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Will Dieting Cure The Obesity Epidemic?
Traci Mann, Ph.D.University of Minnesota
Department of Psychology
No
Traci Mann, Ph.D.University of Minnesota
Department of Psychology
Obesity Rates 1980-2007, U.S.
1980 2007
Definitions of Diet Success(Example: 200 pound woman, 5’5”, BMI = 33)
Years Standard Pounds to Lose
Weight BMI
1940s Metropolitan Life Insurance Tables
66 134 23
Definitions of Diet Success(Example: 200 pound woman, 5’5”, BMI = 33)
Years Standard Pounds to Lose
Weight BMI
1940s Metropolitan Life Insurance Tables
66 134 23
1950s Lose 40 pounds 40 160 27
Definitions of Diet Success(Example: 200 pound woman, 5’5”, BMI = 33)
Years Standard Pounds to Lose
Weight BMI
1940s Metropolitan Life Insurance Tables
66 134 23
1950s Lose 40 pounds 40 160 27
1960s Lose 20 pounds 20 180 30
1970s Lose 10% of starting weight 20 180 30
Definitions of Diet Success(Example: 200 pound woman, 5’5”, BMI = 33)
Years Standard Pounds to Lose
Weight BMI
1940s Metropolitan Life Insurance Tables
66 134 23
1950s Lose 40 pounds 40 160 27
1960s Lose 20 pounds 20 180 30
1970s Lose 10% of starting weight 20 180 30
1995+ Lose 5% of starting weight 10 190 32
Weight Loss Maintenance:18 Months
Long-Term Diet Studies(Mann et al., 2008, American Psychologist)
• Studies with control groups (n=8)– Avg. weight change of dieters: Lost 2.3 lbs– Avg. weight change of controls:
• Studies without control groups (n=13)– Initial weight loss: 39 pounds– Ultimate gain-back:– % regain more than they lost:
Long-Term Diet Studies(Mann et al., 2008, American Psychologist)
• Studies with control groups (n=8)– Avg. weight change of dieters: Lost 2.3 lbs– Avg. weight change of controls: Gained 1.3 lbs
• Studies without control groups (n=13)– Initial weight loss: 39 pounds– Ultimate gain-back:– % regain more than they lost:
Long-Term Diet Studies(Mann et al., 2008, American Psychologist)
• Studies with control groups (n=8)– Avg. weight change of dieters: Lost 2.3 lbs– Avg. weight change of controls: Gained 1.3 lbs
• Studies without control groups (n=13)– Initial weight loss: 39 pounds– Ultimate gain-back: 32 pounds– % regain more than they lost: 31% to 64%
Sources of Bias in Diet Studies
1. Low rates of attendance at follow-ups
2. High rates of self-reported weight
3. Failure to account for additional diets
4. Confounding effects of diet with effects of exercise
Bias I: Follow-Up Rates
Independent evidence: The fewer follow-ups, the steeper the rate of regain
Follow-up rates in the 13 studies: Poor follow-up rate (<25%) in 3 studies Fair follow-up rate (30-50%) in 5 studies Good follow-up rate (70-88%) in 5 studies
Bias II: Self-Reported Weights
Independent evidence: People under-report their weight by about 8 pounds, and obese people tend to under-report by more than that.
61% of all weights in these studies were self-reported.
Bias III: Participation in Additional Diets
Independent Evidence: Survey of Dieters60% weighed more than starting weight at some point since diet
40% weigh more than starting weight now
Rates of participation in other diets 20% to 65% of participants (7 studies) 1 to 3 diets/year (3 studies) 3 studies did not report this
Bias IV: Confounding Diet and Exercise
Independent Evidence Strongest predictor of weight-loss maintenance >90% of successful maintainers use regular exercise
Rates of exercise in the 13 studies: 22% to 46% engaged in regular exercise 8 studies did not report on exercise
Dieting
Psychological Pathways
Biological Pathways
• Negative Calorie Balance
• Short-term Weight Loss
Weight Regain
• Decreased Metabolism
• Increased Food Intake
• Increased Fat Deposition
• Violation / Perceived Violation of Diet
• Cognitive Load
• Negative Affect
Overeating
Stress
• HPA Activation• SNS Activation• Negative Health Behaviors• Increased Food Intake
Biopsychosocial Pathways
Mechanisms of Diet Failure
• Leptin & Insulin Decrease• Ghrelin Increase
• Catabolic Inhibition
• Cholecystokinin Sensitivity• Anabolic Stimulation
Stress
Insulinresistance
Increased food intake
Decreased Physical Activity
Disrupted sleep
Weight Gain
Cortisolincrease
Visceral fatdeposition
HPA axisactivation
SNSactivation
sAAincrease
Increasedcaloric absorption
Mechanisms of Stress-induced Weight Gain
1. Does dieting cause stress?
2. Are biological mechanisms involved?
3. What is it about dieting that is stressful?
Three Questions
Study Design
Monitoring No Monitoring
Restricting Classic Diet Food Provided
No Restricting Food Diary Control
Samplen = 121 femalesMean age: 22Mean BMI: 25
Procedures1. Pre-diet questionnaires and 2 days of saliva sampling2. Three weeks of assigned diet3. Post-diet questionnaires and 2 days of saliva sampling
Sample & Procedures
• Psychological Stress: Perceived Stress Scale (Cohen et al, 1986)
• Biological Stress: Salivary Cortisol – Wake-up – Wake-up + 45 minutes– Wake-up + 12 hours
• Cortisol confounds: Alcohol, exercise, illness, etc.
