Energy Homeostasis in Humans Units of Energy
Calorie
Types of Energy
−Defined as the amount of heat required to rise
the temperature of one kg of water from 14.5
• Solar to 15.5°C
• Chemical −Also defined based on the heat of
combustion of
• Mechanical benzoic acid (thermochemical calorie)
• Thermal −Standardized in 1956—one cal = 4.1868 Joules
• Electrical
Joule
−Defined as the energy expended when
one kg is moved one meter by a force of
one Newton
Watt
−Expresses rate of energy expenditure per unit
time, i.e., work (J/sec)
Bomb Calorimeter
The energy content of a food is calculated from the
heat released by the total combustion of food in a
calorimeter
Energy Combustion
O2 (ml) CO2 (ml) RQ Energy (kcal)
Starch 828 828 1.00 4.183
Fat 2019 1427 0.70 9.461
Protein 966 781 0.81 4.442
The respiratory quotient (RQ) is the ratio of CO2 produced to O2 consumed while food is being
metabolized: ... Most energy sources are food containing carbon, hydrogen, and oxygen.
Energy Balance and Measurement of
Components of EE
Energy Expenditure
*Basal Metabolic Rate(BMR)
Energy IN = Energy OUT
*Thermic Effects of Food(TEF)
24hrs
*Physical Activity (PA)
Energy Energy expenditure
Basal Metabolic Rate (BMR)
Basal metabolism is the energy expended by internal processes during a period of complete rest (non active
state) in a climate controlled environment at least 10 to 12 hrs after the consumption of the most recent meal.
Under the basal condition, several functions within the body:
Some of those processes are breathing, blood circulation, controlling body temperature, cell growth, brain and
nerve function, and contraction of muscles, reabsorption by renal tubules, gastrointestinal motility, ion
transport across membrane .
Factors that influence basal metabolic rate
Body size: Metabolic rate increases as weight, height, and surface area increase.
Body composition: Fat tissue has a lower metabolic activity than muscle tissue. As lean muscle mass
increases, metabolic rate increases.
Gender: The basal metabolic rate (BMR) averages 5 to 10 percent lower in women than in men. This is
largely because women generally possess more body fat and less muscle mass than men of similar size.
Age: A decrease in lean muscle mass during adulthood results in a slow, steady decline of roughly 0.3
percent per year in BMR after the age of about 30. This can be largely avoided by strength training
throughout adulthood.
Environment: In cold climates BMR is higher compared to warm climate.
Hormonal levels: Thyroxine (T4), the key hormone released by the thyroid glands has a significant effect
upon metabolic rate.
Health: Fever, illness, or injury may increase resting metabolic rate two-fold.
Basal metabolism consumes a surprisingly large amount of fuel, and the basal metabolic rate (BMR) varies
from person to person (Figure 9–5). Depending on activity level, a person whose total energy need is 2,000
calories a day may spend as many as 1,000 to 1,600 of them to support basal metabolism. The iodine-
dependent hormone thyroxine directly controls basal metabolism—the less secreted, the lower the energy
requirements for basal functions. The rate is lowest during sleep.[ Many other factors also affect the BMR (see
Table 9–3).
People often wonder whether they can speed up their metabolism to spend more daily energy. You cannot
increase your BMR very much today. You can, however, amplify the second component of your energy
expenditure—your voluntary activities. If you do, you will spend more calories today, and if you keep doing
so day after day, your BMR will also increase somewhat as you build lean tissue because lean tissue is more
metabolically active than fat tissue. Energy spent on voluntary activities depends largely on three factors:
weight, time, and intensity. The heavier the weight of the body parts you move, the longer the time you invest
in moving them, and the greater the intensity of the work, the more calories you will expend.
Be aware that some ads for weight-loss diets claim that certain substances, such as grapefruit or herbs, can
elevate the BMR and thus promote weight loss. This claim is false. Any meal temporarily steps up energy
expenditure due to the thermic effect of food, and grapefruit or herbs are not known to accelerate it further.
Components of energy
expenditure
Typically, basal metabolism 25–50%
represents a person’s largest physical activitya
expenditure of energy, followed
by physical activity and the
thermic effect of food.
5–10% thermic 50–65% BMR
effect of food
a. For a sedentary person, physical
activities may account for less
than half as much energy as basal
metabolism, whereas a very active
person’s activities
may equal the energy cost of basal
metabolism.
