Week 5: Lecture 25: Introduction to Dietary Assessment in Epidemiology

Hello and welcome dear learners to the NPTL course on nutritional epidemology a way towards a healthy life. For the module three dietary assessment, nutritional status and measurement error. For the chapter 25, we'll be studying about the introduction to dietary assessment in epidemiology. So in this chapter we will study why assessment of diet is needed. What is the importance of dietary data in public health? The exposure assessment for diet disease association surveillance and policy will be studied over here. Overview of the main methods, concept of usual intake versus actual intake and the implications for epidemological designs will also be studied. Additionally, the challenges of dietary assessment will be taken ahead. So why assessing the diet? Why do we need to assess the diet? So you can have an question why dietary assessment? Dietary assessment is referring to a very systematic measurement of food. It is about beverages. It is about nutrients. It is about dietary patterns. Whatever we consumed by an individual or a population. So the whole lot of this is dietary assessment. Dietary assessment is a very cornerstone of nutrition pmology because the diet is a complex and modifiable exposure. You may have lot of complexity modifiableness and you may come across with one recipe of a diet may have a different modification association with multiple chronic and infectious disease of a particular diet. And you may see the diet is influenced by cultural, economic, social and environmental factors. So that's the need that you have to take dietary assessment. A good dietary assessment is a better advice and it can lead you to better public health decisions and healthier population. On the other hand, diet as an exposure. How can you see in the epidemology diet as an exposure? Unlike many epidemological exposure, you may come across diet as also an exposure. Diet consists of thousands of foods and nutrients. You may go up for a marriage and you may have a diet which have a different recipes. You may go for a religious function and you may have a very different diet that you can come across. Also food are consumed in combination. Sometimes you may have milk with uh your flakes in the morning. You may have dal with rice. You may have fruits with curds or you may have veggies actually which may be having with dal and too many things. You may have a combination across the globe. Intake varies of diet from day to day. You may say day one I will be taking this, day two I will be taking day three. Okay. So even from timing actually in the morning till the evening you may have variations dietary pattern change over time past present future childhood adolescent mid age old age and even with your economic status with your situation migration. So there are there are diet as an exposure which may come and therefore you require an accurate measurement though it is sometimes very challenging but it is very essential and so where the importance of dietary assessment is being seen. What is the importance of dietary data in public health? Do a public health professional require a dietary data and if how it is important? It is very important in eeological research. It is very important for surveillance. It is equally and more important for policy and design. And no doubt for clinical and transitional it is very very important for ideological research. It identifies a specific dietary pattern like consumption of local oils or food or millets. It estimates exposure response relationship across varied population such as polish rice intake and colon cancer risk. Okay. So you may see blood pressure exposure texture with the regional or the cough texture. So you may have lot of association which are studied in ideological research refined carbohydrates and type 2 diabetes salt intake and hypertension. So you may go with the ideology. Okay. What is the cause? Then comes surveillance. It is very very important as every public health researcher understands the comparison by state level ion status. Comparison of state level you can say calcium urban versus rural macronutrient splits urban versus rural micronutrient splits. So you may have percentiles with age, gender, soio economic status and you may have the percentile distribution of dietary diversity which can be studied across the state and even districts. You may have trends from 1980s to 2000 to even 2020 or even trends which is being compared actually for this part in surveillance. Then comes policy and decision which is very important where you can come across with lot of mandatory fortification which is being seen in most of the policy decision nowadays or evaluate the policy which was existing and now which is being taken. So policy evaluate front of the pack. Actually they also do lot of work on labelings, reformulation and so much of a thing. Even fortified ata the brand now example by ICMRN and certified actually which is being seen as one of a very important decision. Sodium reduction targets evaluate policy impact with pre and post intervention data. So policy design level it is very very important to take the dietary data clinical and translational it is like a supportive individualized counseling actually for a nutritionist or clinical nutritionist to be seen with the help of the nutritional biomarkers can be used in clinical