It is science

In the 1990s when muffins were a craze in the USA my neighbor, a vegan food scientist, kept wondering how anyone thought cake was acceptable for breakfast. I never thought of it as cake until I made a batch and then made a cake and realized they were essentially identical processes.
- How is cake unacceptable for breakfast?
  I mean, even a vegan has to appreciate the power of cake.
  
  It’s a ton of fat and sugars with no added nutritional benefit.
  
  Deep fried cake covered in sugar is the quintessential American breakfast food.
- Brought to you by the same people who say donuts are acceptable breakfast
- I consider all junkfood a type of cake, so I only eat junkfood as often as I would eat cake, which is sadly too often.

My wife's family is extremely health conscious and typically eats like rabbits. There's not a dish they have encountered that couldn't be "improved" with a metric fuck ton of broccoli, kale, onions, zucchini, etc. But they also love brownies. It is typically their only indulgence at family get togethers.
But instead of using eggs and oil in the mix like it calls for, they substitute those evil fats with applesauce instead. It kind of sort of works from a textural standpoint, but it definitely still tastes vaguely of applesauce which is not super desirable in a chocolate brownie. Ostensibly the idea is to make it "healthier" and lower calorie. But given all the sugar and other carbs in the batter (including the added sugar from the apples) the calorie difference is negligible but the end result is not the same at all. It feels like they missed the point and messed up the brownies for no reason at all. Doesn't stop them from calling them "healthy brownies" though. Stretching the definition of "healthy" reeeeaaaal far.
- To quote The Good Place:
  There's something so human about taking something great and ruining it a little so you can have more of it.
- Suggest to them to use pureed pumpkin instead. My wife does that and I can barely tell.
  
  My father used to make delicious pumpkin Marmelade. I couldn't get enough of that stuff.
- and typically eats like rabbits
  They eat their own poop?
  
  I doubt OPs friends are Ethan's Kliens family.

Pro tip for baking modern American recipes is you can cut about 1/3 of the sugar no problem, up to 1/2 on some recipes. Bran goes really well with blueberries. The blueberry muffins I make are basically lightly sweetened wheat bread and they slap. Muffins are a quick bread but somewhere along the line people wanted to lie to themselves and eat cupcakes while pretending they're still muffins
- muffins are essentially cake in most formations. Cake, unlike many baked goods, is one where making massive changes is often ill advised as the chemistry of cakes is a lot more delicate than say bread or cookies. Removing 1/3 of the sugar in a cake/muffin recipe will lead to a tougher and drier muffin than one that has the recommended sugar amount.
  Rather than remove large amounts of sugars it is better to find one that was created to not need the sugar to begin with
  
  It may be semantics but I do not consider muffins to be cake, that would make it a cupcake. Muffins are closer to quick bread to the point where any quick bread recipes I have tried work as muffins with no changes to ingredients only cooking time. For sure if you cut too much sugar out of something you lose structure but that's why I specified American recipes. They generally have way more sugar than what's necessary for structure and there's a lot of wiggle room with how much you can take out
- That's not as much a difference as one might think because the flour too is mainly "sugar", specifically it's starch which gets turned into glucose same as the sweet tasting sugars (side note: it's quite an interesting process since saliva itself containes enzymes that break the starch into glucose and you can actually test this yourself using iodine solutions - which you should be able to get from a pharmacy - which turns starch purple).
  Ultimatelly when it comes to nutrition, you should care mainly about carbohydrates in general (which includes all the stuff that is not sweet tasting but gets turned into glucose by the human body) rather than sugars specifically.
  Once you look at it this way you'll find out that a ton of stuff which is not sweet is none the less rich in "sugars", namelly things like bread, pasta, polished rice and so on.

My wife .... a salad is healthy
Goes on to make a salad fit for a serving of four people filled with ranch dressing, cheese, bacon and nuts.
I love her dearly but she absolutely refuses to admit to a smaller salad.
- I also make fat girl on a diet salads, but I am aware of what I am doing with no illusions about how healthy it is.
- The lady over here: I must buy the thinnest sliced cheese permissible by physics. Also my tea shall be served in a bucket with 3 cups of honey stirred in.
  We have all been damaged by the world in some way.
  
  lol .... I was visiting a friend who was in the hospital over a period of about a month .. all of us had to go stay with him to help the family.
  At one point, I got to know the nurses on the floor and I started offering to buy people coffee just to be nice. I thought if I were nice to them, they would be extra nice to my friend getting treatment.
  Everyone was pretty average with their orders but some of the nurses were pretty strange. One overweight nurse asked for large triple triple (triple cream, triple sugar) ... but the best one was a short petite lady that weighed about 80lbs but tough as nails ... she asked for extra large 7 cream, 8 sugar (nicest lady ever but I just could not believe the kind of coffee she drank, it was basically a milk shake with a shot of coffee)

It's ok, I believe chocolate also has antioxidants so it's healthy too!
- Especially if paired with red wine
- I'm pretty sure chocolate might have some caffeine too
  
  Double healthy!
  
  That's why I make my coffee as mocha, it's a health drink!

You should see some of the "blueberry" muffins they sell at the store nowadays. It's not even blueberry let alone fruit. Some are so bad and cheap it's just fruit flavored pellets with the packaging saying "Blueberry flavored" muffins.

If anything, the chocolate chips are healthier than the blueberries, since chocolate has more antioxidants than blueberries.
- Spoiler: Those usually are not blueberries, they are sugar beets.
  
  I read "sugar bees" and was quite intrigued.
  
  That explains why they don't taste like blueberries.
- Id argue blueberries healthier because of the fibre

Muffins are cake. I don't eat cake except on special occasions. I think this is a pretty good rule.
- Breakfast is a special occasion though.
  
  Especially second breakfast
  
  If you're doing it daily, it's not really special IMHO.

Well, any number other than zero is infinitelly greater than zero.

I want you to put the same number of blueberries into each muffin.
Do you know how long that will take?
I don't care, just do it.