It might not even by psychosomatic. It might simply have to do with disciplined awareness.
For instance, you're forced to take the pills before eating. Since you're aware that you're going to eat, you subtlety change your eating habits (perhaps eating more conscientiously rather than wolfing it down or not overeating or avoiding foods you you you shouldn't eat) such that you ease our condition. Such easing might not be immediate, but over a period of time it could add up.
A good way to test this hypothesis would simply have three groups, "control 1" which does nothing, "control 2" which is asked to record what the person is going to eat before eating it, and the test group which eats the sugar pills.
If the sugar pills still have an effect distinguishable from the control groups, then perhaps sugar *is* an active ingredient and we just don't know it.