Public Health (1990), 104, 249-255
© The Society of Public Health, 1990
Risk Factors of Obesity among Hong Kong Youths S.C. Ho Department of Community and Family Medicine. The Chinese University of Hong Kong, 4th Floor, Lek Yuen Health Centre, Shatin, Hong Kong
Introduction The aetiology o f obesity remains obscure. Although excess caloric intake has been shown to lead to obesity in animal studies, no conclusive evidence on the positive relationship between energy intake and obesity is found in population surveys. Similar uncertainty exists in the relationship between the level o f physical activity and obesity. ~ This paper reports a study which aims to investigate the relationship between dietary intake, level o f physical activity, familial factor and overweight. It will serve to support some o f the previous findings, and to present a preliminary investigation o f the problem in the Asian communities where few such studies have been carried out. Methods One of the Institute o f higher learning included in a survey o f overweight among school children was selected for this case-control study. A previous survey on school adolescence shows that a Body Mass Index (BMI = weight in kg over height in meter squared) o f 25 is at 2 standard deviations above the mean BMI. 2 The cases ineluded in this study were thus those identified to have a body mass index (BMI) over 25. An equal number o f subjects with BMI 25 or below from the same class were selected as the controls. The dietary intake study was divided into two parts: (i) The first part was a weighed food diary. The youths were requested to complete a 4-day weighed food diary during the week. Detailed instructions and demonstrations were given on the methods o f recording and o f weighing the food items. A portable weighing scale was issued to every participating subject. Visual instructions on how to quantify the foods in terms o f c o m m o n household measures were given so that foods could be quantified in household measures if the portable weighing scale could not be conveniently used in situations such as eating out or having a quick snack off the street. A pictorial illustration o f the c o m m o n household measures such as different sizes bowls, plates and spoons as well as a measuring scale in inches were included in the diary. The subjects were requested to carry the diary with them at all times during the four day recording period. Each subject was contacted during the second day to clarify any doubts encountered, and at the end o f the four days so the investigator would have an opportunity to go over the diary together with the subject to clarify any doubts or to rectify any wrong or unclear recordings. The food items were coded and the nutrients analysed based on the computerised F o o d Composition Table for Use in East Asia 3 and food composition compiled by the author, mainly for some local foods such as Dim Sum. A 20% sample o f the 44 food diaries was taken to
250
S. C. Ho
examine the percentage o f the recorded food items based on visual estimates. The mean was found to be 20.7% (s.d. = 12.9) while the median was 25% (ii) The second part consists o f two separate semi-quantitative food frequency questionnaires. One was on fat and the other on dietary fibre intake. The former questionnaire included 57 food items. The calculation o f fat and fatty acids in each food was based on the F o o d Composition Tables for Use in East Asia with supplementation from other Tables. 3-5 The second questionnaire included 51 food items o f commonly consumed cereals, vegetables and fruits and other food items with substantial fibre contribution in the local setting. The calculation o f dietary fibre was based on Widdowson's d a t a : A list of questions on the preference or habit o f fat and oil intake were also asked.
Energy expenditure Methods used to measure energy in terms o f M E T S have been described in a previous paper. 7 5 questions were included to measure the background physical activities (Appendix
1). Familial overweight The subjects were asked to obtain their parents' height and weight and report the data when they returned for the 4-day diary. Self-reported data on height and weight have been shown to be o f acceptable validity in H o n g K o n g populations:
Measurement of blood pressure The measurements were taken at seated position towards the end o f the questionnaire answering session. The first appearing sound was recorded as the systolic, and the last appearing sound as the diastolic pressure. Two measurements were taken with one minute interval in between. The average of the two measurements was used. Results
16 overweight youths were included as cases in the study. They were compared with 29 normal weight youths. Both groups had the mean and median age o f 21 and the age range from 18-26. The socio-economic status was quite similar in both groups with about two-thirds o f the heads of households belonging to the clerical, service or production workers. A quarter o f the cases and 37% o f the controls were female subjects. The cases had a mean body mass index o f 27.5 (s.d. = 2.9) and the controls a mean o f 20.8 (s.d. = 2.1). The body mass indices of the cases ranged from 25.01 to 36.40 while that for the controls 17.39 to 24.71 (Appendix 2).
