Person gets diabetes. Weight gain and obesity, especially from overeating sugars and carbohydrates, can lead to "insulin resistance" disorder. The person's pancreas then has to work super hard to make enough insulin. The pancreas eventually burns out and cannot make enough Insulin. . . At which time the blood sugar will get so high that it spills through the kidneys and into the urine. He has diabetes now.
Glycosuria. There are two categories of glycosuria, renal and non-renal. For each category there are a long list of causes of glycosuria. Obesity in and of itself doesn't cause glycosuria, but it can cause many of the conditions that secondarily cause glycosuria. Not enough room to list all the renal and non- renal causes here. Sorry.