17th century food was fibrous, bland, and surprisingly good for you (if you could get enough of it)

This is not to say that their food tasted bad, necessarily. But it was clearly very simple, and very starch-heavy. From China to Europe to sub-Saharan Africa, gruels and stews made out of staple grains or legumes were the daily fare. Italian farmers weren't eating eggplant parmesan or spaghetti with meatballs. They were typically eating either boiled beans or grains, day after day after day.

First mind-blowing passage from this post:

One example: I didn't realize until recently that broccoli, Brussels sprouts, cauliflower, kale, cabbage, and collard greens are all technically the same species,  Brassica oleracea. The substantial differences between these sub-species are all due to patient intervention by human farmers over millennia. Many of these changes are surprisingly recent. Early versions of cauliflower may have been mentioned by Pliny and medieval Muslim botanists, but as late as 1600, a French author was writing that cauli-fiori "as the Italians call it" was "still rather rare in France." Likewise, Brussels sprouts don't appear to have become widely cultivated until the Renaissance.

Selective breeding and pollination (the original GMOs) have radically altered what our food looks like. See this picture of fruit from the link. Look closely at the watermelons in the right lower corner. They look nothing like the pink, juicy, almost seedless beasts we see in the grocery store circa 2017:

"as time went by, a dish tended to become sweeter, spicer, and more complicated."

We paid for that sweeter, spicier food, and not just in our waistbands. The Columbian Exchange brought diseases to immunologically naive people and turned people in to chattel. The English didn't have bad teeth til sugar came along. 

Eat up.

You'll only gain 0.8 pounds this holiday season. But if you do that every year you get fat

We overestimate our own weight gain a lot over the holidays:

When Jack Yanovski and his colleagues began their study of 200 National Institutes of Health employees,  they were responding to a media environment that frequently cited holiday weight gain averages of 5 to 10 pounds. But they found their subjects gained an average of only 0.8 pounds between mid-November and early January, and that those same subjects overestimated their own weight gain by a factor of 4.

But then we don't lose the modest weight that we do gain, and after a couple decades we're in trouble:

  A 2014 review of six different studies found an average holiday weight gain of 1 pound. A 2017 summary of the research found similar results. Just 1 pound — but a significant pound because research also suggests that it could account for most (if not all) of our average annual weight gain. “Yup, it’s small,” said Dale Schoeller, professor emeritus of nutritional sciences at University of Wisconsin-Madison and author of the 2014 review paper. “But because it’s a large percentage, it’s not unimportant.” Schoeller calculates total annual weight gain by comparing the average weight of a 20-year-old in 1960 to the average weight of a 60-year-old in 2000. By his calculation, Americans gain about 0.8 pounds a year. Over the course of 20 years’ worth of Thanksgivings, he pointed out, it can start to add up.