I often hear people saying they want to get in shape for summer, for their upcoming wedding or to attract a mate. Unfortunately, these events are short-lived: weddings end, summers pass and people “let themselves go” once in a relationship.
I think it’s better to make the goals to do with your overall health and the reasons for doing so to be grand, long-term ones. “I want to be able to spend quality time with my future grand children”, “I want to be of sound body and mind in my older years” and “I want to be a positive influence, health-wise, on those around me for the rest of my life” are probably better. This is what makes your goal “relevant” when using SMART goals.
Both short and long-term goals work. But the long-term ones have more benefits.