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Do Calories Count? 1st Law of Thermo (Part 2)

April 28, 2011

Despite breaking this post up into two parts (part 1 here), this one is still a little long. Push through to the end, and you won’t be disappointed.

Last time we talked about the issues involved with applying the First Law of Thermodynamics to the entire human body as a control volume. Go back and read that post, especially the “Summing Up” paragraph at the bottom.

All caught up to speed? Good, let’s get going.

Let’s frame this discussion by first presenting the two most common fitness goals: losing fat, and gaining muscle. Of course, the holy grail of diet and exercise is doing both at once, often thought to be impossible; we’ll take a look at this as well.

Losing Fat

It is commonly stated that to lose fat, one must reduce the amount of energy stored in the body, and that this requires a caloric deficit. While these statements are certainly common, they are also certainly false. This falsehood arises from the (unnecessary) complicating of the problem that results from applying the first law to the entire body. In the case of fat storage regulation, we should instead be viewing the collection of the body’s fat cells as the control volume:

To lose fat, more energy must exit the fat cells than enters them (meaning that the integral of the dE/dt term must be negative over a given time). Note that this requirement says nothing about how to achieve this or the whole-body energy flow requirement. All that is required for fat loss is a “negative energy balance” in the fat cells as a whole.

Gaining Muscle

It is almost universally preached that to gain muscle, you must have a positive energy balance at the whole-body level. Hard-gainers (those who find it hard to gain muscle) are told in bodybuilding forums across the interwebs that they simply need to eat more. While it is certainly true that eating too little can prevent muscle gain, it is false that a whole-body energy surplus is required for muscle building. Hopefully, you see where this is going – a first law analysis of muscle cells:

To gain muscle, more energy must enter the muscle cells than exits them (meaning that the integral of the dE/dt term must be positive over a given time). Note that this requirement says nothing about how to achieve this or the whole-body energy flow requirement. A requirement for muscle gain is a “positive energy balance” in the muscle cells as a whole. In the case of fat loss, a negative energy balance is the sole necessary condition; for muscle gain, a positive energy balance is only one of the requirements. This leads in to the hormonal discussion in the next section.

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Sidebar: The difference between energy rate balance and energy balance.

The first law equations as I have written them are “energy rate balances,” evaluating the rate of energy change of the control volume. In the case of fat loss, the dE/dt term denotes the rate at which energy is entering or leaving the fat cells at a given time. Let’s see what the energy rate balance may look like over a given day (click to enlarge):

On an energy rate balance plot, each point is the rate of fat gain (positive) or loss (negative) at any given time (at time zero, the dieter is losing fat, at 10am, the dieter is gaining fat). The energy rate balance starts negative and decreases until breakfast, at which point it spikes. It then begins to dip again until a second meal. The negative values until breakfast indicate that this individual is losing fat until breakfast, and storing fat between breakfast and bed time. Most people are not interested in losing fat at a specific time, they are instead hoping to lose fat over a given time period. To determine whether this individual gained or lost fat on this day, we must integrate the data (click to enlarge):

On an Energy Balance plot, each value is the amount of fat gained (positive) or lost (negative) over the day up to that point in time (at time zero, the dieter has lost a small amount of fat, at 9am the dieter has lost a lot of fat). We see that the dieter has lost a lot of fat before breakfast, and that while the day’s meals reduce the fat lost, the net result (final value at the far right of the graph) is that fat was lost on this day.

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The Holy Grail – Simultaneous Muscle Gain and Fat Loss

We’ve shown above that fat loss requires a negative energy balance and that muscle gain requires a positive energy balance. If you’re stuck with the flawed first-law model using the entire body as a control volume, this seems impossible, because the whole-body energy balance cannot simultaneously be both positive and negative. Fortunately for dieters everywhere, the energy balances of the fat cells and muscle cells can be different – these equations are linked by the whole-body energy balance, but their values are not dictated by it. In fact, fat loss actually aids muscle gain, and vice-versa.

