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1. To give up or substitute something for something else, e.g., in physiology, to replace a potassium ion with an ion of sodium.
2. In dietetics, the substitution of an equivalent amount of one food substance for another so that the caloric intake remains the same. Exchange diets are used frequently to help manage diabetes mellitus, and they have been adapted for use in proprietary weight loss programs.
3. In peritoneal dialysis, to drain fluid from the peritoneal cavity and replace it with fresh dialysate.
4. In the Patient Protection and Affordable Care Act of 2009, a virtual health insurance marketplace, in which health insurance customers can compare the value of different insurance plans.

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