“All scientific research begins at the anecdotal level.”
OK, but it ends at the “evidence” level. Amazingly, there is this statistical phenomenon called a Bell curve. Whether or not you have actually met any fat homeschooled children is a moot point.
That is my observation. Perhaps a researcher with experience in this area, will investigate it.
In the meantime.....parents must make their own observations, and make decisions based on imperfect information. Perhaps, they will see, as I do, that homeschoolers are slim and fit, and the rolly pollies riding the government school buses are not.