Basics of Human Body Weight Control – Fact and Fiction

Introduction

In 2006 I was diagnosed with celiac disease, which damages the body’s ability to absorb nutrients and calories. Fortunately, on a gluten-free diet, I have the disease under control and am able to live a normal life. However, on a gluten-free diet, my gastrointestinal system has started working a lot more efficiently and I’ve had to start limiting my daily caloric intake, in addition to exercise, to manage my weight for the first time in my life. So with a more efficient digestive system, I’ve become interested in the biological processes which regulate digestion, absorption, metabolism, and weigh gain and loss. At the same time, I have also become more aware of many popular misconceptions about dieting. There is much bad information floating around. Some of it is due to popular, erroneous traditions and “old wives tales”. Some is due to people who, motivated by greed, “invent” a fad diet, totally without scientific basis, to sell books or DVDs. Some is due to people who, again motivated by greed, come up with a new diet pill, supplement or herbal concoction claiming weight loss benefits. One can also find tons of bad information for free on the internet just because some people feel a need to offer their opinions on various subjects. At the risk of becoming a member of the later category, I’m researching and writing this report, but it is my intent to limit the contents to basic science, verifiable facts and properly vetted clinical research and studies, and to keep my opinions to a minimum. Where I do offer opinion, I have tried to preface it with something like “I think”, “hopefully” or “it seems”. I’m doing the research for this report for myself, but if others can benefit from it also, great!

Disclaimer: I am not a doctor or medical professional, so the following is not intended to constitute medical advice. My attorney made me say that! :-)

Body composition

In the course of trying to understand weight gain and loss, I realized the need to understand body composition, as a prerequisite to understanding weight control. There are several ways to classify human body composition - elemental, chemical, and material being the most common. I will focus mostly on the elemental and chemical. The four most common elements of the body by mass are oxygen, carbon, hydrogen and nitrogen, in that order. In fact, these four elements make up 96% of body weight. It is these elements that comprise the organic compounds which are essential to all life forms.¹ The minerals calcium and phosphorus make up another 3%, totaling 99% of the body’s total weight.

Another way to look at body composition is by its chemical makeup. Most of the body is made up of water, proteins, lipids (fats) and carbohydrates, and all four are required to support life. Of the four, water is by far the most common by weight, comprising 45 – 65% of the body.² Water serves primarily two bodily functions: a solvent for water-soluble compounds and an essential part of many metabolic processes.³ Unlike water, the other three compounds, protein, fats and carbohydrates are capable of storing energy.⁴ Fats have the greatest amount of food energy per gram, 9 calories. Proteins and most carbohydrates have about 4 calories per gram. Carbohydrates that are not easily absorbed, such as fiber, contribute less food energy.

Energy

The most important principle in understanding weight control is the law of conservation of energy which states that the total amount of energy in an isolated system remains constant. A consequence of this law is that energy cannot be created or destroyed. The only things that can happen with energy in an isolated system is that it can change form, that is to say for instance, kinetic energy can become thermal energy ⁵, or it can be moved around within the system. For example, when we apply the brakes to a car, the car’s motion (kinetic energy) is converted to heat (thermal energy) by the friction of brake pads against the brake disk. For the purpose of this analysis, it is necessary to define the “isolated system” very broadly and thusly: the isolated system is defined as an imaginary box which includes the earth and sun. It is necessary to include the sun because when we step outdoors, our bodies absorb energy from the sun in the form of heat.

In the case of a human body, the forms of energy to consider are:

1. Food intake


2. Energy stored in the body


3. Energy transferred from the body in the form of motion


4. Heat energy transferred to the body


5. Heat energy transferred from the body


6. Energy contained in excreted waste

Since energy cannot be created or destroyed, over a fixed period of time the energy absorbed by a human body must always equal the energy stored in the body plus the energy lost by the body. This is absolutely true regardless of the mechanisms of digestion, absorption, metabolism, exercise, etc. or other factors such as disease, time of day of meals, or type of food consumed. Or as I like to say, calories in equals calories out, or more precisely, calories in equals calories out plus calories stored. For those readers who might wish to research this subject further, it is worth knowing a few terms that are used in the scientific literature, especially physiology literature. “Energy balance at low energy flux” refers to the energy equation of a sedentary person who eats just enough to keep his/her weight constant. “Energy balance at high energy flux” refers to the individual who exercises regularly and also eats just enough to keep his/her weight constant. “Positive energy balance” refers to the couch potato who eats more than they burn, and are thus gaining weight. “Negative energy balance” refers to the dieter who is loosing weight.

