Yes. No. Maybe. I don't think this question has a single definitive answer. I'm not sure if we have a single definition of today's beauty standards. I'm also pretty sure that "beauty is in the eye of the beholder" holds true today as in the past.
"Beauty, like supreme dominion. Is but supported by opinion" - Benjamin Franklin 1741
Since we don't have any men/women from the middle ages to show pictures to. How about I show you pictures from the middle ages. Then you can decide if you find the people in them attractive. If you do I think there's a good case that beauty hasn't changed. If you don't we will make the opposite case.
WARNING NSFW
I'm afraid I can't guarantee that what was painted was always the ideal of beauty. Descriptions of beauty from literature of the period are often insulting of fat gluttonous etc. although words like plump and phrases describing large breasts are often used to describe desirability in a woman. Other words with meanings such as petite, skinny, lithe are often used to describe attractive women. Once again we are left with a vague description of ideal beauty. But I think we can safely assume that the basic characteristics of what most people consider attractive hasn't strayed enough that beauty from the 15th century can't be recognized today.
edit: fixed incorrect link
It's impossible to say exactly what any historical person would think about any development today. Your question might be reworded to "What were the beauty ideals in Europe during the middle ages, and how do they compare to those today?", and I can answer that. (At least about the later middle ages - tough to generalize about the entire period.)
Contrary to popular assumption, the ideal female figure for all cultures before the 20th century wasn't plump and voluptuous. A "long and slender body with small breasts but a protruding belly" was the conventional beautiful form throughout later medieval English art and literature; the ideal woman was in her late teens and had fair skin and hair, red lips, and dark eyebrows. While the "perfect age of man" was in his 30s or 40s - having strength, wisdom, power, and maturity at that point - the beauty of a young man in late adolescence was also celebrated, with many of the same attributes that were seen as pleasing in women of the same age: long fair hair, pale skin, slenderness, etc. (Medieval Maidens: Young Women and Gender in England 1270-1540, Kim Phillips 2003; "Beauty", Women and Gender in Medieval Europe: An Encyclopedia, Margaret Schaus; "Young, Rich, and Beautiful: the Visualization of Male Beauty in the Late Middle Ages", Gerhard Jaritz, in The Man of Many Devices, Who Wandered Full Many Ways 1999) This standard of beauty is highly on display in extant art. Turning to just about any page in the Roman de la Rose will show idealized, slender young people; paintings, tapestries, and statues are the same.