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White, Brown, and Beige Fat in the Body: Facts and Functions

Linda Crampton is a writer and teacher with a first-class honors degree in biology. She often writes about the scientific basis of disease.

Newborn babies have more brown fat than adults, which helps them to stay warm.

Newborn babies have more brown fat than adults, which helps them to stay warm.

White, Brown, and Beige Fat

When most people hear the word "fat" in reference to body tissues, they think of the soft material under the skin that is sometimes responsible for weight gain. This picture is not completely accurate, however. There are actually three types of fat in our bodies—the familiar white type and the less common brown and beige type.

White fat has important uses but can be harmful if too much is present. The fat molecules inside its cells can be used to produce energy. If energy isn't needed, the molecules are stored inside the cells and form part of the body fat. Brown and beige fat have special benefits compared to the white type, including helping to control our weight. Once they have been activated, their cells fat break down fat molecules to produce heat instead of storing the substance.

Safely increasing the amount or the activity of brown and beige fat might be a way to reduce obesity and the incidence of some diseases. Obesity is a risk factor for heart disease, high blood pressure, type 2 diabetes, and some types of cancer.

Brown and beige fat cells produce heat from fat during a process called non-shivering thermogenesis.

Brown and beige fat cells produce heat from fat during a process called non-shivering thermogenesis.

Fat Distribution in Our Bodies

White Version

White fat is the kind that collects under the skin, where it's known as subcutaneous fat. It also collects around organs. In this location, it's known as visceral fat. An excessive amount of subcutaneous or visceral fat is dangerous. Fat deposited inside blood vessels is very dangerous and increases the risk of a heart attack or stroke.

Brown Version

It was once thought that brown fat was most abundant in newborn babies and small mammals. Very young babies are unable to shiver to keep warm and therefore need the heat produced by the fat. Small mammals also need brown fat since they lose heat from their bodies very quickly. Adult humans were believed to have no or very little brown fat. Researchers now know that adults have a significant amount of the substance and that it's located in patches around the body.

Beige Version

Beige fat cells are always found within deposits of white fat. The cells have many of the characteristics of brown fat cells, including the ability to produce heat from fat molecules once they are activated. They have some features of their own, however.

Even if the new discoveries about the benefits of brown and beige fat are confirmed, we will probably still need to eat a healthy diet in order to lose weight.

Even if the new discoveries about the benefits of brown and beige fat are confirmed, we will probably still need to eat a healthy diet in order to lose weight.

Differences in Adipocytes

There are some important differences between white, brown, and beige fat and their cells. The cells that store fat molecules are called adipocytes.

  • White fat is also known as white adipose tissue or WAT.
  • Brown fat is known as brown adipose tissue or BAT.
  • One abbreviation that's used for beige fat is iBAT (induced brown adipose tissue).
  • Beige adipocytes are sometimes called brite cells (brown in white cells).
  • White adipocytes contain one large droplet of fat, which consists of triglyceride molecules. The fat droplet takes up so much space in the cell that the nucleus, mitochondria, and cytoplasm are pushed to the periphery.
  • Brown and beige adipocytes contain multiple smaller fat droplets of varying sizes. The droplets are composed of triglycerides and are distributed throughout the cell. The numerous mitochondria are also distributed throughout the cell. The nucleus is located on the periphery of the cell but is often nearer to the center than in white adipocytes.
  • Brown and beige fat cells contain a much higher number of mitochondria than white ones. Mitochondria are the structures that produce energy in a cell. They contain iron, which gives brown and beige fat their color.
Stained brown adipose tissue showing multiple fat droplets in the cells.

Stained brown adipose tissue showing multiple fat droplets in the cells.

Facts About Beige and Brown Adipocytes

Although brown and beige adipocytes are similar, they aren't identical.

  • White, beige, and brown cells ultimately develop from a mesenchymal stem cell. Two developmental lines branch from this stem cell. One line gives rise to white and beige cells. The other line produces brown cells. (The relationship is shown in pictorial form in the fourth reference below.)
  • Brown cells are more closely related to myocytes (muscle cells) than white and beige ones.
  • In early life, a beige adipocyte often resembles a white adipocyte. A suitable stimulus triggers its transition into the beige form.
  • Gene expression (the activation of a gene) is different in brown and beige cells.
  • Despite the differences in their gene expression and life history, a brown fat cell and a beige one perform the same job. They both produce heat from fat molecules.

Scientists are investigating the factors that cause beige fat cells to appear in white fat. These factors aren't fully understood. Understanding them might one day lead to new methods to reduce obesity.

Terminology Problems

The lack of distinction between brown and beige fat cells in some research reports—especially those completed before the beige type was identified in 2012—can be confusing. Some descriptions of brown fat may really be referring to the beige type, especially in reference to stimulating the appearance of "brown" adipocytes in white fat. Though brown and beige adipocytes have major similarities, they aren't identical, so it's important to name them accurately. Hopefully, future discoveries will clarify the terminology and the results of the research.