setups very importantly it validates the biomarkers it come up with a decision that is coming with the dietary interventions and so it is very important for the menu and for the emitters. So clinical and translational dietary data is also very important along with ideological surveillance and policy decision-m in public health. What are the public health issues of dietary data? Do the importance of dietary data in public health always gives you an information for making a decision and action that improves population's nutritional health? The answer is most likely yes. What is the purpose? Purpose of doing surveillance, it monitors population's dietary intake. It tracks the trends and identify the nutritional problems. So where surveillance is very very important, nutrition surveillance is very important. The examples are national dietary surveys. What are national dietary surveys doing? They collect the data on what people eat across the country and over the period of time. So the dietary surveys are very important example that you can take for surveillance. Then comes program evaluation. Suppose a particular program is there. Okay. Assess the performance and impact of that nutrition program. For example, portion aban or midday meal. The school feeding program is one among the example where you can take the evaluate the food intake, meal quality, nutrition impact on the students. Then comes policy development. Here develop and refine policies to create healthier food in environments. In this you can take the example of salt reduction policy which is being targeted towards reducing the salt for better health. Lesser the sodium intake targeting to develop a guidelines and monitor population sodium intake. So it is very important to see that it comes as an issue for the reduction of a particular component in the nutrient to target an intervention. Then comes the purpose of research. Investigate diet disease relationship and understand the mechanism why this research is being conducted. For example, diet and cancer studies. They examine how dietary factors influence the risk of developing cancer and many of the studies have associated the relationship of diet with the cancer and how it lessens the risk actually. Then comes the risk assessment. When you have understand the risk, you will estimate the dietary exposure to contaminants and evaluate the potential health risk. For example, the contaminants can be pesticide, the contaminants can be metals, the contaminants can be even impurities, infection. So, exposure to the contaminants will be assessed and can be seen in the day-to-day or even for a long-term assessment also. No doubt there is a very important purpose of public health issues to study the dietary data for a regular way that is of nutrition education which is very important. If you say eat well, you can say live well. There's a close association of this hypothesis. So nutrition education is to develop educational materials and to guidelines and to promote the healthy habits. The example can be dietary guideline development which is very important to create an very evidence-based recommendation for healthy eating and which is very important for the current times that the challenges that India or country is dealing with exposure assessment for diet disease association surveillance and policy. So if you take the diet disease association you may say the researchers investigate nutrients foods and dietary pattern. Example, nutrient-based approach, vitamin D and association with osteoporosis, exposure of sun and vitamin D and then the bone health or you may see the food based approach red meat and colurectal cancer association is being seen over here. dietary pattern approach Meditarian diet and cardiovascular risk where you can say it is lesser or lower. So what it helps it helps identifying dietary factors linked to the disease risk and productive health effects of that dietary surveillance as stated surveillance involves continuous monitoring monitoring of the population's dietary habit. The objective is to track trends over the time, monitor the changes in the dietary intakes and the pattern. The surveillance uh detect emerging nutrition problems. It gives you early signs of inadequacies and excesses. It also inform the policy decision. It provides the evidence to guide nutrition policies and programs. And you may see the support timely actions which are being taken to improve the population nutrition and reduce the health inequalities. So nutrition surveillance plays a very important role in reducing the health inequalities. So it's a major benefit. Then comes for the policy development. Lot of dietary assessment can form a data. The data can be used for dietary guidelines. Examples are dietary guidelines for Indians particularly based on the diet assessment that has been done over in the country or a who health diet recommendations also food fortification example iodized salt which is being seen as a very important food fortification or iron folic food fortification as in supplement or taxation policies particularly Sugar sweetened beverages can be added more taxes. So evidence-based policy creates a healthier food environments and improve the population health which is very important for a policy purpose. Overview of main dietary assessment method. So there are five very important dietary assessment method. 24 hours recall food record food frequency questionnaire FFQ. Dietary history and biomarkers 24 hours recall interviewer or a software asks subjects to detail all the food and drink consumed in the 24 hours. There are major strength of this. It does not alter normal diet. It has a low respondent burden and captures the detail. So 24 hours recall is very very important at dietary assessment method which is being taken. But the major limitation is it relies on the memory of the respondent. A single day does not reflect usual intake because sometimes you may have a usual intake which came which can be taken over the period of time. [snorts] So this is captured as a major limitation over here. Food record diary which is very important for an respondent for a participant as a patient when you are taking this in an organizational setups. The subject records all the food and drink at a time of consumption usually into 3 to 7 days. So you should take a food diary at least for one week of time. There are a lot of strength of this. It does not rely on memory. It is highly detailed and precise which will give you major benefits compared to the 24-hour recall. 24-hour recall is one day here it is over a week. But there is a major limitation high respondent burden. So everything is to be told by the respondents which is difficult if the respondent has some sort of its bias of own might be with the uh educated people might be someone who can uh really um note it down actually for that it's very important subject often alter their diet relatively while recording and they may uh put up a summer note a different note compared to what they have really consumed. Then comes the FFQs as a questionnaire which is very very objective very pre-coded list of foods where subjects report frequency of consumption over a long period. Example past year FFQs has lot of strength. So they may come up with measure usual long-term intake what they have taken it like in terms of salt sugar and all those low cost because it is like a questionaire usually has a benefit of taking this easier to administer in long larger cohorts larger sample size you can get it but the major limitation lies here like is it relies on the generic portion sizes memory recall bias is again being seen over here and higher cognitive demand where you have to collect everything. No, it is very important. Dietary history detailed interview combining a 24-hour recall and FFQ and a multi- multi-day record. It's like a combination of all highly comprehensive captures both usual intake and a meal pattern. But again the limitation over is highly resource intensive that you have to invest more time resources human resource and all the equipments requires a trained interviewers where you have to be trained and high participant burden where you may say it is very important that the participant has to take more load. Then come biomarkers very objective objective biological measures like uh doubly labeled water for energy urinary nitrogen for protein. So you may say these are the biomarkers who are giving you more objective measurements. The strength may be free from self-report bias because in a self-report bias you may not overcome those but here you can overcome the biomarkers here provide an objective validated standard which are being seen as very important in dietary assessment but the major limitation is they are very very expensive. The cost is something actually which will put you uh to uh give you lesser marks while selecting this as a dietary assessment. They're very invasive where you have to have a system, you have to have an organization and you have to have an equipments only available for a limited number of specific nutrients and not all. So comprehensively it is not covering all the assessment method. So you may have this as a major limitation. Then the concept of usual intake versus actual intake and its implication for epidemological design. Why you can say actual intake as in versus usual intake. What do you mean by that? Understanding the difference and why it matters in epidemology you need to take ahead. Actual intake is something what an individual consume on a specific given day. This is highly variable. It can vary. If you measure someone's actual intake on a day of a festival or a function, it will look vastly different from a typical Tuesday or a Sunday. Every festive day you have a high intake of rich food, sweets, fried items and in a bulk also and a quantity where versus a typical Tuesday will use a usual weekday diet simpler food lesser oil lesser sweetness and also the bulk why usual intake matters it is like chronic disease ideology generally depends on long-term exposure. Therefore, epidemological studies attempts to give you a very characterized usual intake. Single day measure are very poor proxies for usual intake. So while doing this you should do a day-to-day variability which is very important for an actual intake. Very very important usual intake. What is the usual intake? The long-term average daily intake of an individual. So chronic diseases develop over a period of time making long-term usual intake the biologically relevant exposure for the most common epidemological outcomes. So Monday you may have a different diet Tuesday, Wednesday, Thursday, Friday. So in a way actually it it represents a long-term habitual diet the most stable most biological or relevant for a chronic disease factor to come up. What are the implications? The implication is like because of a high day-to-day intra-individual variation, a single 24 hours recall or a one-day food records only measure actual intake and cannot characterize an individual's usual intake. Implications are to estimate usual intake. Researchers must either collect multiple days of actual intake and apply statistical modeling or use FFQs designed specially to capture the long-term habitual consumption. So long-term is very important over here. So there is advantage of user intake as well as actual intake. Challenges again coming over here. high day-to-day variability, recall bias, reporting bias, portion size estimation and food consumption and data limitation, nutrient correlation and measurement errors. So if you take the high day-to-day variability, human diets vary by day, by week, by season, and by social context, especially in country like India, the variance within a single person's diet is often greater than a variance between a person's diet and making the true exposure hard to capture it. A single day does not represent a person's usual diet. You may see in the picture like how a person started with Monday and going with Sunday. Lot of variations, recall bias when a respondent is asked uh to take up what you have taken for snacks, beverages, condiments, portion size and leading with lot of inequities actually. So you have to think so. So you may come up with like what I have taken for evening snacks or what is my sugar drink? what is my extra oil? So lot of recall biases will be seen over here which may take up some sort of biases which are majorly coming from the respondents reporting by it under reportported versus over reported. Lot of a time with social disability you will not really report what is bad food. You will always report a good food or sometimes you will over report a good food. You may over report for veggies. You may over report for lean proteins or fruits or sometimes you are you are very common among the individuals with the higher BMIs but you will again say that okay you're not taking alcohol you are not taking sweets you are not taking fried food then comes portion size estimation and food composition database limitation so portion size estimation is sometimes you may have a photo ads and a standard utensils so you may have a sort of an problem of portion size estimation, inaccurate portion estimation, introducing errors, photographic aids and standard utensils. Exactly. The food consumption should be based on kilo calories, protein, fats, micro and macronutrients. Errors in nutrition estimation and misclassification of intake is very common. Nutrient correlation. How you can nutrient correlate? People eat complex meal not isolated nutrients. Very at the very start we have started it. Nutrients are highly correlated. Now diet high in saturated food is often low in fiber. This is the colinearity which is established and it is difficult to isolate the independent effect of a single nutrient on a disease outcome. So you may say saturated fat, fiber and vitamin C lesser lesser lesser for the part actually when you have more fats high colinity complicates interpretation of nutrient disase relationship. Additionally there is a measurement error both systematic error for example FFQs consistently underestimate energy intake and random error. So systematic error and random error. So this often results in regression to the mean attenuating the true association between disease and diet type of errors might be very evident. Systematic error and random error consequences regression to the mean atunation of the case associates and you will get some or level of fluctuation from day to day. In the summary to this chapter while concluding I would like to state that dietary assessment is the cornerstone of nutrition epidemology the dietary assessment provides essential information for understanding the relationship between diet and health. So dietary assessment is important. The dietary data supports disease prevention. It also supports research on the diet. also gives us a nutrition surveillance and evidence-based policy development which is very important for every country. A common assessment method includes 24-hour recalls, the FFQs, the food records, the dietary histories or biomarkers. Each one has its unique strength and its limitation. A key concept is distinguishing actual intake from usual intake. So what is an actual intake might be differing with a usual intake. These are all very related to the chronic disease risk which we are generally trying to associate with a long-term dietary exposure which is very evident. Whenever you are trying to study a chronic disease, you need to go up for a long-term dietary exposure. Dietary assessment is challenged by day-to-day variability. There are recall bias also along with under reporting and correlation among nutrients. So dietary assessment has even its own challenges. So I can say finally that careful study design and the use of complimentary assessment method can improve the accuracy and validity of the dietary exposure measurement which is a need that we should go for dietary assessment. So with this we come end to this chapter and its discussion. So you can take the help of these references to meet your requirements. Thank you. Thank you very much. >> [music] [music] [music and bell] [music]