Worgen Diets: Diet Size? 
Good question, and quite a specific one! Iām no nutritionist, and neither is Blizzard, but we can speculate.
Often when there is no solid lore on worgen physiology, a reasonable conclusion can be drawn from examining real life human and wolf physiology, finding balance betweenĀ¹, upscaling by a thirdĀ² to accommodate for worgen size, and seeing if it works in accordance to canon material.
Worgen Diet Chart (Theoretical)
In theory, compare a wolf and a human of comparable weight to see how a hybrid might behave, then increase the results by a third to accomodate for worgen growth.
Race: Wolf Wolf*2 (human sized) Human ([w+h]/2) *1.33=Worgen (Speculation) Weight in lb: 100 200 200 = 266 Min lb/day to survive: 2.5 5 - = 6.650 Average lb/day: 10.0 20.0 4 = 15.96 Max lb in one sitting: 22.5 45 1.000 = 30.59 Max days w/o food: 12.0 12-24? 21.00 = 21.945
Is it just that simple?
Of course, it is not quite as straightforward as ā([human+wolf]/2)Ć(1.33)ā. Worgen sometimes have the best of both worlds, or one or the other. For instance, worgen have wolf instincts, but are also fully intelligent. They have a humanoid stature, but can eat entirely meat and are considered predatorsā“ and carnivoresĀ³. And then of course their size, agility, aura sensingāµ are unlike man or wolf.
Average meal sizes?
There is also the dietary habits to consider. Where humans are agricultural and eat regularly every day, wolves are predatory. They go several days without eating, and eat their fill when a kill is made. Worgen are depicted hunting (Genn likes his pork fresh), the Bloodfang Pack even eat Forsaken, and Anduin comments in Before the Storm that worgen are useful as an army because they do not need to be fed: they hunt for their rations. All sources suggest worgen have lupine diets, thus also suggesting worgen eat every so often when a hunt is a success, not every day.
Does is matter which form?
That is a good question, and again there is no direct answer. However, we do know that the transformation is very much physical. Unlike a polymorph, the worgen transformation is gradual, involves the growing of fur, stretching of muscles, popping and cracking (not breaking) of bones, and more. We are also shown that while druid forms shapeshift your clothes as well, worgen form does not, and anything you are wearing is forced to stretch or tear (Genn Greymane, Wolfheart) as you grow a third in height and girth.
In the same way that you - and only you - change form, we can assume the same for anything ingested. Swallow a grape in human form, and it will stay the same size when you take worgen form. This means that in theory, if you are completely full in human form and take worgen form, you may feel less full, contributing to the hunger and rage worgen typically feel when they first change (see Halford Ramsey). If this is true, this would also mean that if you gorge yourself to your fullest as a worgen, and try to take human form right after, you might end up spewing a few pounds of raw meat and fur, which may be appropriately dramatic depending on the scene and story.
Cited Sources
Ā¹ Curse of the Worgen pg 69
Ā² Wolfheart pg 208
Ā³ Wolfheart pg 244
ā“ Wolfheart pg 209, 271
āµ Wolfheart pg 267