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1 From the Department of Pediatrics, Tokyo Women's Medical College, Daini Hospital, Tokyo.
2 Presented at the symposium Fat Intake During Childhood, held in Houston, June 8–9, 1998. 3 Address correspondence to M Murata, Department of Pediatrics, Tokyo Women's Medical College, Daini Hospital, Tokyo 2-1-10 Nishiogu, Arakawa City, Tokyo 116-8567, Japan. E-mail: mm3519{at}mbf.sphere.ne.jp.
ABSTRACT
Changes in the daily macronutrient intake of Japanese children have been studied over the past half century to determine the effects of such changes on a child's healthy growth and development. Data from government and other reports show that in 5-y-old boys in the Tokyo metropolitan area, the intake of fat as a percentage of total energy intake was 12.6%, 20.9%, 28.4%, 33.8%, and 33.2% in 1952, 1960, 1970, 1982, and 1994, respectively. The prevalence of obesity in school-aged children is increasing; recently, nearly 10% of the children in this age group were considered obese. About 5% of obese children experience some adverse effects caused by obesity, eg, hypertension and hyperlipidemia. Nationwide surveys on serum cholesterol concentrations conducted in 1960, 1970, 1980, and 1990 showed that the cholesterol concentrations in 10–19-y-old males and females increased year after year. The height of boys and girls rapidly increased during the 15-y period from 1945 to 1960, and after 1970 the adult height in Japan was thought to have reached its maximum. The factors that contribute to the health problems facing today's Japanese children include their sedentary lifestyle, irregular intake of meals (especially skipping breakfast), and the increasing daily ratio of fat to total energy intake. Presently, changing the sedentary lifestyle is the most significant issue to be resolved.
Key Words: Sedentary lifestyle • obesity • fat intake • cholesterol • secular trend in growth • children • Japan
INTRODUCTION
After World War II, Japan experienced an extended period of socioeconomic development, which evoked many changes within the culture. Changes in eating habits have persisted since that time and have greatly affected the physical size and health of Japanese children. In 1995 the mortality rate in infants <1 y of age was 4.3 per 1000 live births, the lowest rate among the developed countries in the world (1). Since 1945, the Ministry of Health and Welfare has annually reported changes occurring in the intake of fat, protein, carbohydrates, and total energy in the Japanese population as the National Nutrition Survey. The effects of these changes on physical size can be analyzed by using the nationwide School Health Program Report, published annually by the Ministry of Education since 1900. In 1992 the effects of these changes in eating habits on the health of Japanese children were reported (2, 3) and nutritional and secular trends in growth were reviewed (4). In this article, additional data are presented on the secular trends in growth and changes in eating habits in Japanese children.
CHANGES IN CONDITIONS IN THE FOOD SUPPLY AFTER THE SECOND WORLD WAR
Fifty-three years have passed since the end of World War II. From the standpoint of the food supply or nutritional conditions, these 53 y may be divided into 4 periods. The first period constitutes the shortage of the food supply from 1945 to 1950. The second period comprises the recovery of the food supply from 1950 to 1955. The third period is the period of rapid socioeconomic development in a Westernized and industrialized manner from 1955 to 1970. The last period is representative of the sufficient or excessive food supply since 1970. The last period can be divided into 2 parts. The first part is from 1970 to 1980, during which time the Japanese people enjoyed Westernized and industrialized affluent living, along with "delicious food." The second part is from 1980 to the present, during which time people have actually felt that this affluent living has adverse effects on their health.
CHANGES IN THE DAILY INTAKE OF MACRONUTRIENTS AND THEIR EFFECTS ON THE HEALTH OF CHILDREN
Changes in the daily intake of macronutrients in the Japanese population 20 y of age, on the basis of a report on the National Nutrition Survey (5), are shown in Figure 1. In 1946 the average intakes of carbohydrates, fat, and protein as a percentage of total energy were 80.6%, 7.0%, and 12.4%, respectively. It is important to stress that the intake of fat in 1946 was only 7% of total energy. This percentage is almost one-fourth of that considered suitable for adults: the recommended fat intake for adults in Japan is 20–25% of total energy intake. In 1955 the food supply in Japan had experienced a recovery, but fat intake was still insufficient and only accounted for 8.7% of total energy intake.
FIGURE 1.. Changes in the percentage of energy from carbohydrates, fat, and protein in the Japanese population aged >20 y. Data from the National Nutrition Survey (5).
In 1965, when Japan was clearly in its early period of Western-style socioeconomic development, fat intake rose to 14.8% of energy. This intake of daily fat was about one-half of the recommended amount. In 1975, by which time Japan had attained a high level of socioeconomic development, fat intake had reached 22.3% of energy, clearly falling within the acceptable range. The total energy intake was 7966 kJ in 1946 and 8468 kJ in 1994. These figures are almost equal. The changes in the total amount of fat intake and the sources of fat from 1955 to 1994 are shown in Figure 2 (5). In 1955 the total amount of fat intake was only 20.3 g/d and 68% of that was from vegetable oils. In 1965 the total intake of fat was 36.0 g/d and the proportion of animal fat had increased 3-fold compared with that in 1955. By 1975 the total amount of fat intake had risen to 55.2 g/d. This figure is the optimal daily intake of fat for adults. The amount of fat intake increased slightly from 1975 to 1994.
