More on energy balance

After the last post it occurred to me to wonder how the energy content on food is calculated. I can measure the weight easily but how do I know the energy that I am consuming. The major method is to read the label on the packet. This is not very useful for fresh foods, but there are (apparently) on-line sources that can provide the information.
But this only shifts the explanation back a step. Tracking back, further the best explanation I can find is from Scientific American which states:

The original method used to determine the number of kcals in a given food directly measured the energy it produced.The food was placed in a sealed container surrounded by water--an apparatus known as a bomb calorimeter. The food was completely burned and the resulting rise in water temperature was measured. This method is not frequently used today.

And

According to the National Data Lab (NDL), most of the calorie values in the USDA and industry food tables are based on an indirect calorie estimation made using the so-called Atwater system. In this system, calories are not determined directly by burning the foods. Instead, the total caloric value is calculated by adding up the calories provided by the energy-containing nutrients: protein, carbohydrate, fat and alcohol. Because carbohydrates contain some fiber that is not digested and utilized by the body, the fiber component is usually subtracted from the total carbohydrate before calculating the calories.

Which answers another question I had about calories which cannot be absorbed by the body and therefore pass straight through - e.g. fibre. As usual Wikipedia also has a good description.

And this is the simple part of the Energy Balance equation. The link between burning energy and losing weight is still opaque.
Which I suppose is the problem. This explanation is superficially simple, but once the surface is scratched there is a great deal of complexity involved. I don't mean just in the biochemical and physiological reactions taking place - that is expected - but in the actual correlation between energy balance and weight control.
So why is it so widely used when a mass balance would be so much simpler - to apply as well as to explain.

Thinking about it, the mass balance view is purely and simply descriptive. It is self evidentally true but provides no further insights since the "mass out" end is so tightly dependent on the composition of the "mass in" end. And once you get into composition, we start talking about energy content.
On the other hand the energy balance view attempts to provide a simplistic explanation as well as a description. It states a casual association - a body attempts to hold onto excess energy and therefore stores it, generally as fat. In other words - weight gain is caused by ingestion of too many calories. It skips over the source of the fat molecules and the elimination of metobolic by-products, as being a trivial aspect.

But I still think there is some benefit in considering the impacts of this "trivial aspect" of the whole process.

Nutrition and Conservation of Energy

Further to my previous post, I am working out how energy balance (calories in vs. calories out) relates to changes in body weight.
To explain where I am coming from: both energy balance and mass balance provide (different) holistic views of the human body as a system – with biochemistry and physiology providing the ‘zoom-in’ detail.
What I am trying to do is meld them all into a consistent mental model – at least for myself.
I still find the conservation of mass view easier to understand conceptually, but mostly I think because of the short cuts taken in describing the conservation of energy view. The latter is certainly a much more common approach.

 
Conservation of energy does, of course, apply to the human body. Energy into the body must match energy out: E(stored) = E(in) - E(out), this is a fundamental law of physics. The problem is how this relates to body mass - and especially body fat - since mass and energy are not interchangable in chemical reactions.
There is an implicit step in most discussions that is not called out - mostly I think since the majority of people don't care. This is the mapping of variables to aspects of nutrition. Hence:
* E(in) = energy consumed in food. This mapping seems self-evident - which, to a scientist, means it needs to be treated with suspicion. I can understand that there is little energy extractable directly from liquid or gas and so solid input can be considered the only source. Although dissolved solid such as sugar in water also need to be considered.
* E(stored) = fat, sort of. This is useful as a first approximation since other storage mechanisms, such as glycogen and tissues such as muscle have limited energy capacity - and are usually full. It is also the point where energy and mass are most confused. Chemical potential energy is stored in fat in the same way a battery stores energy. Or, since fat is created or destroyed as needed, more like water in a dam supplies hydro-electricity. The water is not energy but the water level can be used to estimate how much energy is being held
* E(out) = energy expended. This is the point where I have most trouble. There are multiple points where energy leaves the body and burning (oxidising) fat is only one of them. BUT, there is no weight loss at the time! The weight is not lost until the by-products of burning the fuel leave the body - things such as carbon dioxide or uric acid and other waste products. There is also energy which was never claimed by the body which escapes in solid form - food residues that were not fully digested

I think it is in the middle there that the talk about calories loses its traction. Weight loss is related to loss of substance, of material, from a body. Burning fat to release energy might be the underlying reason why waste products need to be removed but it is the actual removal of the "ash" that results in weight loss.
Most of the articles I have seen talk about the different ways in which energy is expended without ever discussing this final step in the process.

