I was trying to make what is quite a complex metabolic process as easy as I could but you are right it is not "totally" true.

Ham is protein and fat. The creation of fat in our bodies...the storage mechanism and the burning of fat for energy release are affected by two different hormones..Insulin and Glucagon. They act in different ways.

When we eat, insulin drives our metabolism to store the excess food energy for use later. When later comes ....Glucagon drives the metabolism the other way, letting us burn our stored fat for everyday needs.

The chief priority of Insulin (it has other reasons to be) is to keep blood sugar from rising to high. Glucagon on the other hand is there to prevent blood sugar from falling to low.

This little game that the two hormones play with each other is vital. Without either one we would literally be dead within days.
If a diabetic does not get insulin they will die. Coma will be in hours and death is inevitable.

Without Glucagon, the brain would soon begin to dsyfunction and then too death will follow.

Now these two hormones get along quite nicely together and we cannot change our Insulin and glucagon directly. There is no such thing as Insulin or Glucagon pills. They would be destroyed in the digestive system. Diabetics have to inject insulin in the blood stream.

The only way that we can affect the production of insulin is to change our blood sugar level by ingestion. Take a spoon of sugar or mollasses and blood sugar will climb within minutes.

To affect glucagon, with out artificially lowering blood sugar by the injection of insulin. just eat nothing for a few hours... let the blood sugar decline naturally until the the pancreas gets stimulated to produce Glucagon.

Now why am I banging on about this to explain why the extra slice of ham is less likely to make you fat than say an extra slice of bread. It has nothing to do with the calories. For the sake of my point let us assume that we eat the same caloric content of ham as bread. A ham sandwich if you like And then we should examine how we can affect the hormones by eating either the ham or the bread or both together.

In the battle of the hormones and their effect of our fat cells and our cholesterol levels you can see that Insulin is the bad guy and Glucagon is the good guy in the white hat!

I hope you are still with me because I am getting to the point. Insulin does a number of things..it converts glucose and protein to fat. Glucagon converts protein and body fat to glucose.

Insulin removes fat from blood and moves it to fat cells. Incidently fat cells do not get eliminated when we lose "fat" by dieting ,they just get smaller. But I digress.

Glucagon converts dietary fat to ketones and sends them for stotrage in tissues. it also releases fat from fat cells for use as energy. It also reduces cholesterol.

This then is the the key to what is going on and why we are less concerned with calories. Through experimentation science now nows what effect food has on Insulin and Glucagon.

Protein raises Insulin a little and raises Glucagon a little

Carbohydrate raise Insulin a lot and has no change to Glucagon

Fat... Does not do anything..it does not exist as far as insulin is concerned.This is the problem with low fat products. When they take the fat out of chips you are are left with a greater amount of Carb.

High carb and low protein together, incredibly, raises insulin higher than carb alone and raises glucagon less than protein alone. Moral: Take the burger out of the bun.

So... I think it is therefore Ok to say that the extra slice of ham is unlikely to have a significant impact on Insulin. Is therfore unlikely to trigger the fat storage system. The slice of bread?...... feed it to the ducks

This also explains why Atkins suggests the fat fast which is eating food that is more than 80% fat. It is as neutral to insulin as you can get. However there is only so much fat that we can take in that type of quantity. We can only do it for small bursts.