The first law of thermodynamics The first law of thermodynamics has been oversimplified to the slogan “energy in equals energy out”. However, the first law does not say that energy in equals energy out. (And, if it did, surely the corollary would be less energy in equals less energy out?) The first law says that, in a closed system, in thermal equilibrium, the form of energy may change, but the total is always conserved. Let us take a simple example – we can put a gallon of petrol into a petrol car and it will go, say, 30 miles. At this point we may be confident that energy in equals energy out. However, we can then put a gallon of diesel into the same car and it will go nowhere. Immediately we can no longer argue that energy in equals energy out. We can see that energy has been conserved – which is what the first law of thermodynamics says. We have not created or lost energy, but energy in does not equal energy out. Energy in equals energy out (none in this case), plus energy stored – this is crucial. What if, for example, the vast numbers of empty calories, such as sugar, which we consume today in unprecedented quantities, are the nutritional equivalent of putting diesel into a petrol car? Citizens of the UK consume 1.6 pounds of sugar per week, which translates into approximately 400 empty calories, per person, per day. Citizens of Australia consume an average 600 empty sugar calories per person per day. Are we absolutely sure that the human body is designed to run on sugar, emulsifiers, yeast autolysate, high fructose corn syrup (also known as glucose-fructose syrup amongst other names), maltodextrin, hydrogenated fat, butylated hydroxyanisole (BHA), butylated hydrozyttoluene (BHT), dextrose, Acesulfame-K and many other common ingredients that we will find in processed foods consumed daily? I doubt that we will get any better performance out of a human, by putting the wrong fuel into the body, than we will by putting diesel into a petrol car. This is just a question to pose to you – my arguments to follow do not rely upon it. Energy in and out is often simplified further to energy balance. I have used this term for the chapter title, to capture the extreme of one simplification on top of another, but I won’t use it again. I apologise in advance if energy in and out become a bit repetitive, but we need to be precise in our language, to correct errors constantly being made. The term energy balance has many underlying assumptions at best and can be a tautology at worst.
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