Since we’re talking about energy, let’s examine how energy is measured. Today, the international standard (SI) unit of energy is the joule, which is the work done by a force of one Newton acting to move an object through a distance of one meter in the direction in which the force is applied.⁶ Other common units of measure of energy are the watt-hour, erg, BTU and calorie. Regardless of the unit, energy is energy, and it can be neither created nor destroyed. For the remainder of this report, we’ll use calories, since that is the most familiar when talking about food energy and body weight. A calorie is the amount of energy required to raise the temperature of one gram of water by 1° C.⁷

So let’s examine the equation further. How can a body absorb energy? There are several ways a human body can absorb energy, but only one practical way to absorb energy and store it for more than a few minutes, and that is through the intake of food. A body can also absorb radiant energy in the forms of heat, light and other forms of radiation such as microwaves and infrared waves. These simply serve to increase body temperature. I could find no source which says that a human body can absorb radiant energy and convert it to fat or other biological storage mediums, so I think it is irrelevant to this paper and not a significant consideration in weight gain and loss analysis. Of the radiant energy sources, the far more significant is heat. A corollary to the 2nd law of thermodynamics is that heat energy will always spontaneously flow from a hot material to a cold material.⁸ This means that a human body in air which is cooler than 98.6 (or the body temperature at the time) will loose thermal energy and a body in air which is hotter than 98.6 will absorb thermal energy. Absorbing thermal energy causes the natural body cooling system to kick in and try to lower body temperature through perspiration. If the body temperature cannot be controlled through this mechanism, and the heat source is not removed death will eventually occur. A human body can also be heated through microwaves, and other forms of radiation, but with microwave doors engineered to keep the radiation inside the unit, this is hopefully never a consideration! I can envision that heating or cooling a body from the normal body temperature could affect the basal metabolic rate (defined below), but I did not research this possible effect.

The main and perhaps only way a human body can absorb and store energy long term is through food intake. Caloric content in food may be precisely measured in the laboratory by burning the food in a closed container and measuring the heat emitted. The more heat emitted, the higher the specific caloric content. The calorie counter lists one finds are created by taking a weighed sample of each listed food and burning it completely until nothing is left but ash. All the energy formerly stored in the food is converted to heat energy and measured.

Body processes

What happens to food after it is eaten? The first process is digestion. This is the body’s conversion of food through chemical reactions to a simpler form which can be absorbed.⁹ Since this is not a medical report, I won’t go into the digestion process, but for the purpose of the discussion, it is adequate to state that some of the calories in ingested food are converted and some aren’t. And some foods are more easily digested than others. The calories digested divided by the calories ingested can be called the digestion ratio. That which isn’t converted to an absorbable form is expelled in the stool.

The next process is the absorption process. Some food which is converted to an absorbable form is absorbed and some isn’t. The calories absorbed divided by the calories digested can be called the absorption ratio. The medical community also talks about speed of motility, which is the speed at which food traverses the GI track and thus can influence how much is absorbed. For simplification I will include motility as part of the absorption process. Before my celiac disease was under control, my stomach was converting food to an absorbable form, but the damaged cilia were not able to absorb it into my body very well, resulting in weight loss regardless of how much I ate. Food energy which isn’t absorbed is expelled in the stool. People may erroneously refer to variations in digestion ratio and absorption ratio as “differences in metabolism”, but neither has anything to do with metabolism.

