Glycemic index and glycemic load of the diets of Japanese adults: the 2012 National Health and Nutrition Survey, Japan

Highlights

• White rice is a major contributor to dietary glycemic index (GI) in Japanese adults.

• Dietary GI is relatively high in Japan compared with Western countries.

• A low-GI diet is related to both favorable and unfavorable aspects of dietary intake.

Abstract

Objective

The aim of this study was to examine the dietary glycemic index (GI) and glycemic load (GL) of Japanese adults, as well as their nutritional correlates, in the 2012 National Health and Nutrition Survey, Japan.

Method

Dietary data from 15 618 adults aged ≥20 y, collected using a 1-d weighed dietary record, were analyzed. The GI of foods was assigned based on a stepwise published strategy using values from common GI databases.

Results

Mean (SD) dietary GI and GL were 65.9 (4.9) and 190.1 (59.7), respectively, for men and 63.9 (5) and 149.1 (44.1), respectively, for women. Regardless of sex, the top contributor to dietary GL was white rice (GI = 76; >50%), followed by bread (6–8%), noodles (5–6%), and confectioneries (4–7%). White rice was not only positively associated with dietary GI but also contributed most (∼38%) to interindividual variation in dietary GI. For dietary GL, ∼90% of the interindividual variation was explained by carbohydrate-rich foods (mainly white rice; ∼50%), all of which were positive predictors. At the nutrient level, only carbohydrate intake was positively associated with dietary GI and GL, whereas intakes of all other nutrients including saturated fatty acid and sodium showed inverse associations (with some exceptions).

Conclusion

Dietary GI and GL of Japanese adults were primarily determined by the high GI food white rice, and were thus relatively high compared with values observed in Western countries. A low GI and GL diet was associated with both favorable (higher intakes of micronutrients) and unfavorable (higher intakes of saturated fatty acid and sodium) aspects of dietary intake patterns.

Introduction

Accumulated evidence suggests a potential role of diets with a low glycemic index (GI; a measure of carbohydrate quality) [1] and glycemic load (GL; a measure of carbohydrate quality and quantity) [2] in the prevention and management of chronic diseases [3], including type 2 diabetes [4]. Findings have not always been consistent, however, particularly with regard to obesity [5], [6], [7], [8]. Such heterogeneous results may be at least partly due to cultural differences in dietary intake patterns in relation to dietary GI and GL. In Western populations, dietary GL has generally been associated with many carbohydrate-rich foods, and hence strongly with carbohydrate intake, whereas dietary GI has been associated with not only higher intakes of major carbohydrate-rich foods (such as breads and potatoes) but also lower intakes of other low- or noncarbohydrate foods (such as fruit and dairy products). However, the associations between dietary GI and GL and intake of each of the food groups and nutrients vary considerably in magnitude and direction, depending on different food culture contexts [6], [7], [8], [9], [10], [11], [12], [13], [14]. These differences highlight the need to gather country-specific data on dietary GI and GL to better inform nutrition and public health policy in each country [14].

The diets consumed by Japanese people are typically characterized by high intakes of white rice, soybean products, fish, seaweeds, and green tea [15]. Furthermore, Japanese diets are known to be high in dietary GI and GL (range of median values: 65–67 and 141–185, respectively; GI for glucose = 100) [16], [17], [18], [19], [20] compared with Western countries (range of median values: 50–61 and 80–140, respectively; GI for glucose = 100) [3], mainly because white rice, a food with a high GI (76), is the major contributor to dietary GI and GL (46–64%) [16], [17], [20], [21]. Thus, associations of dietary GI and GL with food groups and nutrient intakes may differ between Japanese and Western diets. Information about the nutritional correlates of dietary GI and GL in Japanese populations is sparse [21], however, and this idea remains speculative. More importantly, previous studies on dietary GI and GL of Japanese have been conducted either in a limited number of individuals [17], based on the questionnaire-based dietary assessment with a very limited number of food items [16], [20], [21], or mainly among women [16], [20], [21]. Further research based on detailed dietary intake data in a more representative sample of Japanese is warranted.

Therefore, the aim of the present study was to examine dietary GI and GL of Japanese adults, as well as nutritional correlates at both the food group and nutrient level, based on dietary intake data from the weighed dietary record in the 2012 National Health and Nutrition Survey, Japan (NHNSJ).