What happens when energy is imbalanced? Well, we'll either lose weight or we'll
gain weight. In this lesson, we'll talk a little more
about this idea, and also discuss some specifics about body composition.
As we talked about earlier, when we're not in energy balance, we'll see changes
in body weight. If we're at equilibrium, we'll maintain
our body weight. Another way to assess body weight is
through BMI, body mass index. This was originally developed for
clinical use, not for the general public but it is now used by people to evaluate
their weight. BMI is specifically equal to weight in
kilograms divided by height in meters squared.
We have a range of values that we can use to assess someone's weight.
A BMI less than 19 kg/m^2 is underweight. Normal ranges from 19 up to 25.
Overweight from 25 to 30. And 30 and over is obese.
In order to assess body weight, first we need to know how much we weigh.
Weigh, we do that with a scale, and then we can use that and compare to height and
other factors to evaluate it. The simplest tool is the weight per
height table. This is a standard reference and can give
a healthy weight range. What this allows for is some error.
We're not going to give someone a specific weight they need, because they
may have a larger bone structure, they may have more muscle mass, and this can
vary how much they're going to weigh at a certain height.
Here's a sample calculation. Try it yourself and then go ahead and do
your own BMI calculation. Now BMI can be a little bit deceiving its
only concerned with height and weight. Muscles weighs more than fat so a very
muscular person may weigh more even though they're not actually overweight.
BMI doesn't take this into consideration so very muscular people usually qualify
as obese. Take this guy in the picture.
He's 6 foot Three, weighs 245 pounds. His BMI is 30, but would you call him
obese? You might not like the buff type, but he
certainly would not be considered obese. Since you've learned a little bit about
how energy is generated, let's talk about where that energy goes.
How you use it and how we can balance our energy intake and output.
Energy balance is quite simple its energy in versus energy out.
If they're equal, you're in equilibrium, you're in balance.
Think about it like this, when the work coming in is larger than the work you're
putting out, you're going to have a big stack of work next to you.
But if you can manage to keep up with that workload, you won't see a stack
build up. The same thing can happen with our
bodies. If we're not able to put out enough
energy that energy builds up in the form of fat.
So in terms of energy balance we can either be in equilibrium, positive
balance where we'll experience weight gain, or negative balance, where we'll
experience weight loss. When we talk about our desire to eat, or
our need to eat, there's. Two terms we should consider, hunger and
appetite. When I refer to hunger I am referring to
the physiological and when I refer to appetite I am referring to the
psychological drive to eat. Hunger is controlled by hormones and your
nervous system. Based on chemical triggers the brain to
tell you, I'm hungry, I'm full, I am not hungry yet.
Various triggers send these signals including the presence or the absence of
nutrients in your stomach and your body as a whole.
The size and the composition of the the last meal can influence how quickly we
get hungry again later. We have more fiber in our meals for
example, it'll take longer to digest that, empty our stomach, so there'll be a
longer period of time before we get hungry again.
Regular eating patterns can also influence this.
We will see that if you eat breakfast every morning, you wake up hungry.
You eat lunch at a certain time every single day, you get hungry at that time
of day. Your body can settle into this pattern at
a hormonal and nervous system level. Environment and activity level can also
influence, if it's cold, we need more kilocalories, so we'll be hungrier, and
if we're active, we'll see the same. Hormones can also stimulate hunger; as
hormones fluctuate in both men and women, we see alterations in hunger.
And health, if we're sick, we may either feel more hungry or less hungry depending
on what happens to these hormonal signals due to the illness that we have.
The feeling of satiation will signal to your brain to stop eating.
develops during a meal, while you are eating you can actually eat fast enough
that you beat the signal so you devour everything on your plate, and then later
you realize I am full or I am over full . This is why its good eat slowly to allow
time for the signal to get to your brain. Energy density You have a meal can
influence how quickly we might feel satiation.
Foods that are energy dense are actually less satiating then foods that are high
in fiber. Remember, it's the stomach distension
that's at play. So, if I eat a handful of peanuts or a
handful of popcorn, the popcorn's going to satiate me more.
More and actually be lower in calories than the peanuts.
Once we've experienced satiation, and until we experience hunger again, we are
experiencing satiety. So satiety occurs between meals.
It's the signal that says, you don't need to start eating again yet, we don't need
nutrients. It's influenced by nutrient metabolism,
and again, both the hormonal and[INAUDIBLE].
Nervous system level. This differs from appetite.
You may eat a meal, and have an appetite for something, but that doesn't mean you
have a true hunger. You can override satiety by your
appetite, by your psychological need, your cravings, your desire for dessert
for example, after an adequate meal. Relative to psysiological hunger,
psychological appetite. Can sometimes be harder to control.
It's often food-specific, that craving for popcorn from movies that can occur in
the absence of hunger, wanting that chocolate cake after a meal.
And it can override signals of satiety. You had a nice lunch, and then you go to
an early tailgate for some football, and even though you're not really hungry, you
stand around munching at the food that's around you.
Hunger signals are integrated at the level of the hypothalamus.
Its here that we're sending signals from our stomach or our fat cells, and then
triggering release of other hormones that then elicit a response, hunger or lack of
hunger. The integration of signal and response
also requires hormones. Hypo Thalamic hormones that release to
stimulate reduce hunger include the orexigenic and anorexigenic.
Anorexic is simply a term that means to lose appetite.
Anorexia nervosa is a disorder. So, don't confuse that with a simple term
anorexic. Anorexigenic is something that would
generate a lack of hunger. Orexigenic is the opposite it's
stimulating a need to eat. It is stimulating hunger.
