A number of things can stimulate adipogenesis in adults including medications (e.g. TZDs) and yes, Obesity.
Check out this PubMed article:
www.ncbi.nlm.nih.gov/pmc/articles/PMC8879274/Particulary this part right here
Excessive food/energy intake leads to the expansion of adipose tissues, including both increased numbers of fat cells, i.e., adipogenesis, and increased size of individual adipocytes (hypertrophy).
To my understanding, our bodies will generate new fat cells well beyond puberty if we keep gaining weight. When our fat cells are full, they will both enlarge in size and increase in number.
Here is another example from this pubmed study:
www.ncbi.nlm.nih.gov/pmc/articles/PMC8879274/In adults, fat cell number is constant over time in spite of a large turnover (about 10% of the fat cells per year) when body weight is stable. A decrease in body weight only changes fat cell size (becoming smaller), whereas an increase in body weight causes elevation of both fat cell size and number in adults.
The increase in size is bad for us, so ideally the more we can do to stimulate adipogensis, the more likely we are to be metabolically healthy while obese.
Also if you look at the wikipedia page for Lipotoxicity, you'll see that it's still undetermined whether or not Obesity is the cause.
The causative role of obesity in lipotoxicity is controversial. Some researchers claim that obesity has protective effects against lipotoxicity as it results in extra adipose tissue in which excess lipids can be stored.
MitchHedberg:
My personal theory is that when you combine weight gain with "healthy" behaviors like exercise, our bodies are move in the direction of adipogenesis over fat cell hypertorphy. However, I'm willing to bet that it's mostly determined by genetics and that you're only able to influence things to a certain degree.
Your genetics play a huge role. Yes, eating nutritiously and exercising help a lot. But some people tolerate things differently. I have seen people that are fine are very high body weights (400+) and others who can't gain without getting violently ill.