Functions of the Different Types of Fat

White Fat Functions

White fat under the skin has several important functions. For example, it insulates the body from heat loss, cushions organs from blows, and stores energy. The triglyceride molecules in the adipocytes can be broken down to produce ATP (adenosine triphosphate) molecules. These are able to quickly release energy when it’s needed. If we don’t need the the energy, fat continues to be stored in the cells.

Researchers have discovered that white fat releases multiple hormones that have important uses. It's a vital material. When it's present in quantities beyond the body's requirements, however, problems can result.

Brown and Beige Fat Functions

In brown fat and beige fat, triglyceride molecules are broken down instead of being stored for a long time. The cells produce a large quantity of heat from the molecules in a process called non-shivering thermogenesis.

Brown adipocytes contain a high concentration of a protein known as UCP1. Mitochondria need this protein in order to produce heat from triglycerides. Beige adipocytes also produce the high level of UCP1 when necessary. They are stimulated by a hormone named irisin, which is described below.

Researchers are investigating the quantity and behavior of brown and beige adipocytes at different times of the year and under different conditions. The results of the investigations might be interesting as well as useful.

Activation of brown fat burns calories, improves insulin sensitivity and even affects appetite regulation.

— Camilla Schéele. University of Copenhagen, via Medical Xpress

A Recent Discovery About Brown Fat Cells

Brown fat offers some tantalizing possibilities with respect to our health. Researchers have recently discovered that activating the beta2-adrenergic receptors on brown fat cells stimulates thermogenesis. In cell biology, a receptor is a protein on the surface of a cell that becomes active when it binds to the appropriate substance. As a result of the activation, the receptor triggers a particular process inside the cell.

The researchers suspect that activating the beta2-adrenergic receptors on the adipocytes might help people with obesity and perhaps people with type 2 diabetes. They say that activated brown fat not only burns calories but also improves insulin sensitivity. Further research might enable scientists to learn how to stimulate the receptor efficiently and safely and to discover more about the benefits of this process.

Regular endurance exercise increases the irisin level in the body.

Regular endurance exercise increases the irisin level in the body.

Irisin, Weight Loss, and Insulin Sensitivity

Research has shown that when mice and humans exercise, a hormone that was unknown until quite recently appears in their bloodstream. This hormone has been named irisin after Iris, the Ancient Greek messenger goddess.

Like other hormones, irisin carries messages to body tissues and triggers specific effects. Researchers have found that mice and humans who have been participating in exercise sessions for a greater number of weeks than other members of their test groups have a larger concentration of irisin in their blood.

In an experiment with mice, researchers have discovered that some significant effects of irisin—at least in obese, pre-diabetic, and non-exercising mice—are to cause more beige fat cells to appear in white fat (a process known as browning), to activate the beige fat cells, to induce a small weight loss, and to make the body's cells more sensitive to insulin. Insulin is a hormone made by the pancreas that helps to control the blood sugar level.

Irisin and Insulin Resistance

Insulin travels from the pancreas to the body's cells via the bloodstream. The insulin molecules join to receptors on cell membranes. As a result of this union, glucose is able to leave the blood and enter the cells. Glucose is an energy source for the cells.

In people suffering from Type 2 diabetes, the pancreas still produces insulin, but the cells aren't responding properly to the hormone. This condition is known as insulin resistance. Insulin resistance is often a precursor to full-blown diabetes.

Obese people have a higher chance of developing insulin resistance. Since irisin affects beige fat and body mass and also improves the insulin sensitivity of cells, it could be very helpful for people with Type 2 diabetes (if it has the same effects in humans as it does in mice).

Hiking over rough terrain and uphill is great exercise for reducing the amount of white fat in the body and possibly for increasing the amount of brown fat.

Hiking over rough terrain and uphill is great exercise for reducing the amount of white fat in the body and possibly for increasing the amount of brown fat.

Other Potential Benefits of Irisin

The irisin level in humans rises after regular and moderately intense aerobic exercise that requires endurance. It certainly seems like a hormone that we would want to increase. Research suggests that it has a range of benefits.

Much of the irisin research has been done by Dr. Bruce Spiegelman and his colleagues at the Harvard Medical School and the Dana-Farbar Cancer Institute. In 2013, the team found that irisin acts on the brain of mice as well as on their fat. The hormone not only improves the cognitive abilities of mice but also stimulates the growth of new nerve cells, or neurons.

Irisin is made by skeletal muscles. In 2017, scientists at Tufts University found that it's also made in bone, at least in mice. After two weeks of "voluntary wheel running", mice had an increased level of irisin in their bones as well as increased bone mass. Administration of irisin to mice who didn't exercise also increased bone mass.

We need to be careful when reading about irisin benefits. Some discoveries have been made only in lab animals. These discoveries may or may not apply to humans. In addition, sometimes a discovery is made by one scientist but either can't be duplicated by others or is shown to be wrong.

