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NUTRITION RESEARCH, Vol. 6, pp. 731-733, 1986 0271-5317/86 $3.00 + .00 Printed in the USA. Copyright (c) 1986 Pergamon Journals Ltd. All rights reserved.
COUNTRY REPORT JAPAN In 1986, the a v e r a g e 20 y e a r old Japanese men are 170 cm tall and weigh 61 kg. Women, in the same age, are 157 cm tall and weigh 51 kg. In 1950, these f i g u r e s were 161 cm and 55 kg f o r men, and 151 cm and 51 kg for women, respectively. Improvement in n u t r i t i o n has u n d o u b t e d l y played a major role in the changes in these a n t h r o p o m e t r i c parameters among Japanese population d u r i n g the past q u a r t e r o f a c e n t u r y . The n u t r i t i o n a l problem in Japan has sh ift e d from u n d e r n u t r i t i o n in 1950s to o v e r n u t r i t i o n in 1980s. How then have the topics of research i n t e r e s t among Japanese n u t r i t i o n and food scientists been adapted to the c h a n g i n g problems d u r i n g this period? TABLE I Titles Presented at the A n n u a l Meetings o f Japanese Society o f N u t r i t i o n and Food Science Year Fields Food Composition Safety o f Food
1975
1980
1985
26
41
45
7
17
6
Carbohydrates
3
3
12
D i e t a r y Fiber
0
I0
18
Lipids
14
16
28
Protein and Amino Acids
31
41
41
N u t r i e n t Metabolism and Physiology
14
63
56
Minerals
12
12
34
Vitamins
9
13
31
Clinical N u t r i t i o n
21
60
28
N u t r i t i o n a l S u r v e y and Community N u t r i t i o n
18
40
52
155
316
351
Total
I have classified the titles presented at the annual meetings o f Japanese Society o f N u t r i t i o n and Food Science a c c o r d in g to v a r i o u s research fields o v e r the past 10 y e a rs ( T a b l e I ) . P a r t i c u l a r l y n o t e w o r t h y is the increasing i n t e r e s t in the field o f d i e t a r y f i b e r f o r the past several y e a r s , which was v i r t u a l l y n o n - e x i s t e n t 10 years ago. Indeed, the topic of a major symposium in 1986 meeting (Nagoya, May 2-4) is " N o n - n u t r i e n t s and Physiological F u n c t i o n " . A l t h o u g h n o n - e x p l i c i t in Table I , a sizable p o r t i o n in the field of clinical 731
732
Y. NATORI
nutrition in recent years is devoted to the problem of obesity. To exemplify the recent activities of nutritional scientists in Japan, I have taken the l i b e r t y of selecting several contributions from Japanese laboratories made during the past year. In the area of the regulatory mechanism of gene expression by nutrient intake, we ( I ) found that feeding-induced RNA synthesis in the nuclei of newly hatched chick l i v e r was accompanied by profound changes in the u l t r a s t r u c t u r e and function of chromatin. The greater template capacity of chromatin in the l i v e r of fed animals was found to be related to the increased content of a group of non-histone chromatin proteins, called HMG. Noguchi et al. (2) studied regulation of the expression of the hepatic pyruvate kinase (PK) gene by insulin and dietary fructose. By in v i t r o transcription assay, involving hybridization of transcribed RNA to cDNA probe, they showed that insulin increased transcription of the PK gene while dietary fructose simply stabilized the transcribed message without inducing the transcription. The two studies, cited here, may point to a direction of the application of up-to-date molecular biological techniques to nutritional problems. The physiological mechanism of hunger and satiety has been actively pursued in the laboratory of Y. Oomura. The ventromedial nucleus of the hypothalamus (VMH) and the lateral hypothalamic area (LHA) have been shown to be functionally related in the regulation of feeding, and referred to as the satiety and feeding centers, respectively. These two areas possess specific glucoreceptor or glucose-sensitive neurons that respond to extremely small quantity of glucose. In an attempt to identifying various blood factors that might be related to hunger and satiety, Puthuraya et al. (3) recently obtained evidence suggesting that certain endogenous sugar acids such as 3, 4-dihydroxybutanoic acid and 2,4, 5-trihydroxypentanoic acid act as endogenous satiety and hunger substances, respectively. There is now ample evidence to show that brown adipose tissue (BAT) is a major site for energy expenditure in spontaneous hyperphagic rats fed on a cafeteria diet as well as in cold-acclimated animals and that failure of its