Do the Math
To estimate basal energy output:
• Men: kg body weight X24 = cal/day.
•Women: kg body weight X23 = cal/day. (To
convert pounds to kilograms [kg], divide
pounds by 2.2.)
Significance of BMR
•Calorie requirement of an individual
•Planning of diet
•Assessment of thyroid function
•Starvation and certain diseased condition
Thermic Effect of Food (TEF)
The thermic effect of food (TEF) is the increase in energy expenditure associated with food .
Thermic effect of food (abbreviated as TEF), also known as specific dynamic action (SDA) of a food
or dietary induced thermogenesis (DIT), is the amount of energy expenditure above the resting
metabolic rate due to the cost of processing food for use and storage. It is one of the
components of metabolism along with resting metabolic rate and the exercise component. A
commonly used estimate of the thermic effect of food is about 10% of one's caloric intake,
though the effect varies substantially for different food components. For example, compared to
protein, dietary fat is easy to process and has very little thermic effect, while protein is hard to
process and has a much larger thermic effect
SDA (Special Dynamic Action) for different foods
For 25g of protein, caloric value is 100 kcal, however, when 25g
protein is utilized by the body, 130 kcal heat is liberated. The extra 30
kcal is the SDA of protein. For fat this is 113 kcal and for carbohydrate
it is 105 kcal.
SDA for protein, fat and carbohydrate are 30%, 13% and 5% respectively.
**Proteins possess the highest SDA; carbohydrate the lowest
Key POIntS
Mechanism of SDA Two major components of energy
• The exact cause of SDA is not known. expenditure are basal metabolism and
• SDA of foods is due to the energy required for digestion, voluntary activities.
absorption, transport, metabolism and storage of foods in the body.
• The SDA of proteins is primarily to meet the energy A third component of energy
requirements for expenditure is the thermic effect of
deamination, synthesis of urea, biosynthesis of proteins etc. food.
• The SDA of carbohydrate is attributed to the energy expenditure
for the conversion of glucose to glycogen. Many factors influence the basal
• For fat, the SDA may be due to its storage, mobilization and
metabolic rate.
oxidation.
The glycemic index (GI) is a number associated with a
particular type of food that indicates the food's effect on a
person's blood glucose (also called blood sugar) level. A
value of 100 represents the standard, an equivalent amount
of pure glucose.
The GI represents the total rise in a person's blood sugar
level following consumption of the food; it may or may not
represent the rapidity of the rise in blood sugar. The
steepness of the rise can be influenced by a number of other
factors, such as the quantity of fat eaten with the food. The
GI is useful for understanding how the body breaks
down carbohydrates and only takes into account the available
carbohydrate (total carbohydrate minus fiber) in a food.
Although the food may contain fats and other components
that contribute to the total rise in blood sugar, these effects
are not reflected in the GI.
The glycemic index is usually applied in the context of the
quantity of the food and the amount of carbohydrate in the
food that is actually consumed.
Graph describing the rise of blood sugar after meals.
Determining the GI of a food
Foods with carbohydrates that break down quickly during digestion and release
glucose rapidly into the bloodstream tend to have a high GI; foods with carbohydrates
that break down more slowly, releasing glucose more gradually into the bloodstream,
tend to have a low GI. The concept was developed by Dr. David J. Jenkins and
colleagues in 1980–1981 at the University of Toronto in their research to find out
which foods were best for people with diabetes. A lower glycemic index suggests
slower rates of digestion and absorption of the foods' carbohydrates and may also
indicate greater extraction from the liver and periphery of the products of
carbohydrate digestion. A lower glycemic response usually equates to a lower insulin
demand but not always, and may improve long- term blood glucose control and blood
lipids
Classification GI range Examples
fructose; beans (white, black, pink, kidney, lentil, soy, almond, peanut, walnut,
chickpea);
Low GI 55 or less small seeds (sunflower, flax, pumpkin, poppy, sesame,hemp); most whole
intact grains (durum/spelt/kamut wheat, millet, oat, rye, rice, barley); most
vegetables, most sweet fruits (peaches, strawberries, mangos); tagatose;
mushrooms; chilis
white sugar or sucrose, not intact whole wheat or enriched wheat, pita bread,
basmati rice, unpeeled
Medium GI 56–69 boiled potato, grape juice, raisins, prunes,pumpernickel
bread, cranberry juice,[10] regular ice cream, banana
glucose (dextrose, grape sugar), high fructose corn syrup, white bread (only wheat
endosperm), most white
High GI 70 and above rice (only rice endosperm), corn flakes,extruded breakfast cereals, maltose,
maltodextrins, sweet potato (70), white potato (83), pretzels, bagels
A low-GI food will release glucose more slowly and steadily, which leads to more suitable postprandial (after meal) blood
glucose readings. A high-GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after
exercise or for a person experiencing hypoglycemia.
