When it comes to health and wellness, some people definitely prioritize their health more than others while some people do not care about their health whatsoever. While I do think it is very difficult to find someone who totally shares the same views and habits in regards to their health, it is definitely possible to find someone who has a similar lifestyle. The question is, how much does this matter in a relationship?
I would compare health and fitness to religion, where it is something that could matter significantly and when there are contrasting views, it can cause some conflicts and tension over time. If you have someone who is very health conscious, this person can grow very resentful over time if their partner is not and can feel like they are a burden by their poor health decisions. The person who is less healthy can also grow resentful of their partner if they feel that their healthier partner cannot accept them for themselves and that their significant other is trying to change them to become more healthy. I can see how both parties could get frustrated at each other for different reasons. I think the underlying issue here is a lack of ACCEPTANCE and/or unrealistic expectations. When two people love each other, they should find a way to accept each other which means accepting the good and the bad traits. If two people learn to accept each other, then this would never become a major issue in a relationship. While I also believe that setting expectations in a relationship can be a positive thing, it is not positive if you set an unrealistic expectation to change someone who most likely will not change their habits. The only way a change can be made is if the person intrinsically wants to change and not trying to change because the other person is pushing them to.
At the same time, if you detect early on within a relationship that a person does not have the same views and/or habits as you when it comes to health and this is something that is extremely important to you, I advise it is best to move on and to look for someone who can be on the same page as you. It is better to break it off and find a partner who is in alignment with your lifestyle as opposed to trying to change the person because as I mentioned previously, the person most likely will not change. You will be much happier in the long run and feel closer to your partner when you are with someone who has very similar health habits as you–given that is a high priority in your life.