For a number of reason I still find conservation of mass a better way of thinking about the issue.
For instance - the way that waste products are removed nearly always requires water and so, while restricting fluid intake reduces weight in the short term, it is a very BAD approach for health - or long term results.
(BTW - thanks to Peter Attia for letting me work some of this out in his blog comments)

Logic and the Body Weight Issue.

Through a number of links my attention has been drawn to the works of Gary Taube and particularly his post on how the science should work. I haven't read in detail but this recalls my own confusion on the standard advice on wieght control.
As I have said before, the calorie in/calorie out argument is obviously incomplete at a very basic level. A calorie is a measure of energy - not weight. Hence there must be significant complexity involved in the advice that is being completely hidden. I can't see to get this message across to people around me; my wife is trained in bio-science and just says that of course there is complexity, but it is not possible to describe the physiology to the layman. Her sister was a personal trainer and seems to have swallowed the party line without analysis (along with an Atkins focus - after all, it worked for her).
They may well be right, but I can't just accept it at face value and it is almost certain that any hidden complexity is also likely to hide mistakes in interpretation.

From the beginning then: the basic physics principle of conservation of mass. Body weight must equal mass in minus mass out. I'll take this as a starting point. So to reduce weight one must decrease solid/liquid/gas intake and/or increase solid/liquid/gas outflow. As I understand it the major complexities relate to the tight dependencies between these - reducing intake automatically reduces output until there is no net change. This is homeostatis and is a good thing, if a little inconvenient for those trying to institute a change.
The input end of this flow is the point where we have the most control and I am not going to even suggest that anyone take direct control over their outflow (except in one specific case that I will get to later).

Many years ago I read the Hacker's Diet which had the following image:

which shows the relative importance of various forms of intake and outflow. At first blush it would seem to indicate that water intake is the most likely point of approach. But the volume of water in a body is relatively static (At least, it makes sense for it to be so, I am happy to be corrected). Additionally, it is the prime medium through which metabolic residues - the 'ash' from 'burning calories' - are removed.
Besides, look at the difference between intake and outflow in each of phase. Obviously significant water and carbon are coming in through food and but not going out in solid form.
Here's where I suggest a means for controlling outflow - get more exercise. There is a significant increase in liquid and gaseous loss of material from the body both during and after exercise. Personally I know that I can lose well over a kilogram during an intensive exercise session  - which of course comes back as soon as I re-hydrate. The take-away message being that rapid changes in weight are almost certain to be fluid related and short term.

I seem to have drifted so back to the original point. Control of outflow is difficult and potentially damaging depending on how it is done (I can't think of any healthy way). Control of gaseous intake would be almost impossible and is likely to have only minimal impact anyway.
Control of liquid intake is easy and possible and has the largest impact on total body weight. However, indications are that it is temporary, unhealthy and potentially counter-productive. The first I have mentioned already and the health issues with dehydration are well documented. With regards to counter-productive - apart from water being the medium for flushing waste products from the body, I understand that lack of regular fluid intake results in the body retaining water - hence leading to a higher base weight. I have only anecdotal evidence of these points but the arguments are reasonable.
This leaves control of food intake as being the most effective means of weight control. And recall that I am talking about the sheer quantity of food, not the calorie content. Having said that, it is almost certain that different types of food have different impacts on the body and how long the material remains.
My personal response to this is to (try to) stay with foods that are high in nutrient/weight ratio. By default this appears to result in a diet high in vegetable matter and meats - dense foods and low in carbohydrates which tend to be fluffy fillers. It is interesting how closely this replicates the current fad diets - albeit for different reasons.
There may be a vast amount of complexity still involved in how bodies process inputs and execrete outputs, but there is much that can be achieved through simple reasoning from some basic principles.