thermogenic function contributes to the development of some type of obesity. Since thermogenesis in BAT is under direct control of sympathetic nervous system and since VMH involves the sympathetic neural component, it might be expected that thermogenesis in BAT is modulated by the VMH. Saito et al. (4) found that thermogenesis in BAT was indeed impaired in obese rats with VMH lesions, probably due to decreased t r i g l y c e r i d e turnover in BAT. Two physiological papers, cited above, point to the importance of central nervous system in the regulation of appetite and, eventually, of obesity. Regarding cholesterol metabolism, vegetable protein is known to exert a hypocholesterolemic effect as compared with animal protein. Although reduced cholesterol absorption a n d increased fecal steroid excretion appear to be responsible for the cholesterol-lowering action of soybean protein as compared to casein, the mechanism of these modulations has remained obscure. Yashiro et al. (5) have shown that the peptic digest of soybean protein displayed the hypocholesterolemic effect in the same degree as intact protein in rats. The peptic digest of soybean protein may contain physiologically active peptides that affect cholesterol metabolism. Department of Nutrition Tokushima U n i v e r s i t y , School of Medicine Tokushima, Japan
Yasuo Natori
COUNTRY REPORT: JAPAN
733
1. OKA, T . , HAN, J . P . , NATORI, Y . , HASEGAWA, N., KANAI, M. and WATARI, N. Enhancement of RNA Synthesis in Chick Liver by Food Intake: Possible Role of High Mobility Group Nonhistone Proteins. J. N u t r . , 115: 1504-1514, 1985. 2. NOGUCHI, T . , INOUE, H. and TANAKA, T. Transcriptional and Posttranscriptional Regulation of L-type Pyruvate Kinase in Diabetic Rat Liver by Insulin and Dietary Fructose. J. Biol. Chem., 260: 14393-14397, 1985. 3. PUTHURAYA, K . P . , OOYAMA, Y. and SHIMIZU, N, Effects of Endogenous Sugar Acids on the Ventromedial Hypothalamic Nucleus of the Rat. Brain Research, 332: 165-168, 1985. 4. SAITO, M., MINOKOSHI, Y. and SHIMAZU, T, Brown Adipose Tissue after Ventromedial Hypothalamic LeSions in Rats. A m. J. Physiol., 248 (Endocrin. Metabol. 11}: E20-E25, 1985. 5. YASHIRO, A . , ODA, S. and SUGANO, M. Hypocholesterolemic Effect of Soybean Protein in Rats and Mice after Pectic Digestion. J. N u t r . , 115: 1325-1336, 1985.
COUNTRY REPORT JAPAN In 1986, the a v e r a g e 20 y e a r old Japanese men are 170 cm tall and weigh 61 kg. Women, in the same age, are 157 cm tall and weigh 51 kg. In 1950, these f i g u r e s were 161 cm and 55 kg f o r men, and 151 cm and 51 kg for women, respectively. Improvement in n u t r i t i o n has u n d o u b t e d l y played a major role in the changes in these a n t h r o p o m e t r i c parameters among Japanese population d u r i n g the past q u a r t e r o f a c e n t u r y . The n u t r i t i o n a l problem in Japan has sh ift e d from u n d e r n u t r i t i o n in 1950s to o v e r n u t r i t i o n in 1980s. How then have the topics of research i n t e r e s t among Japanese n u t r i t i o n and food scientists been adapted to the c h a n g i n g problems d u r i n g this period? TABLE I Titles Presented at the A n n u a l Meetings o f Japanese Society o f N u t r i t i o n and Food Science Year Fields Food Composition Safety o f Food
1975
1980
1985
26
41
45
7
17
6
Carbohydrates
3
3
12
D i e t a r y Fiber
0
I0
18
Lipids
14
16
28
Protein and Amino Acids
31
41
41
N u t r i e n t Metabolism and Physiology
14
63
56
Minerals
12
12
34
Vitamins
9
13
31
Clinical N u t r i t i o n
21
60
28
N u t r i t i o n a l S u r v e y and Community N u t r i t i o n
18
40
52
155
316
351
Total
I have classified the titles presented at the annual meetings o f Japanese Society o f N u t r i t i o n and Food Science a c c o r d in g to v a r i o u s research fields o v e r the past 10 y e a rs ( T a b l e I ) . P a r t i c u l a r l y n o t e w o r t h y is the increasing i n t e r e s t in the field o f d i e t a r y f i b e r f o r the past several y e a r s , which was v i r t u a l l y n o n - e x i s t e n t 10 years ago. Indeed, the topic of a major symposium in 1986 meeting (Nagoya, May 2-4) is " N o n - n u t r i e n t s and Physiological F u n c t i o n " . A l t h o u g h n o n - e x p l i c i t in Table I , a sizable p o r t i o n in the field of clinical 731
732
Y. NATORI
