To recharge my phone, all I need to do is
plug it into an electrical outlet. If I were to put my fingers in the electrical socket,
however, all I would accomplish is risking an electrocution. As we already learned, our
only option to ‘recharge’ ourself is eating food. Every day we need to spend energy to
stay alive and perform all of our activities, and this energy we need to get back from food.
From the food we eat, we extract the energy we need to survive. But what if we eat more
than what we need? And what if we eat less? One of the most basic concepts in nutrition
is that of energy balance: a good diet should provide, on average, just about the amount
of energy that we need to spend. Of course this doesn’t happen exactly every day. Some
days we eat more than what we spend, some other days we spend more than what we eat,
and things will balance out. Furthermore, our body has an extraordinary ability to maintain
a good energetic balance: if we tend to eat a little less, our body will find ways to
save energy, while if we tend to eat a little more, it will find ways to increase our energetic
expense to dissipate some extra energy and maintain that balance between energy in and
energy out. However, if we keep doing this over the long term, by significantly under-eating
or overeating compared to our energy expenses, we will create a situation of energy unbalance
that exceeds the homeostatic ability of our body, and will result in either weight loss
and loss of both fat and lean mass, or weight gain and fat accumulation. The traditional unit of measure for the energy
that comes from food is the kilocalorie. 1 kilocalorie is the amount of heat required
to raise the temperature of 1 kg of water by 1 degree celsius, and is equivalent to
4.184 kJ. In this course, for simplicity, we will use the word calories instead of kilocalories.
This is common practice. If you look at any nutrition facts label you will also see the
word calories, but those are actually kilocalories. There is no possible confusion because this
is the only unit of measure we use in nutrition, the actual ‘calorie’, meaning one thousandth
of a kilocalorie – just like a gram is one thousandth of a kilogram – is never used.
So remember, when we say calorie or kilocalorie, we are talking about the same thing. The concept of energy balance is just a reminder
that the laws of physics and thermodynamics apply to our body as well. What else did we
expect? Energy can’t be created and can’t be destroyed, and not even the most miraculous
weight loss diet can elude this simple principle. What you see here is a scale, that exemplifies
the concept of energy balance. On one side of the scale, we have the energy input, which
is the amount of energy we introduce every day into our body by eating food. On the other
side of the scale, we have the energy output, the amount of energy we expend every day to
make our body function and perform all of our activities. Suppose that one day we introduce
21 hundred calories with food, and we also spend 21 hundred calories with our activities.
What we have is a situation of energy balance, that in the long term will result in maintenance
of body weight. Suppose now that our little pink friend starts eating a lot less, say
only 800 calories every day. However, he keeps spending 2100 calories. What we have now is
a situation of negative energy balance, more energy was expended than what was introduced
with food. To gap the difference, our friend had to use his body stores of fat, glycogen
and protein, and in the long term, this results in weight loss.
Conversely, his twin brother has done the exact opposite. Without changing his lifestyle
and thus his energy expenditure, he has started eating a lot more, 35 hundred calories a day.
Since he didn’t need to extra energy for his activities, he just converted it to fat
and stored it in his adipose tissue. As a result of this positive energy balance, in
the long term he has become overweight. Note that he didn’t become overweight just because
he was eating more, but because he was eating more calories than he was spending. If he
had decided to still eat his 3500 calories, but together with that he also had increased
his energy expenditure, say, by working out at the gym, his energy balance would have
been kept, and he would have maintained his healthy weight. We are already familiar with the energy input
side of the equation. Our energy coming from food is provided by the three macronutrients:
carbohydrates, which provide 4 calories per grams, fats, which provide 9 calories per
gram, and proteins which provide 4 calories per gram. Alcohol also provides calories,
about 7 per gram. I’d like to stress the concept that in the
long term, eating more calories than we expend will lead to weight gain NO MATTER WHICH FOODS
THEY COME FROM. They may be fats, they may be carbs, they may be protein, they may come
from junk food or from the healthiest food of all, but if they are in excess to our needs,
they’ll result in fat accumulation and weight gain regardless. In the next video, we will examine more in
detail the other side of the scale, and learn more about the components of energy expenditure.