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Comment by kmm | Hacker News Reader

> Obesity = more cells

That's not true. Not only do fat cells just grow bigger (a skinny person has just as many as a fat person), you'd expect the increase in cancers to be mostly liposarcomas ("fat cell cancer"), which stay very rare.

Other organs might be distended or enlarged, but they don't contain more cells.

The reason obesity leads to cancer is not very well understood, but it's probably a complicated process involving abnormal hormone levels usual in obese people, and the constant low-grade inflammation their body is usually suffering from

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I don't believe this is how it works.

https://news.yale.edu/2015/03/02/new-fat-cells-created-quick...

I'm no longer deeply involved in this area so my information might be dated, though years ago it was pretty well understood based on the evidence that fat cells were created _and_ grew bigger as person got heavier, however, fat cells (once created) were never eliminated from the body, meaning they would shrink though they would be around forever once created.

It was also understood (if I recall correctly) that the faster someone gained fat, the easier it was for fat cells to be created. Meaning rapid weight gain was more likely to create new fat cells. (not sure if I'm remembering that one right)

It was surmised from these that this is why rebound weight gain (aside from rebound lifestyle factors) was quite easy for many, particularly the incredibly obese. It was also why it was strongly recommended to take fat gain incredibly seriously as the creation of fat cells was deemed potentially lifelong damaging.

> That's not true

Do you have a source for that? I find that claim interesting because I'd be surprised if obesity != more cells.

Update: I found this link about a study that found as you gain weight, you grow new fat cells (2010). I can't find the paper though.

http://www.foxnews.com/health/2010/10/05/gorging-study-shows...

Update 2: I believe this is the paper: https://www.ncbi.nlm.nih.gov/pubmed/?term=20921416%5Buid%5D

Update 3: Another paper that found growth of new fat cells on weight gain (2015): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4380653/

From this article found in this thread: https://news.yale.edu/2015/03/02/new-fat-cells-created-quick...

How can that be true? Don't fat people at least have more skin cells than skinny people? Also, I can't imagine that enormously obese people just have larger fat cells than skinny people. I have read that it is harder to get rid of fat cells once they shrink, but not that we don't get more of them.

A common misunderstanding is that organs are made up entirely of "cells" but, they are not. There are other materials involved, such as collagen. We call these names like "connective tissues" and they take up a lot of the space.

That doesn't mean they aren't involved, proteins can go wrong, but, that is usually associated with other types of diseases besides cancer.

That still leaves me confused. A skinny adult who becomes obese has the same number of skin cells? That sounds hard to believe.

Yes, the number of skin cells will increase. They will also need more blood vessel cells, immune cells, etc.

I would like to point out also, that many people who would be described as "skinny" would almost never become obese. Neither would they be able to put on much muscle mass. It is a huge misconception that our bodies are just blank templates that can become fatter or more muscular. Different bodies have affinities for different shapes.

Someone who is very ectomorphic and "scrawny", will often have severe difficulty gaining a substantial amount of weight.

I disagree, (would be open to sourcing from this) but there are photos of people I know from 15-20 years ago where you would look at them and think they’re scrawny, and now they are visibly obese.

Sorry, but this just sounds wrong. Even if the only evidence I can point to is life experience.

Oh sure they increase, but, not at a plainly obvious rate, it depends on the tissue and the like. But the majority of that mass is not cells.

Stretch marks are the areas where fibroblasts just lay down a thin patch of fibers because there's insufficient ability to grow skin to keep up with the required surface area.

What about muscle? Does that follow the same thing as fat cells, they just stretch/grow, not increase in count? I always just assumed more cells were created as you got bigger.

Human muscle cells experience hypertrophy (growth) but not hyperplasia (increase in number). (Post-puberty, anyway)

The low grade inflam and hormones are definitely causal. Another that biologists don't really from is the simple increased temp these people live at due to fat being insulation: Simple thermodynamics starts to creep in over 50 years.

Speaking of hormones, being overweight or obese may also increase the risk of breast cancer. The development of breast cancer involves estrogen, and fat cells produce estrogen.

Excess fat tissue also isn't vascularized to the same degree normal quantities of tissue are, resulting in an inflammatory cascade via Hypoxia- Induced Factor.

I have a rather large amount of loose skin that begs to differ with your "Obesity != more cells" assertion.

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