nutrition in recent years is devoted to the problem of obesity. To exemplify the recent activities of nutritional scientists in Japan, I have taken the l i b e r t y of selecting several contributions from Japanese laboratories made during the past year. In the area of the regulatory mechanism of gene expression by nutrient intake, we ( I ) found that feeding-induced RNA synthesis in the nuclei of newly hatched chick l i v e r was accompanied by profound changes in the u l t r a s t r u c t u r e and function of chromatin. The greater template capacity of chromatin in the l i v e r of fed animals was found to be related to the increased content of a group of non-histone chromatin proteins, called HMG. Noguchi et al. (2) studied regulation of the expression of the hepatic pyruvate kinase (PK) gene by insulin and dietary fructose. By in v i t r o transcription assay, involving hybridization of transcribed RNA to cDNA probe, they showed that insulin increased transcription of the PK gene while dietary fructose simply stabilized the transcribed message without inducing the transcription. The two studies, cited here, may point to a direction of the application of up-to-date molecular biological techniques to nutritional problems. The physiological mechanism of hunger and satiety has been actively pursued in the laboratory of Y. Oomura. The ventromedial nucleus of the hypothalamus (VMH) and the lateral hypothalamic area (LHA) have been shown to be functionally related in the regulation of feeding, and referred to as the satiety and feeding centers, respectively. These two areas possess specific glucoreceptor or glucose-sensitive neurons that respond to extremely small quantity of glucose. In an attempt to identifying various blood factors that might be related to hunger and satiety, Puthuraya et al. (3) recently obtained evidence suggesting that certain endogenous sugar acids such as 3, 4-dihydroxybutanoic acid and 2,4, 5-trihydroxypentanoic acid act as endogenous satiety and hunger substances, respectively. There is now ample evidence to show that brown adipose tissue (BAT) is a major site for energy expenditure in spontaneous hyperphagic rats fed on a cafeteria diet as well as in cold-acclimated animals and that failure of its thermogenic function contributes to the development of some type of obesity. Since thermogenesis in BAT is under direct control of sympathetic nervous system and since VMH involves the sympathetic neural component, it might be expected that thermogenesis in BAT is modulated by the VMH. Saito et al. (4) found that thermogenesis in BAT was indeed impaired in obese rats with VMH lesions, probably due to decreased t r i g l y c e r i d e turnover in BAT. Two physiological papers, cited above, point to the importance of central nervous system in the regulation of appetite and, eventually, of obesity. Regarding cholesterol metabolism, vegetable protein is known to exert a hypocholesterolemic effect as compared with animal protein. Although reduced cholesterol absorption a n d increased fecal steroid excretion appear to be responsible for the cholesterol-lowering action of soybean protein as compared to casein, the mechanism of these modulations has remained obscure. Yashiro et al. (5) have shown that the peptic digest of soybean protein displayed the hypocholesterolemic effect in the same degree as intact protein in rats. The peptic digest of soybean protein may contain physiologically active peptides that affect cholesterol metabolism. Department of Nutrition Tokushima U n i v e r s i t y , School of Medicine Tokushima, Japan
Yasuo Natori
COUNTRY REPORT: JAPAN
733
1. OKA, T . , HAN, J . P . , NATORI, Y . , HASEGAWA, N., KANAI, M. and WATARI, N. Enhancement of RNA Synthesis in Chick Liver by Food Intake: Possible Role of High Mobility Group Nonhistone Proteins. J. N u t r . , 115: 1504-1514, 1985. 2. NOGUCHI, T . , INOUE, H. and TANAKA, T. Transcriptional and Posttranscriptional Regulation of L-type Pyruvate Kinase in Diabetic Rat Liver by Insulin and Dietary Fructose. J. Biol. Chem., 260: 14393-14397, 1985. 3. PUTHURAYA, K . P . , OOYAMA, Y. and SHIMIZU, N, Effects of Endogenous Sugar Acids on the Ventromedial Hypothalamic Nucleus of the Rat. Brain Research, 332: 165-168, 1985. 4. SAITO, M., MINOKOSHI, Y. and SHIMAZU, T, Brown Adipose Tissue after Ventromedial Hypothalamic LeSions in Rats. A m. J. Physiol., 248 (Endocrin. Metabol. 11}: E20-E25, 1985. 5. YASHIRO, A . , ODA, S. and SUGANO, M. Hypocholesterolemic Effect of Soybean Protein in Rats and Mice after Pectic Digestion. J. N u t r . , 115: 1325-1336, 1985.