How low should blood sugar be? 28. February 2010 William Davis (0) What should your blood sugar (glucose) be after eating? Take a look at the data from the Whitehall study reported in 2006. The Whitehall Study stands apart from other studies in that it was very large (over 18,000 participants) who were observed for an unusually long time (33 years). All participants were administered a 50 gram glucose "challenge" at the start with glucose levels checked after the glucose challenge. Here's what they found:From Brunner et al 2006.