The Mystery of Metabolism

A reader asked me to explain further about "The Dieter's Law" or the first law of thermodynamics. This law states, "Energy cannot be created or destroyed; it can only be transformed into another form of energy".

According to the University of California's nutrition manual, the simplest way to remember the law is "If you eat it and don't burn it, you sit on it", which is a tactful way of saying that if you eat too many cookies, they may end up on your behind if you don't burn them.

The reader wanted to know how the law applies to people who eat a lot and don't exercise but don't seem to put on a pound. He said, "The output does not match input but they don't gain weight. What happens to all the calories they eat? Where do those calories go?"

I'm sure people at the other end of the spectrum, those who watch what they eat and who exercise a lot but have a hard time losing weight, would also like to know how the law of thermodynamics applies to them.

For some people, losing or gaining weight is pretty straightforward. Eat more than you need and/or exercise less than you are used to and you gain weight. Eat less than you need and/or exercise more than you are used to and you lose weight. These people are classic examples of the law of thermodynamics at work.

However, for other people things are a little more complicated than that. Some people seem to make calories vanish into thin air. These are the people who can eat as much as they want and not gain weight. Other people only need to look at a piece of cake and miraculously the calories appear on their hips.

This does not mean that the bodies of these people are defying the law of thermodynamics. The calories that these people are eating are either being burned or stored. Calories do not just appear out of nowhere or disappear into nowhere. What it means is that the body has an amazing ability to increase or decrease metabolism depending on the type of genes you have and how those genes respond to your environment.

There is still a lot that is mysterious about how the body manipulates its metabolic rate and only future research will fully uncover the truth and perhaps develop a way to control raise and lower metabolism to help people lose or gain weight more easily. Here are some theories about human metabolism.

Even when you are lying motionless, your body continues to burn calories so that your brain can think, your heart can pump, your lungs can breathe, your body can stay warm, you can digest your food, and you can repair your cells. The rate at which you burn these "housekeeping" calories is what is known as your basal metabolic rate or your resting metabolism.

Dr. Eric Ravussin is a leading researcher in the field of metabolism. In one of his studies, he put people inside a 'calorie-measuring' room that measured how many calories they consumed by analysing their breath. He measured their resting metabolism by making them lie down for 40 minutes without moving. He found that people with the same weight, height, and body shape can burn different amounts of energy each day. He found ranges of 1,067 to 3,501 calories per day.

Ravussin believes that one explanation for this large range of difference is nerves. He explains that since nerves control things like muscle tension, breathing, and heart rate, people who are the nervous or "hyper" type probably have nerves that run at a higher level than everyone else's and, therefore, burn more calories even when they are forced to lie still.

Another explanation for the difference in metabolic rate is the body composition theory. Your body is divided into 'fat mass' and 'lean body mass' (also called 'fat-free mass'). Lean mass is everything in your body that is not fat - muscle, bones, blood, organs, skin, hair, teeth, etc.

Lean mass is highly metabolic meaning it requires many calories to maintain itself. Your internal organs like your brain, kidneys and liver are working non-stop and need fuel to keep going. Muscles, including the heart, are also 'calorie-hungry'. People with a higher lean body mass or more muscle mass will have a faster metabolic rate. Researchers at Tufts University in Boston have found a significant similarity in lean body mass, especially muscle, in members of the same families implying that there is a genetic component involved.

Ravussin also discovered that the tendency to have a slow or fast metabolism runs in families. Members of the same family tended to have the same metabolic rate.

Another metabolism expert, Dr. Claude Bouchard, confirms that weight gain appears to be influenced by genetic factors. In his study, twelve pairs of lean young male twins were fed 1,000 extra calories for 100 days. Theoretically, they should have all gained the same amount of weight - approximately 29 pounds since it takes 3,500 extra calories to make one pound of fat. Instead, each twin pair gained almost exactly the same weight in the same place (upper bodies, abdomen, legs, etc.) but there was a 91/2 to 29-pound difference between the twelve pairs.

