ExCalc, a weight loss calculator and exercise calculator, but one that understands thermal effect of food, basal expenditure, running, cycling, alcohol, glycogen and ketosis

This calculator allows you to specify food eaten, exercise performed and at what time of the day, it then calculates the effect on body weight in small time intervals, between 15 and 60 minutes for 1 to 5 days.

At first glance this sounds like absurd overkill but actually it makes a great deal of sense. The problem with most weight loss advice is that it is very high level, "eat less, exercise more and you will lose weight" when often what is needed is detail.

How much less? What effect will a 5 mile bike ride have if I do one every day? Surely that snack doesn't really matter that much?

Once you try to answer these questions it becomes clear that the longer the calculation periods become the more that answers are hidden. Well, did that 20 minutes of exercise and that extra chocolate bar cancel each other out or not? You can't tell if you look at the day as a whole.

Currently exercise can be cycling or running along with background exercise, the walking that is part of a normal day.

Although exercise calculations have to be approximations, they are pretty detailed ones. For walking general fitness is not taken in account but it is for cycling and running. This fitness level affects the exact balance of fat and glycogen used during the exercise and the recovery load.

To get this fitness level a couple of apparently irrelevant exercise specific questions are asked, so you can be running fit but not cycling fit.

As keen cyclists may have access to a power meter which will tell them exactly +-2% or less what their power levels are they can use this number, runners don't seem to have similar tech yet so their values always have to be calculated.

For exercise purposes energy expended is based on a 25% bodily efficiency, if you need 200kc to do the exercise then you will need to eat 800kc. Again this is an average number and is in part the reason why so many sources give so many different answers to the same question.

As might be expected the calculator is a simplified version of the body and exercise, many assumptions are made, default values used and handling of special cases limited.

Some might notice that the calculator uses blood glucose and glycogen interchangeably, this is clearly inaccurate but it only has any real effects if you try to set up a scenarios that don't reflect reality just to "prove that the calculator is rubbish".

Clearly if you are an expert on human physiology then the accuracy of these simulations can be ripped apart especially when you look at short time periods, but I am optimistic that on balance the results are sufficiently close to reality that they are informative and useful.

The simulation is intended for people who are looking for a general overview on food, exercise and bodyweight rather than elite level athletes looking for a tool to use as part of a training plan or someone looking for something that is so accurate that it can be relied upon to lose weight.

Firstly when you eat food its digestion requires energy, calories, and this cost is significant.

The Thermal Effect Of Food is the most commonly used term to describe this and like most diet related processes nearly everyone agrees on the basic principles but the devil is in the detail.

So if you eat food which yields 1kc then something between 0.1kc and 0.3kc will be required to digest it and we can't simply say carbs require .... etc. as different types of carbs, proteins, fats etc have different energy costs.

Even less frequently discussed is how this energy cost can change.

If you eat some carbs and your glycogen level is below your capacity then the carbs will end up as glycogen, this has an energy cost. If you have reached your glycogen capacity then these carbs are going to end up as fat and the energy cost will be different.

It's the same with exercise, exercise powered by glycogen uses a different total amount of energy to exercise powered by fat and most exercise is a combination of both.

Ultimately muscle movement is powered by adenosine triphosphate (ATP). ATP can be created from fat, glycogen, or ketones, but the complexity of this conversion is different and as conversion of fat to ATP is more complex than glycogen to ATP it requires more energy.

Although the conversion costs are quite small in comparison to the total requirements they do exist and they do need to be considered.

Just to make it even worse a fit person may use less energy performing a task than an unfit person. Although the energy required to move a 70kg person from Point A to Point B is the same regardless of that person's fitness, the fitter person may waste less energy in the process.

Think of an experienced runner jogging along at 7mph with a new runner alongside who is panting and gasping.

Often a web site will can say that on average the TEF is around 10% of the total calories eaten, but this calculator calculates it based on the fat, protein, carbohydrate and alcohol contents of each food item.

The Basal Metabolic Rate is the cost of living, how much energy you need to power your body without doing anything else.

If you are not an enthusiastic sportsman and have an office job then your BMR is going to be far greater than the energy expended by exercise.

To give this some context, for a 70kg man the BMR is around 1680kc per day and a one mile walk uses around 100kc.

The BMR is also 1 MET, so a 10 MET activity sustained for a whole day for this 70kg man would use 16,800kc which sounds good, unfortunately this is so demanding that it would also be undoable by nearly everyone.

The Land's End to John o' Groats record by bike requires slightly more calories per day than this, but if you can cycle 1,000 miles in two days then it is unlikely that weight loss is going to be a target for you.

The body's special handling of alcohol has some interesting side effects, most of which aren't that significant for a few drinks on a Friday night, but are significant if you have 5 pints a day, 7 days a week.

When alcohol is consumed it enters the blood stream very quickly, the exact speed being affected by the type and quantity of food recently eaten, it is then processed from the blood stream rather than the stomach and intestines.

Because of this the calculator shows alcohol as two values, the blood alcohol level (mg/100m) this is the well understood number and the number of calories that this represents (kc) as it is processed.

The rise and fall of blood alcohol and available calories are independent of each other as the alcohol get absorbs into the blood stream much faster than it can be processed, the often quoted one unit per hour.

In the body the by-products of alcohol processing are used as an energy source in preference to glycogen, ketones or fat.

The processing of alcohol is a high priority process, it stops the conversion of food to glycogen or fat. Possibly surprisingly the TEF of alcohol is high, in the calculator all alcohol is processed with a TEF of 17%.

