- [Voiceover] In this video, we're going to talk about
body mass or what is it in your body
that determines how much you weigh?
Well, you can kind of think of it like a scale,
where the things that determine
whether you're heavy or you're light
are based on opposing forces,
where some things cause you to put energy into your system,
and there are other things that cause you
to get rid of energy, or that means
you lose energy or energy out.
And as you might remember, food is a type of energy.
So we'll put diet in this column as a way that you
get energy into your bloodstream.
If you eat a lot of sugar or carbohydrates or fats,
that's energy for use.
But then remember, once we've eaten things
there are hormones that regulate
whether we store things or we get rid of them
and just discard what we ate.
One hormone is insulin,
and that regulates blood glucose levels.
There's also leptin, which is related to
blood lipid levels,
and then there's also another hormone
that's called ghrelin that's related to
whether the stomach is full or not.
These three hormones help regulate
whether the energy or the food that we've just consumed
is stored or if we just let it pass through
and become waste that we get rid of.
Now the things that we do that get rid of energy
or consume energy include things like
our basal metabolic rate or the amount of energy
we burn just at rest.
That comes out to be, in the average person,
about 2000 calories in a day.
What about from just getting up,
moving around, and being active?
Well, in the normal person, activity or the use of energy
to perform tasks comes out to be
about 500 calories in the average person.
And finally, there's this phenomenon that's called
diet-induced thermogenesis,
and that's just the energy
that we use or we burn to store the food that we eat,
and that comes out to be about 10%
of the amount of calories we bring in from our diet.
So this means on average, whether we are eating more
or if we are doing things.
So this means on average, whether we are a person
that tends to eat more and be sedentary,
or if we're a person that's more active and eats less
and burns more calories, that helps determine
what our body mass will be.
But one of the things I want to highlight is
the effect that hormones can have on this process,
on determining whether we have a high body mass
or a low body mass.
And the best example of this is a mouse experiment.
In this experiment, three mice were studied over time.
The first mouse, which for simplicity sake let's say
it was a normal mouse.
So there's nothing genetically unusual
or different about this guy.
The other two mice, however, had some specific gene
that was knocked out.
Knocked out meaning missing.
So there was a gene that was not there
that the normal mouse had.
And so, what they did next is
that they took these two mice and they fed them,
and they gave them equal amounts of food
and let the mice eat whenever they wanted to
and saw what happened.
Well, over time the normal mouse just stayed the same.
No difference.
But when they let the genetically altered mouse
eat for as long as it wanted to, this guy got huge.
The researchers found that when this gene was missing,
these mice tended to eat more,
because they were hungrier.
But then the unusual thing was
that when they took this same strain of mouse
that had this exact same gene knocked out or missing
and then fed them, but also injected the serum
from the normal mouse or injected blood
from the normal mouse, they found that over time
the mouse looked pretty much the same as the normal mouse,
and it was this experiment that led scientists along the way
to determine that this gene was actually
encoding the hormone leptin.
Leptin is a hormone that lives in our fat tissue,
our adipose tissue, and goes to our hypothalamus,
this part of the brain that tells us we're not hungry.
In people or in mice that don't have any leptin,
these guys are always hungry.
And so, they just keep on eating.
So this just goes to highlight how important it is
to have the correct hormones flowing through the bloodstream
to talk to your brain based on the nutrients
or the diet that you have to regulate your body mass.