The below article makes mention of a fact that may complicate things though - big strong slaves were worth more. Presumably slave owners had this in mind so had an ulterior motive for feeding slaves better.
It’s one bleak subject.
https://www.researchgate.net/publication/11718681_The_Height...
Very bleak, but slave owners had a large economic incentive to make sure their slaves were fit for work (although that didn't cause qualms on other, more brutal forms of mistreatment). The only way they treated them well was in providing food, but that wasn't due to kindness but more from the same motivation to feed a team of draft horses well. It's tough reading, but some of the ledgers kept by plantation owners really drive the point home that they viewed slaves more akin to livestock than people. And they somehow justified what they were doing as christian and moral.
I believe the average member of the House of Commons was visibly shorter than the members of the House of Lords at least through WWII. Certainly Americans were obviously taller than Europeans until after WWII. Even American slaves were taller and children were generally malnourished until about seven when they became capable of working. Adult height seems to have been unaffected reflecting just how rich the US was comparatively. Complete unfeeling bastards didn’t malnourish children enough to do permanent damage.