[MUSIC] In order to survive, the human organism
needs to take in oxygen, water, and food. We can survive only about
three minutes without air, three days without water, and
three weeks without food. Because food is so important to our
survival, it's been studied extensively. And since 1827 when a British
physician by the name of William Prout first proposed that humans need
three macronutrients to survive, physicians, scientists, and increasingly
the general public have trying to figure out exactly how much of each of
these nutrients will optimize our health. But to some extent, the focus on nutrients
rather than food has confused many people. >> And we tend to get lost in this
conversation about nutrients, good and bad and
it's understandable because scientists need to reduce things to
a single variable to study them.
And the variable in food would
appear to be the nutrient. But we also have lots of studies
that show that simply removing or boosting nutrients or turning them
into supplements doesn't seem to work. That food is much more complicated,
it's a system. >> A basic understanding of the nutrients
can give us a helpful background for our discussions about food. So we'll review the nutrients and
how the body uses them, but most of this course will focus on
discussions about food and health. Because ultimately,
people eat food, not nutrients. Dietary carbohydrates are combinations of
sugar units that come in both simple and complex forms. Simple carbohydrates include
the monosaccharides, or single sugar units like glucose and
fructose. As well as the disaccharides, or two-sugar
units like sucrose, or table sugar.
Complex carbohydrates, or polysaccharides, include the dietary starches that
our body can break down and digest, and also the indigestible polysaccharides
that make up dietary fiber. During the process of digestion,
carbohydrates are broken down and converted to glucose,
which can then be metabolized by the body to produce usable energy
in the form of ATP. If energy demands are low,
glucose can be stored, and most of the time it's
stored as adipose tissue. Dietary proteins are also broken
down into their component parts, amino acids,
during the process of digestion. And these amino acids
can be used to build and repair lean tissues in the body and
perform many other important functions. But amino acids can also be
broken down and used for energy. And if they're consumed in excess, they can contribute to fat
stores in the body as well.
Dietary fats can also be broken down into
smaller components and used for energy. [MUSIC] Or, they can be stored as adipose tissue,
depending on our energy needs. Fats are the most energy dense storage
form, providing nine calories of energy for every gram, and
alcohol provides seven calories per gram. In contrast, carbohydrates and proteins
provide only four calories per gram. This is one of the reasons we've
evolved to store excess nutrients as adipose tissue, and
this brings us to the underlying physiologic cause of overweight and
obesity. Any calories that aren't
converted into usable energy in the form of ATP are stored
in the body for later use. Most of the time they're
stored as adipose tissue. So disturbing the energy balance
to favor energy expenditure over energy storage needs to
be one of the priorities for people who are trying
to lose excess weight. This can be achieved by
consuming fewer calories, burning more calories through exercise,
or a combination of both. But in addition,
when long term health is the end goal, the quality of our food matters just as
much as the number of calories we consume.
Within each category of macronutrients,
we need to choose foods that will support our health,
rather than working against it. [MUSIC].