Posted by: SLS | November 2, 2010

Thermodynamics in weight control

The most over utilized paradigm of weight loss is the concept of calories in – calories out, and that in order to lose weight, one must reduce the total amount of calories consumed (calorie restriction or CR) so that their energy output exceeds their energy input. This belief is further illustrated by the following equation:

ΔE = E(in) – E(out); the change in total energy equals the difference between energy in and energy out of a system, or:

Change in weight = Calories consumed – Calories expended

The above equation describes energy change in a closed system. The human body is not a closed system. We interact with varying temperature and are not in thermal equilibrium with our environment. We are capable of large mass flows such as in respiration, and we can sequester entropy through metabolic effects like protein synthesis whereas a closed system would evolve towards a state of maximum entropy. To truly account for the energy in a system as complex as a living organism, the equation would have to look something more like this (taken from here with credit for the idea to Michael Eades):

The reason calories in and calories out does not hold is because as you reduce your caloric intake, your body actually slows down. Body temp lowers, enzyme reactions slow, metabolic rate decreases as your body diverts energy to only necessary processes, making you lethargic and tired. This thermodynamic assumption is also your assumption that, if you are lean, you are allowed to remain lean on presumably normal caloric intake, while the obese person next to you cannot be lean unless he/she eats less than normal caloric intake.

You can’t assume that E(in) and E(out) are independent variables that respond only directly to changes upon them alone. Instead, E(in) and E(out) are dependent variables. In other words, you can’t change E(in) without expecting a change in E(out). You can’t tell someone to eat less and not expect their energy out, what they expend, to compensate. An animal who’s food is restricted responds by being less active, reducing energy use in cells, and therefore losing less weight. Reminder: we are animals. As soon as you lift the calorie restriction, you will eat more to regain the weight you may have lost during energy restriction.

To further illustrate the preposterous attempt at counting calories to stay in “energy balance”, assume you eat 2700 cal/day on average:
= 1,000,000 cal/year
= 10,000,000 cal/decade
= 12 tons of food/decade
So maintaining your weight to within 10 lbs over the course of a decade requires an accuracy of counting calories to better than .4 percent. Your theory maintains that if you err by 11 calories/day, you will become obese as you add 10 lbs /year. How are we all not either morbidly obese or anorexic? We cannot possibly maintain this degree of accuracy for the course of our lives. People do attempt it with meticulous calculations or with the aid of computer software, but they still fall far short on the accuracy of their predicted expenditures. The regulation is not through our cognizant manipulation of how much food we eat, it is through our automatic metabolic response to the quantity and type of calories we consume. Fat and protein signal maintenance, growth, repair, and energy; carbohydrates signal storage, lassitude and impermanence.

This is just the first of major discrepancies evoked by an oversimplification of energy exchange in an organic metabolic system. The next main problem with the original equation is that there is no direction or arrow of causality to tell you which part of the equation directs energy use or consumption. Most of us assume that the right side precedes the left, however, there is no reason to believe this is always true. Instead of saying “you’re fat because you eat too much,” you could say “you eat too much because you are fat.” The first is blamed on psychology, the second on physiology. This is not limited to just fat gain, this is growth in general. Pubescent adolescents go through a marked period of growth and development, and during this time, they tend to eat more. By the time they reached their adult stature, you wouldn’t look back on pictures a decade earlier and remark that “they grew because they ate too much”! No, instead, you’d say “they ate too much because they grew”. These were hormonally controlled metabolic and physiological changes. Psychology is not the cause of obesity. An obese infant is no more to blame for gluttony as is a starving but overweight impoverished individual. We see obesity coinciding with poverty all too often and it is a contradiction to the notion that obesity is the result of wealth and prosperity and an overabundance of food.

Fat distribution of overweight individuals is also distinctly sexually dimorphic, meaning men and women acquire fat on different parts of their body based on the amount and type of circulating androgen hormone. Men typically deposit fat above the waist, women below. Again, this is hormonally controlled.

The fat is not an inert mass but rather a metabolically active and storage driving force. Adipose tissue actively express insulin and glucose receptors to dock nutrients at the cell in order to support growth and maintenance of itself. It will actively direct nutrients away from your brain and muscle tissue where it could be used for energy, movement, maintenance, and thought and converts it to fat for storage.

Calorie restriction is an abysmal failure in the health science and dietary industry. Controlling caloric balance by monitoring consumption and expenditure is meticulous and not maintainable at best, but ultimately impossible. Caloric intake is best left to the control of signaling hormones in a healthy metabolism, and in absence of that, a low carbohydrate dietary intervention.



  1. Interesting post. To play the devil’s advocate here, most bodybuilders and athletes require some caloric management, once a proper diet has been established, to further increase muscle mass or decrease body fat but I suppose your post was more towards the general population than athletes.

    • Hi Alex, I believe establishing the proper diet, as you said, is the most important factor. There are studies supporting an optimal protein amount, especially the branched chain amino acids, to stimulate protein synthesis in muscle for growth and repair. Beyond that, people should eat to fill of meats and veggies. I believe this pertains to everyone, including athletes who are competitive. Body builders in the strictest sense desire hypertrophy, which is an unnatural look and requires unnatural feeding habits. At a certain point, they sacrifice health for look or performance.

  2. Haha Hard to argue with fill of meat and veggies. Looking forward to reading more of your stuff.

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