by Gina Scarano-Osika, Ph.D.

Physiology and Why You'll Never Say "Diet" Again

In reading about the endocrine system, I was continually awestruck at how intricate and delicate the system is; yet, its mission determines life or death. This section introduces the endocrine system and describes how it executes its mission to enhance survival. Concepts presented here will be sprinkled throughout future chapters so that you can then see weight loss as involving an intricate system involving the mind and the body. A little knowledge about this hormonal scenario will hopefully help you understand why fad diets will never work over the long term.

Basal Metabolic Rate (BMR or metabolism) is the amount of energy (usually measured in calories) that the body requires during a typical day. A fully functional and healthy body requires a specific amount of energy to produce brain waves, to move muscles, and to speak in sentences.Even when you sleep, your body is very active and using fuel. Even if you lay on the couch all day, your body needs fuel (food) to sustain life.

Twenty-four hours per day and seven days a week, our bodies are using food for fuel to execute all vital and non-vital bodily functions, each of which require a specific amount of fuel. Vital bodily functions are those upon which life is immediately dependent upon. Examples of a vital bodily function are when you breathe, when your heart pumps, and when blood circulates. Without these functions, life will immediately cease. A non-vital function is any bodily system without which the body can remain alive. Examples include excretion, digestion, our immune functions, and reproduction.You will need the most amount of fuel if all vital and non-vital functions are fully functional.

Your BMR is analogous to the fuse box in your home. Usually, our houses are powered by a seemingly unlimited supply of power. We don't have to worry about picking and choosing whether we want the refrigerator or the vacuum cleaner to run at any given time. We typically don't have to worry about our lights blacking out because we are running our dishwasher. A fully functional body has both vital and non-vital bodily systems running at full capacity. This, however, requires a limitless supply of calories or fuel (food) and is an indication of health. Formulas to calculate your approximate BMR follow. Please understand that this formula for BMR represents the number of calories your body requires without additional physical exercise; if you exercise regularly, your body will require more fuel based on the duration and intensity of the exercise.

BMR for women= [weight (lbs.) X 10] + weight (lbs.)
For example:
The BMR of a 250 lb. woman = [250 X 10] + 250 = 2750 calories

BMR for men= [weight (lbs.) X 10] + [weight (lbs.) X 2]
For example:
The BMR of a 250 lb. man = [250 X 10] + 250 X 2 = 3000 calories

There exist digital scales that calculate your BMR based on your age, height, gender, activity level and body fat percentage. Keep in mind that, in theory, these scales should theoretically be more accurate than the formula method because your muscle mass is being accounted for when you calculate BMR via digital scales; the BMR formula above only takes into account overall weight. More specifically, when using the BMR formula, two men who weigh 250 pounds will have a BMR that is identical, regardless of how "fit" they are. When using the scales to calculate BMR, a more "fit" person will generate a higher BMR (as compared to a man of the same body weight who is unfit) because the "fit" man's poundage is mostly muscle, a factor that is accounted for during the scale's calculation.

When the power supplied to our homes is limited or interrupted, electricity may temporarily need to be produced by a generator. The problem is that a generator can only produce a certain amount of power at any given time. Consequently, when using a generator, you must manually control the fuse box by turning on and off the various appliances and other amenities that you would like to use.For example, if you want to vacuum the house, you may need to turn off the lights and furnace for a while. You may not have enough energy to use the automatic dishwasher and the clothes washer at the same time. You have to pick and choose which household appliances are most needed at any given time. As you can imagine when the energy supply is limited, survival depends upon keeping your priorities straight. If you wash load after load of clothes, your perishable foods may expire and you may become unbearably cold in the house. The endocrine system is responsible for choosing which non-vital bodily systems to "shut down" during times of stress.

The Physiology of Stress Induced by Fasting. The endocrine system determines which non-vital system will be turned off in order to conserve fuel.This process is called physiological adaptation and is a survival mechanism used by both animal and human species since the beginning of time. The purpose of adaptation is to help the body maintain homeostasis or a "steady state". Whenever this "steady state" is threatened, an organism is considered to be "stressed" and the endocrine system begins to analyze the stress and makes bodily adjustments based on the immediate needs. This adaptive stress response attempts to help the organism regain a homeostatic state, thus enhancing survival rates. The hypothalamus is responsible for executing these endocrine processes.

The hypothalamus is the command center of the brain, the dictator of the endocrine system, and responsible for the successful execution of physiological adaptation. Based on environmental conditions and the needs of the body, the hypothalamus tells which vital organ to do what and when. The hypothalamus continually monitors the environment and makes internal changes designed to maximize survival and maintain a homeostatic state. The hypothalamus is like an air traffic controller who is continually on watch, assessing the weather, wind velocity, and volume of air traffic.If it's too windy, he guides planes down differently than if it is calm. If it is icy, he puts planes on a different route in order to avoid accidents or death. If there are too many planes in close proximity, he tells each plane to take some alternative route. Like an air traffic controller, the hypothalamus is directly responsible for survival under unstable or threatening conditions.

The hypothalamus "talks" to vital organs via hormone secretions, which are little messengers which travel around your blood stream telling each vital organ what to do and when. By way of hormone secretion, the hypothalamus executes or suspends the functions of each vital organ. The hormones don't ask why, they just do what the hypothalamus tells them to.There are dozens of hormones, each secreted from distinct receptor cites and each with a distinct job to do. For example, the hypothalamus regulates the hormonal fluctuations involved in the female reproductive cycle. The hypothalamus releases hormones which tinker with levels of neurotransmitters in the brain, which are responsible for mood regulation. All of this occurs invisibly and effortlessly, with only one goal in mind: survival during times of stress.

