Download Your Metabolism: Facts and Fables - ASU

Your Metabolism:
Facts and Fables
David C. Nieman, DrPH, FACSM
Appalachian State University, NCRC, Human Performance Lab
[email protected]
Resting Metabolic Rate (RMR)
Description
 The basal metabolic
rate (BMR) represents
the energy needed to
support the basic cost
of living.
 The BMR is typically
measured in the
morning after an
overnight fast and lying
down for 30 minutes.
 RMR is any time of day.
RMR Variance
 WOMEN: slightly less than 1
kcal/min (1,150 to 1,440 kcal/day)
 MEN: somewhat more than 1
kcal/min (1,580 to 1,870 kcal/day).
 One kcal/min equals the heat
released by a burning candle or by a
75-watt light bulb.
 About 70-80% of RMR variance
between individuals is due to
differences in body composition,
with the greatest RMR found in
those with the largest fat-free mass.
Daily Energy Expenditure
 The largest number of calories expended by most people
(except for athletes during heavy training) is from the
resting metabolic rate (RMR). Am J Clin Nutr 55:242S-s45S, 1992.
Activity
23%
RMR
67%
TEF
10%
Energy Expenditure and Body
Mass Change
 The resting metabolic rate is directly related to body
weight (higher in the obese, lower in the lean), and
parallels changes in weight. N Engl J Med 332:621-628, 1995
-300
10% weight loss
Back to initial weight -25
500
10% weight gain
-400
-200
0
200
400
Energy Expenditure Change (kcal/day)
600
RMR Measurement
The accurate measurement
of BMR and RMR requires
sophisticated methods that
are typically conducted in
research laboratories.
All of these methods are
costly and cumbersome to
conduct, require highly
skilled technicians, and are
impractical for most clinical
and community settings.
RMR Estimation Through
Equations
 BMR prediction equations have been developed
using easily and accurately measurable
variables such as age, height, and body weight.
 The Food and Nutrition Board of the Institute of
Medicine recently developed these equations for
estimating BMR in adults:
 Men: BMR (kcal/day) = 293 - (3.8 x age) + (456.4 x
height) + (10.12 x weight)
 Women: BMR (kcal/day) = 247 - (2.67 x age) +
(401.5 x height) + (8.6 x weight)
 [Age is in years, height is in meters, and weight is in kilograms].
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids,
Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, D.C.: The National Academies Press, 2002.
BMR Equations (IM) for Boys and Girls
 Normal Weight Boys (BMI  85%, ages 3-18)*
BEE = 68 – (43.3 x age) + (712 x height) + (19.2 x weight)
 Overweight/Obese Boys (BMI > 85%, ages 3-18)*
BEE = 419.9 – (33.5 x age) + (418.9 x height) + (16.7 x weight)
 Normal Weight Girls (BMI  85%, ages 3-18)*
BEE = 189 – (17.6 x age) + (625 x height) + (7.9 x weight)
 Overweight/Obese Girls (BMI > 85%, ages 3-18)*
BEE = 515.8 – (26.8 x age) + (347 x height) + (12.4 x weight)
*Height in meters, weight in kilograms, age in years.
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids,
Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, D.C.: The National Academies Press, 2002.
Equation Example
40 yr old woman, 65 inches, 140 pounds
 Women: 65 inches x 0.0254 = 1.65 meters
 140 pounds x 0.4536 = 63.5 kg
 BMR (kcal/day) = 247 - (2.67 x age) + (401.5
x height) + (8.6 x weight)
 BMR (kcal/day) = 247 - (2.67 x 40 yr) + (401.5
x 1.65 m) + (8.6 x 63.5 kg) = 1,349
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol,
Protein, and Amino Acids (Macronutrients). Washington, D.C.: The National Academies Press, 2002.
Limitations of Equations
 Unfortunately, only 50% to 75%
of the variability in BMR is
explained by these equations,
and they tend to misclassify
obese children and adults,
critically ill patients, and
individuals with eating disorders.
 Ethnicity affects BMR and RMR.
 Thus it is highly recommended
that BMR and RMR be
measured.
RMR of Three Obese Women
Mean of 2 Douglas bag tests, >4 h postprandial, 4:00-5:00 pm
Data from Nieman’s Human Performance Laboratory, ASU
Comparison of Measured Vs. Estimated RMR
Douglas bag
Age 46, BMI 36.7
1617
1269
Age 42, BMI 42.1
1549
+348
1689
+140
-506
1594
Age 47, BMI 33.4
1000
IM Equation
1200
1400
1600
2100
1800
RMR (kcal/day)
2000
2200
FFM Equation: RMR = 418 + 20.3 FFM
Challenge---accurately measuring fat-free mass (kg)
Arciero PJ, Goran MI, Poehlman ET. Resting metabolic rate is lower in women than in men. J Appl Physiol 75:2514-2520, 1993.
Human calorimeter, starting in the
late1800s (direct calorimetry)
Indirect calorimetry, closed-circuit
spirometry, starting early 1900s
Indirect calorimetry, open-circuit
spirometry, computerized metabolic
carts, 1980s -to present
Challenge has been finding an instrument to
measure oxygen consumption accurately in
non-laboratory settings.
First portable spirometer, open circuit,
to measure oxygen consumption during
exercise, Germany, 1940s
Cosmed produced a portable,
computerized spirometer, open circuit,
starting in the 1990s.
Cosmed: “FitMate” can
measure both resting and
exercise energy expenditure
($10,000; www.fitmate.net).
Cannon
Village
600 Laureate Way
ASU-NCRC Human
Performance Lab (Rm 1201)
UNC-Chapel Hill, Nutrition Research Institute,
Metabolic Chamber
How to Use the RMR in Weight
Loss/Maintenance Programs
 RMR x 0.85 = 1.0-1.5 pounds weight loss per week for
obese clients during first 12 weeks.
