Few soldiers were obese due to constant exercise and restricted rations. Beer and wine did provide carbohydrates.

No not really, you cannot get obese due to constant exercise and restricted rations - as you rightly point out the body will mobilize reserves in case he gets into a calorie deficiency - the proteins unfortunately are "easier" to mobilize than fat (needs itself again a lot of energy and water to get converted into energy modules - ATP) you will loose muscle mass as well as fat loss, but you won't get obese, this is only possible in higher intake of calories (regardless of what quality, fast - carbohydrates, proteins) - however due to extensive protein loss you might get an ödema - like the starving belly which is caused by water, by definition this is not obese.

Beer and wine provide mostly alcohol as well, lesser carbohydrates (the sugar of the fruit or rye, malt, is essential to produce alcohol) - alcohol is falling in the "fat" category of calorie supply.

There bread is a classic supplier of carbohydrates, which can be easiest transferred into ATP - soldiers were usually looking forward for their bread rations - when bread was substituted with meat only, that caused problems as well, there again proteins had to be used as ATP sources which requires again a lot of biochemical processes compared to carbohydrates.

So you are right that not only calories count but also the quality of the basic food components, but usually you get fat when your intake in carbohydrates is exceeding your consumption of them, the excess gets converted into fat.

It is very unlikely that Boney had hunger ödema - he just was eating immense amount of food to obtain a beer keg belly.