Let’s assume that the human body is very simple (it’s not) and incoming energy is only used or stored in three places: fat, muscle, and option “C” (huge simplification, but it works for the purposes of this discussion). Here’s a constraint on the energy rate balances in the body:

We can integrate the above to yield the corresponding energy balance constraint:

Some of the more astute readers out there may be asking “Aren’t you just applying the first law to the whole body, a method you decried in your last post?” Good question! I am. I’m applying the first law to each energy storage/utilization entity within the body, then applying a constraint over the whole body reflecting the conservation of energy. Now that we’re viewing the body as a collection of control volumes (instead of just one), we have the resolution necessary in our model for intelligent discussion.

This more detailed model allows for different energy balances in different subsystems of the body. Let’s look at how the constraint governs muscle energy balance:

As outlined above, if the goal is to build muscle, then E_Muscle must be positive. We can see in the above model that this can be achieved in a number of ways. The classic “bulk” approach (eating more) simply increases E_Body. It is clear that this will increase E_Muscle if E_FATCELLS and E_C remain constant. Of course, in the complicated system of the body, changing one thing will often change others (pharmacists call these “side effects”), and we know that most people eating more to gain muscle will also gain fat. This is a huge bummer – you’re spending more money and time eating, and the food isn’t all going where you want it to.

Hopefully, this model has made clear that there is a better option. If the dieter holds E_Body and E_C constant, but decreases E_FATCELLS (making it more negative by using stored fat for energy), E_Muscle will increase. This is how losing fat helps build muscle.

Real-World Applications

This may seem like a lot of math and hand-waving (it is), but it has value. I’ve shown that concurrent fat loss and muscle gain is possible, but I haven’t told you how to make it happen in your body. The key is, in a word, hormones.

To free up more incoming calories for muscle building without increasing your calorie intake, you have to burn more fat for energy than you did before. Let’s talk about how to do that.

Many people have trouble losing fat (largely due to poor diet) and as a result, we end up with explanations from doctors like “your fat cells are a living organism; it is their mission to store fat and they don’t want to let it go.” In people with a healthy flexible metabolism, the collection of fat cells is more like a gas tank in a car, simply a reservoir of stored energy that can easily be filled or emptied on command.

Lower your carbohydrate intake, and your metabolism will become a lot better at burning fat for energy (beta-oxidation). Insulin does a good job of keeping fat in fat cells; the lower insulin levels generally seen on a low-carb diet will make your fat-cells act more like a gas tank and less like a jail cell.

Another option is to increase the proportion of E_Body allocated to E_Muscle by creating a hormonal environment that demands more energy for your muscles. You could achieve this with anabolic steroids, but I’ve heard that will deflate your basketball or something (more research needs to be conducted on the link between steroids and basketball air pressure). A more natural way to get the job done is good, old-fashioned resistance exercise. Weight lifting will put your body in an anabolic state, funneling incoming energy to muscles for hours after your workout. It is worthwhile to note that while “cardio” also requests more calories at the muscles, it burns those calories for energy instead of using them to build muscle. Since you’re burning more energy than you’re storing (even muscle construction is a form of energy storage), you’ll get hungry and eat more (now you’re increasing E_Body and not gaining any muscle, which seems silly). Also, “cardio”, you know, kills you.

The Bottom Line

Applying the first law to the body as a whole is practically useless, until you break it up into smaller sub-system control volumes. “Calories in, Calories out” is still true, it’s just stupid to say (especially over and over again) because it doesn’t offer any insight into how the body actually handles energy.

Success in achieving the typical fitness goals of losing fat and/or burning muscle is dictated primarily by hormonal environment, but may be limited by whole-body energy balance. In other words, it’s more important to have your hormones working for you than it is to worry about weighing and measuring food. A low-carb diet and resistance training are two powerful tools for creating a favorable hormonal environment.

So drop the bread (and neurotic food relationship), lift a dumbbell, and provide this article to anyone who so much as whispers “first law of thermodynamics.”

Entry filed under: Basics, Calories, Food Choices. Tags: .