By Rachna Uppal and Nell Mackenzie LONDON (Reuters) - Bridgewater founder and the firm's former CEO Ray Dalio says gold (GC=F) might be a way to shield investors from unhealthy markets, overburdened with debt. Dalio warned that as the U.S. spends more to service its debts, this "squeezes out other spending" and builds up as plaque would in a clogged human circulatory system. "A doctor would warn of a heart attack," he said. "A well-diversified portfolio would have somewhere between 10% and 15% in the p ...