Do free lunches really influence docs?

The writer of this editorial in the New York Times thinks so:

The doctors always insist that they can‘t be bought. But a former sales representative for two drug companies said the lunches were “incredibly effective” in lifting the number of prescriptions from practices that got the free food, and a medical school doctor who is examining the issue believes the lunches do influence prescribing. Some doctors seem to rely on free lunches as a fringe benefit for their staffs.