Metabolism is the process involving a set of chemical reactions that modify a molecule into another for storage, or for immediate use in another reaction or as a by-product.¹⁰ How the human body metabolizes food is a very complex subject involving enzymes, hormones, the pancreas, thyroid, hypothalamus, etc. and is beyond the scope of this report. But it is sufficient for the purpose of understanding weight loss and gain to understand that there are two types of metabolism: 1) that which converts food or stored energy to energy to support life’s processes and enable us to move about and do manual work and 2) that which converts food to stored energy in the form of starch, sugar, protein, fatty acids, and other storage mediums. So if our body absorbs more energy than needed for 1, it is automatically stored as 2, resulting in weight gain.

Another factor worth mentioning is the basal metabolic rate. Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state, meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans. This is also called resting metabolic rate (RMR) in some of the literature. The release of energy at rest is sufficient only for the functioning of the vital organs, such as the heart, lungs, brain and the rest of the nervous system, liver, kidneys, sex organs, muscles and skin.¹¹ BMR varies from individual to individual based on a number of factors, including age, genetics, and exercise.¹² For example, at 80 years old, my dad tended to want to keep the thermostat set on 80 degrees, and as I’ve gotten older, I’ve become more cold-natured, supporting that BMR decreases with age. Someone with a high BMR is going to tend to be more hot-natured because their body burns more energy at rest and expels it in the form of heat, and conversely someone with a low BMR is likely to be cold-natured. It logically follows that everything else being equal, hot-natured individuals should be thinner than cold-natured ones.

Another factor in the energy equation is the energy expended by the digestion, absorption, and metabolism of the food you eat. This is referred to as thermic effect of food (TEF).¹³ It tends to make us feel warmer for some time after consuming a large meal.

Once energy is taken into a body it may be expelled or removed from the body via the following mechanisms:

1. Physical exertion (work)


2. Radiated body heat


3. Radiated infrared energy


4. Expelled heat in the breath


5. Calories in the stool


6. Calories in urine


7. Calories in excised tissue

Physical exertion is the conversion of stored body energy into physical energy, i.e. moving our bodies or moving an object against a force, such as picking up a weight against the force of gravity. Radiated body heat can be due to a couple of mechanisms: 1) heat generated as part of the basal metabolic process and 2) heat generated by the muscles with physical exertion. Radiated infrared energy is probably an insignificant amount, but it is a fact. Just watch some of the night-vision video from Iraq as our troops find and neutralize the bad guys. Military night-vision equipment works by sensing infrared body emissions. So also do infrared motion sensors in our homes. Expelled heat in the breath is probably insignificant, but a finite amount of energy is expelled this way. We become acutely aware of this when on a very cold day, we cup our hands over our mouth to redirect warm breath to our face and nose. Body waste can have significant amounts of energy in the form of methane, combustible solids and heat, and can vary from one individual to another based on disease processes and other factors. An example of the last item is the removal of a limb where the energy content of the limb’s tissue is removed from the body.

There is another process which has nothing to do with the energy equation but which directly affects body weight and that is mass transfer. An example of this is the loss of body weight through perspiration, resulting in dehydration. I personally can loose up to 5 pounds of water during a hard day’s work on a hot day. On the flip side, eating a heavy meal temporarily adds the weight of the meal to the body, some of which is usually water. For these reasons, it is important when tracking weight to weigh at the same time each day consistently either before or after a given daily meal and not after a long, hot day outside.

When a dieter begins to loose weight, there are a couple of effects on metabolism. Obviously, it takes less energy to propel a smaller, lighter-weight body. This is simple thermodynamics. For example it takes fewer calories to move around a 150 pound body weight than a 200 pound body weight. This means that if for example one suddenly reduces daily caloric intake from 2000 to 1500 calories and maintains that intake and exercise pattern over time, the absolute weight loss in the 8th week will be less than in the 1st week because the body is loosing weight and becoming more efficient. Another effect is a reduction in the basic metabolic rate.¹⁴ This is a physiological response to attempt to conserve energy and is the body’s natural defense against starvation. A well-documented effect of this is anorexia nervosa patients being cold much the time.¹⁵ Both of these effects work against the dieter. But the first one is desirable if weight loss is the goal. The second one, not so much, because it could signal the beginning of starvation.

