The First Law of Dieting

*** Disclaimer: While the laws of thermodynamics apply unconditionally to everyone, I am no dietician, and so my proposed law of dieting is based on opinion, and may not apply to all dieters. ***

The holiday season is upon us, and there are two things we can expect with certainty once December is complete: (1) 2010 will become 2011, and (2) in the month of January, we will be inundated with new dieting suggestions. 

A quasi-doctor with nice teeth and salon-fresh hair will push her new-age plant diet, which involves eating anything in your home that grows from soil.  A very muscular chiropractor who graduated from I-Wish-I-Was-A-Dr. University will counter this ad with his “Nothing but Brownie” diet, which promises to make each of your bowel movements smell like Parisian baked goods.   

Many of us consume more Calories than usual during the cold holiday season.  Then, we make the unrealistic New Year’s resolution to transform from couch potatoes into gym nuts as the clock strikes midnight on December 31^st.  Some people follow through with their plans to exercise more, but most do not, as is evidence by how busy gyms are in January versus March.  Some people who give up on their exercise plans take solace in the fact that they are still eating a magical cookie for breakfast and lunch; they get oatmeal raisin Monday to Thursday, but chocolate chip on Friday.  On the weekend they are rewarded with non-cookie items, just as long as they think of cookies while they are being consumed.

It may all seem ridiculous, and that is because it is.  There is a lot of false science out there, but few domains of science contain more myths and misinformation than that of nutrition.  It is a shame, because at the root of diet and exercise is one very simple scientific law that, if considered, can solve the issues pertaining to weight and overall fitness for the majority of the population in developed nations.

It is known as the First Law of Thermodynamics, which may sound complicated or scary to someone with distaste for science.  This law states that energy can be neither created nor destroyed, only converted from one form to another.  In the simplest case, that of a closed system, we can easily appreciate this law at work.  It is somewhat more complicated for the human body, but the “First Law of Dieting” is simple: if you wish to lose weight, you need to burn more energy than you consume. 

Let us first consider the closed system of a wooden block sliding along a flat, rough surface, like a table.  We will place a dome over the table, and call the system a closed one consisting of the table’s top surface, a wood block in motion, and the air under the dome.  Initially, the block has a lot of kinetic energy due to its speed, and everything in the closed system is at room temperature.  At a later point in time, say, two seconds later, the block has slowed down due to friction between it and the table.  Less speed means less kinetic energy.  So, where did the energy go?  It was not destroyed, for this would defy the first law of thermodynamics.  It was converted, due to friction which worked against the direction of motion, into heat. 

Indeed, the surfaces in contact, the bottom surface of the block and the path of the table it slid across in that time, have increased in temperature.  The sliding process caused the kinetic energy to be converted into heat.  The path of the table eventually cools off, but the air under the dome heats up slightly as a result.  At any moment in time, the total mechanical energy of the system is conserved.

While the human body is encapsulated by a large dome or boundary (skin), the skin itself is full of holes, or pores.  Regarding energy and mass transfer, there are three other relevant openings to the body (orifices): one inlet, known as the mouth, and two familiar outlets.  Due to all of these openings, the human body may be viewed as an open system.  The first law applies to open systems as well as closed ones so long as we account for all that comes in and goes out.  In addition to the energy conservation law, the mass passing through and maintained within the system must also be conserved (not created nor destroyed).  These conservation laws are actually quite simple.  They work like your chequing account at the bank.  No money is created, and hopefully none is destroyed.  If your account has $200, and you deposit $50, you can take out no more than $250.  Furthermore, the teller at the bank will never remind you to stop filling your account.  Expanding accounts is good, while expanding waistlines is often not.

All foods have a certain caloric value associated with them.  Let us take Multi-Grain Cheerios for example, for which one serving (30 grams) corresponds to 120 Calories.  The “Calorie” is a false unit of energy when used to describe food products, as the true “calorie” (non-capitalized) is the amount of energy it takes to raise the temperature of one gram of water by one degree Celsius.  The Calorie on the side of your cereal box actually refers to kilocalories (1 Calorie = 1000 calories).  Engineers use Joules (J) as the standard unit of energy, and they refer to the amount of energy required to accelerate a 1-kg block by 1 m/s² along a frictionless surface over a 1 metre length.  One calorie is equal to 4.184 Joules, so my thirty grams of cereal (without milk) corresponds to 120,000 calories or 502,080 J, or about 500 kJ.

When I consume this amount of cereal, the total amount of mass and energy in my body increases by 30 g and 500 kJ, respectively.  The food is then in for quite a trip.  Bypassing the details, some of the nutrients are kept, and some are discarded by the body as waste.  More mass enters than leaves, and so, the mass of the body increases ever so slightly.  Fortunately, pores are another place where mass, in the form of fluid, can leave the body.

Many people do not realize this, but a large percentage of the total energy taken in when eating is spent during the digestion process.  This is why we often feel exhausted after a big meal.  Some buffet restaurants actually have beds for rent adjacent to the dining room ... OK, I made that up, but the idea could take off one day considering North American eating habits.  We are unaware of much of the energy that our body expends.  Our hearts beat, our lungs inflate, and our neurons fire; each of these involuntary processes require energy.  Still, if we lead a stagnant life, completely devoid of voluntary muscle contractions, ie, exercise, we will voluntarily take in more energy than we involuntarily use, and invariably gain weight over time.

The overall message I mean to deliver is that if possible, we ought to consume a rational amount of food, which corresponds to a rational amount of energy.  If you will spend the afternoon camping, skiing, or helping a friend move heavy boxes, then a calorie-rich lunch, consisting of a double-portion of lasagna (1000 Calories, or 4184 kJ) makes sense.  However, if the afternoon is spent typing in your seat at a computer, then 400 Calories from a salad and a slice of bread should do you just fine.  The alternative meal choice, the double-portion of lasagna  would quickly find itself floating around in your buttocks region. 

An individual with average weight who leads a reasonably active lifestyle (moderate intensity cardiovascular activity for thirty minutes five times per week) should consume roughly 2,000 Calories per day.  Athletes require more like 4,000, but those who watch athletes do not.  If you want to lose weight, you need to reduce caloric intake and increase voluntary activity.

The above paragraph is a good guideline.  I suppose that so many of us invest our time and money into cookie diets and other fads because we want to believe there is an easier solution than rational diet and exercise.  Of course, my 30 grams of cereal contains more information than the energy content, but none are nearly as important.  I don’t mean to belittle the Nutrition industry, which is very interested in fats, carbs, proteins, and vitamins.  These aspects of food are important, but for most, they are of secondary importance.  The science behind nutrition is indeed much more complicated than the simple conservation laws I have described.  

Still, we are left with the question, “What should I eat?”  For this question, I will offer a rule of thumb that I heard of some years ago: “Eat food, not too much, mostly plants.” 

As for the Dieting industry, I have every intention of belittling it.  It is an industry that would be crushed if the general population were both well-educated about nutrition and disciplined.  I have little care for industries that are fueled by misinformation.  

Let us put fad diets to rest this holiday season, and replace them with some common sense.