Principles of Energy Metabolism
Body Energy Stores of Lean 70-kg Man
Adipose tissue triglyceride = 120,000 kcal
Muscle triglyceride = 3000 kcal
Liver triglyceride = 450 kcal
Liver glycogen = 400 kcal
Muscle glycogen = 2500 kcal
Obesity Is Caused by Long-Term Positive Energy Balance
Fat Stores
Components of Daily Energy Expenditure
Segal KR et al. Am J Clin Nutr. 1984;40:995-1000.
Thermic effect of feeding
Energy expenditure of physical activity
Resting energy expenditure
Sedentary Person (1800 kcal/d)
Physically Active Person (2200 kcal/d)
8%
17%
75%
8%
60%
32%
Relationship between Tissue Energy Expenditure and Mass
REE = Resting energy expenditure
Energy Expenditure (%REE)
Liver, Brain, Kidneys, Gut, Heart
Tissue energy expenditure
Tissue weight
Weight (% Body Weight)
80
60
40
20
0
Skeletal Muscle
Adipose Tissue, Lean Person
Adipose Tissue, Obese Person
Relationship Between Resting Energy Expenditure and Fat-free Mass
REE = Resting energy expenditure
Fat-Free Mass (kg)
REE (kcal/24 h)
Owen. Mayo Clin Proc 1988;63:503.
Lean females
Obese females
Lean males
Obese males
Energy Metabolism in Lean and Obese Subjects
Energy Expenditure (k/cal/d)
Resting Energy Expenditure
*P<0.05 vs lean subjects
Ravussin et al. Am J Clin Nutr 1982;35:566.
Total Energy Expenditure
Lean (BMI=21 kg/m2)
Obese (BMI=38 kg/m2)
*
*
Discrepancy Between Reported and Actual Energy Intake and Expenditure
Kcal/d
Reported
*P<0.05 vs reported.
Lichtman et al. N Engl J Med 1992;327:1893.
Energy Intake
Actual
Reported
Actual
Energy Expenditure
*
*
Energy Metabolism Before and After Weight Loss
Energy Expenditure (kcal/d)
Before
*P<0.05 vs before weight loss
Amatruda et al. J. Clin Invest 1993;92:1236.
Predicted
Mean BMI Reduced from 31 to 23 kg/m2
After
Before
Predicted
After
Resting Energy Expenditure
Total Energy Expenditure
*
*
*
*
Regulation of Food Intake
Brain
NPY
AGRP
galanin
Orexin-A
dynorphin
Stimulate
α-MSH
CRH/UCN
GLP-I
CART
NE
5-HT
Inibit
Central Signals
Glucose
CCK, GLP-1, Apo-A-IV Vagal afferents
Insulin
Ghrelin Leptin Cortisol
Peripheral signals
Peripheral organs
Gastrointestinal tract
Adipose tissue
Food Intake
Adrenal glands
Lifetime Food Intake
*kcal in millions
Water
45,300 kg
Fat
2300 kg
21 kcal*
Cholesterol
8000 kg
31 kcal*
Protein
1900 kg
7 kcal*
0 0.5 1 5
12 25 125
Cumulative Effect of Small Daily Imbalances in Energy Intake on Body Fat Mass
Excess intake (% total)
Excess intake (kcal/d)
Rosenbaum M et al. N Engl J Med. 1997;337:396-408.
1 million
Energy intake (kcal/y)
1 million
Energy expenditure (kcal/y)
Overweight or Obese (BMI >25 kg/m2)
Age-Adjusted Prevalence of Overweight or Obesity in Adults
Population (%)
National Center for Health Statistics Website.
Overweight (BMI 25-29.9 kg/m2)
Obese (BMI >30 kg/m2)
NHANES II (1976-1980)
NHANES III (1988-1994)
NHANES (1999-2000)
Relationship Between Adoptee Weight and Weight of Biological or Adoptive Parents
Thin
BM of Parents (kg/m2)
Stunkard et al. N Engl J Med 1986;314:193.
Copyright ? 1986 Massachusetts Medical Society. All rights reserved.
Weight Classification of Adoptees
Fathers
Mothers
Median
Overweight
Obese
Biological Parents
Adoptive Parents
Thin
Median
Overweight
Obese
Gene-Environment Interaction in the Pathogenesis of Obesity
Body Mass Index (kg/m2)
Ravussin E et al. Diabetes Care 1994;17:1067-1074.
Pima Indians
Maycoba, Mexico
Arizona
P <0.0001