Although FET switches often have a body diode associated with them, it is often much more efficient to utilize the FET ON resistance as a safe path for current decay. When the controller coordinates the turning ON and OFF of FET switches as a means to offer a safe path to current during decay, this is referred to as synchronous decay. The time of when the FETs are brought online to carry the current is known and fixed.
It is impossible to instantaneously offer a safe path for decaying current by turning opposing FETs, since this would cause shoot through. As a result, every controller employing a synchronous decay mechanism will, for a very small period of time, employ a form of asynchronous decay through the FET switches’ body diodes.