Weight control

So what does this all mean and what can we control? And what myths can we debunk?

Since energy can be neither created nor destroyed, if we eat more calories that we burn, we’ll gain weight. We can control our caloric intake and our exercise. That’s about it. Be wary of any claims you might read on the internet, in dieting books, on supplement bottles or elsewhere which don’t involve one or both of these two controls. If claims seem too good to be true, they probably are.

Myths and dubious claims:

Metabolism boosters – These range from the intriguing to the ridiculous. One such claim is that eating grapefruit will help burn fat. There is no scientific evidence that any of these work. If such a simple weight control device were proven, it would be a breakthrough report in a reputable medical journal and front page news on all the popular media. But don’t hold your breath. Of the body’s three types of metabolism: exercise, thermic effect of food and basal metabolic rate, it seems that the BMR is the only one which could possibly be chemically affected. Artificially increasing the BMR would increase the heat generated by the body, and I think the resulting hot flashes would be very unpleasant. For this reason metabolism boosters just seem to be theoretically unviable to any significant extent. I sampled some of the many “metabolism booster” listings on the internet, and started noticing two things: either 1) the product recommendations include diet and/or exercise in conjunction with usage, or 2) many of the reviews by those who claimed success, also claimed to have started exercising, dieting or both at the same time.

Eating close to bedtime causes weight gain – As the science discussed above suggests, weight gain is caused by ingesting more calories than are expended. Even though it is true that metabolism while asleep is at its lowest, any calories stored in the body during the night can be burned the next day just as easily as they could have the evening before. See “Myth: Eating after 8 p.m. causes weight gain”¹⁶

Certain herbs can burn off calories or naturally cleanse the system – The 1986 State of California injunction against Herbalife is a good example of science’s and the law’s view of this claim. Herbalife was permanently enjoined from “Representing that defendants' products contain herbs: (1) which in and of themselves naturally curb the appetite; (2) which burn off calories; or, (3) which naturally cleanse the system.”¹⁷

Laxatives to loose weight – I could find no scientific evidence that this will work, and lots of opinions that long-term laxative use can be dangerous. The one clinical trial I did find showed that the laxative PEG could be taken safely for six months to treat constipation.¹⁸ But I don’t think any reputable doctor would recommend laxatives for weight control, even if it worked.

Things that may work:

Appetite control drugs – Anything which assists with controlling food intake could be effective, in conjunction with a low-calorie diet. Appetite control drugs operate on the central nervous system to suppress appetite. A lot of research is going on in this area. Google “appetite control drugs studies” to find some of it. The actual internal biological mechanisms of appetite control are beyond the scope of this report. Just be sure to consult a doctor if there is any concern about the safety of an appetite control drug.

Vegetarians can control their weight better than meat eaters – Maybe, but it is still possible on a vegetarian diet to consume more calories than are burned, resulting in weight gain.

Getting 100 calories of one type of food will produce less weight gain than eating 100 calories of another type of food - On the surface, it seems to defy common sense. I will however allow that some foods could yield higher or lower digestion or absorption ratios than others, due to their chemistries. Also see “Dietary fiber” below. An example of the type-of-food issue is the current debate over the low-carb diet, which is mildly interesting. Now of course this ignores the nutrient differences, which is beyond the scope of this report. No doubt, the body needs a balance of certain nutrients to continue to be viable. At the extreme, one could get all their calories from Jack Daniels, but their days on this earth would be short on that diet. Seriously though, any extreme diet such as Atkin’s should be undertaken only under a doctor’s supervision. For example, the AMA Council on Foods and Nutrition, Consumer Reports, and many individual experts have warned that the unlimited intake of saturated fats under Atkins' food plan can increase the dieter's risk of heart disease.¹⁹ Other studies haven’t supported this finding, so the jury is still out.

