Jake's food selections at meal times are more strongly influenced by his momentary enjoyment of high-calorie foods than by the prospect of an unhealthy weight gain and elevated blood pressure levels. This best illustrates the impact of:

immediate reinforcer

Explanation:

The immediate reinforcement is a process of providing the reinforcer in response to enhance a behavioral response in the subject being studied. The reinforcer is presented immediately so that the subject repeat the behavior again.

For example, a student is provided with a treat immediately on competition of  homework. The reinforcer here is the treat which is likely to enhance the behavior in the student again.

According to the given situation, the immediate reinforcer is the high-calorie food. The subject here is neglecting the unhealthy weight gain and elevated blood pressure associated with the reinforcer in order to enjoy the food.