By 2050, there will be 9 billion people on earth. It will be necessary to feed them to avoid the population catastrophe predicted by Malthus 150 years ago. Yet a major issue facing governments is that the current method by which food demands are estimated is widely acknowledged as completely inaccurate. An accurate method is available. It is based on measurements of isotope elimination, called the doubly labelled water (DLW) method. In 2018, the International Atomic Energy Agency (IAEA) hosted and compiled a database of measurements using this technique. It showed that the use of the DLW method has been mostly restricted to the USA and Western Europe. It has rarely been applied across Africa and Asia. The database also focused on adults, leaving much unknown about the energy balance in children and adolescents. There is a clear need to fill this gap in knowledge, providing information that governments across Low- and Middle-Income countries can use to forecast future food demands. In China, the prevalence of overweight and obesity among children and adolescents is increasing. In 2009, 22.1% of Chinese youth aged 7-17 years were either overweight or obese, according to the China Health and Nutrition Survey. The obesity rate has increased fourfold since 1995. One of the most concerning problems is the persistence of childhood obesity into adulthood. The causes of this obesity epidemic are strongly disputed, with some suggesting it is due to increasingly sedentary lifestyles (computers, cars, phones, etc.), while others suggest it is mostly due to changing food patterns (junk food and sugar-sweetened beverages). Measuring energy expenditure in children and adolescents in China will address whether declining expenditure due to reduced physical activity is a key cause of the epidemic. Most measurements come from urban populations, leaving rural populations greatly underrepresented.

The investigators will recruit healthy Chinese children aged 7-13 years to participate in a study investigating growth and energy needs. Each participant will complete basic anthropometric measurements-including height, weight, waist and hip circumference, and mid-upper arm circumference. Questionnaires will be used to assess family socioeconomic status, dietary intake, and pubertal development. The investigators will also measure total energy expenditure, basal metabolic rate, physical activity, body composition, and environmental temperature exposure.

This research will provide accurate data on the energy expenditure of children and adolescents living in China. These data will inform national estimates of food and energy requirements, support public health nutrition strategies, and help fill critical data gaps in the IAEA Doubly Labeled Water (DLW) database.

Study Details Anthropometric Measurements

1. Height: Height will be measured using a Seca 217 stadiometer. Participants will stand barefoot with feet approximately 60° apart. Heels, sacrum, and shoulder blades will be placed against the stadiometer's vertical rod. The head will be aligned so that the upper margin of the ear canal is level with the lower margin of the eye socket. The horizontal plate will be lowered gently to rest on the crown of the head. Two measurements will be taken and averaged; values will be recorded to the nearest 0.1 cm.
2. Body Weight: After an overnight fast, body weight will be measured in the morning using a calibrated TANITA MC-780 scale. Participants will wear light clothing and no shoes.
3. Waist Circumference: Waist circumference will be measured at the midpoint between the iliac crest and the lower edge of the 12th rib. Participants will stand with feet 25-30 cm apart and body weight evenly distributed. A flexible tape will be wrapped snugly (without compression), and two measurements will be averaged to the nearest 0.1 cm.
4. Hip Circumference: Hip circumference will be measured with the participant standing straight, legs together, arms relaxed. The tape will be placed horizontally at the level of the pubic symphysis and the most prominent part of the buttocks. Two measurements will be taken and averaged.
5. Mid-Upper Arm Circumference: The participant will stand or sit upright with the arm relaxed. The midpoint between the acromion (shoulder) and olecranon (elbow) will be marked. A measuring tape will be wrapped around this midpoint with light contact. Two measurements will be taken and averaged.

Questionnaires

1. Family Socioeconomic Status: Will be assessed using a structured SES questionnaire.
2. Pubertal Development: Will be assessed via Tanner staging for secondary sexual characteristics.
3. Dietary Intake: Will be assessed using three 24-hour dietary recall questionnaires administered on non-consecutive days.

Body Composition (BIA) Bioelectrical impedance analysis (TANITA MC-780) will be used to measure segmental weight (arms, legs, trunk), total body fat percentage (fat%), fat mass (FM), fat-free mass (FFM), total body water (TBW), muscle mass, and BMI.

Basal Metabolic Rate Basal metabolic rate (BMR) will be measured using indirect calorimetry via a Cosmed Quark system with a ventilated hood. After a 10-hour overnight fast and no strenuous activity in the preceding day, participants will lie supine under the hood for 30 minutes. Oxygen consumption and carbon dioxide production will be monitored, and the final 10 minutes will be used to calculate BMR (Weir, 1949). Equipment will be validated monthly via alcohol burn tests and turbine flow calibration.

Total Energy Expenditure (DLW Method) Total energy expenditure (TEE) will be measured using the doubly labeled water (DLW) method. Urine samples will be collected and stored at -20 °C, then shipped on dry ice to Dr. John Speakman's laboratory at the University of Aberdeen or to the Shenzhen Institute of Advanced Technology. Isotope ratios will be analyzed using a near-infrared isotope gas analyzer. Mean CO₂ production will be calculated using equations developed by Speakman et al. (2021), and TEE will be derived using the Weir equation (1949).

Environmental Temperature Exposure Environmental exposure will be monitored using iButton sensors (DS1921G). These will be placed in the participant's living environment (e.g., on a backpack, clothing, indoor wall, or building exterior) using waterproof medical-grade adhesive. This will allow measurement of ambient temperature during the study period.

Physical Activity Physical activity will be monitored using ActiGraph GT3X accelerometers worn at the waist for 14 consecutive days, except during water activities (e.g., bathing or swimming). Data will be considered valid if the monitor is worn for at least 12 hours on four days, including at least two weekdays and two weekend days. The first day of wear and any day with insufficient data will be excluded from analysis.

Inclusion Criteria:

-Healthy participants

Exclusion Criteria:

1. Malnutrient as defined by the Chinese national standards WS/T 456-2014 and WS/T 586-2018

   1. Nutritional deficiencies
   2. Overweight
   3. Obesity

2. Acute illness within the past 7 days

   1. Fever
   2. Diarrhea
   3. Vomiting

3. Chronic diseases

   1. Cardiovascular diseases

   2. Diabetes mellitus or any form of metabolic disorders

      • Type 1 or Type 2 diabetes
      • Metabolic syndrome
      • Hyperlipidemia
      • Dyslipidemia

   3. Renal diseases

      • Chronic kidney disease
      • Nephrotic syndrome

4. Musculoskeletal injuries

5. Disabilities

The study population will consist of healthy children aged 7 to 13 years who exhibit normal growth and development. Participants will neither be overweight nor obese, nor will they have any nutritional deficiencies. They will be capable of cooperating to complete all required measurements. None of the children will have been diagnosed with chronic diseases or musculoskeletal injuries or disabilities. Additionally, all participants will be free from acute clinical illnesses for at least seven days prior to the study.