The Study On Dietary Reference Intakes Of Energy For Chinese Female Youths And The Energy Expenditures Of Daily Physical Activities

ObjectiveThe reports from the 2002 National Health and Nutrition Survey in China show that the actual intake level of energy is 2250 kcal/d that account for 94%of the recommended nutrient intake(RNI) of energy.At the same time,the population of overweight and obesity in China has approached to a quarter of all Chinese people.This puzzled phenomenon can attribute to the deficiency of physical activities of Chinese inhabitants that result in the reduction of energy expenditure on the one hand.On the other hand,we have to bring forth questions about our currently recommended nutrient intake of energy.To investigate this issue,we set about from the two aspects:the assessment of recommended nutrient intake of energy and the evaluation of physical activity.So it looks forward to provide basic information for the revision of our recommended nutrient intake of energy and correct evaluation of physical activity.MethodsFrom the point view of energy metabolism,took the youth as the research subject,our study was carried through in two fields:1.Doubly Labeled Water FieldThe field place was located in Bethune Military Medical College.In this study,16 healthy female youths were selected as our subjects.Using the gold standard method for the measuring of energy expenditure---doubly labeled water method,the energy expenditures of the 16 subjects were measured under designed conditions.The result was compared with the corresponding recommended nutrient intake of energy.Meanwhile,the result of energy expenditure from the doubly labeled water method was compared with those from some other methods such as energy balance method,criteria method,motion sensor method and time-motion method so as to make a comparison and evaluation of these methods.2.Physical Activity FieldSome young students from the Peaking University were enrolled as our research subjects.Firstly,Quark K4b² Pulmonary Function Equipment,Douglas bag and Medgraphics CardiO₂ System were used respectively to determine the energy expenditures of the subjects under three typical activity intensities:resting,middle intensity and high intensity.Compared with the reference standard method——Douglas bag,the validity evaluation of K4b² in assessing energy expenditure was made.And then,the subjects participated in several different physical activities such as strolling(3 km/h),fast walking(6 km/h),jogging(8 km/h),bicycle(12 km/h),up and down stairs as well as in quiescent condition,the energy expenditures of these daily physical activities were measured by using the gas metabolic method—K4b² and the metabolic equivalents(METs) were calculated respectively.Results and Conclusions1.According to the actual TEE values determined by using the doubly labeled water method, we considered that the energy requirement for the female adults aged from 20 to 25 years old(55kg) who engaged in light to middle intensity physical activities were 1827 kcal/d. Compared with the corresponding value from RNI,the value from RNI was 273 kcal higher than that from doubly labeled water method.RNI overestimated energy requirement by 15%.2.The results from the correlative experiments on the methodology showed that,the value from energy balance method was nearly consistent with that from doubly labeled water method,just overestimate 0.2%,then the criteria method,underestimate 3.8%.Compared with the doubly labeled water method,time-motion method and motion sensor method overestimated and underestimated the energy expenditures by 21.9%and 16.8% respectively and the differences were statistically significant.(P＜0.05).3.In the study of validity evaluation for K4b²,made Douglas bag as the reference standard method,the values measured by the K4b² and MedGraphics were compared with those from Douglas bag by paired t-test respectively,the results showed that there were no significant differences at all(P＞0.05).K4b² seemed an accurate measuring tool in studying the energy expenditure under resting and middle intensity condition,the error was less than 1%.It had about 5%underestimation under high intensity condition,but the difference had no statistical significant.MedGraphics would somewhat underestimate the energy expenditure, especially at resting state(underestimate about 8%),but the difference had no statistical significant.Moreover,the data were assessed by the Pearson correlation analysis and the results showed that the energy expenditure values measured by K4b² and MedGraphics were positively correlated with those from Douglas bag(P＜0.05).This study demonstrated that K4b² had good validity in assessing the energy expenditure.4.The energy expenditures measured by K4b² and MET values of daily physical activities were listed as follows:Resting1.08kcal/h.kg,1MET.Strolling(3km/h) 1.24kcal/h.kg1.2MET. Treadmill(3.6 mph,10%slope gradient) 7.43 kcal/h.kg,7.1 MET.Treadmill(1.7 mph,10% slope gradient) 4.81 kcal/h.kg,4.6 MET.Upstairs(1.6 step/s) 3.87 kcal/h.kg,3.8MET. Downstairs(1.8 step/s) 2.59 kcal/h.kg,2.5MET.ErgometerCycling(100W,60rpm) 6.40 kcal/h.kg,6.2MET.Bicycle(12km/h) 4.30 kcal/h.kg 4.2MET.Fast walking(6 km/h) 3.75 kcal/h.kg,3.6MET.Jogging(8 km/h) 6.26 kcal/h.kg,6.0 MET.According to the METs values,except the treadmill(3.6mph) fitted into high intensity physical activity,strolling (3km/h) fitted into light physical activity,all the other activities we measured belonged to middle intensity physical activities.