Testing mean difference on group means, multiple independent groups/sites

#1
Hello Talk Stats group,

I am trying to find out what statistical tests to run on a set of aggregate data (no individual data) on 3 different groups. My variables are summarized below (but I aam attaching a random example to make it more clear):

Group 1 in site 1: Mean value (blood sugar) of the total sample before treatment (MeanG1Bef), and mean value (blood sugar) of the same group after treatment (MeanG1Aft)
Group 2 in site 2: same as above (MeanG2Bef and MeanG2Aft)
Group 3 in site 3: same as above (MeanG3Bef and MeanG3Aft)

For now all what I can think of is Paired t-test on each group separately for the group difference in blood sugar means after treatment and before treatment (to test if any increase or decrease in the whole group average is statistically significant, for instance if difference between MeanG1Aft and MeanG1Bef is statistical sign - for this I know I would need the SD as the sample size for each group)

Where I start struggling is when I think of the tests to apply for the difference between the 3 groups. I can calculate absolute difference in the means after and before treatment for each group (MeanDiff Group 1 = MeanG1Aft - MeanG1Bef, same for other groups/ same for MeanDiff Group 2 and MeanDiff Group3)
Can I then run an ANOVA on the difference means between the three groups?? If yes what other data do I need if any??? and how will I interpret my results??

Thanks for whoever is willing to help!
Pamela