Measurement of Energy in Food and During Physical Activity
Computerized Instrumentation
A computer interfaces with at least three instruments: A system that continuously samples the subject's expired air A flow-measuring device that records air volume breathed Oxygen and carbon dioxide analyzers that measure the composition of the expired gas mixture
Portable Spirometry
Ambient air passes through a two-way valve Expired air travels through a gas meter that measures total expired air Cosmed Kb42 Pulmonary Gas Exchange (VO2, VCO2) Breath by Breath Technology Telemetry Data Transmission up to 800m Indirect Calorimetry Integrated GPS System Integrated Oxygen Saturation (SpO2) Integrated 12-lead Stress Testing ECG
Comparing the energy available of the Macronutrients
CHO= 4.2 kCal, Fat= 9.4 kCal, Protein= 5.65 kCal
The Calorie
Calorie Raise the temperature of 1 kg (1 L) of water by 1° Celsius. Kilocalorie Kilojoules Megajoule Conversions 1 cal = 4.186 J 1 kCal = 1000 cal = 4186 J
Closed- and Open-Circuit Spirometry
Closed-Circuit Subject breathes 100% oxygen from a prefilled container A canister of soda lime absorbs the carbon dioxide in exhaled air Open-Circuit Subject inhales ambient air with 20.93% oxygen, 0.03% carbon dioxide, and 79.04% nitrogen. Indirectly reflects the ongoing process of energy metabolism Closed-circuit disadvantages: bulky equipment, speed of carbon dioxide removal inadequate during heavy exercise Open circuit most widely used and provides a useful way to measure oxygen uptake and infer energy expenditure.
Direct Calorimetry
Directly measures energy expenditure (heat) Human Calorimeter Airtight chamber A person lives or works in the chamber for an extended period of time. Changes in water temperature relate directly to an individual's energy metabolism. A known water volume at a specified temperature circulates through a series of coils at the top of the chamber. This water absorbs the heat produced and radiated by the individual while in the calorimeter. For adequate ventilation, the person's exhaled air continually passes from the room through chemicals that remove moisture and absorb carbon dioxide. Oxygen added to the air recirculates through the chamber.
Bag Technique
Douglas Bag" Ambient air is breathed through one side of a valve Air is expelled through the other side of the valve
Coefficient of Digestibility
How much ingested food is available (digested and absorbed) for the body's metabolic needs Affected by dietary fiber Atwater general factors: Carbohydrates, 97% digested and absorbed: 4 kCal/gram Lipids, 95% digested and absorbed : 9 kCal/gram Proteins, 92% digested and absorbed: 4 kCal/gram
Indirect Calorimetry
Indirect Calorimetry infers energy expenditure from measurements of oxygen uptake and carbon dioxide production using: Closed-circuit spirometry Open-circuit spirometry Portable spirometry Douglas Bag technique Computerized instrumentation Doubly labeled water technique
Bomb Calorimeter
Measures total energy value of foods (kcals) Type of direct calorimetry Sealed chamber charged with oxygen Increase in water temperature directly reflects the heat released during a food's oxidation. Heat of combustion= amount of heat liberated by oxidizing a specific food
Doubly Labeled Water Technique
Provides a useful way to estimate total daily energy expenditure in free-living conditions Expensive ($400-$500) Provides an ideal way to assess total energy expenditure (volume) of groups over prolonged time periods (1-2 weeks) Limitations? Do not know intensity of PA Do not know the modality Expensive (low numbers of participants)
The Respiratory Exchange Ratio
Ratio of carbon dioxide produced to oxygen consumed Computes in exactly the same manner as RQ R above 1.00 Overbreathing R below 0.70 Following exhaustive, submaximal exercise
Basal Metabolic Rate (BMR)
Requirements for measurement: Postabsorptive- 12 hours no food No undue muscular contractions 12 hours prior Measured after person lying quietly for 30-60 minutes in a temperature controlled room (NOT SLEEPING!!) Minimum energy requirement sustains the body's functions Regular exercise slows a decrease in metabolism with age
Total Daily Energy Expenditure (TDEE)
Resting Metabolic Rate (RMR) Thermogenic Effect of Food (TEF) Physical Activity Energy Expenditure (PAEE) and Recovery Energy Expenditure
Temperature Vs Heat
Temperature reflects a quantitative measure of an object's hotness or coldness Heat describes energy transfer from one body or system to another
The Respiratory Quotient (RQ)
The ratio of carbon dioxide produced to oxygen consumed The RQ provides information about the nutrient mixture catabolized for energy *The RQ= 1.00 for CHO, 0.70 for fat* The RQ for a mixed diet= 0.82 Book states that Weir assumes that ~12.5% of TEE comes from protein (Rather high estimate?)
