An overweight adult who has been overweight all of his life, experiences easy weight gain after successful weight-loss attempts, and feels his genes are resisting his efforts at weight loss is illustrating a belief in .

set point theory                                                                        

Explanation:

Set point theory: The term "set point theory" is described as a phenomenon that suggests that an individual's body weight is being regulated at a preferred or predetermined level through a "feedback control mechanism". However, in an adult, body weight is being maintained at some "relatively stable level" for quite a long period in time. In other words, it refers that an individual's body will fight to "maintain" a specific body weight.

In the question above, the given statement illustrates the set point theory.

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