Disease prevention
Several lines of recent scientific evidence have shown that individuals who
followed a low-GI diet over many years were at a significantly lower risk for
developing both type 2 diabetes, coronary heart disease, and age-related
macular degeneration than others.
In the past, postprandial hyperglycemia has been considered a risk factor associated
mainly with diabetes. However, more recent evidence shows that it also presents an
increased risk for atherosclerosis in the non-diabetic population and that high GI diets,
high blood-sugar levels more generally, and diabetes are related to kidney disease as
well.
A study from the University of Sydney in Australia suggests that having a breakfast of
white bread and sugar-rich cereals, over time, may make a person susceptible to
diabetes, heart disease, and even cancer.
A study published in the American Journal of Clinical Nutrition found that age-related
adult macular degeneration (AMD), which leads to blindness, is 42% higher among
people with a high-GI diet, and concluded that eating a lower-GI diet would eliminate 20%
of AMD cases.
The International Life Sciences Institute concluded in 2011 that because there
are many different ways of lowering glycemic response, not all of which have
the same effects on health, "It is becoming evident that modifying the glycemic
response of the diet should not be seen as a stand-alone strategy but rather
as an e l e me nt o f a n ove ra l l b a l a n c ed d i et an d l i fe st y l e .
Estimated Energy Requirements (EER)
A person wishing to know how much energy he or she needs in a day to maintain Weight.
**The DRI Committee sets an Estimated Energy Requirement (EER) for a
reference man and woman:
•Reference man: “Active” physical activity level, 22.5 BMI, 5 ft 10 in.
tall, weighing 154 lb.
•Reference woman: “Active” physical activity level, 21.5 BMI, 5 ft 4 in.
tall, weighing 126 lb.
Among real people, about 80% fall into the sedentary or moderately active
categories.
• Taller people need proportionately more energy than shorter people to balance their
energy budgets because their greater surface area allows more energy to escape mas
heat. Older people generally need less than younger people due to slowed metabolism
and reduced muscle mass, which occur in part because of reduced physical activity.
These losses may not be inevitable for people who stay active. On average, though,
energy need diminishes by 5 percent per decade beyond the age of 30 years.
• In reality, no one is average. In any group of 20 similar people with similar activity levels,
one may expend twice as much energy per day as another. A 60-year-oldmperson who
bikes, swims, or walks briskly each day may need as many calories as a sedentary person
of 30. Clearly, with such a wide range of variation, a necessary step in determining any
person’s energy need is to study that person.
Key POInt
The DRI Committee sets Estimated Energy Requirements for a
reference man and woman, but individual energy needs vary greatly.
The DRI Method of Estimating Energy Requirements
The DRI Committee provides a way of estimating EER values for individuals. These
calculations take into account the ways in which energy is spent, and by whom. The
equation includes:
Gender. Women generally have less lean body mass than men; in addition, women’s
menstrual hormones influence the BMR, raising it just prior to menstruation.
Age. The BMR declines by an average of 5 percent per decade, as mentioned, so age is
a determining factor when calculating EER values.
Physical activity. To help in estimating the energy spent on physical activity each day,
activities are grouped according to their typical intensity (Appendix H provides details).
Body size and weight. The higher BMR of taller and heavier people calls for height and
weight to be factored in when estimating a person’s EER.
Growth. The BMR is high in people who are growing, so pregnant women and
children have their own sets of energy equations.
Instructions for estimating EER values are presented in Appendix H. Alternatively, the margin
note offers a quick-and-easy way to approximate your own energy need range.
Key POInt
The DRI Committee has established a method for determining an
individual’s approximate energy requirement.
Do the Math
Here’s a quick-and-easy method for estimating energy needs:
First, look up the EER listed for your age and gender group (inside front cover).
