What difference does it make whether I am in the described groups or not? You can argue that IQ doesn't exist, or shouldn't affect engineer value, or that the correlations don't exist, but telling the author "you won't like it when it happens to you, so agree it doesn't exist" is weird.

> "Up until around age 35 or so, I was generally very lean and did not get noticably fat regardless of my lifestyle."

It's tempting to read this as saying "I didn't choose it to happen, so I'm excused from any negative effects", although that would be taking a negative view on it. But if not that, what else is this sentence here for? Maybe you're saying that there's more to fat than lifestyle - then skim read "Ten Putative Contributors to the Obesity Epidemic"[1] (PDF or online PDF) where they discuss things like viral infections, environmental triggers, socieo-economic contributers, and other things which aren't diet or exercise related. Does any of that change whether obesity does or doesn't correlate with IQ? Or maybe you're saying you got fat despite exercising - which only says exercise didn't save you, it doesn't need to change whether IQ and obesity are correlated or not. Plus exercise was suggested as a counter to age related decline, not as a counter to fat, only as a thing people might think when seeing fat.

> "I know I haven't gotten any stupider."

Who ever thinks they have? Would you honestly know? You ought to have lost some abilities just going from age 35 to 55 alone. See[2]: "Age and individual productivity: a literature survey" - "The ability levels of employed white men and women up to the age of 65, using data from the General Aptitude Test Battery collected in the U.S. from 1970-1984, is shown in Figure 2. These findings suggest a relatively sharp decline in most abilities, after maximum values are reached in the 20s and early 30s (Avolio and Waldman 1994). The decline of mental abilities from early adulthood is a universal phenomenon. The age-induced changes in cognitive abilities are similar across countries and within population subgroups, such as between men and women (Park et al. 1999, Maitland et al. 2000). Further individuals with high and low ability levels are subject to the same age-induced changes in cognitive functioning (Deary et al. 2000). Even among non-human species, ranging from fruit flies to primates, age-reductions in memory and learning capabilities have been observed (Minois and Bourg 1997, Bunk 2000)."

[1] https://www.researchgate.net/publication/40447388_Ten_Putati...

[2] https://www.demogr.mpg.de/papers/working/wp-2003-028.pdf