Another explanation for why people burn calories differently is called the "fidget factor". Fidgeting is spontaneous physical activity or movement made without thinking. Examples of fidgeting are twirling your hair as you talk on the phone or jiggling your leg as you work at your desk.

In his calorie-measuring room experiment, Ravussin installed motion detectors to monitor how much movement the study participants made. He discovered there is a big difference in the way people perform an everyday activity like watching TV. Some people sat as still as statues without moving a muscle. Others couldn't stop from changing position every so often. Others kept getting up and moving around the room. Ravussin calculated that fidgeting alone could burn anywhere from 300 to 800 calories a day. He found that the tendency to fidget or to be restless also ran in families.

In another experiment at the Mayo Clinic in Minnesota, researchers James Levine and Norman Eberhardt found that people who fidget while seated burn 40 to 60 more calories compared to people who sit motionless. Fidgeters burn 70 to 100 calories more per hour when they stand compared to laid-back people who stand still.

To find out how much of a role fidgeting plays in weight gain, Levine and his team fed 16 normal weight sedentary men and women an extra 1,000 calories a day for two months. The participants gained between 2 to 16 pounds. The ones who gained the least were the ones who did the most fidgeting.

The last explanation for calories that just seem to evaporate is called "facultative thermogenesis" or heat production not related to resting metabolic rate. It seems that some people are "efficient" (from a survival standpoint) calorie burners and store most excess calories as fat or fuel for the future. Others are "inefficient" calorie burners and "waste" the excess calories as body heat. No one can fully explain the mechanism behind this. Some think it is related to the "brown fat theory". Brown fat is a special kind of fat that helps regulate body temperature. How much brown fat you have depends again on your genes. Judith Wurtman of the Massachusetts Institute of Technology found that the more obese the person, the less active the brown fat cells were. However, she also noted that exercise increases brown fat activity.

A related theory is that heat is always escaping from the core of your body through your skin out to the environment. People who are tall, lean and lanky have more skin surface area than people who are short and stocky and, thus, burn more calories because more heat is escaping through their skin.

So the law of thermodynamics applies to everyone. Some people are just better calorie burners than others. It's difficult to change your basal metabolic rate but there are some things that you can do and some things that you should avoid to make the most of your unique metabolism to help you lose weight.

Your body conserves energy by lowering your metabolism when it has not eaten for quite some time. So skipping breakfast, skipping meals, and going on starvation diets are counter-productive to weight loss. Not only do you keep your body in a prolonged lowered metabolic state, the tendency is to eventually give in and binge.

Studies show that severe dieting and regular meal skipping will result in some muscle loss as the body "cannibalizes" muscles fibers for additional energy. The less muscle you have, the lower your metabolism.

The good news is that metabolism is not permanently lowered. It eventually bounces back when the dieter goes back to more normal eating patterns. The bad news is it takes quite a while for muscle mass to return to normal and by that time, most dieters of very low calorie diets end up putting on more weight than they started with because the body "over-responds" to the previous famine-like state by increasing fat storing enzymes and other metabolic mechanisms to store as much fat as possible. Not to mention the fact that food deprivation leads to increased appetite and big-time bingeing.

Lifting weights or some other type of resistance exercise like rubber bands, yoga, aqua exercise, or Pilates with machines is a good idea to build more muscle mass to rev up your natural metabolic rate. Resistance or strength exercise is even more important as people age because muscles atrophy from disuse the older one gets. Loss of muscle mass is one reason why middle-aged people find themselves gaining weight in spite of eating the same amount they used to while they were young.

Lastly, someone with a slower metabolism would benefit greatly from trying to be as physically active as possible throughout the day to burn calories instead of storing them. You may not be a natural-born fidgeter but you can burn calories as if you were one by following the advice of Frank Butterfield of the American Council of Exercise: "Sitting up is better than lying down, standing is better than sitting up, and walking is better than standing".

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