清淡 (qīngdàn) describes food that is light, not greasy or strongly flavored, and is the positive, neutral term you'd use for a healthy diet. It can also mean 'slack' for business, but unlike 不景气 (bùjǐngqì), which implies a serious economic downturn, 清淡 is milder — just slow or quiet. For 'bland' in a negative sense, use 淡 (dàn) instead.