lntake of energy and macronutrients The 4-day dietary weighted food record shows that although the overweight group had a lower energy intake (1,877 Kcal versus 2,036 among the controls), they had a slightly higher total fat intake in absolute value (60 grn vs 58 gm in controls) and after adjustment for energy (32 gm vs 29 grn per 1,000 cal in controls). The carbohydrate intake was lower among the cases (261 gm vs 294 gm in controls) who also had a higher percentage (29%) of
Obesity in Hong Kong Youths
251
Table I Comparison of mean fat and fibre intake (gm) per day between cases and controls (based on semi-quantitative food frequency method) Fat Total fat Total fatty acid Saturated fatty acid , Unsaturated fatty acid Linoleic acid Oleicacid Unsaturated/Saturated Fibre
Cases Mean (SD)
Controls Mean (SD)
P-value (t test)
74.4 (40.5) 68.8 (37.5) 26.0 (14.4) 42.6 (23.2) 10.2 (6.2) 29.9 (16.1) 1.6 (0.13) 9.0 (3.1)
55.1 (27.2) 51.2 (25.3) 19.5 (9.4) 31.4 (16.1) 7.4 (4.3) 22.0 (11.6) 1.6 (0.24) 8.6 (3.1)
0.07 0.07 0.12 0.07 0.09 0.07 0.46 0.68
Number in brackets() = standard deviation their energy intake f r o m fat c o m p a r e d to the controls (26%). H o w e v e r , n o n e o f the differences o f the means between the cases a n d controls were statistically significant by the t-test. Table I shows the types o f fat intake o b t a i n e d f r o m the semi-quantitative f o o d frequency method. The cases had a higher m e a n intake in b o t h the total fat a n d fatty acids as well as in the saturated a n d u n s a t u r a t e d fatty acids. Similar differences were observed after controlling f o r sex. However, the fibre intake a n d the ratio o f u n s a t u r a t e d to saturated fatty acids were quite similar in b o t h groups. Table II shows that the cases tended to have a higher preference for fat and m e a t Table II
Comparison of habit of oil and fat intake between cases and controls Case n (%)
Control n (%)
O.R.
95% C.I.
(79) (21)
0.6 1.0
0.1-2.9
Type of cooking oil Peanut Corn
11 5
Eat visible fat in meat Most or all Little or no fat
10 (62) 6 (38)
14 (50) 14 (50)
1.7 1.0
0.4-7.1
Chicken or duck with skin Often/always Seldom/never
14 (87) 2 (13)
14 (50) 14 (50)
7.0 1.0
1.2-40.9
Prefer vegetable to meat Same/no Yes
12 (75) 4 (25)
17 (61) 11 (39)
1.9 1.0
0.4-9.5
4 24
7.7 1.0
1.543.5
Time per week eating dim sum 2+ 0-1
9 7
(69) (31)
(56) (48)
22 6
(14) (86)
S.C. Ho
252 .Table
III
Relationship of subjects' BMI with parents' BMI O.R.
C.I.
Father's BMI > = 25/< 25
4.8
0.9-26.7
Mother's BMI > = 25/< 25
4.5
1.0-22.5
BMI > = 25 Both or one parent/None
4.0
0.8-21.6
c o m p a r e d to the controls. The risk of overweight a m o n g those who often or always ate chicken or duck together with its skin and those who had dim sum twice a week or m o r e were observed to be around 7.0.
Activity and energy expenditure The cases were found to have a slightly higher m e a n energy expenditure of 42.8 M E T S (s.d. = 1.6) c o m p a r e d to the controls 42.0 (s.d. = 1.3). When the background activity score was divided into low ( < 4), medium (4-5) and high ( > 5), the risk o f overweight was !.7 (C.I. 0.3-11) a m o n g the medium, and 2.5 (C.I. 1.3-21.4) a m o n g the low when c o m p a r e d with the high score group.
Relationship with parents' body mass index Table I I I shows the relationship between the weight categories o f the subjects and that o f their parents. The risk of overweight increases to a r o u n d 4 if either one o f their parents or both parents were overweight. However, no association o f overweight between the parents was observed.
Relationship of B M I with blood pressure A positive and moderate association of the subjects' B M I with their blood pressure was observed. The relationship seems to be slightly stronger with the systolic (r=0.4689, P < 0.0012) c o m p a r e d with the diastolic blood pressure (r = 0.3742, P < 0.0113).
