Are All Calories the Same?

          Let’s be honest.  If losing weight was as simple as burning more calories than we eat, as easy as exercising more and eating less, then the gyms and fitness centers would be full of lean, lithe people, and there would be much less of an obesity problem.

           Of course we know otherwise.  What person is there, struggling with a weight issue, who has not tried eating less, exercising more, or doing both, with little to show for his or her efforts?

Calories and the Laws of Thermodynamics

         The problem is that few scientific principles have been misappropriated and misapplied more than the first two Laws of Thermodynamics when it comes to nutrition.

           The First Law of Thermodynamics states that energy cannot be created or destroyed—it remains constant in a system.  If energy can’t be created or destroyed, then it stands to reason that a calorie is always a calorie, that all calories are the same. That’s where the second law comes in.

           The Second Law of Thermodynamics says that it is impossible for a system to turn a given amount of energy into an equal amount of work.

           These two laws of thermodynamics can be summed up thusly: The first law says you can’t get something for nothing, and the second law tells you that you can’t break even.

           It is the second law that is most described as the “a calorie is a calorie” law, when, in fact, the second law shows, in terms of weight loss at least, that all calories are not necessarily the same.

          And herein lies the rub: We don’t convert calories to energy on a one-to-one basis because energy is dissipated or lost to the universe as described by the second law.

           Look at it another way. It takes energy to drive the infinite chemical reactions that sustain life. Some of this energy is perpetually lost due to the second law. Therefore, a large portion of the energy available in a certain number of calories cannot be converted to meaningful work and is lost. The more chemical reactions that take place, the more energy is lost to the environment.

           Take another example.  Only 10 to 12% of the energy in a gallon of gas is used to drive the car.  The rest is lost to heat.  The same principle applies to biological reactions.

Macronutrients and Calories

             Macronutrients—proteins, carbohydrates, and fats—all obviously contain calories.  The problem with the “calories in, calories out” mantra, however, is that the body does not treat the calories from each macronutrient the same way.

             Glucose is the elemental sugar that the body burns for energy.  Carbohydrates (which are simply sugar molecules linked together in varying chain lengths) are broken down to glucose by the body with relatively little effort.  Therefore, while some energy is lost during the process, it’s a rather small amount.

              But converting proteins or fats to glucose requires a much more intense process, involving more reactions and a lot more energy. The process is much less efficient, and therefore much more energy is lost in the process.

              This efficiency in calorie burning can be determined by measuring the metabolic rate, or what is known as the Resting Energy Expenditure (REE).  And, in fact, such a study was recently published.

              Researchers looked at the effect of three different diets on REE.  Subjects were put on either a low-fat/high-carbohydrate diet (60% of energy from carbohydrate, 20% from fat,20% from protein; high glycemic load), a moderate fat/moderate carbohydrate diet (40% from carbohydrate, 40% from fat, and 20% from protein; moderate glycemic load), and very low-carbohydrate diet (10% from carbohydrate, 60% from fat, and 30% from protein; low glycemic load) in random order, each for four weeks.  (Source: JAMA, June 27, 2012, Vol 307, No. 24.)

              A key point in this study is that all three diets contained the exact same amount of calories; 2000 each.

              At the end of the study researchers found that the dieters on the high-carbohydrate diet had the greatest decrease in REE, while those on the high-protein diet had the least decrease in REE.  In other words, even though the calories eaten were the same, the high-carbohydrate diet resulted in the most

unfavorable effect on metabolism (slowed it down the most) while the high-protein diet had the most favorable effect.

             This study proved what Dr. Atkins and other contrarian weight-loss experts have argued for years, namely that not all calories are the same, and that a high-carbohydrate diet has a greater negative effect on the body than does a low-carbohydrate higher-protein diet.

Summary

             The problem with applying laws of physics to human systems is that biological systems are not machines. Our bodies are dynamic organisms, constantly adjusting and adapting to our environment, and the “energy” we consume in the form of calories is diverse also.  So the Laws of Thermodynamics cannot be applied the same way to human systems as to mechanical systems.

              As Michael Eades, MD writes in his blog, “Bear all this in mind the next time you tell someone that it is possible to lose more weight on a greater number of calories as long as those calories are low-carb calories, and that someone pooh-poohs you with the old ‘That can’t be possible. It violates the laws of thermodynamics. A calorie is after all a calorie.’ Ask them precisely which laws of thermodynamics it violates and ask them to tell you how. Then sit back and watch the fun.”