This is a great point that alot of people don’t realize. I call it being selfish in the negative way if someone, especially a spouse or parent, does not take the best care of their own health. Like you mentioned in the last paragraph, we should take care of ourselves so we can be around for our loved ones. By neglecting your health and wellness, leading to either a shorter life, or an unhealthy life that requires ongoing care from others is a very negatively selfish way to live.
Another thing people can consider to make this seem less selfish is to get their loved ones involved. Exercise can be a family activity. Eating nutritious meals together as a family is a routine every family should do regularly.
Once again you’ve provided some great useful info. Hopefully many will heed your advice.