This is an area where the calculator takes certain liberties, it uses glycogen and blood glycose interchangeably and although this is not correct I do believe that it is a reasonable simplification.

The calculator show three glycogen related values, the weight of glycogen within the body, the calories it will yield along with the weight of water that is bound to the glycogen.

As you can see from the results screen for every gram of glycogen there are 3.5 grams of water.

Glycogen is processed with a reasonable degree of reality, there is maximum capacity of around 1,800kc and when exhausted the specified exercises are changed to a reduced intensity.

The calculator starts off with around 1,400kc of glycogen depending upon the body weight.

The calculator varies from reality in that when a gram of glycogen is used its bound water also disappears, rather than waiting for it be passed as urine but it does emphasis the principle.

For many people coming to this calculator glycogen will be new, so seeing the effects on body weight shown so clearly outweighs trying to be 100% accurate. Especially as there is no real way to work out if this now surplus water will be retained or simply sweated out.

Glycogen is currently handled as being in one of three chunks, liver, upper body muscle and lower body muscle and so far this simplification has not seemed significant.

Ketosis is often described as a process that occurs when the body has run out of glycogen and the body derives energy from ketone bodies, a fuel source generated by the body from fat. These ketone bodies are then used in a very similar way to glycogen.

Ketosis is actually an ongoing process that ramps up and down depending upon the amount of carbohydrates that are being absorbed, as carbohydrate digestion decreases ketone production increases.

Ketones are produced by breaking down fat and once created serve a very similar function to glycogen but they are not bound to water in the same way as glycogen.

The problem with ketosis is that the body seems to regard ketones as inferior to glycogen as a power source so as soon as carbohydrates are available ketosis is reduced to background process and glycogen production is resumed.

This why low carb diets can offer such large weight losses in the first few days and then such large weight gains when they are stopped. The glycogen is used up and its associated water is lost, then the glycogen is recreated and its associated water is needed when more carbs are eaten.

Excess Post-Exercise Oxygen Consumption definitely exists, all the experts agree as does our own experience, however this seems to be where agreement ends.

Looking at the research I can make a strong case for the recovery from 20 minutes of exercise at 70% of VO₂ Max as being between 1.9kc and 2.8kc, that is of course a huge difference.

What is clear is that intensity and duration drive the recovery which might seem obvious, the more you work the more damage you do to your muscles.

But the two are significantly unbalanced, for example one study had the recovery energy consumption for the same total work done at 70% VO₂ max as twice that of the same total exercise expenditure at 50% VO₂.

As exercise duration increases beyond an hour the amount of research available plummets, putting the calculations here into an "interesting guess" territory. There also appears to be no consensus over whether or not sex make a difference.

When discussing weight loss it is sometimes useful to make calculations static and say that cycling one mile at 20mph uses say 30kc. At the very highest level this is fine as it gives a starting point for discussion, but it must be seen as a starting point.

As you exercise more you become fitter, which means that your energy requirement for a specific piece of exercise decreases, and in this context it is likely that over time you will also be losing weight so will require less energy for the same exericse.

For example a 60 year old man weighing 90kg going for a 60 minute ride at 16mph could use Fat 161kc, Glycogen 283kc, totalling 443kc, if drops his weight to 70kg the numbers drop to Fat 152kc, Glycogen 267kc, totalling 419kc.

Okay the difference doesn't seem that great, it's about 5%, because this is a calculation on the flat.

Research suggests that Paula Racliffe, an elite level, athlete became 15% more effecient as a runner over her career. Given that the starting point of this research was an athlete who had just won the World Junior Cross Country champsionship, what would the improvement be for the Couch To 5K type person?

There are some things that the calculator does that appears odd, don't really matter and are necessary if you want to produce a meaningful result.

The way that the calculator reports things make it seem like there is sequential food processing instead of the reality where all the food is mixed up as chyme and chocolate bar 1 and chocolate bar 2 are indistinguishable.

But reporting things as one lump makes reporting on the energy derived from that "extra chocolate bar at lunch" much harder to see.

The calculator has the concept of background walking, this is walking that is not done as a specific exercise but takes place during the day as and when, the walk to the bus or around the factory etc.

The calculator reports this by breaking up the miles walked evenly across the day and reports it even when an activity such as running or cycling takes place. This looks silly but there isn't an obviously preferable way to display it.

There are a lot of health and exercise web sites and many of them will have statements and possibly calculators that won't sit well with the results that this calculator produces.

I am very happy to discuss areas where the calculator could be improved or is actually wrong.

What I don't intend to do is to try and reconcile my results with someone's favourite site that says something like ...cycling typically uses 40 calories per mile... without any supporting arguments.

Many web sites want to be concise so pick averages that seem reasonable to the author and are typical of the expected readership, but without knowing these assumption the articles can be hard to fully understand if you come across them as a result of a web search. If your search gives you a number of sites with the same assumptions then you can end up with a different impression to mine.

What I mean by this is that if you go to a body building site then don't expect the discussion to be about the nutritional needs of an Ironman triathlete and the triathlete's site won't have much to say about the best protein powder to build muscle and minimize fat.

Of course some web sites exist only to post advertising links and simply cut and paste text without any real understanding or interest in the subject. In order to appear higher in search results it may actually be advantageous to have contentious content, you can get your site mentioned on other sites with thing like xyz is saying ..... and is wrong because.