The Thermodynamic Diet - what do I mean by that?

What I really mean by the thermodynamic diet is that if I use up more calories than I take in, I'll lose weight. If I take in more calories than I use up, I'll put it on. It's that simple.

While it is actually that simple at its most basic level, there are one or a few more considerations we might need to think about.

One fundamental thing to consider though, is that this is a diet, it's not a physics project, so there's really no point in over-analysing things and getting into the minutiae. By sticking to that central theme, you can lose weight.

The thermodynamic diet

 

The key phrase that sums up what we want to get out of the first law of thermodynamics is that energy cannot be created or destroyed, it can only be changed from one form into another.

So, from that statement, we can say that if we don't put any energy into our bodies, and our bodies continue to use energy, that energy must be provided from what is already stored in our bodies and we will lose weight.

There are no calories in air, and we can't create them out of nothing, so if we don't eat and continue to live, we have to get the energy we need to maintain our bodies from our energy stores.

Now, searching for 'thermodynamic diet' on the wonderful world of the internet reveals quite a few hits. I took a look at a lot of the top-ranked ones, and found them to be mostly nonsense.

Admittedly, some of them used some scientific words, some of them talked about some published studies, one of them said that thermodynamics is 'utterly irrelevant', and another said that it 'has no place in human nutrition'. Interesting.

Oh, and I came across one article that said the exercise made so little difference it wasn't even worth considering. That one seems particularly odd. Speaking for myself here, with the extra walking I do to and from the bus stop to work - if I get off early and walk through the park - that extra exercise gets through enough calories to balance out a chocolate chip cookie or a doughnut - each day!

I would say that was worth considering. If I didn't have the treat, it would account for about half a pound of weight loss a week.

Ever heard of "calories in equals calories out"?

 

I hadn't, until I started exploring a few diet and nutrition websites. As soon as I read that, I instantly leave the site and try to forget everything I have 'learned' from it.

Calories in equals calories out is not a thing. It is exactly what thermodynamics and dieting does not mean.

Of course, I could just be interpreting the statement incorrectly. To me, saying calories in = calories out means that I can put as many calories in my body as I like, and I won't put on any weight as they'll all just come out.

I don't think that's how it works. As soon as I see a site that uses this phrase I, just about instantly, write them off as not knowing what they're talking about and move on.

So how does the first law of thermodynamics apply to dieting?

 

The way I apply it is as follows. My body cannot create energy, it can just convert the chemical energy contained in what I eat to other forms. What it doesn't use, it stores as glycogen and fat. If my energy requirement is greater than my energy intake, my body makes up the shortfall by using the stored chemical energy in my fat and glycogen.

So what else is at play here? Well, the one thing I rarely encounter in any of the articles I've read about thermodynamics and weightloss is the concept of 'efficiency'. No 'machine' (at least none that I can think of) is 100% efficient. Your car does not convert 100% of the energy contained in the fuel to movement.

Thermodynamics, dieting and efficiency 

 

Your body is the same. It does not convert 100% of the chemical energy contained in your food to its 'working' forms of energy. As an example, glycolysis, the citric acid cycle and oxidative phosphorylation are central pathways that convert the energy contained in our food into energy the body can use, chiefly a compound called ATP.

Ah, this brings back memories. Second year undergraduate biochemistry. I knew all these pathways by heart. They formed the basis of an exam I would really rather forget...

ATP Synthase animation (MRC)

Looking at the process on paper, 1 molecule of glucose that goes into these processes should produce 38 molecules of ATP. In practice however, the number is closer to 30, due to the nature of the process. We're not taking full advantage of the calories that go into the system.

What happens to the energy that we don't convert? As with most things in thermodynamic efficiency, it probably ends up just generating heat, thus conserving the first law of thermodynamics: we are not destroying energy, we are just converting it into other forms.

These energy generating pathways are actually how out brown fat tissue generates heat to keep us warm-blooded animals at the right temperature. The enzyme that produces the ATP is called ATP synthase (it's also a very beautiful example of the complex molecular machinery at work inside us) and it uses the energy from our food (after the various biological processes have created what's called a proton gradient) to convert ADP into one of our energy sources: ATP.

In the brown adipose tissue, the part of the ATP synthase that does the ADP -> ATP bit is 'uncoupled' from the rest of the enzyme, so all the energy from that protein gradient is used to spin the enzyme without producing ATP, turning all that proton motive force into heat.

Sources of variability

 

A frequent argument against thermodynamics in dieting is the one that says "well, what about my friend who eats all the time and never puts any weight on?". Well, that doesn't disprove thermodynamics at all. It just says that they either do more exercise than you see (or that they let on), that you only see them when they're eating vast amounts (and not when they're being very careful with their diet the rest of the time), or they're simply not very efficient, and they're just turning all of those extra calories into heat.

The first law of thermodynamics - a central component of how the entire universe works - is not violated by your friend who seems to eat a lot and who doesn't seem to put any weight on. They're just using the energy in different ways.

Another argument is the idea that a "calorie isn't always a calorie", something that is used to promote low carbohydrate, high protein diets for example. I would argue that a calorie is always a calorie. Where any differences come from is in how efficiently our bodies are able to utilise them from various sources, something that may depend on many things, from host genetics, to how much glycogen you currently have, to whether or not you ate something that disagreed with you and that makes everything move through you faster than normal.

Whatever the reasons, I wager that the laws of thermodynamics remain unviolated.

This is a big subject, so we'll leave it there for now, but I guarantee we'll be back.

Day 34 - 2300 calories

Breakfast
Milk (200)
2x poached eggs on toast (300)

Lunch
2x poached eggs on toast (300)

Snack
Apple pie (250)

Dinner
Burgers (400)
Mixed vegetables (100)
Beer (200)
Wine (250)
2x Weetabix, raisins and milk (300)

Exercise
45m walking

Day 35 - 1900 calories

Breakfast
Milk (150)
5x jam doughnuts (1150)

Lunch
Ham sandwich (200)

Dinner
Lentil soup (400)

Exercise
40m walking
2m planking

Day 36 - 2400 calories

Breakfast
Milk (100)
Protein bar (100)

Lunch
5x jam doughnuts (1150)
Ham Sandwich (200)

Snack
Lentil soup (350)

Dinner
2x poached eggs on toast (300)
Plum (50)
Glass port (150)
 
Exercise
3x 2m planking
70m walking