 RMR x 1.0 = 0.5-0.75 pounds weight loss per week.
 RMR x 1.3 = 0-0.5 pounds weight loss per week.
 RMR x 1.4-1.6 = weight maintenance for most people
(low activity).
 RMR x 1.6-1.9 = weight maintenance for moderately
active people.
 RMR x 1.9-2.5 = weight maintenance for very active
people (athletes).
Sources:
1.
2.
Powell LA, Nieman DC, Melby C, et al. Assessment of body composition change in a community-based weight management program. J Am Coll Nutr
20:26-31, 2001.
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and
Amino Acids (Macronutrients). Washington, D.C.: The National Academies Press, 2002.
Misconceptions About Exercise
and Metabolism
 Does one bout of exercise increase
RMR for a long time afterwards,
burning a significant number of
extra calories?
 Can exercise counter the dietinduced decrease in RMR?
 Do physically fit compared to unfit
people have higher RMRs, helping
them to stay lean?
 For most fitness enthusiasts, the
answer to these questions is “no”.
Misconception #1: Exercise Causes the Resting
Metabolic Rate to Stay Elevated for a Long
Time after the Bout, Burning Extra Calories
 The truth is that the energy
expended after aerobic exercise is
small unless a great amount of
high intensity exercise is engaged
in.
 Moderate intensity exercise for
30 min increases the RMR for
only 20-30 min, burning 10-20
extra calories.
 Thus when the obese individual
walks for 20-30 min, about 10
extra calories will be burned
afterwards, hardly enough to be
meaningful.
Energy Expenditure (kcal/min)
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Sitting
Standing
Rest
Rest
5-min
10-min
15-min
1-min
2-min
3-min
4-min
5-min
10-min
15-min
20-min
25-min
30-min
Exercise Exercise Exercise Post-Ex Post-Ex Post-Ex Post-Ex Post-Ex Post-Ex Post-Ex Post-Ex Post-Ex Post-Ex
RMR back to pre-exercise level in 5 minutes following 15 min calisthenics using the
PowerPlate (whole body vibration exercise).
Influence of 47-min
vigorous cycling on
post-exercise RMR
14
Exercise Day
Exercise (47 min)
519±57.8 kcal
(P<0.001)
12
Rest Day
Post-exercise (18.7 h)
223±82.4 kcal
(P<0.001)
8
6
Sleep (8 h)
45.0±50.2 kcal
(P=0.025)
4
2
Br
Dr
Lu
Di
LO
WU
8 am
6 am
4 am
2 am
12 am
Time
10 pm
8 pm
6 pm
4 pm
2 pm
12 pm
10 am
0
8 am
kcal / min
10
2.6
Exercise Day
Rest Day
2.4
2.0
1.8
1.6
1.4
1.2
LO
WU
Time
7 am
6 am
5 am
4 am
3 am
2 am
1 am
12 am
11 pm
1.0
10 pm
kcal / min
2.2
RMR
100
Fat Mass
90
75
80
Percentage
Fat-Free Mass
60
50
40
50
25
20
10
0
-20
-40
-5
-15
1200-1500
400-800
-25
Fasting
Energy Intake (Kcal/day)
During caloric restriction (dieting), the resting metabolic rate
drops 5-30%, and the fat-free mass drops 10-50% (with
degree of decrease depending on the severity of the energy
decrease).
Misconception #2: Exercise counters the dietinduced decrease in RMR.
 Most studies have found that exercise during dieting
does not counter the decrease in RMR and fat-free mass.
 65 obese, 8 wk, formula diet at 70% RMR; aerobics 3/wk,
leg/arm cycling; weights 3x/wk, 3x6, 8 stations.
 Am J Clin Nutr 66:557-563, 1997.
0
Change in RMR (kcal)
-20
-40
Diet Alone
Aerobics & Diet
Weights & Diet
-60
-80
-100
-88
-120
-127
-140
-160
-148
Percent Decrease in RMR
0
-2
Diet Alone
Aerobics & Diet
Weights & Diet
-4
Diet &
Aerobics/Weights
-6
-8
-9
-10
-10.3
-10.6
-12
90 day study of 69 obese females, all
on 520 kcal/day formula. Aerobics = 4
d/wk, 20 min progressing to 60
min/session; weights = 4 d/wk, 2-3
sets, 6-8 reps.
Am J Clin Nutr 54:56-61, 1991.
-10.3
Misconception #3: Fitness
Accelerates the RMR
Fitness and RMR
 Most studies have concluded
that there is little difference in
the RMRs of aerobically fit
and unfit people. (Am J Physiol
260:E257-261, 1991; Am J Clin Nutr
61:473-481, 1995).
 Even highly trained
endurance athletes who have
rested for two days have
RMRs that are about the
same of sedentary individuals
of the same weight and body
composition.
During periods of heavy training, athletes eat more,
increasing overall energy turnover and RMR. But when
athletes don’t exercise, they also don’t eat as much, and
RMR returns to normal.
Weight Training and RMR
 Weight training can add fat-free
mass, and RMR increases 7-10
kcal/day for each pound added.
 However, most fitness
enthusiasts who take up weight
training only add 4-5 pounds of
fat-free mass, increasing RMR
by 28-50 kcal/day, hardly an
impressive gain.
 Bodybuilders and strength
athletes, however, can put on
high amounts of fat-free mass,
significantly increasing RMR.
Practical Conclusions
 To sum up, individuals
adopting a moderate
exercise program to
lose weight should not
count on a revved up
metabolism to burn a
significant amount of
extra calories beyond
that linked to the
exercise itself.
 Vigorous and prolonged
exercise does increase
the RMR for 19 hours.