The population is diverse (nearly everyone). Why test on soldiers?
They already volunteered. Fit service members are not self selecting for phony sugar because they are already obese. In other words, they are not overweight already; they have no reason to use artificial sweeteners. Logistically, it would be more convenient to study the military and their spouses and families.
It would also be easier to test HFCS sweetened pop versus sucrose sweetened pop. I have no more reason to trust the makers of HFCS than the makers of artificial sweeteners. The link in comment# 20 is a review article. I'ts quite damning of HFCS. I used to think all 6 carbons sugars were functionally equivalent. Fructose promotes lipid production in hepatocytes.