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Walk, Walk, Walk; Take Advantage of The Chilly Early Mornings!

Over the past 3 decades, scientists have discovered natural molecules in the body which influence your appetite and our metabolism—and, hence, your weight. Your muscle cells need energy when they are activated. That energy comes from burning fat and sugar in the blood. This has been known for over a century but that's not the whole story.

Nearly a decade ago, scientists of Harvard Medical School discovered that when you exercise, your body chemistry changes. The exercising muscle produces a hormone called irisin.

You've known for some time that a regular program of moderate exercise protects you against type 2 diabetes. For example, a lifestyle program that included regular moderate exercise reduced the risk of developing type 2 diabetes by nearly 60%—more than any medicine yet invented.

How does that happen? Irisin may be an important part of the answer. In addition to its effect in creating brown fat cells, it also helps prevent or overcome insulin resistance, which leads to type 2 diabetes. Although these studies were made on mice, irisin have been found in humans too. While not yet proven, it is very likely that irisin has similar effects in humans.

Yes, other medicines with a similar promise have come and gone. However, irisin is not an unnatural pharmaceutical. Theoretically, the discovery of irisin as part of our natural body chemistry, could have some very practical and beneficial applications, becoming a possible treatment to maintain a healthy body weight and reduce the risk of diabetes. So there is justifiable excitement about the discovery of irisin, and about the speed with which science is discovering the chemistry of exercise, appetite, metabolic rate and body weight. However, our environment, and its effect on our own behavior, plays a huge role in determining how much we exercise and how much we eat, and therefore how much we weigh.

Body fat has always been villainized; but all fat is not created equal.

We all know that the body fat is stored inside fat cells. Our two main types of fat—brown and white—play different roles. Most of the fat cells are white fat cells, and their function is to store fat.

Why do we store fat?

When we eat more calories than we burn, the extra calories are stored partly as fat. The biologic reason is simple: Our distant ancestors didn't eat as regularly as we do. Thousands of years ago, our hunter-gatherer ancestors were able to get a serious meal only a few times every other week. In between meals, they needed some source of energy. A large part of that energy came from the fat they stored away after a meal.

Brown Fat Cells

Babies are born with rich stores of brown fat (about 5% of total body mass) on the upper spine and shoulders to keep them warm. Scientists used to believe that only babies had brown fat. They also thought that this brown fat disappeared by the time most people reached adulthood. In 2009, scientists discovered the presence of small reserves of active brown fat around the shoulders and neck in human adults. It used to be thought that brown fat disappeared by adulthood—but it turns out we harbor small reserves in our shoulders and neck.

BAT is a specialized fat depot that stores energy in a smaller space than white fat. and can increase energy expenditure and. Brown fat expansion and/or activation results in heat production and increased energy expenditure, creates a negative energy balance and limits weight gain. Why would we want to change white fat into brown? White fat stores energy as large fat droplets, while brown fat has much smaller droplets and is specialized to burn them, yielding heat. Brown fat cells are packed with energy generating powerhouses called "mitochondria that contain iron"—which gives them their brown color.

The brown color is also referred to as inducible brown adipose tissue (BAT).

 Credit: Patrick Seale, University of Pennsylvania School of Medicine
Brown fat cells (stained brown with antibodies against the brown fat-specific protein Ucp1) nestled in amongst white fat cells.

Increasing browning may be an efficient way to increase whole brown fat activity. AND conveniently, prolonged cold exposure can induce browning of white adipose tissue.

NIH-funded research discovered that the body can recruit white fat and transform it into brown fat. It was also discovered that the development of brown fat can be triggered by a genetic switch.

In mice, brown fat does something remarkable: it burns more calories when mice are overfed, protecting them from obesity. (Don’t you wish eating a plate of fries did that for you?) Furthermore, mice genetically predisposed to have with extra brown fat are actually leaner and healthier. In humans, there is evidence that more brown fat is associated with a lower body weight.

So, how else might we increase our brown fat production besides taking cold morning walks and cold morning showers?

The team led by the University of Pennsylvania figured out the switch for creating a brown fat cell—a protein called early B cell factor-2 (Ebf2). Comparing the active genes in brown and white fat cells, they discovered Ebf2 is present in larger quantities in brown fat. This protein seems to mark which genes will later be turned on to transform certain types of precursor cells into brown fat. When the team engineered mice lacking this protein, the animals had white fat cells on their upper back and spine rather than the typical brown. When the team expressed high levels of Ebf2 in white fat, these cells turned brown and consumed more oxygen—a sign they were producing more heat.

The second team, led by Harvard’s Joslin Diabetes Center, noted that mice have two types of brown fat: "constitutive" brown fat, which they have from birth, and “recruitable” brown fat, scattered throughout the muscles and white fat. Under the right circumstances, the “recruitable” fat cells can change to brown fat.

When researchers engineered mice lacking a protein called Type 1A BMP-receptor (BMPR1A) —which is needed for the correct development of brown fat— the mice were born with just a tiny bit of constitutive brown fat on their back. You would think that these mice would be terribly cold. Surprisingly, they kept a normal body temperature. How did they manage this feat? The lack of brown fat apparently sends a signal via the brain to the “recruitable” fat cells, telling them to make the switch and transform into brown fat. The mice stayed warm, and the recruited brown fat even protected them from obesity.

In humans, too much abdominal white fat promotes heart disease, diabetes, and many other metabolic diseases. It would be potentially therapeutic if we could transform some of our white fat into brown. Determining which genes control the development of white and brown fat may be the first step toward developing game changing treatments for diabetes and obesity.

Brown fat is highly regarded as a possible treatment for obesity and some metabolic syndromes.

If your goal is to lose weight, you want to increase the number of your brown fat cells and to decrease your white fat cells. Brown fat cells don't store fat: they burn fat. Those newly-created brown fat cells keep burning calories after your exercise is over. Remember! Prolonged cold exposure can induce browning of white adipose tissue. Sooo, take your cold morning walks!


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