Primary Determinants of Body Weight Change in a Population of Young Adults

Amber R. Merfeld, Exercise ScienceGregory A. Hand, PhD MPH, Dept. of Exercise

Science

Clinical Exercise Research Center Staff

Obesity• The prevalence of obesity has

increased over the last 4 decades. • Based on general thermodynamic laws, it is commonly

believed that the general cause is that people are in a chronic state of positive energy balance.

• No large, clinical studies have measured the three components of energy balance (intake, expenditure, and stores).

• This paucity of information is severely hindering the development of impactful policies to address the obesity epidemic.

Negative Impact of Obesity• The obesity epidemic in adults and children is

the primary health risk for Americans.• Obesity-related conditions result in over

400,000 deaths per year in the US with an economic impact of almost $123 billion per

year. • However, the determinants

of obesity and weight gain are not well understood.

Energy Balance• The basic components

of energy balance include energy intake, energy expenditure and energy storage.

• The body is in energy balance when energy intake equals energy expenditure, and body energy, which is generally equivalent to body weight, is stable.– Thus, energy consumed must equal energy expended

for a person to remain at the same body weight.

Energy Balance Maintenance• Important of maintaining energy balance:

– A state of positive energy balance occurs when energy intake exceeds energy expenditure and the consequence is an increase in body mass, of which 60% to 80% is usually body fat (Hill, 2012).

– Conversely, a state of negative energy balance occurs when energy expenditureexceeds energy intake andthe consequence is a decrease in body mass, again with 60%–80% frombody fat. (Hill, 2012).

Research Question and Purpose of the Study

• What are the primary determinants of body weight change over a 12-month period?

• The purpose of the Energy Balance Study is to provide very precise measurements that will facilitate informed policy development to address the obesity epidemic.

Project Design

• The Energy Balance Study is a large-scale, comprehensive observational study that is designed to measure the components of energy balance more accurately than have been measured previously.

• The study will follow 400 healthy adults, between the ages of 21 and 35, for 12 months with measurements taken quarterly, with the option of continuing for another 12 months.

• Analyses will be made based on body weight change retrospectively from baseline to 1 year self-reported weight.

Energy Balance Recruitment Report

Methods (Prior to Baseline)• All interested and eligible participants will be

scheduled to take part in a 3-week run-in period. – During week 1, participants will be asked to complete the

informed consent form, some questionnaires, have their height and weight assessed, and complete the DXA measure.

– During week 2, participants will be asked to complete the resting metabolic rate assessment (RMR), some questionnaires, and have their blood drawn.

– During week 3, another DXA measure will be conducted and a maximal fitness test will be administered. For a two-week period, participants will have activity and energy intake measured

Lab Measurements

•Height/Weight•Resting BP•Waist/Hip Circumference•Body Composition (DXA)•Cardiorespiratory Fitness•Blood Chemistry•Resting Metabolic Rate•DLW

Timing of Lab Measurements

Measurement Baseline

Month 3

Month 6

Month 9

Month 12

Month 15

Month 18

Month 21

Month 24

Height/Weight X X X X X X X X X

Resting BP X X X X X X

Waist/Hip Circumference X X X X X X

Body Composition X X X X X X X X X

Cardiorespiratory Fitness X X

Blood Chemistry X X X X X

Resting Metabolic Rate X X X X X

DLW X

Energy Storage Measures

• At baseline and every follow-up visit, a body composition scan, also known as a DXA scan, will be performed to measure total percent body fat.

Energy Expenditure Measures• Participants will wear the SenseWear Armband for 10

consecutive days at baseline and at every follow-up visit.• To prevent the armband from becoming an ‘intervention,’

feedback from the armband will not be available to participants (screened/blinded).

Men Women0

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587 471

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759440

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57 VigorousModerateLightSedentarySleep

Kcal

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Energy Intake Measures• During the 10 consecutive days while the participant is

wearing the SenseWear Armband, they will also complete 3 random 24-hour dietary recalls. • Administered by a trained dietitian over the telephone

using the Nutrition Data System for Research software• Portion estimation training using 2D models

administered during the afternoon follow-up visits.

Results• We created linear regression graphs to show

the correlation of each of the three independent factors (energy storage, energy intake and energy expenditure) on the dependent factor, weight change.

• In addition, we also created a multiple linear regression equation to determine which independent factor had the most influence on weight change.

Energy Storage vs. Weight Change

Energy Storage

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Total Fat vs Weight Change Plot 1 Regr

Energy Intake vs. Weight Change

Energy Intake

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Energy Intake vs Weight Change Plot 1 Regr

Energy Expenditure vs. Weight Change2D Graph 19

Energy Expenditure

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Energy Expenditure vs Weight Change Plot 1 Regr

Multiple Linear Regression Equation• Weight Change = 3.225 - (0.000206 * Total Fat) - (0.000456 * Energy

Intake) + (0.000664 * Energy Expenditure)

• N = 402 Missing Observations = 28

• R = 0.361 Rsqr = 0.13

• Standard Error of Estimate = 5.243

• Coefficient Std. Error t P VIF• Constant 3.225 1.654 1.950 0.052• Total Fat -0.000206 0.0000274-7.518 <0.001 1.066• Energy Intake -0.000456 0.000470 -0.970 0.333 1.338• Energy Expenditure 0.000664 0.000582 1.141 0.254 1.272• The dependent variable Weight Change can be predicted from a linear combination of the independent

variables:• P • Total Fat <0.001• Energy Intake 0.333• Energy Expenditure 0.254

Conclusions

• Energy storage is the number one influential factor of energy balance, while energy intake and energy expenditure were less significant.

• Sources of error: self report could have caused incorrect measures– Energy intake– Previous 1 year weight measurement

Future Directions• Finishing total study

– Rely on actual measurements instead of self-reported measurements

• Emphasis on the energy storage dependant variable– Biochemical markers and how they influence peoples’

habits– How the amount of fat affects a person’s appetite

• It is anticipated that our findings will be published in a major clinical research journal such as the New England Journal of Medicine or The Lancet.

Questions?