Apologies for late comment, but thought you might be interested.

It appears that monks were the couch potatoes of the Medieval Times.

"The way to a man's heart is through his stomach and this seems specially to have been the case with monks," Philippa Patrick, of the Institute of Archaeology, at University College, London told The Guardian Newspaper. "They were taking in about 6,000 calories a day, and 4,500 even when they were fasting."

A study of 300 sets of bones found at Tower Hill, Bermondsey, and Merton abbeys in the UK, includes information on a medical condition known now as Dish (diffuse idiopathic skeletal hyperostosis) triggered by overeating and a rich diet.

"The marks of Dish keep appearing on their skeletons. It forms a coating on the spine like candlewax dripping down the side," said Ms Patrick.

The findings tally with satire that developed a keener edge after the Black Death and food shortages. Friar Tuck was only one of many fat fictional characters based on medieval churchmen by resentful lay storytellers.

The new evidence backs records from Westminster Abbey, showing that six eggs a day was normal for monks. In the middle ages, monkish obesity was Europe-wide.

The Portuguese Cistercians had a test: monks unable to squeeze through a certain doorway at Alcobaca monastery's dining room had to fast while slimmer colleagues tucked into "pastry in vast abundance".

A 13th century Cluniac friar's possible daily intake based on Ms Patrick's studies:

11am-1pm Three eggs, boiled or fried in lard. Vegetable porridge with beans, leeks, carrots and other produce of monastery garden. Pork chops, bacon, and mutton. Capon, duck and goose with oranges. Half pound of bread, to use as sop. Peaches, strawberries and bilberries with egg flan. Four pints of small (watery) beer.

4-6pm Mutton gruel with garlic and onions. Posset of egg, milk and figs. Venison with rowanberries, figs, sloes, hazelnuts and apple. Stewed eels, herring, pike, dolphin, lamphreys, salmon, cod and trout. Half pound of bread as sop, sometimes soaked in dripping or lard. Syllabubs of fruit. Four pints of ale. Flagon of sack or other French, Spanish or Portuguese wine.

Friar Tuck indeed!

Source: https://www.theguardian.com/uk/2004/jul/15/highereducation.artsandhumanitie

Obesity would have been a very rare problem in the Middle Ages for the most part. While alcohol contributes to obesity and was very prevalent in medieval times, most of the peasantry would have spent their days doing manual labor in some fashion. This would have resulted in a population who was constantly active in some regard. Also, the peasantry would often live off of bread, cheeses and whatever vegetables were available to them. Chicken was the most common meat as even then they were an cheap and easy to raise livestock. So, the general population had a very slim chance of obesity being a problem for them during the Middle Ages.

The nobility was a different story.

Even the lowest of the nobility could expect many different options to be added to their menu. As they did not participate in agriculture, the ruling class did not receive nearly as much exercise as the peasantry and so fat would be more common amongst them. Also, with their wealth, it was possible to receive meat from pigs, cattle, sheep, and still chicken. Beef and mutton contain more fat than chicken and pork and so one could expect to be consuming more fat than others in the area. Again, alcohol was very prevalent and wines and beers were easy to access in larger quantities. In summation, a lower ranking noble could develop some sizable body fat as they had access to fattier foods and had a less intense lifestyle.

The monarchs and dukes would have certainly been able to reach obesity in the Middle Ages. Massive feasts filled with all sorts of delicacies would be made on a regular basis and the staple wine and beer would never stop flowing. These nobles and their guests spent much of their time engaging in feasts as it was, and still is, a wonderful and delicious past time. To cap it off, obesity would be seen as a symbol of success since you have access to more than enough food.

TLDR:

Peasant: very very unlikely Minor noble: possible Major noble: Very likely