Fatty Acids

The long-FFQ consisted of 172 food and beverage items and nine frequency categories, ranging from almost never to seven or more times per day (or to 10 or more glasses per day, for beverages). It asked about the usual consumption of listed foods during the previous year. The food list was initially developed according to percentage contributions based on absolute values of energy and intake of 14 target nutrients from weighed food records in 1989–1991^{8 (link)} and used for the Japan Public Health Center-based prospective Study,^{8 (link)–12 (link)} for which it was modified for middle-aged and elderly residents in a wide variety of areas of Japan. With regard to this modification, the following criteria were considered: calculation for an additional 17 nutrient items, such as fiber and folate, change of foods contributing to the absolute nutrient intake according to the updated Standard Tables of Food Composition in Japan,^{13 ,14} and dietary regionality and change in generation for the present cohort (data not shown). As a result, 33 foods were added, and 5 foods and beverages were excluded.^{15 (link)} Moreover, six foods were also added to account for potential inter-individual variation in specific nutrients, such as isothiocyanate and isoflavone. With regard to alcoholic beverages, choices of intake amount were changed from the initial JPHC-FFQ.
To develop the food list for the short-FFQ, we selected and combined items and supporting questions from the original long-FFQ. We selected the three major foods and beverages that contributed to inter-individual variation for each of 40 nutrients according to a cumulative R² for the 40 nutrients,¹⁶ based on the multiple regression coefficient with total intake of a specific nutrient as the dependent variable and its intake from each food as the explanatory variable. Inter-individual variation was calculated by gender among 45 869 men and 52 989 women who responded to the JPHC Study 10-year follow-up survey. Consequently, cumulative R² for the nutrients ranged from 0.4 to 1.0. For potential inter-individual variation in intake of specific food groups, some foods, such as coffee, were added. Ultimately, 66 food and beverage items were selected for the short-FFQ. In this validation study, information on alcoholic beverages was substituted with those from the long-FFQ (united with overall information of lifestyle), because these questions were not included in the short-FFQ. This was because information on alcoholic beverage intake was structured in pages for lifestyle other than diet, such as smoking status and physical activity, and the reproducibility of alcoholic beverage intake was relatively high even if questionnaires were administered at a 1-year interval.^{17 (link),18 (link)}Intakes of energy, 53 nutrients, and 29 food groups were calculated using the Standard Tables of Food Composition in Japan 2010,¹⁹ Standard Tables of Food Composition in Japan Fifth Revised and Enlarged Edition 2005 For Fatty Acids,²⁰ and a specifically developed food composition table for isoflavones in Japanese foods.^{21 (link)}

We created an overall plant-based diet index (PDI), a healthful plant-based diet index (hPDI), and an unhealthful plant-based diet index (uPDI). The procedure we used to create these indices is similar to the one used by Martínez-González et al. [13 (link)]; their “provegetarian food pattern” is similar in composition to our PDI. Frequencies of consumption of each food were converted into servings consumed per day. Then the number of servings of foods that belonged to each of 18 food groups were added up. The 18 food groups were created on the basis of nutrient and culinary similarities, within larger categories of animal foods and healthy and less healthy plant foods. We distinguished between healthy and less healthy plant foods using existing knowledge of associations of the foods with T2D, other outcomes (CVD, certain cancers), and intermediate conditions (obesity, hypertension, lipids, inflammation). Plant foods not clearly associated in one direction with several health outcomes, specifically alcoholic beverages, were not included in the indices. We also excluded margarine from the indices, as its fatty acid composition has changed over time from high trans fat to high unsaturated fat. We controlled for alcoholic beverages and margarine consumption in the analysis.
Healthy plant food groups included whole grains, fruits, vegetables, nuts, legumes, vegetable oils, and tea/coffee, whereas less healthy plant food groups included fruit juices, sugar-sweetened beverages, refined grains, potatoes, and sweets/desserts. Animal food groups included animal fats, dairy, eggs, fish/seafood, meat (poultry and red meat), and miscellaneous animal-based foods.
S1 Table details examples of foods constituting the food groups. The 18 food groups were divided into quintiles of consumption, and each quintile was assigned a score between 1 and 5. For PDI, participants received a score of 5 for each plant food group for which they were above the highest quintile of consumption, a score of 4 for each plant food group for which they were above the second highest quintile but below the highest quintile, and so on, with a score of 1 for consumption below the lowest quintile (positive scores). On the other hand, participants received a score of 1 for each animal food group for which they were above the highest quintile of consumption, a score of 2 for each animal food group for which they were between the highest and second highest quintiles, and so on, with a score of 5 for consumption below the lowest quintile (reverse scores). For hPDI, positive scores were given to healthy plant food groups, and reverse scores to less healthy plant food groups and animal food groups. Finally, for uPDI, positive scores were given to less healthy plant food groups, and reverse scores to healthy plant food groups and animal food groups. The 18 food group scores for an individual were summed to obtain the indices, with a theoretical range of 18 (lowest possible score) to 90 (highest possible score). The observed ranges at baseline were 24–85 (PDI), 28–86 (hPDI), and 27–90 (uPDI) across the cohorts. The indices were analyzed as deciles, with energy intake adjusted at the analysis stage.