Discussion
The finding that the overweight group had a slightly lower total energy intake was in similar direction as that f r o m some other epidemiological studies. 9a° A higher fat intake and higher preference for fatty foods were indicated in this study. The food frequency method gave a larger difference between the cases and controls c o m p a r e d to the 4-day food diary, probably because the latter was held during weekdays and the in-school meals could have resulted in a more homogeneous intake a m o n g the subjects. A b o u t 25% o f the recorded food items were found to be based on visual estimates. Such process had been facilitated
Obesity in Hong Kong Youths
253
with the inclusion of pictorial presentation of household containers and measuring scale in the diary. However, the accuracy of the visual estimates had not been validated. A recent study among the nurses also found a significant correlation between the relative weight and their total fat and saturated fatty acids intake. 9 However, the dietary fibre intake among the two groups was observed to be quite similar suggesting that the controls did not necessarily have a higher consumption of complex carbohydrates. Further investigations into the role and relationship of the macronutrients in obesity are indicated. Inconsistent data have been found on the relationship between physical activity and obesity, u-12 and little data are available on the role of background physical activities. A recent study by Meyers et aL ~3found that obese people were far less likely to take the stairs than were non-obese persons. Our study found that even though the assessment of overall physical activity showed a slightly higher level in the overweight group, the normal weight subjects tend to take the trouble to incorporate activities in daily lives in order to increase their level of activity. These activities included walking the stairs instead of taking the lifts, walking to the place of destination instead of taking means of transport etc. Perhaps the persistent daily intentional exercise are more important than sporadic exercises in the prevention of overweight. There has been suggestion that the finer differences in activity level which is difficult to be detected in the gross measures of exercise may be responsible for the weight difference between the obese and non-obese groups. The intentional activity also reflects a degree of conscientiousness among the subjects to keep fit and this habit is perhaps more important in urban living where the level of exercise of the average man had been reduced to a minimum by the presence of all the conveniences such as lifts and easy access to places by different means of transport. The incorporation of some activities such as walking stairs into the daily routine would be a valuable behaviour for the prevention as well as the treatment of obesity. This study observed a higher level of background activities among the controls. Perhaps the persistent daily activities are useful especially in the prevention of overweight in urban living where sporting facilities are not readily available. Some research studies also suggest that lower intensity lifestyle exercises performed throughout the day is probably more effective than intensive exercises in maintaining weight loss in children. 14 Moreover, the low intensity type of exercise is also more easily acceptable to most individuals compared to the intensive type. '5 Familial aggregation of obesity has been found by a number of researchers. ~6-~7This study also shows a higher risk of becoming overweight if either parent was overweight. It is not sure whether the association was due to the genetic influence, or due to the familial dietary habit and life style. However, as in Patterson's study, no association was found between the parents' BMI. Obesity is of increasing prevalence among children and youths. Such subjects are at increased risk of morbidity including hypertension, ~8 psychosocial problem, 2 respiratory disease, '9 diabetes and orthopaedic conditions.2° The US study suggested the increase in childhood hypertension associated with obesity. The present study also revealed a moderate and significant correlation between BMI and blood pressure, especially systolic blood pressure. In conclusion, this study can be treated as an exploratory investigation on the risk factors of obesity among Hong Kong Chinese youths. The sample size is rather small but quite detailed methods have been used especially in the assessment of dietary intake. The findings seem to indicate that the amount of fat intake and background activities may play an important role in the study of overweight.
254
S. C. Ho
Acknowledgements The author wishes to thank Professor S Donnan for his support in this study. Sincere appreciation also goes to the staff and students of Hang Seng Commercial School for their participation and cooperation in this study.
