think about body fat, it’s probably white fat that comes to mind. That’s where
our bodies store excess calories, and it’s the stuff you want to get rid of
when you are trying to lose weight.
Potential of brown fat to curb weight
fat isn’t the only kind of fat in the body – you also have brown fat and beige,
or brite, fat, which can actually burn calories instead of
burns calories instead of packing them on the body sounds like the Holy Grail
of obesity treatment, and researchers want to find ways to activate or increase
these types of fat in our bodies. In fact, the National Institutes of Health
(NIH) has put out a call for research to figure out how to do it. But is the
potential of brown fat to curb weight all it’s cracked up to be?
So what makes brown and beige fat different from white fat?
think that white fat just stores calories, but it actually does much more than
that. It insulates the body, protects the internal organs and also produces proteins that regulate food intake,
energy expenditure and insulin sensitivity.
Brown fat is
rich in mitochondria, which gives it a brown appearance. You may remember from
high school science class that mitochondria are the “powerhouses” of the cell
because they burn fatty acids and glucose for energy, releasing it as heat.
That is why
brown fat burns calories instead of storing them, like white fat does. White
fat also has mitochondria, but not nearly as much as brown fat does.
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babies have brown fat because it generates heat and helps them maintain body
temperature. Rodents also have brown fat for the same reason. Until recently,
it was thought that brown fat disappeared during the course of childhood.
to advances in imaging technology, we know that adults also possess brown fat.
brown fat tends to be located around the neck and clavicle, but can also be
found in a few other locations around the body. Weight can influence how active
a person’s brown fat is, so the more a person weighs, the less active their brown
fat is at burning fatty acids and glucose.
brite fat is made up of “brown-like” fat cells present in traditionally white
fat deposits. Studies using animal models have shown these beige fat cells can
form in white fat deposits under certain treatments, including cold exposure.
these beige fat cells were pre-existing white fat cells that turned into beige
cells in a process called “transdifferentiation” or they are brand new
cells is a point of contention among researchers. Like brown fat
cells, beige fat cells appear to have the ability to burn fatty acids and
glucose as energy.
Calories in, calories out
principle behind weight loss or weight gain is called energy balance, which is
the difference between energy intake (how many calories you eat) and energy
expenditure (how many calories you burn).
a low-calorie diet and an exercise-heavy lifestyle to lose excess weight isn’t
always easy, so researchers have been looking for other ways to tip the energy
balance in favour of expenditure.
think that increasing the activity or quantity of brown or beige fat in the
body might be one way of doing it.
certainly appears to be the case in rodents. Studies have found that the
chemical norepinephrine, cold exposure, diets and various proteins made in the
body can all induce “browning” of white fat or activate brown fat to burn more
calories in rodents.
these treatments also have some effect on energy balance, often increasing
energy expenditure and causing weight loss.
we could do the same thing in humans and transform the metabolically inert white
fat that is weighing so many of us down into metabolically active brown fat
that actually burns calories throughout the day.
Increase in energy expenditure
sounds like it could be a game changer in the fight against obesity, the
research isn’t clear on how much of a difference brown fat might make for
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instance, some research has shown that activation of brown fat by cold exposure
in humans translates to an increase in energy expenditure equivalent to less
than 20 calories per day, which is hardly enough to
have the kind of effects on obesity that we all hope for.
research has estimated that activation of brown fat in adults could burn up to 125
extra calories per day.
that activated brown fat makes a relatively small contribution to daily energy
expenditure is unknown, though it may be because brown fat is present in the
body in minuscule amounts compared the less metabolically active white fat.
instance, a recent study showed that out of 14 subjects, only
five had more than 10 grams of activated brown fat.
And we also
wouldn’t want to convert all of our white fat into brown fat, because white fat
is actually something our bodies need.
instance, in rare conditions in which there are no fat deposits, people often
have insulin resistance, fatty liver disease and other
partially due to the lack of proteins that are produced by the white fat, and
also because the excess calories that should be stored in the fat have to be
stored in other organs, such as the liver.
might do more than burn calories
Even if the
data show that activating brown fat doesn’t seem to burn many extra calories in
humans, it could have other health benefits.
that transplanting brown fat from donor mice into the abdominal cavity of age-
and sex-matched recipient mice reversed high-fat diet-induced insulin
resistance, a condition that contributes to Type 2 diabetes in humans.
studies have shown that beige and brown fat has beneficial effects on glucose
metabolism and insulin sensitivity that appear to be greater than the modest
effects on body weight.
has the ability to clear lipids (fats) and glucose from the blood, resulting in
lower concentrations of circulating triglycerides, cholesterol
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contribute to the beneficial health effects of brown fat, independent of weight
human research may lie in how these fats can positively influence insulin
sensitivity, or glucose and lipid metabolism, rather than body
much interest in being able to harvest the power of brown fat in humans to
combat obesity and accompanying metabolic disease, but this research is
relatively in infancy.
answer these questions, the NIH has announced grant opportunities to identify conditions
that trigger the “browning” of white fat, or increase quantity of brown fat in
humans, find ways of testing for brown fat that don’t require needle biopsies,
and explore the biological functions of these fats. This push means we should
be learning more about this intriguing tissue soon.
Desiree Wanders, Assistant Professor of
Nutrition, Georgia State University
was originally published on The Conversation. Read the original article.
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