Then, calculate a range of energy needs. For most people, the energy requirement falls
within these ranges:
(Men) EER ± 200 cal.
(Women) EER ± 160 cal.
Virtually everyone’s energy requirement falls within these larger ranges:
(Men) EER ± 400 cal. (Women) EER ± 320 cal.
Body Weight vs. Body Fatness
Calculate the BMI for various people when given their height and weight information, and describe the
health implications of any given BMI value.
For most people, weighing on a scale provides a convenient way to monitor body fatness, but
researchers and health-care providers must rely on more accurate assessments. This section describes
some of the preferred methods to assess overweight and underweight.
High Body Mass Index (BMI)
Clinicians and researchers use BMI values to help evaluate a person’s health risks associated with both
underweight and overweight. BMI values correlate significantly with greater body fatness and
increased risks of death from diseases, such as heart disease, stroke, diabetes, and non alcoholic fatty
liver disease.
No one can tell you exactly how much you should weigh, but with health as a value, you have a starting
framework in the BMI table (inside back cover). Your weight should fall within the range that best
supports your health. As Table 9–1 showed, underweight for adults is defined as BMI of less than 18.5,
overweight as BMI of 25.0 through 29.9, and obesity as BMI of 30 or more. The BMI values have two
major drawbacks: they fail to indicate how much of a person’s weight is fat and where that fat is located.
These drawbacks limit the value of the BMI for use with:
Athletes (because their highly developed musculature falsely increases their BMI values).
Pregnant and lactating women (because their increased weight is normal during child-bearing).
Adults older than age 65 (because BMI values are based on data collected from younger people
and because people “grow shorter” with age).
Women older than age 50 with too little muscle tissue (they may be overly fat for health yet still fall into
the normal BMI range).
Key POIntS
The BMI values mathematically correlate heights and weights with
health risks.
The BMI concept is flawed for certain groups of people.
Do the Math
To determine your BMI:
In pounds and inches
weight (lb) × 703
▪ BMI = height (in.2)
In kilograms and meters
weight (kg)
BMI = height (m2)
Measures of Body Composition and Fat Distribution
A person who stands about 5 feet 10 inches tall and weighs 150 pounds carries about 30 of those pounds as fat.
The rest is mostly water and lean tissues: muscles; organs such as the heart, brain, and liver; and the bones of
the skeleton (see Figure 9–6,np. 344). This lean tissue is vital to health. The person who seeks to lose weight
wants to lose fat, not this precious lean tissue. And for someone who wants to gain weight, it is desirable to gain
lean and fat in proportion, not just fat.
Health professionals often use both BMI and waist circumference to assess a person’s health risks and
monitor changes over time. Researchers needing more precise measures of body composition may
choose any of several techniques to estimate body fatness, including the skinfold test. Body fat distribution
can be determined by radiographic techniques, such as dual-energy X-ray absorptiometry.
Figure 9–6 Average Body Composition of Men and Women
The substantially greater fat tissue of women is normal and necessary for reproduction. Normal
body fat percentages for people in the healthy BMI range:
• Male: 12 and 20%. Female:
• Female: 20 and 30%. 36% muscle
24% organs
• Male
27% fat
45% muscle 13% bone
25% organs
15% fat
15% bone
Three Methods Used to Assess Body Fat
Skinfold measures. Body fat is Waist circumference. Central Dual-energy X-ray absorptiometry
measured by using a caliper to obesity is measured by placing a (DEXA). Two low-dose X-rays
gauge the thickness of a fold of skin nonstretchable measuring tape differentiate among fat-free
on the back of the arm (over the around the waist just above the bony soft tissue (lean body mass), fat
triceps), below the shoulder blade crest of the hip. The tape is snug but tissue, and bone tissue, providing a
(subscapular), and in other places does not compress the skin. precise measurement of total fat and
(including lower-body sites), and its distribution in all but extremely
then comparing these obese subjects.
measurements with standards.
Body weight and health
• Body weight has long been used as a predictor of health because of its association with
body composition, specially for inactive people
• Concept of healthy weight develops to identify a body weight specific to an
individual’s gender, height and frame size
Body weight: is the total mass of a person and is expressed as pound or
kilogram
Body composition: refers to the relative contributions to a persons mass
made by different substances or tissues that make up the body