References I. Braitman, L. E., Adlin, E. V. & Stanton, J. L. Jr. (1985). Obesity and caloric intake: the National Health and Nutrition Examination Survey of 1971-1975 (HANES I). Journal of Chronic Diseases, 38, 727-732. 2. Ho, S. C. & Donnan, S. P. B. (1986). Prevalence of overweight and self perception of overweight among the school adolescents in Shatin. Journal of the Hong Kong Society of Community Medicine, 16, 7-19. 3. US Department of Health, Education and Welfare; & Food and Agriculture Organization of the United Nations. (1972). Food Composition Table for Use in East Asia, Department of Health Education and Welfare: Bethesda, USA. 4. Institute of Health, Chinese Academy of Medical Sciences. (1983). Food Composition Table. Beijing: Chinese People's Health Publishing Co. 5. Adams, C. F. (1975). Nutritive Value of American Foods in Common Units. Agriculture Handbook No. 456. United States Department of Agriculture Washington DC: US Government Printing Office. 6. Paul, A. A. & Southgate, D. A. T. (1978). McCance and Widdowson's The Composition of Foods. Fourth revised and extended edition of MRC Special Report No. 297. London: Her Majesty's Stationery Office. 7. Ho, S. C. (1987). Assessment of overweight and physical activity among adolescents and youths in Hong Kong. Public Health, 101,457-464. 8. Ho, S. C. (1989). Self-reported height and weight--validity and bias. Journal of the Hong Kong Society of Community Medicine, 19, 29-36. 9. Romieu, I., Wilier, W. C., Stampfer, M. J., Colditz, G. A., Sampson, L., Rosner, B., Hennekens, C. H. & Speizer, E. E. (1988). Energy intake and other determinants of relative weight. American Journal of Clinical Nutrition, 47, 406-412. 10. Kromhout, D. (1983). Energy and macro nutrient intake in lean and obese middle-aged men (the Zutphen Study). American Journal of Clinical Nutrition, 37, 295-299. 11. Johnson, M., Burke, B. & Mayer, J. (1956). Relative importance of inactivity and overeating in the energy balance of obese high school girls. American Journal of Clinical Nutrition, 4, 37-44. 12. Sunnegardh, J., Bratteby, L. E., Hagman, U., Samuelson, G. & Sjolin, S. (1986). Physical activity in relation to energy intake and body fat in 8- and 13-year-old children in Sweden. Acta Paediatrica Scandinavica, 75, 955-963. 13. Meyers, A. W., Stunkard, A. J., Coil, M. & Cooke, C. J. (1980). Stairs, escalators and obesity. Behavioural Modification, 4, 355-359. 14. Cureton, K.J. (1987). Commentary on 'Children and fitness: a public health perspective'. Research Quaterly for Exercise & Sport. 58, 315-320. 15. Mason, J. O., Powell, K. E. (1985). Physical activity, behavioral epidemiology, and public health. Public Health Report, 100, 113-115. 16. Patterson, R. E., Typpo, J. T., Typpo, M. H. & Krause, G. F. (1986). Factors related to obesity in preschool children. Journal of the American Dietetic" Association, 86, 1376-1380. 17. Stunkard, A.J., Sorensen, T. I. A., Hanis, C., Teasdale, C. R., Schull, W.J. & Schulsinger, F. (1986). An adoption study of human obesity. New England Journal of Medicine, 314, 193-198. 18. Gortmaker, S.L., Dietz, W.H., Sobol, A.M. & Wehler, C.A. (1987). Increasing pediatric obesity in the United States. American Journal of Diseases of Children, 141, 535-540. 19. Tracey, V. V., De, N. C. & Harper, J. R. (1971). Obesity and respiratory infection in infants and young children. British Medical Journal, 1, 16-18. 20. Kelsey, J. L., Acheson, R. M. & Keggi, K.J. (1972). The body build of patients with slipped capital femoral epiphysis. American Journal of Diseases of Children, 124, 276-81.
Obesity in Hong Kong Youths
255
Appendix 1 1. 2. 3. 4. 5.