Absorption control medicines – Xenical is a drug which inhibits the absorption of fat, i.e. it modifies the absorption ratio. It works by suppressing an enzyme produced by the pancreas. Xenical is also available in a ½-strength OTC product called Alli. Weight loss is modest, side effects can be very unpleasant, and anecdotally, some people loose no weight at all after taking it for a year.²⁰ Not surprisingly, side effects mimic those of celiac disease (See Celiac disease below).

Things that have been proven to help control weight:

Exercise – Exercise burns stored calories, pure and simple. It also has many other benefits, not the least of which is cardio conditioning and muscle strengthening. Yes, it takes time, and that is the commodity that few people have plenty of. But if you can overcome the scheduling issue, the biggest key to successfully staying on an exercise plan is to do something that you enjoy. If you don’t enjoy it, the odds are that you won’t stick with it. Also make a firm commitment to it such as setting firm dates and times to work out with a friend or family member. Another possible benefit of exercise to the energy equation may be that it increases the resting metabolic rate.²¹ But studies published in 1992 and 1997 indicate that anaerobic exercise such as weight lifting may be more effective in raising BMR than aerobic exercise such as running.11 The reason for this is thought to be that anaerobic exercise builds more muscle mass than aerobic exercise.

Limiting caloric intake – There are two ways to do this: 1) limiting the quantity and 2) eating low energy density (low-calorie) foods. Eating low-calorie foods has more leverage, as it also tends to satisfy the appetite by filling the stomach. The leverage is extremely phenomenal. For example, one cup of cooked green beans weighs 125 grams and contains 44 calories. The same weight of chuck roast beef contains 415 calories, almost 10 times as much. Stated another way, one cup of green beans is much more filling than 1-1/2 tablespoons of roast beef, and both contain about the same calories.

Dietary fiber – Fiber works in part in a manner similar to low-calorie foods in that it dilutes the energy density of the diet. But additionally it seems to have the ability to signal to the brain a sense of fullness (satiety) sooner than other low energy density foods.²² The differences in fiber content between foods could explain why some foods appear to produce less weight gain than others, the caloric content being equal.

GI surgery – This works by reducing the size of the stomach or bypassing part of the intestines, thus limiting the stomach’s caloric capacity or shunting food around the absorption organ. Both are serious, invasive procedures. Stomach surgery carries a high risk of complications, including death, so it is only done for the morbidly obese whose life expectancy can be statistically improved by the procedure.

Electrically altering GI motility – It has been shown in clinical trials that applying short electrical pulses to various parts of the GI tract can speed up motility and thus reduce the absorption ratio to control or reduce weight. This is called implantable gastric stimulation (IGS).²³ I don’t know if IGS is in common use yet, but it is an invasive procedure so would probably only be considered for extremely obese patients.

Liposuction – Liposuction is the physical removal of fatty tissue using a special vacuum cleaner. An immediate weight loss equal to the weight of the fat removed is effected. This is an invasive procedure and involves medical risks.

Celiac disease – CD damages the intestinal cilia, suppressing nutrient and caloric absorption. As a result, one of the 16 recognized symptoms of CD is weight loss. There is no cure for celiac disease, but a gluten-free diet allows the regeneration of the cilia over time in most cases, and allows patients to return to normal lives. So for the approximately 1% of the general population who have the disease, the controlled ingestion of gluten could be used to impair the absorption ratio. Due to the many adverse effects of celiac disease on a person’s health, no sane medical professional would advocate doing this, but in the interest of completeness, I included it.

Future possibilities:

Digestion and absorption modifiers – If either the digestion ratio or the absorption ratio could be reduced, the calories absorbed from food could be reduced. The first person to invent and patent a safe and effective product to do this to a significant degree with no harmful or unpleasant side effects can retire very wealthy. But this is not a new concept. As early as 1955, Coates et al. determined that adding a small percentage of penicillin to chicken feed produced a noticeable increase in growth of young chickens.²⁴ It works by making the intestinal microflora more absorbent. This takes the digestion/absorption ratio in the wrong direction for weight control, but it demonstrates the theoretical possibility.

