The dotted lines show those who took vinegar before meals.
Another study found that when ingested before bed, vinegar reduces waking blood glucose levels in type II diabetics . The authors believe this is due to the effects of acetic acid, the active ingredient in vinegar. Acetic acid suppresses the enzyme that helps breakdown some complex carbohydrates into glucose, which could decrease the storage of glucose (glycogen) and therefore keep insulin sensitivity higher .
I strongly urge diabetics to avoid carbohydrate-dense foods in general. However, consuming vinegar before a high carb meal seems to blunt the harmful effects for diabetics, at least in the short term.