FIGURE 2.. Changes in the total amount of fat intake and source of fat in the Japanese population aged >20 y. Data from the National Nutrition Survey (5).
Changes in the daily intake of macronutrients in 5-y-old boys in the Tokyo metropolitan area are shown in Figure 3 (6–8). In 1952 the average intakes of carbohydrates, fat, and protein as a percentage of total energy were 74%, 12.6%, and 13.4%, respectively. It is again important to stress that the intake of fat in 1952 was only 12.6% of total energy. These percentages are half of those considered suitable for young children.
FIGURE 3.. Changes in the daily intake of the main nutrients in 5-y-old boys in the Tokyo metropolitan area. Data from the Bureau of Public Health (6–8).
In the most recent survey conducted in 1994, fat intake was 33.2% of energy (8). During the 42-y period from 1952 to 1994, the intake of protein as a percentage of total energy intake was 13–14% and the daily total energy intake was 6700 kJ. Also, as evident in Figure 3, the ratio of animal to vegetable proteins was 0.66 in 1952, 1.0 in 1960, 1.37 in 1982, 1.20 in 1987, and 1.53 in 1994. As the amount of animal protein intake has increased, so has the intake of animal fat. The changes in the daily intake of macronutrients in young girls were almost the same as the aforementioned changes in young boys. Nearly one-half of the young children in the Tokyo metropolitan area consume an excessive amount of fat, ie, >50 g/d.
The changes in the prevalence of obesity observed in the nationwide school health program that is conducted by the Ministry of Education are presented in Figure 4 (9). An obese school-aged child is defined as one whose weight is 120% of the standard weight as determined by sex, age, and height (9). The prevalence of obesity in 1996 was more than twice that in 1970.
FIGURE 4.. Changes in the prevalence of obese children. In 1990, n = 72380 kindergarteners, 270720 elementary school children, 225600 junior high schoolers, and 126900 senior high schoolers. In 1970, 1980, and 1996, n approximated the same numbers as in 1990. Data from reference 9.
On the basis of data presented in the report on the school health program prepared in 1996 by the Ministry of Education, the prevalence of obesity in school-aged children in each district from Hokkaido in the north to Kyushu and Okinawa in the south was almost the same (9). In general, the prevalence of obesity is 5% in younger age groups and 10% in elder age groups of school-aged children. The importance of this observation is that obesity in children is clearly a nationwide problem.
Changes in total cholesterol concentrations in the serum of Japanese males are shown in Figure 5 (10, 11). Nationwide surveys were used to evaluate total cholesterol concentrations by age in 1960, 1970, 1980, and 1990 with financial support from the government. The survey in 1970 was not controlled effectively; therefore, the data in 1970 have been omitted. The total cholesterol concentrations in 1980 were higher for ages 0–69 y than in 1960, especially for the 10–19-y-old age group. In this age group, the difference between total cholesterol concentrations in 1960 and 1980 was 0.2586 mmol/L, and the difference between cholesterol concentrations in 1980 and 1990 was 0.2586 mmol/L. In contrast, cholesterol concentrations have been decreasing in the United States; however, concentrations in the United States are much higher than those in Japan.
FIGURE 5.. Serum cholesterol concentrations in males in Japan (J) and the United States (U) from 1960 to 1990. Data from reference 11.
Changes in total cholesterol concentrations in the serum of Japanese females are shown in Figure 6 (10, 11). The source of the data were the same as that for the males and the trend was almost the same as in the males. In Japanese females, the cholesterol concentrations in 1980 and in 1990 were similar, except for the slightly higher concentrations in 1990 in the 10–19-y-old age group. The average total cholesterol concentrations in school-aged children, reported in the most recent survey performed by the Japanese Society of School Health in 1997 (12), are shown in Table 1.
FIGURE 6.. Serum cholesterol concentrations (mmol/L) in Japan (J) and USA (U) from 1960–1990. Data from reference 11.
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TABLE 1. Average total serum cholesterol concentrations in school-aged children in 19971
PROBLEMS FACING TODAY'S JAPENESE CHILDREN
The first problem facing today's Japanese children is the lack of daily physical exercise (sedentary lifestyles), caused by stressful academic studies over prolonged periods of time, captivating indoor entertainment (eg, television shows and games), and increased automobile transportation. Currently, 95% of the Japanese population goes on to senior high school and is required to pass an entrance examination and, upon entering high school, must prepare for the extremely difficult university or college entrance examination. The percentages of pupils and students who performed physical exercise or played in sports outside school on the day before the nationwide survey conducted by the Japanese Society of School Health in 1997 are shown in Figure 7. About 80% of all students in junior high school (12–15 y) and senior high school (16–18 y) in Japan have developed a sedentary lifestyle outside school. This sedentary lifestyle of school-aged children is one of the most significant issues to be addressed at present.
