I have heard many times in my life that the nutrition content of some vegetables is contained mostly in the skin. Is there any factual information that backs this up?
I know it’s not true of potatoes, one of the vegetables this claim is most commonly made for. The potato skin is, however, the tastiest part.
I was told growing up that it wasn’t in the skin so much as right beneath the skin. Thus you would lose a lot of it when the vegetable was peeled. Utter bollocks. You lose some fiber by discarding the skin, but the nutrition ought to be fairly evenly dispersed throughout the vegetable, especially tubers and roots. The Old Wisdom is total bunk when you start talking about squashes.
I love the USDA’s FoodData Central web site. You can look up just about any food you can think of and see the nutrients contained within. There is a bit of a learning curve to use it, but it’s a very good tool to use when you want to find out info about the nutrients contained in foods. I’ve certainly had some surprises
Iron and folate mostly in/under the skin. More important for young women than for some other people.
Not being either I’ll take your word for it. 
The iron part is important for children, albeit, most children are not relying on potatoes as a source of iron-- but in Ireland, in the years before the potato famine, they actually were a significant source of iron. Interestingly, adults tended to eat the skins, and leave the insides, which was the “choice” part for children, and so adults, who needed it less, were getting all the iron.
It got balanced out, though, by the fact that what little meat available usually went first to children as well, and children also got oatmeal every day.
And because quite a bit of the vitamin C in potatoes was usually retained after cooking, particularly if they were baked, mainly toward the center of the potato, children got vitamin C from the potatoes.
This was all part of a science unit I had in fifth grade that had particular sticking power, because the stories of vitamin discoveries were all presented as mysteries-- people got strange diseases, and a scientist was a detective out to solve the puzzle. Might have taken some liberty with the historical record, but ever since, I have been able to tell you what every vitamin listed on a bottle did, the time when this was first known, and what foods were good sources for it.
My grandmother always said the nutrition “was in the last bite”. These old sayings are often just a way of encouraging you to eat. Mangia!
But the skin often has more fibre. Sometimes more or less of other stuff. Cooking and processing has widely varying effects on nutrition balancing nutrient loss, breakdown (which often does not matter), etc. with making nutrients more accessible, easier to digest or even increasing them. Presumably cooking in the skin might help increase nutrients, maybe not significantly.
As applied to cookies, cupcakes, etc., I guess that means the calories are in the last bite too.
So eat one, except the last bite. No cals; no problem. Eat a second one except the last bite. Still no cals; still no problem. Lather rinse repeat UFN.
I could certainly see someone’s oversized parent or grandparent advertising this seductive idea. 
I like that idea very much. I mean, if you buy a big enough package than all the calories don’t count. Kind of like homeopathy for gluttons.
Two terms can get conflated.
Nutrition and diet.
Humans can’t digest and hence get no nutrition from the crude fibre, hemicellulose, NDF, ADF or pectins etc fractions in the skin or within the body of the vegetable.
But having a balanced level of fibre makes for a healthy diet.
I bet Zeno’s parents had their own version of this.
Zeno had a couple of doctors who were responsible for his medical/nutritional education.
I thought having a healthy level of fiber makes for healthy pooping. Which isn’t so much “healthy diet” as “healthy elimination of waste”
That’s maybe hair splitting. All these terms are about choong what and how much to eat for their positive influence on the body. Rather than falling simply for gluttony & flavors like a dog or a 5 yo would do.
Stop sass-talking and eat your squash rind!
'Zactly. Well played!
My grandmother claimed the tip of a green bean (end opposite the stem) was where the vitamins were. Fifty years later, I’m wondering if she just didn’t want to be bothered with trimming off the tip?
No, he had one doctor, and a half a doctor, and a quarter of a doctor, and an eighth of a doctor, and…
Which doctor was just about to finish their residency?