America’s three largest banks have demonstrated a healthy appetite as they help Washington clean up our messy economic table.  J.P. Morgan Chase gulped down both Bear Stearns and Washington Mutual, Wells Fargo swallowed Wachovia, and Bank of America is trying to digest Merrill Lynch & Co. But news reports are suggesting that they each may be in for a period of significant indigestion as they merge very different corporate cultures. Witness Robert McCann, Merrill’s former brokerage head, who announced his departure just four days after the BofA takeover was complete.

The fact that these mergers were made under extraordinary economic circumstances is likely to exacerbate the problem. Our proprietary research among hundreds of corporations shows that the acquisition of a like-minded company pursuing a complimentary strategy can, like a well-balanced meal, contribute to healthy growth.  But more often than not, corporate acquisitions are more like junk food–they taste great but go down hard. Now that the calories have been consumed from these drive-thru mergers, their nutritional value will become apparent.

The strong acquiring the weak may be a net benefit to the economy at large as events play out. But the odds are strong that one or more of these big banks will come to regret their gastric choices.