Studies correlating obesity and poor sperm quality are numerous and easy to find. https://www.hsph.harvard.edu/news/hsph-in-the-news/excess-weight-sperm-fertil

Studies correlating obesity and poor sperm quality are numerous and easy to find. https://www.hsph.harvard.edu/news/hsph-in-the-news/excess-weight-sperm-fertility/ https://www.hsph.harvard.edu/news/hsph-in-the-news/excess-we... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3521747/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3521747/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5657098/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5657098/ You can find more without much effort. What I don't see are epidemiological studies trying to track the prevalence of obesity vs. the average sperm quality across different nations. Unfortunately.