FIGURE 7.. Percentages of pupils and students who did physical exercise or sports outside on the day before the survey. Data from reference 12.
A second issue is irregular food intake. Many school-aged children do not eat breakfast. School-aged children usually prepare for the entrance examination the night before school, so they are prone to excessive food intake at night and have a tendency to frequent fast-food outlets. The percentages of school-aged children who skipped meals during the National Nutrition Survey (3 d) in 1994 (5) are shown in Figure 8.
FIGURE 8.. Percentage of school-aged children who skip meals. Data from reference 5.
The third issue is the increasing ratio of daily fat to total energy intake, as discussed earlier. The fourth issue is the increase in the percentage of families who are eating out, especially for dinner. The percentages of families, including children, who went out to eat dinner at least once during the National Nutrition Survey (3 d) in 1988 and 1994, are shown in Figure 9. Noodles, sushi, rice dishes, pasta, curry and rice, and breads make up 70 % of foods ordered when dining out with children aged 1–14 y. These foods consist of mainly carbohydrates and lack protein and yellow or green vegetables.
FIGURE 9.. Percentages of families including children who went out for dinner at least once during the National Nutrition Survey (3 d) in 1988 and 1994. Data from reference 5.
NUTRITIONAL CONDITIONS AND SECULAR TRENDS IN GROWTH
Nationwide statistical reports conducted by the Ministry of Education on the physical measurements of height and weight have been published since 1900 with some exceptions during World War II. The group born in 1940 was 6 y old in 1946, 7 y old in 1947, and so on, respectively. The longitudinal (more precisely, semi-longitudinal) height data, from the age of 5 or 6 y (the maximum age for kindergarten or the first grade of elementary school) to the age of 17 y (at present the third grade of senior high school) for the group of children born in 1940 can be given by sequentially collecting the data on height in the annual reports on the physical measurements taken by the Ministry of Education. The longitudinal data on height in the groups of children who were 5 y old in 1948, 5 y old in 1950, and so on are referred to as "Data1948," "Data1950," and so on, respectively. Using these longitudinal data, the relation between nutrition and secular trends of growth was analyzed (4).
The changes in the peak height age (PHA, the age when the speed in height growth is at its peak) and the heights at age 17 y for Data1948, Data1950, Data1955, Data1970, and Data1980 are shown in Table 2. The PHA of boys decreased slightly during the period when there was a shortage in the food supply (1945–1950) and decreased considerably during the period of recovery of the food supply (1950–1955). The PHA in girls decreased at almost the same rate. The PHA was almost the same in the 5-y-old groups in 1970 and during the years after 1970, namely, during the period of sufficient or excessive food supply (1970 to present). At present, the age at which speed in height growth is at its peak is 12.55 and 10.5 y of age in boys and girls, respectively. Consequently, the physical size of Japanese children and adolescents is supposed to have reached its maximum.
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TABLE 2. Changes in peak height age (PHA) and height at 17 y of age1
CONCLUSIONS
As shown in Figure 1, the average intake of fat as a percentage of total energy intake by adults in 1975 was 22.3%. In 1975 the nutritional status was quite good in Japan. In 1985, fat was 24.5% of the diet, and in 1994 it was 25.8%. If this pace continues, the average intake of fat for adults in the near future will be 60 g/d and the ratio of animal fat to vegetable and fish fat (oil) will be 2:3.
Young children consume a larger proportion of fat and animal protein than do adults. But, as shown in Figure 3, the intake of fat as a percentage of energy by 5-y-old boys in the metropolitan area was 33.8% in 1982 and 33.2% in 1994. If the average intake of fat in young children persists at 30–35% of energy, then almost half of the population of young children will continue to consume >50 g of fat/d.
An important risk factor in Japanese children is their lack of daily physical exercise and activities (sedentary lifestyle) (12). In Japan, coronary heart disease is still not a serious problem, but type 1 diabetes is becoming one of the big risk factors. On the basis of a recent survey, using glycohemoglobin as an index for cases suspected to have contracted type 1 diabetes (a random sample of 5883), the Ministry of Health and Welfare reported that 6.9 million persons, ie, 8.2% of the population 20 y of age, were strongly suspected to have type 1 diabetes. In a 1990 survey, that number was 5.66 million. Since 1992 a urine sugar test has been conducted once a year in the nationwide school program to ensure that type 1 diabetes can be detected in the early stages.
On the basis of reference materials in Japan, the biggest problem in considering atherogenic risk factors as a result of the changes in lifestyle in Japanese children lies in the fact that childhood lifestyle varies significantly from generation to generation. For example, persons in their 60s could never have imagined the lifestyle of today's teenagers. Therefore, it is not reasonable for us to predict the future health conditions of today's teenagers by referring to statistical data on the atherogenic risk factors in children 50 or 60 y ago, namely in the populations of 60–70-y-olds at present. Time is the only factor that can solve this problem.
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