Measures
• Sticking to 1200 kcal diet– Restricting conditions: 1260 kcal– Non-restricting condition: 1704 kcal
• Weight change– Restricting conditions: -1.9 lbs– Non-restricting conditions: +2.6 lbs
Manipulation ChecksOnly one non-restricting condition monitored calories
Perceived Stress: Main effect of monitoring
Monitoring diet: Perceived stress increased
Not monitoring diet: Perceived stress did not change
Total Cortisol Output: Main effect of restricting
Restricting diet: Cortisol output increased
Not restricting diet: Cortisol output did not change
Results(Tomiyama, Mann et al., 2010, Psychosomatic Medicine)
(Tomiyama, Mann et al., 2010, Psychosom Med)
(Tomiyama, Mann et al., 2010, Psychosom Med)
1. Does dieting cause stress?It did in this study
2. Are biological mechanisms involved?total cortisol output was involved in this study
3. What is it about dieting that is stressful?Monitoring one’s diet increases perceived stress
Restricting one’s diet increases cortisol
Conclusions
• Monitoring: Increased perceived stress– It’s another hassle
– Each food item recorded is a “failure”
– We eat more than we realize
• Restricting: Increased cortisol– Cortisol’s main job: Gluconeogenesis
Why Are These Behaviors Stressful?
• Monitoring: Did not increase cortisol– Maybe a prolonged increased in perceived stress would have?
• Restricting: Did not increase perceived stress– Correlational studies find it: but they confound the two tasks
– “Restricting Only” condition – provided free and delicious food
– Working successfully towards a goal – positive emotion
Why Aren’t These Behaviors Stressful?
Obesity Rates 1980-2007, U.S.
Mortality Rates 1980-2007, U.S.Obesity Rates 1980-2007, U.S.
Deaths per 100,000
Mortality Age 18+, U.S. Deaths per 100,000
CardiovascularCancers
All Causes
Diabetes
Copyright restrictions may apply.
Relative Risks of Mortality by BMI Category and Age
Ages 25-59 Ages 60-69 Ages ≥ 70
<18.5 25 30 35 35+ <18.5 25 30 35 35+ <18.5 25 30 35 35+
BMI Ranges
Relative Risk
* * * *
37
Obesity-Health Confounds
– Sedentary lifestyle
– Weight cycling
– Under-use of the medical system
– Poverty/SES
Mor
talit
y R
ate
Should we recommend
dieting to treat obesity?
Do not recommend
Is dieting safe?
Is dieting effective?
Do not recommend
Do not recommend
Recommend
Is obesity unhealthy?
YesYes Yes
NoNoNo
Is Dieting Safe?
Controlling for BMI, chronic dieting is associated with:– Cardiovascular disease1
– Myocardial infarction2
– Stroke2
– Diabetes2
– Increased blood pressure3
– Increased HDL4
– Suppressed immune function5
– All-cause mortality6-9
1Hamm, Shekelle, & Stamler, 1989 2French et al., 1997 3Olson et al., 2000 4Kajioka, Tsuzuku, Shimokata, & Sato, 2002 5Shade et al., 2004 6Andres, Muller, & Sorkin, 1993 7Blair, Shaten, Brownell, Collins, & Lissner, 1993 8Lee & Paffenbarger, 1992 9Pamuk,
Williamson, Serdula, Madans, & Byers, 1993
Kiefer et al., 2008
Kiefer et al., 2008
Aglets
Kiefer et al., 2008
•Telomeres = aglets for your chromosomes•Marker & mediator of biological aging
Aglets
Dieting is Associated with Telomere Length
Kiefer et al., 2008
•Telomeres = aglets for your chromosomes•Marker & mediator of biological aging•More dietary restraint, shorter telomeres
Aglets
Effects of Exercise on Health
Lost “expected” amount of weight
Resting Heart Rate Improved
Systolic Blood Pressure Improved
Diastolic Blood Pressure Improved
Waist Circumference Improved
Cardio-Respiratory Fitness Improved
Effects of Exercise on Health
Lost “expected” amount of weight
Didn’t lose “expected” amount of weight
Resting Heart Rate Improved Improved
Systolic Blood Pressure Improved Improved
Diastolic Blood Pressure Improved Improved
Waist Circumference Improved Improved
Cardio-Respiratory Fitness Improved Improved
FundersNational Institute of Mental Health
National Heart, Lung, and Blood Institute
US Department of Agriculture
University of Minnesota
UCLA Health and Eating Lab UMN
Health and Eating Lab UCLA Students in Psychology of Eating
Research AssistantsDanielle VinasJeff HungerKate E. Byrne Haltom
Acknowledgements
Main CollaboratorsJanet TomiyamaAndrew Ward
Defrayer of Cortisol Assay Costs Clemens Kirschbaum