Use the stairs instead of taking the life Walk instead of taking means of transport Take a walk after lunch or dinners Get off at a stop not closest to the destination, then walk there Do activities similar to the above for the purpose of health promotion
Often/occasionally/no Often/occasionally/no Often/occasionally/no Often/occasionally/no Often/occasionally/no Score: Often = 2 Occasionally = 1 No = 0
Appendix 2 Body mass index values by cases and controls Cases 25.01 25.18 25.28 25.49 25.69 25.82 26.14 26.20 26.56 27.18 27.89 28.52 28.70 29.49 29.82 36.40
Controls 17.39 18.17 18.23 18.46 18.76 18.92 19.16 19.35 19.50 19.57 19.68 19.72 19.75 19.80 20.12 2O.25 21.40 21.67 21.74 22~01 22.02 22.07 22.65 23.04 23.47 23.53 24.61 24.69 24.71
© The Society of Public Health, 1990
Risk Factors of Obesity among Hong Kong Youths S.C. Ho Department of Community and Family Medicine. The Chinese University of Hong Kong, 4th Floor, Lek Yuen Health Centre, Shatin, Hong Kong
Introduction The aetiology o f obesity remains obscure. Although excess caloric intake has been shown to lead to obesity in animal studies, no conclusive evidence on the positive relationship between energy intake and obesity is found in population surveys. Similar uncertainty exists in the relationship between the level o f physical activity and obesity. ~ This paper reports a study which aims to investigate the relationship between dietary intake, level o f physical activity, familial factor and overweight. It will serve to support some o f the previous findings, and to present a preliminary investigation o f the problem in the Asian communities where few such studies have been carried out. Methods One of the Institute o f higher learning included in a survey o f overweight among school children was selected for this case-control study. A previous survey on school adolescence shows that a Body Mass Index (BMI = weight in kg over height in meter squared) o f 25 is at 2 standard deviations above the mean BMI. 2 The cases ineluded in this study were thus those identified to have a body mass index (BMI) over 25. An equal number o f subjects with BMI 25 or below from the same class were selected as the controls. The dietary intake study was divided into two parts: (i) The first part was a weighed food diary. The youths were requested to complete a 4-day weighed food diary during the week. Detailed instructions and demonstrations were given on the methods o f recording and o f weighing the food items. A portable weighing scale was issued to every participating subject. Visual instructions on how to quantify the foods in terms o f c o m m o n household measures were given so that foods could be quantified in household measures if the portable weighing scale could not be conveniently used in situations such as eating out or having a quick snack off the street. A pictorial illustration o f the c o m m o n household measures such as different sizes bowls, plates and spoons as well as a measuring scale in inches were included in the diary. The subjects were requested to carry the diary with them at all times during the four day recording period. Each subject was contacted during the second day to clarify any doubts encountered, and at the end o f the four days so the investigator would have an opportunity to go over the diary together with the subject to clarify any doubts or to rectify any wrong or unclear recordings. The food items were coded and the nutrients analysed based on the computerised F o o d Composition Table for Use in East Asia 3 and food composition compiled by the author, mainly for some local foods such as Dim Sum. A 20% sample o f the 44 food diaries was taken to
250
S. C. Ho
examine the percentage o f the recorded food items based on visual estimates. The mean was found to be 20.7% (s.d. = 12.9) while the median was 25% (ii) The second part consists o f two separate semi-quantitative food frequency questionnaires. One was on fat and the other on dietary fibre intake. The former questionnaire included 57 food items. The calculation o f fat and fatty acids in each food was based on the F o o d Composition Tables for Use in East Asia with supplementation from other Tables. 3-5 The second questionnaire included 51 food items o f commonly consumed cereals, vegetables and fruits and other food items with substantial fibre contribution in the local setting. The calculation o f dietary fibre was based on Widdowson's d a t a : A list of questions on the preference or habit o f fat and oil intake were also asked.
Energy expenditure Methods used to measure energy in terms o f M E T S have been described in a previous paper. 7 5 questions were included to measure the background physical activities (Appendix
1). Familial overweight The subjects were asked to obtain their parents' height and weight and report the data when they returned for the 4-day diary. Self-reported data on height and weight have been shown to be o f acceptable validity in H o n g K o n g populations:
Measurement of blood pressure The measurements were taken at seated position towards the end o f the questionnaire answering session. The first appearing sound was recorded as the systolic, and the last appearing sound as the diastolic pressure. Two measurements were taken with one minute interval in between. The average of the two measurements was used. Results
16 overweight youths were included as cases in the study. They were compared with 29 normal weight youths. Both groups had the mean and median age o f 21 and the age range from 18-26. The socio-economic status was quite similar in both groups with about two-thirds o f the heads of households belonging to the clerical, service or production workers. A quarter o f the cases and 37% o f the controls were female subjects. The cases had a mean body mass index o f 27.5 (s.d. = 2.9) and the controls a mean o f 20.8 (s.d. = 2.1). The body mass indices of the cases ranged from 25.01 to 36.40 while that for the controls 17.39 to 24.71 (Appendix 2).
