a whole
• public service
• healthier communities

Question 15

How has nutritional epi influenced public health?

Answer 15

• direct relevance to human diet and disease (folate fortification)
• direct relevance to the food supply (removal of trans fatty acids)
• direct relevance to policy (ban children’s toys in restaurant meals)

Question 16

What are historical challenges with nutrition epi?

Answer 16

• ecological studies (eg. the diet-heart hypothesis); measures mean exposures in populations
• 7 countries study in 50’s- trying to decide and figure out causes of heart disease
• went to different countries and looked at association of % of calories from saturated fat and 10 year coronary deaths per 10 000
• over the following years, hypothesis has been refuted/debated, led to thought about dietary fat in diet,
• learned that amount of fat and type of fat matters
• historically we didn’t have a lot of knowledge about this because we were looking at it ecologically

Question 17

What are other challenges with nutritional epi?

Answer 17

• temporality is difficult to ascertain unless the same people are followed over time (need a prospective cohort that watches people with the same diet and see if they develop outcome- otherwise you don’t know if they changed their diet)
• case control studies: recall bias
• cohort studies: long follow ups
• RCTs: compliance with diets, ethics

Question 18

What are methodological challenges with nutrition epi?

Answer 18

• how to measure diet accurately
• self reported measures don’t generally correlate with what they’re eating

Question 19

Describe the impact of misreporting diet and other errors in nutrition epi

Answer 19

• foods that we are trying to measure have to be good sources of nutrients for them to be affected by misreporting
• foods with little content of a nutrient are less affected by misreporting
• depends on your hypothesis and exposure of interest
• if we assume everyone eats generally the same way, you can misclassify someone’s exposure (certain people won’t eat that way)
• compound error: all of the things we eat we don’t eat that much of so we expect them to have little impact BUT we are eating them all the time so we are getting small errors every day which leads to big error over time
• diet may be a specific exposure: some foods will have specific ingredients so if you don’t report that food, your exposure will be off
• metabolism is a mother: inability to link dietary intake of cholesterol and serum cholesterol in early studies (serum cholesterol exhibits biologic and genetic variation within persons, regardless of dietary cholesterol intake)

Question 20

Describe challenges that arise from foods not being consistent in different conditions (a food is not a food)

Answer 20

• Portion size: affects absolute amounts of all nutrients but not relative amounts (if you said a banana was large or small, all of the nutrients would be over or under estimated by the same amount)
• exact brand or variety (may affect absolute and relative amounts of all nutrients)
• cooking or ripeness (bananas contain different starch:sugar depending on ripeness)

Question 21

What makes it difficult or harder to measure amounts of food eaten

Answer 21

• single serve items are easier to measure (eg. Mars bar is 50g- if you ate half you know you ate 25g)
• harder to measure bag of chips, blueberries, apple, etc. (when you don’t have a single reference serving size it can get hard to remember how much you ate)

Question 22

What does total energy intake show us?

Answer 22

• consequence of body size, activity, metabolic efficiency
• computed using FFQ or physical tests such as heart rate monitoring
• measured in kilocalories/day or megajoules/day
• overall measure of bodily health, including nutritional status
• often included as a confounder in nutritional epi studies; people who eat well tend to be healthier which tends to be associated with developing disease or not but also associated with how much you eat

Question 23

Why is total energy intake an important confounder to control for?

Answer 23

• total energy intake is an important confounder that needs to be controlled for
• total energy intake is often a risk factor for disease
• individual differences in total energy intake can affect nutrient intakes
• not everyone who eats a Whopper takes in an identical amount of nutrients
• people who eat more food eat more of the nutrients
• if total energy (food intake) is associated with disease, then we must control for this in analyses

Question 24

How is diet and chronic disease measured?

Answer 24

• estimate the effect of long term dietary choices/intake on disease risk
• tutorial study looked at macronutrients and cardiovascular disease- measured diet once to reflect “habitual”
• standard in the field has become prospective cohort studies with long term follow up
• large RCT are difficult and expensive (good for short term biomarkers)

Question 25

What are ways to measure diet?

Answer 25

• 24 hour recall questionnaires: retrospective measure of exposure so recall bias (people forget- non differential misclassification), does not represent long term diet, atypical days
• prospective weighed diet records: have people record everything you eat as you eat it, provide a scale for weighing, avoids recall bias, respondent burden, cost of food scales, people might change what they eat knowing they have to write it down
• semiquantitative FFQ: ask about food consumption over a time period, recall bias (people forget what they ate- non differential misclassification, people with certain diseases are more likely to remember what they ate- differential misclassification), social desirability bias (underreport poor dietary habits, exaggeration of good dietary habits- nondifferential misclassification)
• apps (bitesnap, my fitness pal): these are still self report, don’t know how valid they are

Question 26

How are foods converted to quantities?

Answer 26

• use food composition database to convert food intakes to nutrients
• typically assessed by multiple laboratories and database value is an average
• publically available

Question 27

How is self reporting overcome?

Answer 27

• biomarkers: sensitive and specific for the nutrient of interest, reflects period of interest concerning health or disease, unaffected by diseases or conditions of importance for metabolism of the nutrient, unaffected by other environmental or genetic factors, inexpensive and reproducible to measure
• adipose tissue biopsies (for fatty acids), hair sample for selenium, blood test, metabolomics

Question 29

What are problems with biomarkers?

Answer 29

• not all chemicals are sensitive to diet intake (ie. they do not change according to type and level of food consumption); serum calcium, sodium, and cholesterol are not sensitive
• not all chemicals reflect food intake over long periods of time (eg. vitamin C)
• many chemicals are influenced by non-dietary factors (eg. serum iron levels)
• methods of obtaining biomarkers can be uncomfortable

Question 30

What is the method of triads?

Answer 30

• measure diet using different methods
• different ways we measure diet don’t share similar sources of error
• eg. FFQ, biomarker, and 24 hour recall
• reasons that someone may misreport on FFQ is a different reason for why their biomarker might be off
• 3 independent methods (wouldn’t share sources of error)
• if they give us the same answer, pretty sure that way of measuring diet was pretty accurate

Question 31

What are weaknesses of nutritional epi?

Answer 31

• shared by other exposure-outcome assessments
• intractable bias: systematic error resulting in an overestimation or underestimation of the true association
• proving causality; many dietary factors are closely linked, hard to isolate specific culprit food or nutrient
• diseases are multifactoral (diet, genes, exercise, infections, etc.)
• health effects can be direct or indirect (ie. is the problem that you are eating pancakes, eggs, and bacon for breakfast every day or is the problem that you are not eating fruit?)
• diet may only matter during critical exposure issues (eg. folate and NTDs, adolescent diet and breast cancer) so difficult to know when to look to correctly associate it with a disease
• diet isn’t all or nothing; everyone eats, we are exposed to most dietary factors, eating patterns evolve slowly
• golden range of nutrient intake; if you supplement someone who is deficient, you will see a benefical effect but if you give someone in the optimal range the same amount you may see no effect