Humor:

In my research, I found the following statement quite humorous: “Our findings suggest that a continuation of reduced food consumption is not critical to maintain a reduced body weight as long as there is a sustained increase in energy expenditure." Well, duh! Making it more striking, this quote is actually from the Journal of Clinical Endocrinology & Metabolism, a reputable medical journal.²⁵

References:

1 Wikipedia online – Composition of the Human Body:
http://en.wikipedia.org/wiki/Composition_of_the_human_body

Note: I have used care in referencing Wikipedia, since it is a collaborative, community collection of “facts” which anyone can edit. I only reference articles which have passed Wikipedia’s standards and policies for properly cross-referenced works with multiple citations.

2 Wikipedia online – Body Water:
http://en.wikipedia.org/wiki/Body_water

3 Wikipedia online – Water:
http://en.wikipedia.org/wiki/Water

4 Wikipedia online – Food Energy:
http://en.wikipedia.org/wiki/Food_energy

5 Wikipedia online – Conservation of Energy:
http://en.wikipedia.org/wiki/Conservation_of_energy

6 A Dictionary of Units of Measure online:
http://www.unc.edu/~rowlett/units/dictJ.html

7 The Free Dictionary online:
http://www.thefreedictionary.com/calorie

8 Wikipedia online:
http://en.wikipedia.org/wiki/Second_law_of_thermodynamics

9 Stedman’s Concise Medical Dictionary, Third Edition

10 Biology Online:
http://www.biology-online.org/dictionary/Metabolism

11 Wikipedia online:
http://en.wikipedia.org/wiki/Basal_metabolic_rate

12 Basal Metabolic Rate:
http://www.shapefit.com/basal-metabolic-rate.html

13 Does Exercise Affect Resting Metabolism?:
http://sportsmedicine.about.com/od/anatomyandphysiology/a/rmr.htm

14 Metabolism and Starvation, Cari, Naomi & Abbey
http://www.ferris.edu/htmls/academics/course.offerings/balandap/BiochemStuff/Starvation.ppt#272,18,Overall
15 Anorexia Nervosa – Understanding the Signs, Symptoms, Causes, and Treatment:
http://www.helpguide.org/mental/anorexia_signs_symptoms_causes_treatment.htm

16 Diet Scam Watch:
http://www.dietscam.org/basic/myths.shtml

17 MLM Watch:
http://www.mlmwatch.org/04C/Herbalife/1986order.html

18 Medical News Today 2007, Clinical Trial Confirms New Laxative Safe For Everyone, Including Elderly:
http://www.medicalnewstoday.com/articles/75099.php

19 Low-Carbohydrate Diets, Stephen Barrett, M.D.:
http://www.quackwatch.org/06ResearchProjects/lcd.html

20 MayoClinic.com, Alli weight loss pill; Does it Work?:
http://www.mayoclinic.com/health/alli/WT00030

21 Effects of increased energy intake and/or physical activity on energy expenditure in young healthy men:
http://jap.physiology.org/cgi/content/abstract/77/1/366

22 Family Practice Vol. 16, No. 2, Effects of dieting and exercise on resting metabolic rate and implications for weight management:
http://fampra.oxfordjournals.org/cgi/content/full/16/2/196
Journal of Nutrition 2000, Dietary Fiber and Energy Regulation:
http://jn.nutrition.org/cgi/content/full/130/2/272S

23 Obesity Journal 2003, Alterations of Gastrointestinal Motility in Obesity:
http://www.nature.com/oby/journal/v12/n11/full/oby2004213a.html

24 Determination of Veterinary Residues in Food:
http://books.google.com/books?id=tht2qXZpyzYC&pg=PA150&lpg=PA150&dq=digestion+modifier+drugs&source=web&ots=iqhQ_mML9z&sig=jVbK_-dB9RFM4SFRlbWLo7j7-uc&hl=en&sa=X&oi=book_result&resnum=1&ct=result

25 Plasma Ghrelin Levels in Lean and Obese Humans and the Effect of Glucose on Ghrelin Secretion:
http://jcem.endojournals.org/cgi/content/full/87/1/240?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=1&andorexacttitle=and&andorexacttitleabs=and&fulltext=ghrelin&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT