Use of Dietary/Nutrient Data in the WHI

Transcription

1 Use of Dietary/Nutrient Data in the WHI Marian L. Neuhouser, PhD, RD WHI Data Training Workshop May 6, 2009 or

2 Presentation Outline & Objectives 1. Review dietary assessment procedures in WHI 2. Present types of dietary data available for analysis 3. Special examples for using nutrient data 4. Using computed variables from the FFQ line items 5. Summary 6. Q and A

3 How Was Diet Measured (DM)? Study Start Year 1 Year 2 Closeout Food Frequency Questionnaire All Food Frequency Questionnaire All Food Frequency Questionnaire Rotating 1/3 of participants Year 3,6,9 4-day food records 4-day food records 4.6% of ppts Repeat (x2)24 hr Recalls 4.6% of participants 24 hour recalls 1% of participants Dietary

4 How Was Diet Measured (OS)? Study Start Year 3 Food Frequency Questionnaire All Food Frequency Questionnaire All Note: CT participants not in the DM only have SV (baseline) FFQ) Dietary

5 Which dietary data are available? Only FFQ data have been released to Food record data have been used in selected publications (including some in process) but these data are not posted. The focus of this presentation will be on the FFQ data.

6 FFQ Data Availability & Analysis 1. Analysis by nutrients 2. Analysis by food groups (computed variables) 3. Analysis by individual or grouped line items, adjustment questions and summary questions Potentially useful for index or dietary pattern type analyses (computed variables not yet made)

7 FFQ analysis by nutrients and use of nutrient data Standard analysis of FFQ data yields nutrients per person per day 135 nutrients/important compounds: Fat, fatty acids protein, carbohydrate, vitamins, minerals, carotenoids, genestein, daidzein, sugars, fiber, vegetable protein Most WHI analyses have used the standard nutrient data

8 WHI FFQ Structure and Format The WHI FFQ has three parts 19 Adjustment Questions Food preparation, fats added in cooking/table 122 line items of foods or food groups Frequency and portion size 122 line items = > 350 foods 4 Summary Questions Overall usual intake of fruits and vegetables, fats added to foods in cooking Used to reduce measurement bias of over-reporting long lists of foods

9 Processing the WHI FFQ and creation of nutrient output Step 1: FFQ are passed thru a marksense scanner. Responses are converted into ASCII data. Step 2: ASCII data checked for errors (ie, missing) Step 3: Calculating nutrient intake

10 Processing the WHI FFQ and creation of nutrient output 1. Processing system estimates annual medium portion sizes by multiplying frequency * portion size Example: Medium portion of eggs once a week = 52 annual medium portions. Small portion of eggs once a week = 26 annual medium portions [s =.5(med)] 2. Annual medium servings are multiplied by the nutrient string for the food code (135 possible nutrients) 3. All nutrient results for all foods are summed and divided by 365 = average daily nutrient intake of each nutrient

11 Processing the WHI FFQ and creation of nutrient output Note that many line items have multiple foods Example: peaches, nectarines, plums rice, grains and plain noodles Each food is proportionately represented on the line item. Proportional weights are based on national consumption data and expert opinion. The processing stream occurs for each food. USDA (NCC) may have several food codes for each item. Careful assignments are made by nutritional epidemiologists.

12 FFQ analysis by nutrients: caveats know what you are analyzing Example 1: Folic Acid/Folate Which variable to use? Dietary Folacin Dietary Folate Equivalents Dietary Synthetic Folate Dietary Natural Folate

13 FFQ Analysis by Nutrients Dietary Folacin Old folate values that represent the pre-1998 food fortification values. Approximately equivalent to natural folate PLUS foods already fortified pre-1998 (e.g., some cereals) Dietary Synthetic Folic Acid The enriched/fortified portion (post )

14 FFQ Analysis by Nutrients Dietary Natural Folate Folate from natural sources only, such as fruit, vegetables, liver, egg Dietary Folate Equivalents Combines synthetic folic acid and natural folate but takes into account the lower bioavailability of natural folate DFE = [µg of food folate + (1.7 x µg folic acid)]

15 FFQ Analysis by Nutrients Example 2: Vitamin E Dietary Alpha-Tocopherol Dietary Beta-Tocopherol Dietary Delta-Tocopherol Dietary Gamma-Tocopherol Dietary Natural Alpha-Tocopherol Dietary Synthetic Alpha-Tocopherol Dietary Total Alpha-Tocopherol Equivalents Dietary Vitamin E

16 FFQ Analysis by Nutrients Example 2: Vitamin E Dietary Alpha-Tocopherol Dietary Beta-Tocopherol Dietary Delta-Tocopherol Dietary Gamma-Tocopherol Dietary Natural Alpha-Tocopherol Dietary Synthetic Alpha-Tocopherol Dietary Total Alpha-Tocopherol Equivalents Dietary Vitamin E (IU) Use others at your own discretion

17 FFQ Analysis by Nutrients Example 3: Trans Fats Many investigators interested in trans fats due to the purported associations with disease risk Caution: not all trans fats are created equal Some trans fats are naturally occurring, some are created during food processing (but not hydrogenation) and some created by hydrogenation

18 FFQ Analysis by Nutrients Example 3: Trans Fats Which trans fat variable(s) should be used? Dietary Trans Fatty Acid16:1T Dietary Trans Fatty Acid18:1T Dietary Trans Fatty Acid18:2T Dietary Total TransFattyAcid Be very cautious about trans16:1t and total trans fats

19 FFQ Analysis by Food Groups Food groups are constructed variables made by grouping and summing the line items from the FFQ

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21 Computed variables are available for the following food groups: Fish Red Meat Poultry Grains Whole Grains Nuts Soy Milk Dairy These have all been created from the line items and are now posted. Are there other uses of the line items?

22 New Food Group Example: Cruciferous Vegetables 1. There is no line item called cruciferous vegetables so it must be constructed from existing line items 2. Find line items with cruciferous vegetables 3. Summing across yields medium servings per participant per day

23 So far so good these are all in the Brassica or Cruciferae Family

24 But here is a problem since spinach is not in the Brassica family, but the other greens listed are Brassica.

25 Other uses of the FFQ line items Dietary Patterns or Indices 1. Diet Quality Index Reflects adherence to the 8 Diet and Health recommendations of the National Academy of Sciences Estimates of nutrient intakes are scored Neuhouser et al J Am Diet Assoc : Neuhouser et al Pub Health Nutr : High-Fat Snacks/Desserts Index Potischman et al Cancer Causes Control 2002; 13: Mediterranean Diet 4. Healthy Eating Index 5. MPEDs (My Pyramid Equivalents) We don t have these food groups/indices set-up as constructed variables. Some manuscript writing groups are doing on their own

26 FFQ Adjustment Questions (newly posted) 19 Adjustment Questions at start of FFQ Types of cereal Types of milk on cereal and in beverages Food preparation, fats added in cooking/table Types of cookies and pastries These questions were designed to more precisely adjust the fat content of the line items since fat reduction was a primary goal of the WHI-DM

27 One response option permitted for this adjustment question

28 The choice selected in the adjustment question is applied to the response for this question. Thus, is someone marked regular then the nutrient string for regular ground beef is used for this question. If someone marked extra lean then the extra lean nutrient string is used for this question.

29 And so on. 5 possible choices. Participants permitted to mark one or two responses.

30 The adjustment question is used for this line item. If only one option is marked, then the marked option used as 100% of the nutrient string. If two options are marked, ½ of the nutrient string comes from each option. For example, ½ from highly fortified cereals and ½ from granola.

31 FFQ Adjustment Questions: Note: the adjustment questions were not originally designed to be used by themselves. Therefore, we cannot provide any data on the validity or reliability of using the adjustment questions alone (ie did you eat popcorn? or What type of salad dressing did you use? Caveat emptor!

32 FFQ Summary Questions Four summary questions at the end of the FFQ on: Fat used to deep fry or sauté Fat added in cooking Vegetable intake Fruit intake Note that these questions are frequency, not what kinds of fat so they are different than the adjustment questions Used to adjust the frequency of fruit or vegetables since respondents may tend to overreport when long lists are provided The fruit and vegetable summary questions have previously been used to create the fruit and vegetable variables already in the database.

33 Summary The FFQ data are posted on whiops.org; recall and food record data are not posted. The nutrient data are the primary data generated from the FFQ. The output yields average daily intake of 135 nutrients per person per day. When using nutrient data be careful about which nutrients to use. Know what you are analyzing. Examples: folate, trans fats and vitamin E variables.

34 Summary The individual 122 line items, 19 adjustment questions and 4 summary questions are also now posted. No known validity/reliability of using the adjustment questions by themselves. The 122 line items represent about 350 foods, each with a proportional weight. Don t deconstruct the line items under the assumption that you know the weights. Selected constructed variables from the line items are now posted.

35 Summary We did not cover: Measurement error in the FFQ Use of calibrated estimates of energy, protein or percent energy from protein Adequacy of the actual nutrient values in the database. Imputation of various nutrients.

36 Questions? Marian Neuhouser, PhD, RD or Lesley Tinker, PhD, RD