What Is Brown Adipose Tissue?
Brown adipose tissue (BAT) is a type of body fat that exists primarily in humans and other mammals. BAT is found throughout the body, but it’s most prominent location are in your legs and feet. There are two types of BAT: brown fat and white fat. White fat cells produce heat through chemical reactions called thermogenesis or “browning.” They burn energy from food and oxygen through aerobic metabolism. Your body produces its own supply of brown fat cells, which you don’t need. However, if you exercise regularly enough, your body will start producing more of them to keep warm during cold weather.
The amount of BAT varies greatly between individuals and depends on many factors such as age, gender, physical activity level and genetics. Some studies have shown that women tend to have more BAT than men do.
How Does BAT Work?
Your body uses BAT to regulate your core temperature. When you’re active, your muscles use up calories while you move around. These calories must come from somewhere so they go into creating heat inside your body. If there isn’t enough heat in the house, then the refrigerator might work, but not if it’s freezing outside! Your body uses brown fat cells to make extra energy to compensate for these metabolic changes.
Your body doesn’t want to waste energy though. That’s why the brain is in control of where the heat comes from. If you’re standing around, your muscles are using up a lot of energy just standing there. If you’re sitting down or lying in bed, your muscles aren’t burning as many calories. The brain regulates this by turning on or off brown fat cells in your body.
The more active you are, the more calories your muscles burn. The brain turns on more brown fat cells to help keep you warm. The more sedentary you are, the less active your muscles are, so the brain turns off brown fat cells to conserve energy.
When Does Brown Fat Develop in a Fetus?
The primary development of brown fat happens during the second trimester of pregnancy. Unfortunately, after the baby is born, most of this BAT either disappears or becomes inactive. If a child interacts with cold temperatures a lot, then they may retain some of these brown fat cells as adults.
Does Cold Temperatures Turn On Brown Fat?
There are several theories about why cold temperatures turn on this specific type of fat cell. Brown fat is activated when exposed to certain hormones or the nervous system. This type of fat can be stimulated to burn more calories when the body is exposed to cold temperatures, which may protect the body from hypothermia.
Another theory suggests that brown fat develops as an evolutionary defense against hypothermia. If a mammal is exposed to cold temperatures, then this type of fat can help keep them warm and protect them from dying.
How Effective is Brown Fat in Regulating Body Temperature?
Most of the time, brown fat cells are inactive in adults. If a person is exposed to cold temperatures, there are a variety of events that occur before these cells become active. First of all, a nerve impulse travels from the brain to the brown fat cell. The cell then responds by either pumping out heat or not pumping out heat based on the command from the brain.
These cells can also be stimulated to produce heat by the hormone norepinephrine. Similar to the nervous system, when a certain amount is reached, the brown fat cells begin to pump out more heat. Norepinephrine and the nervous system do not always have an effect on the brown fat cell though. This only happens in response to cold temperatures.
What Determines How Many Brown Fat Cells a Person Has?
There is still a lot to learn about this type of fat and how it works. However, there are some things that science has discovered about brown fat and why some people have more than others.
When a child is still in the womb, they are not able to shiver if they get cold. Because of this, brown fat cells develop in order to generate heat to protect the body. The more brown fat cells that a person has, the easier it is for them to stay warm. The number of these cells usually decline after the age of three, but the ones that are left can play a role in an adult’s ability to regulate body temperature.
This type of fat can be more common in males than in females. It might also be more common in people who naturally have high body temperatures.
Does Weight Affect How Many Brown Fat Cells a Person Has?
The amount of brown fat a person has is not affected by their weight. Even if a person is overweight, they can still have an average amount of brown fat, or even more than an average person.
Sources & references used in this article:
Brown adipose tissue and heat production in the newborn infant. by W Aherne, D Hull – Journal of Pathology and Bacteriology, 1966 – cabdirect.org
Brown adipose tissue. by O Lindberg – 1970 – cabdirect.org
The absence of brown adipose tissue in birds. by DW Johnston – Comparative Biochemistry and Physiology, 1971 – cabdirect.org
Brown adipose tissue in morbidly obese subjects by GHEJ Vijgen, ND Bouvy, GJJ Teule, B Brans… – PloS one, 2011 – journals.plos.org
The lowering of basal metabolism by the brown adipose tissue of the hibernating hedgehog and by prolan. by CF Wendt – Hoppe-Seyler’s Zeitschrift fur physiologische Chemie, 1943 – cabdirect.org
Control of fatty-acid oxidation in brown-adipose-tissue mitochondria. by B Cannon – European Journal of Biochemistry, 1971 – cabdirect.org
Studies with Cultured Brown Adipose Tissue. I. Persistence of Rabies Virus in Bat Brown Fat. by R Allen, RA Sims, SE Sulkin – American journal of hygiene, 1964 – cabdirect.org