lntake of energy and macronutrients The 4-day dietary weighted food record shows that although the overweight group had a lower energy intake (1,877 Kcal versus 2,036 among the controls), they had a slightly higher total fat intake in absolute value (60 grn vs 58 gm in controls) and after adjustment for energy (32 gm vs 29 grn per 1,000 cal in controls). The carbohydrate intake was lower among the cases (261 gm vs 294 gm in controls) who also had a higher percentage (29%) of
Obesity in Hong Kong Youths
251
Table I Comparison of mean fat and fibre intake (gm) per day between cases and controls (based on semi-quantitative food frequency method) Fat Total fat Total fatty acid Saturated fatty acid , Unsaturated fatty acid Linoleic acid Oleicacid Unsaturated/Saturated Fibre
Cases Mean (SD)
Controls Mean (SD)
P-value (t test)
74.4 (40.5) 68.8 (37.5) 26.0 (14.4) 42.6 (23.2) 10.2 (6.2) 29.9 (16.1) 1.6 (0.13) 9.0 (3.1)
55.1 (27.2) 51.2 (25.3) 19.5 (9.4) 31.4 (16.1) 7.4 (4.3) 22.0 (11.6) 1.6 (0.24) 8.6 (3.1)
0.07 0.07 0.12 0.07 0.09 0.07 0.46 0.68
Number in brackets() = standard deviation their energy intake f r o m fat c o m p a r e d to the controls (26%). H o w e v e r , n o n e o f the differences o f the means between the cases a n d controls were statistically significant by the t-test. Table I shows the types o f fat intake o b t a i n e d f r o m the semi-quantitative f o o d frequency method. The cases had a higher m e a n intake in b o t h the total fat a n d fatty acids as well as in the saturated a n d u n s a t u r a t e d fatty acids. Similar differences were observed after controlling f o r sex. However, the fibre intake a n d the ratio o f u n s a t u r a t e d to saturated fatty acids were quite similar in b o t h groups. Table II shows that the cases tended to have a higher preference for fat and m e a t Table II
Comparison of habit of oil and fat intake between cases and controls Case n (%)
Control n (%)
O.R.
95% C.I.
(79) (21)
0.6 1.0
0.1-2.9
Type of cooking oil Peanut Corn
11 5
Eat visible fat in meat Most or all Little or no fat
10 (62) 6 (38)
14 (50) 14 (50)
1.7 1.0
0.4-7.1
Chicken or duck with skin Often/always Seldom/never
14 (87) 2 (13)
14 (50) 14 (50)
7.0 1.0
1.2-40.9
Prefer vegetable to meat Same/no Yes
12 (75) 4 (25)
17 (61) 11 (39)
1.9 1.0
0.4-9.5
4 24
7.7 1.0
1.543.5
Time per week eating dim sum 2+ 0-1
9 7
(69) (31)
(56) (48)
22 6
(14) (86)
S.C. Ho
252 .Table
III
Relationship of subjects' BMI with parents' BMI O.R.
C.I.
Father's BMI > = 25/< 25
4.8
0.9-26.7
Mother's BMI > = 25/< 25
4.5
1.0-22.5
BMI > = 25 Both or one parent/None
4.0
0.8-21.6
c o m p a r e d to the controls. The risk of overweight a m o n g those who often or always ate chicken or duck together with its skin and those who had dim sum twice a week or m o r e were observed to be around 7.0.
Activity and energy expenditure The cases were found to have a slightly higher m e a n energy expenditure of 42.8 M E T S (s.d. = 1.6) c o m p a r e d to the controls 42.0 (s.d. = 1.3). When the background activity score was divided into low ( < 4), medium (4-5) and high ( > 5), the risk o f overweight was !.7 (C.I. 0.3-11) a m o n g the medium, and 2.5 (C.I. 1.3-21.4) a m o n g the low when c o m p a r e d with the high score group.
Relationship with parents' body mass index Table I I I shows the relationship between the weight categories o f the subjects and that o f their parents. The risk of overweight increases to a r o u n d 4 if either one o f their parents or both parents were overweight. However, no association o f overweight between the parents was observed.
Relationship of B M I with blood pressure A positive and moderate association of the subjects' B M I with their blood pressure was observed. The relationship seems to be slightly stronger with the systolic (r=0.4689, P < 0.0012) c o m p a r e d with the diastolic blood pressure (r = 0.3742, P < 0.0113).
