Game of thrones and the “A Song of Ice and Fire” series have been described as food porn by some, with its vivid and imaginative descriptions of food and feasts written by George R.R. Martin. Being a huge geek that loves the fantasy world of Westeros, I had to take a crack at the healthiness of their diets.
Firstly, we must keep in mind and understand that the level of technology in the series is equal to that of Medieval Europe. Good old George himself stated that the series is loosely based on the Wars of the Roses that happened in England in the 1400s.
From that we can deduce that there is no industrially processed food as there is today (neither have I seen any signs of industry in Westeros).
I will make a comparativistic analysis of their geographical location and climate. From that I will extrapolate what are the most likely foods that represent the bulk of their food intake.
There are lower amounts of sugar available, the available fruits and vegetables are seasonal, and grains are a staple food as well, depending on the kingdom.
Different types of meats are probably mostly grass-fed and free range. And a lot of the eaten meat is wild game – considering that a popular pastime is wild animal hunting. Ok, a popular pastime is also human hunting for certain people (Yes, I’m looking at you Mr. Ramsay “likes to chop people’s belongings off” Snow).
But let’s shut one eye for a moment.
Let’s pretend Westeros is a land of peace. Where people don’t die at weddings and death by sword (axe, knife, arrow, poison, ghosts) is a rare occurrence. People live freely and die due to illnesses.
With taking the ways of dying out of the equation, we can attribute a lot more of death to more natural causes – in this case their food becomes more important.
So how do they eat?
Well, let’s pretend Winterfell still stands, at least 50% of the family is alive, and they are still enjoying some peaceful time up in the North without any Wrights or Wildlings knocking on the wall.
Winterfell castle is way up North, it is far away from sea and as such we can deduce that they have little fish in their diets. Their climate doesn’t allow for too much fruits and vegetables. Their food could be considered robust, rustic, and essential. There is little color, exotic spices or anything like that. Most of their food is meat, root vegetables, and some fruits and plants that grow up north. It’s a mostly protein based diet, along with fats from the meat. A minority of calories come from carbs. This could be considered as a sort of ketogenic diet which would make seizures less common up in the North.  Too bad no one told Jojen about this.
King’s landing in particular is totally different than Winterfell. The food in King’s landing is rich in fruits of different colors, they have berries, and are not foreigners to spices. There is plenty of fish and different types of meat as well. Grains are not a stranger either. This type of diet would be rich in carbs, vitamins, minerals, proteins, antioxidants, and polyphenols too. It is somewhat reminiscent of a Mediterranean diet which has various health benefits from better heart health to lower LDL cholesterol. 
But I guess that didn’t turn out that well for Joffrey.
Dear Daenerys is mostly eating, well, she gets fed with her huge ego, so there’s not much more we could say about that.
The Iron Islands are a hard place that breeds hard men. As such, the »Ironmen« from the Iron Islands have plundered and terrorized the seas for hundreds of years. Even their own motto »We Do Not Sow« tells us a lot about what they eat and how they (have) live(d). Centuries of raiding, their soil is thin and poor, very few crops can grow on such ground. For food they had to mostly rely on raiding nearby isles, tending goat and sheep or other types of livestock. Their food is heavily based on fish, other meats, and different foods they got on their raids.
House Martell from Dorne lives in a land that is rich with different exotic products uncommon in the rest of the Seven Kingdoms. Citrus fruits and Dorne’s special wine being most predominant here. Lemons, olives, and pomegrates can be mostly found in Dorne and as such are one of the main exports. The capital of Dorne, Sunspear, also has a smaller port that trades with different nearby cities and islands, adding food of different cultures into the mix. Judging by higher amounts of alcohol, olives, and citrus fruits, we can assume a low risk for heart disease and increased blood pressure.  At the same time, I wouldn’t be surprised if more people were dying from liver cirrhosis either. 
The Night’s Watch has similar food as they have in Winterfell (but worse quality). Their diet would be predominately consisted of meat that has to be cooked a long time to be edible again, even less vegetables, fruits, and other seasonal foods. They have grains in their diet as well. Their food could be considered hearty and easy to prepare due to the nature of their duty. It’s highly likely at least some of them were/are suffering from malnutrition which could explain some of the irrational decisions they have made – malnutrition has been shown to impair cognitive functioning among which is decision making. 
Due to the fact that there are times when they eat, and there are times when they don’t eat, we could say they follow the intermittent fasting principles. Well, truth be told, in this case the intermittent fasting is just a fancy name for them not having enough food to eat at all.
So what do you think – which house eats the healthiest in your opinion? Did I miss something important?