Cortisol is referred to as the "stress hormone"since it is solely responsible for stimulating a hormonal sequence designed to improve survival rates when a species is threatened. Cortisol is the stress hormone, which is automatically secreted when we are stressed and has been documented to be elevated in anorexics and those undergoing intense military training. Abnormally high cortisol levels have also been documented in non-dominant fish species, hibernating bears, and injured animals. Animal studies tell us that cortisol spikes just prior to hibernation, when a smaller animal is being chased by a larger one, or when an animal is injured and can't get to food or water. Animal studies have confirmed that cortisol is elevated during the breeding season, captivity, and in overcrowded living conditions.

Cortisol affects the body in two substantial ways. The major effect of cortisol is on glucose metabolism, which places it in a larger class of hormones called glucocorticoids. In short, glucocorticoids set off a process whereby glucose is internally produced in order to assure that the threatened species has a sufficient and never ending supply of energy available, regardless of eating. Cortisol enhances survival because it immediately transforms muscle mass into blood glucose (or fuel) to fight a perceived threat. Elevated blood glucose enhances survival because the brain has a seemingly endless supply of energy to feed itself and fully execute all vital functions. Cortisol sets off an immediate internal "domino effect" to ensure survival. When the mind or body is stressed, cortisol prepares the body for "fight or flight" by supplying glucose internally as converted from lean muscle mass. In animals, elevated glucose levels help animals to run (or fly) from the larger animal trying to move up the food chain.

In addition to increasing the supply of glucose, cortisol simultaneously shuts down non-vital bodily functions in order to reduce the body's overall metabolism. That way, the body can fight the stress for an even longer period of time. Cortisol temporarily suspends or slows non-essential functions such as reproduction, digestion, immunity, and growth. This temporary "shut down" helps maximize the nutrients and bodily resources available to the ailing body in the hopes that the stress will be brief.So, in addition to increasing the amount of glucose available, cortisol increases survival by being sure that all vital bodily functions are the main recipients of the glucose. Cortisol helps the endocrine system "keep its priorities straight" so to speak.

The sequence of cortisol's effects follow. Instead of glucose being supplied by just food intake, cortisol triggers muscle tissue and stored body fat to metabolize and travel to the liver where they are transformed into glucose. After the glucose is released into the bloodstream, Cortisol inhibits glucose from being absorbed by muscle tissue (i.e., the uptake mechanisms are shut off), which results in large amounts of glucose floating freely in the bloodstream.This "free floating" glucose is a state similar to the elevated blood glucose levels typical of diabetes.In order to further conserve energy, cortisol then inhibits or slows other metabolic functions like bone formation, calcium absorption, and wound healing. In this way the endocrine system and it's hormonal messengers (led by cortisol) play a vital role in helping all species survive hostile predators and adapt to intolerable environmental conditions (e.g., excruciating heat or dehydration).So, this one hormone is responsible for the loss of lean muscle mass, the internal production of glucose, and the shutting down of bodily systems, all of which dramatically reduce BMR and can have devastating effects on weight control. Examples of this stress response are best exemplified with examples from the animal kingdom.

If an animal has a broken leg and is unable to search for food, they are more likely to starve to death than die from the broken leg itself. Consequently, the hypothalamus makes a number of critical adjustments to help that animal conserve energy and create it's own internal fuel source. The hypothalamus puts the animal into an internal state similar to that of the hibernating bear. Internal muscle and fat mass are used as an alternative source of fuel so that the digestive process is no longer needed. Other non-vital functions such as immunity and reproduction will also be shut down. In this way, survival is enhanced because the body will temporarily require less fuel and use it's own muscle mass as an internal fuel source. If this state is prolonged, however, you can see how this animal would be at high risk for infection, illness, or infertility.

There exists a mountain of research supporting the genetic link to obesity. Cortisol plays a part here as well.Cortisol is suspected to bind to a cells DNA, resulting in a permanent change in the cells phenotype, or genetic expression. These changes, then, are permanently passed on through the generations. So, not only does cortisol help with the immediate effects of stress, but it predisposes the next generation of species to do the same. The role that heredity plays in passing on obesity genes is supported by this link. Cortisol studies are beginning to look at cortisol levels in humans. There are a handful of research studies which tell us that cortisol is elevated in people with acute Bulimia, Anorexia, and Army Rangers completing an 8 week intensive training course. These studies confirm cortisol's shut down of reproductive hormones and other non-vital systems. For the Army Rangers, in addition to elevated cortisol, testosterone levels reached "castration" levels and growth hormones were virtually nonexistent. The reproductive hormones for women with ammenoreah (without menstruation) are well below an adequate threshold and, correspondingly, they have above average cortisol levels.

Studies of Army Rangers and French Commandos suggest that large discrepancies between calorie intake and energy requirements, stimulates cortisol secretion.For example, in order to fuel their 14 hours of intense physical activity, French Commandos required about 10,000 calories of food per day. Cortisol secretions were well above average for this group as their calorie intake averaged about 4,000 calories per day. The same appears to be true for Army Rangers: a mere 1500-calorie deficit per day elevated levels of serum cortisol. It would make sense then, that cortisol levels are also elevated in Anorexic and Bulimic women who are dieting unnecessarily. Keep in mind, however, that in all cases, as refeeding begins, growth and reproductive hormone levels return to normal, suggesting that although intense, the effects of cortisol are not permanent.