Benefits of Exercise and a Healthy Diet

Health experts already know that exercise and a healthy diet can help us to lose weight and also offer many other benefits. One of the reasons for some of the benefits may be the control of fat type. The effects of irisin might be significant. Researchers have discovered that a substance in some types of fruit may also be significant with respect to fat type.

Scientists at Washington State University have found a possible link between the addition of fruits containing resveratrol to the diet and the production of brown fat. Resveratrol causes browning of white fat in mice. The discovery may or may not apply to humans, but it's interesting.

Some Goals of Future Research

Investigating the role of brown and beige fat in adult humans is a relatively new area of research, but it could produce some very exciting health benefits. Interest in the topic is escalating, especially since it offers hope for dealing with the increasingly common problems of obesity and type 2 diabetes.

More research needs to be done in order to determine the differences between the two fat types. We need to understand their effects on our body in more detail and to determine the methods, effects, and safety of changing one type of adipocyte into another. We also need to investigate the safety of artificially increasing the activity of either fat type. The research may enable brown and beige adipocytes to be very helpful for us in the future.

References

  • Brown fat benefits from the BBC
  • Benefits of beige fat from the Harvard Gazette
  • Scientists turn white fat into the beige type in mice with the help of resveratrol from Washington State University
  • Production of the three types of adipocytes from mesenchymal stem cells from the National Library of Medicine
  • Hormones from fat cells from Chemical and Engineering News
  • Irisin benefits from Psychology Today
  • Exercise-induced hormone irisin is not a myth from the Medical Xpress news service
  • Irisin and fat loss from the University of Florida
  • Bone formation after irisin administration from Tufts University
  • Scientists discover how to activate brown fat from Medical Xpress

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2012 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on January 21, 2012:

Thank you very much, Peggy. Yes, it seems that researchers are discovering more and more reasons why we should exercise! I'm hoping that scientists will find out more about irisin soon.

Peggy Woods from Houston, Texas on January 21, 2012:

Very interesting hub about the value of fat in our bodies...especially the brown fat. Also interesting about the irisin after doing exercise. We all know that exercising is good for us and this just gives us another reason to keep doing it. Thanks Alicia! Up, interesting and useful votes.

Linda Crampton (author) from British Columbia, Canada on January 18, 2012:

Thank you very much for the comment and for sharing, b. Malin! I enjoy doing research and reading the latest health news. You are so right - trying to maintain health is important.

b. Malin on January 18, 2012:

Always a good read Alicia, you certainly do your research. Our Health is the only thing that Money Can't Buy...so it should be precious to all of us. This Hub is one I will Bookmark and share.

Linda Crampton (author) from British Columbia, Canada on January 18, 2012:

Thank you, Eddy. I appreciate your comment and the vote. Have a great day!

Eiddwen from Wales on January 18, 2012:

A very interesting and useful hub. Thank you for sharing this and has to have a vote up.

Take care and enjoy your day.

Eddy.

Linda Crampton (author) from British Columbia, Canada on January 16, 2012:

Hi Maren Morgan. That's a sad story! It's good for the mind and the body to get short periods of exercise throughout the day. I sure that they help us to become more productive at work!

Maren Elizabeth Morgan from Pennsylvania on January 16, 2012:

Yet more evidence that humans are meant to exercise! And I got yelled at in my last job for getting up from my desk (to do photocopying, filing, whatever) TOO frequently. My plump supervisor wanted me to combine everything into one trip. And then sit.

Linda Crampton (author) from British Columbia, Canada on January 15, 2012:

Hi, Prasetio. Thank you so much for commenting and for the rating! I appreciate your visits.

prasetio30 from malang-indonesia on January 15, 2012:

I love the way you present all the useful information related with health. Without no exception, I also love this one. Alicia, thanks for writing and share this information with us. Well done and rated up!

Prasetio

Linda Crampton (author) from British Columbia, Canada on January 15, 2012:

Thank you for the comment, chspublish. Yes, I hope that there is more good news about brown fat as well!

chspublish from Ireland on January 15, 2012:

Good news and information about brown fat cells. Here's hoping research brings more good news. Interesting hub.

Linda Crampton (author) from British Columbia, Canada on January 15, 2012:

Hi, Tina. I'm looking forward to the future discoveries about brown fat too! They could be very important for human health. Thank you very much for the comment and the votes.

Linda Crampton (author) from British Columbia, Canada on January 15, 2012:

Thank you for the visit and the comment, RNMSN!

Christina Lornemark from Sweden on January 15, 2012:

Very interesting article and it will also be interesting to know more about brown fat in the future! I don't think I have so much of the brown fat, since I always feel cold, especially during winter!

This is amazing news about the human body and you did a great job explaining!

Thanks, voted up, interesting,

Tina

Barbara Bethard from Tucson, Az on January 15, 2012:

very interesting!