The release of hormones from the hypothalamus is triggered by.
hormones in other parts of the body. This includes the GI tract hormones and
adipose tissue. There are three hormones that we should
know Ghrelin, Peptide YY and Leptin. The hormone Ghrelin makes us hungry and
Peptide YY and Leptin make us less hungry.
Ghrelin acts on the orexigenic hormones while Peptide YY inhibit the orexigenic
hormones. Ghrelin stimulates orexigenic hormone
release while. Peptide YY inhibit them.
These are both produced by the GI tract. Leptin found in the adipose tissue
stimulates the release of[UNKNOWN] hormones and simultaneously inhibits your
oxygen requirements. So, Leptin is a very powerrul hunger
reducer and Ghrelin is the primary hunger inducer.
So we now had to measure energy intake. We know how to measure calories.
We talked a little bit about what controls our desire to put those calories
into our bodies. So let's move on to how we get rid of
those calories, how we burn those calories.
This is energy output. The primary component of our energy
output is resting or basal metabolism. This is what we need to breathe, for our
heart to beat, for cells to grow. When we're children, this is what we need
to get from infancy to adulthood. It is 60 to 75% of our energy
expenditure. Now, there's some extreme conditions
where other things can increase above basal metabolism.
But that might be an example of the Olympic athlete, someone who is so
excessively active that their energy output with physical activity is greater
than that for basal metabolism. But for most of us, even those of us that
are athletes, basal metabolism is the most significant component of energy
output. Resting metabolic rate, this basal
metabolism rate Is measured in calories per unit time in both men and women.
This could be calories per hour or calories per day.
Many factors can influence resting metabolic rate.
Factors that increase this include total body weight and surface area.
If you weigh more or if you have more surface area.
You will have a higher metabolic rate. Hot and cold temperature.
If it's cold outside or if it's very hot outside, your body needs to regulate its
own internal temperature and that takes more calories, that increases metabolic
rate. Fever will increase metabolic rate,
hyperthyroidism, the overactivity of the thyroid gland, stress, caffeine, smoking,
muscle mass. Muscle is what burns calories, not fat.
So the more muscle mass you have, the higher your resting metabolic rate will
be. This means you exercise and build muscle,
even when you're sitting watching television you're burning more calories.
Rapid growth, during young age and adolescence we see big growth spikes.
During that period time Time, resting metabolic rate goes up.
Pregnancy and lactation. That's pretty obvious.
There's a baby growing inside. Our metabolic rate goes up, because we're
needing to nourish that child. When we're lactating, we're generating a
product. We need to be able to produce milk for
the baby. And therefore, we increase metabolic
rate. Doctors that decrease metabolic rate
include aging as we get older. It just goes down.
The female gender, women do tend. tend to burn less calories than men.
fasting and starvation, even when we're sleeping it decreases a bit, if we
continually fast, if we continually starve ourself our body goes into panic
mode. It's worried that we're not going to get
food, so it's going to reduce the resting metabolic rate, for survival purpose.
Hypothyroidism, the underactive thyroid gland, And related to that fasting part,
sleep. Not only are you not eating, but your
entire body system is slowing down, it's in the rest state.
Between these two lie genetics and medication.
These can either increase or decrease your resting metabolic rate.
The next component of energy output is physical activity.
This is the second largest component technically .
This is the energy we need for activity beyond rest.
So, this means walking toward car region, going upstairs, walking round our
building, going for a walk, going for a run, biking, hiking, working out at the
gym, all of these things. And this can account for 15 to 30% of
expenditure. This is highly variable value.
You can imagine there will be a difference between someone who just walks
around their home and someone who is an athlete.
Now thinking about percentage though, the athlete, most likely have a higher
percentage of muscle. Since muscle increases basal metabolic
rate, the athlete's basal metabolic rate's greater than the person who's just
walking around their home. And so still, relative to one another, we
see a similar relationship between the amount that basal metabolism takes up and
the amount of energy output that physical activity takes up.
The final component of energy output is the thermic effect of food.
May not realize but you do generate heat when you eat.
Some people do more than others and this can range from about 5 to 10% of your
total energy expenditure. So estimated energy requirement is some
value you get. We're predicting the amount of energy,
the amount of calories needed to maintain balance or equilibrium in a healthy
adult. EER is based on data from doubly labeled
water method that That isomptope method. And we'll estimate total energy
expenditure with considerations for age, gender, height, weight and physical
activity level. These equations we're going to go over
don't apply to growth periods or for people that are significantly overweight.
So let's go ahead and calculate total energy expenditure.
Here's the equation. TEE, total energy expenditure equals REE,
resting energy expenditure, plus PA, physical activity, plus TEF, the thermic
effect of food. To estimate resting energy Expenditure.
We use a value of one kilocalorie per kilogram per hour for men.
And 0.9 kilocalories per kilogram per hour for the women.
Therefore, calculations with males will be easier than that with women.
You're just going to use a factor of one. Next comes physical activity.
We have ranges that we can use here. If I were to ask to a calculation I would
actually give you a specific number, not just expect you to memorize what
moderate, light, or heavy is. The exceptional down there, that's the
Olympic athlete that I referred to. There we can actually see potentially
that physical activity is greater than resting energy expenditure.
Lastly, we have the thermic effect of food, which is 10% of the sum.
On arresting energy expenditure and physical activity.
So lets do a sample calculation of energy expenditure.
Follow along with the next several slides and do the calculations yourself.
Then practice more calculations using your own body weight, and activity level.
And maybe that of a friend, stateroom or relative .
That concludes the energy lecture. So I suggest you get up and go spend some
now.