Discussion
The finding that the overweight group had a slightly lower total energy intake was in similar direction as that f r o m some other epidemiological studies. 9a° A higher fat intake and higher preference for fatty foods were indicated in this study. The food frequency method gave a larger difference between the cases and controls c o m p a r e d to the 4-day food diary, probably because the latter was held during weekdays and the in-school meals could have resulted in a more homogeneous intake a m o n g the subjects. A b o u t 25% o f the recorded food items were found to be based on visual estimates. Such process had been facilitated
Obesity in Hong Kong Youths
253
with the inclusion of pictorial presentation of household containers and measuring scale in the diary. However, the accuracy of the visual estimates had not been validated. A recent study among the nurses also found a significant correlation between the relative weight and their total fat and saturated fatty acids intake. 9 However, the dietary fibre intake among the two groups was observed to be quite similar suggesting that the controls did not necessarily have a higher consumption of complex carbohydrates. Further investigations into the role and relationship of the macronutrients in obesity are indicated. Inconsistent data have been found on the relationship between physical activity and obesity, u-12 and little data are available on the role of background physical activities. A recent study by Meyers et aL ~3found that obese people were far less likely to take the stairs than were non-obese persons. Our study found that even though the assessment of overall physical activity showed a slightly higher level in the overweight group, the normal weight subjects tend to take the trouble to incorporate activities in daily lives in order to increase their level of activity. These activities included walking the stairs instead of taking the lifts, walking to the place of destination instead of taking means of transport etc. Perhaps the persistent daily intentional exercise are more important than sporadic exercises in the prevention of overweight. There has been suggestion that the finer differences in activity level which is difficult to be detected in the gross measures of exercise may be responsible for the weight difference between the obese and non-obese groups. The intentional activity also reflects a degree of conscientiousness among the subjects to keep fit and this habit is perhaps more important in urban living where the level of exercise of the average man had been reduced to a minimum by the presence of all the conveniences such as lifts and easy access to places by different means of transport. The incorporation of some activities such as walking stairs into the daily routine would be a valuable behaviour for the prevention as well as the treatment of obesity. This study observed a higher level of background activities among the controls. Perhaps the persistent daily activities are useful especially in the prevention of overweight in urban living where sporting facilities are not readily available. Some research studies also suggest that lower intensity lifestyle exercises performed throughout the day is probably more effective than intensive exercises in maintaining weight loss in children. 14 Moreover, the low intensity type of exercise is also more easily acceptable to most individuals compared to the intensive type. '5 Familial aggregation of obesity has been found by a number of researchers. ~6-~7This study also shows a higher risk of becoming overweight if either parent was overweight. It is not sure whether the association was due to the genetic influence, or due to the familial dietary habit and life style. However, as in Patterson's study, no association was found between the parents' BMI. Obesity is of increasing prevalence among children and youths. Such subjects are at increased risk of morbidity including hypertension, ~8 psychosocial problem, 2 respiratory disease, '9 diabetes and orthopaedic conditions.2° The US study suggested the increase in childhood hypertension associated with obesity. The present study also revealed a moderate and significant correlation between BMI and blood pressure, especially systolic blood pressure. In conclusion, this study can be treated as an exploratory investigation on the risk factors of obesity among Hong Kong Chinese youths. The sample size is rather small but quite detailed methods have been used especially in the assessment of dietary intake. The findings seem to indicate that the amount of fat intake and background activities may play an important role in the study of overweight.
254
S. C. Ho
Acknowledgements The author wishes to thank Professor S Donnan for his support in this study. Sincere appreciation also goes to the staff and students of Hang Seng Commercial School for their participation and cooperation in this study.
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Obesity in Hong Kong Youths
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Appendix 1 1. 2. 3. 4. 5.
Use the stairs instead of taking the life Walk instead of taking means of transport Take a walk after lunch or dinners Get off at a stop not closest to the destination, then walk there Do activities similar to the above for the purpose of health promotion
Often/occasionally/no Often/occasionally/no Often/occasionally/no Often/occasionally/no Often/occasionally/no Score: Often = 2 Occasionally = 1 No = 0
Appendix 2 Body mass index values by cases and controls Cases 25.01 25.18 25.28 25.49 25.69 25.82 26.14 26.20 26.56 27.18 27.89 28.52 28.70 29.49 29.82 36.40
Controls 17.39 18.17 18.23 18.46 18.76 18.92 19.16 19.35 19.50 19.57 19.68 19.72 19.75 19.80 20.12 2O.25 21.40 21.67 21.74 22~01 22.02 22.07 22.65 23.04 23.47 23.53 24.61 24.69 24.71
