Thermogenesis

by Dr. Fred Spencer, DMD

Thermogenesis really has to do with energy. The concept is pretty well accepted that energy is neither created nor destroyed. Energy is transformed, converted, transported, and stored. In the human body it is the same way. Our energy comes into our body as food that we eat. Everyone knows the measure of the energy is in calories. A calorie is the amount of heat needed to heat one gram of water one degree Celsius. Calories are the energy stored in food. As we take it into the body, energy is either transformed or stored.

As it goes through the system, some energy leaves the body as fecal energy. That energy can not be counted. Other energy is lost through the urinary system. What is not lost in these two ways is available for metabolism. One of the biggest energy expenditures in the human body is thermic (heat) energy. Thermic energy differentiates an endoderm (mammal), which humans are, from an ectoderm (reptile). The endoderm's basal metabolism is 8 to 10 times higher than for an ectoderm. So tremendous amounts of the energy that we use is for thermic energy. That which is not used for thermic energy is then available as net energy for the body's cellular reproduction, growth (especially in children), work (muscle movement), and storage. We all know the common storage form is fat.

Thermogenesis means the creation of heat. There are three types of thermogenesis. The first kind is work-induced from exercise. It is necessary for our muscles to create heat because warm muscles work much more effectively than cold muscles. The next form is called thermo-regulatory thermogenesis. This is involved with keeping the temperature of the human body regulated. The average body temperature is 98.7 degrees (F), which is quite a bit higher than the ambient (surrounding) temperature in most cases. There are two types of thermo-regulatory thermogenesis: shivering and non-shivering. Shivering helps the body create heat. The skeletal muscles create the shivering. There's a little muscle on each hair that helps to create a better blanket for us. The shivering heats up the body. The non-shivering thermogenesis fits into the third classification, which is called diet-induced thermogenesis.

When you eat a large meal, you start to get hot and sweaty. You might have to loosen your tie, or other clothing. That's called diet-induced thermogenesis. That comes into play mostly because we're going to need more energy to digest this food that we're eating. There are centers in the body that can measure this. So, we go to non-shivering and diet-induced thermogenesis. The main organ responsible for this mechanism in humans as well as other mammals is the brown fat tissue. This diet-induced thermogenesis is very important in animals that hibernate, such as bears, or small animals with a very large surface area compared to body weight. Brown adipose tissue is also very prevalent in newborn babies, who exhibit tremendous amounts of non-shivering thermogenesis to regulate their body temperature. As we grow older, this system depletes a little bit, but it stays with us.

It's also important to know that the brown fat (adipose tissue) is located around blood vessels and major organs. When it is triggered into activity, it causes the warming of the blood and then the warm blood can be circulated throughout the body to spread this warmth.

The thermogenic system of the body is fascinating. It is triggered by the sympathetic nervous system. Under conditions of cold or eating a lot of food, the hypothalamus gland can register this and then trigger the sympathetic nervous system, which is an automatic nervous system. The sympathetic nervous system controls many things, such as heartbeat and breathing, that we are not normally conscious of. The autonomic (automatic) nervous system uses up energy all the time.

In the area where the nerves transmit altogether, there is a chemical transmitter called neuroepinephrine. The triggering of the sympathetic nervous system causes neuroepinephrine to be released from the synapse and accepted by the receptors on the other side. So this happens in the sympathetic nervous system: a release of neuroepinephrine from the one dendrite across the synapse and activate a nerve impulse.

This then turns up the thermogenesis as well as other activities generated by the nervous system. It's important to note that thermogenesis is one of the very important parts that uses up energy as this is happening. It's kind of turning up the thermostat on the body. We all have a basal metabolism which can be measured by a doctor or scientist and tells us how much activity or energy is consumed just by running our body. We can turn up the thermostat.

I have talked to quite a few people who say they have experienced an increase in sweating. If we turn up the thermostat, we're causing more of the energy we take in to go into thermogenesis as well as other areas of the sympathetic system, so less of the energy is used in work and less is used for storage and less goes to fat. The brown fat is activated, and it calls into service the white cells, which are the primary storage of fat in the body.

Although we have a consistent number of fat cells, the size can vary tremendously. The number remains the same, but the size changes.

Interestingly enough, one of the consequences of thermogenesis is a loss of appetite. If I'm not as hungry, I'm not going to eat as much. The same thing for exercise; when the thermostat is turned up, the metabolism is up, and I'll feel more energy. So, when people feel they have more energy, they will be able to do more, which will also help them to utilize fat.

The brown fat cell is unique in its mitochondria. The mitochondria is the energy source, or power plant. In the brown fat cell, the unique mitochondria helps it create energy. The brown fat cell is a real energy burner and really burns heat. Part of the problem of human obesity has very little to do with eating habits as much as it does with brown fat cell deterioration.

They have and are now conducting studies on human obesity. They are speculating that part of the problem with human obesity lies in the amount of adipose tissue activity. They've done studies with people as far as foods eaten and energy produced in lean and obese people and have found a difference in the amount of brown fat activity. Post-obese people still have a deficiency in the brown fat system. So it must either be rebuilt or they must always be careful about their diet.

The average person may never have heard the word "thermogenesis" and may need to have it explained. The knowledge for this comes out of physiology books, and another book which is called "Mammalian Thermogenesis." This is the basis of my theories.

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