For decades, the relationship between dietary fats and health
was at the center of our attempts to understand the underlying cause of the
obesity epidemic. Despite the important roles that fats play in our bodies,
this entire category of food was shunned for much of the 20th century. This led
to an enormous increase in the availability of fat free and reduced fat foods.
But in spite of this, obesity rates continue to rise. Today, rising awareness
about the difference between the so-called good fats and bad fats have allowed
this important part of our food supply to make a comeback. But once again, the
pendulum threatens to swing too far in the opposite direction. Dietary fats can
be divided into two families, the saturated and the unsaturated fats. Saturated
fats get their name from the fact that their fatty acids are saturated with
hydrogen molecules. This means that they can lie flat and pack together densely
so that saturated fats tend to be solids at room temperature. Animal fats, like
lard and butter, are good examples. In contrast, the fatty acids that make up unsaturated
fats are kinked in places where double bonds between the carbon atoms cause the
chains to be less saturated with hydrogen. This also means that these fatty
acids don't pack together as tightly, leaving most unsaturated fats in the
liquid state at room temperature. Omega 3 fatty acids are a special kind of
unsaturated fatty acid, with double bonds in specific positions of the
hydrocarbon chain They're found in high concentrations in fish oil, and also to
some degree in nuts, flax seeds, and other vegetable oils. Omega-3 fatty acids
are the only kind of fatty acid that the human body can't make, so they're
essential for our health and they need to be consumed via the food we eat.
Unsaturated fats can be naturally occurring like the fats
found in olive oil, nuts and avocados. Or they can be man-made or chemically
manipulated to become unsaturated. These are the fats found in some margarines
and in the kinds of oils that are often used for repeated cooling and reheating
in deep frying machines like the ones used in many fast food restaurants. The
problem with chemically engineered unsaturated fats is that the chemical bonds
between the carbon atoms are less stable, so they easily flip into a trans
orientation, rather than a cis orientation. And this is where we get the name
trans fats.
Trans fats are problematic for our health because they
increase the amount of LDL cholesterol in the blood and they lower the amount
of HDL cholesterol, the good cholesterol in the blood. By doing this trans fats
promote to formation of arterial plaques and increase the risk of heart
disease.
While saturated fats have also been shown to contribute to
increases in LDL cholesterol, they haven't been shown to lower HDL cholesterol
or to contribute to the development of arterial plaques as significantly as
trans fats.
So, what's the bottom line when it comes to foods that
contain fat? Probably the most sensible food recommendation is this. Enjoy
reasonable amounts of foods that contain mostly naturally occurring unsaturated
fats like those found in olive oil, nuts and avocados. Avoid all foods
containing trans fats. And limit your intake of foods like red meats that are
high in saturated fats.
