I wish this wasn't true but insurance companies have every right to change a claimant's premium if they are diagnosed with health issues that may have a direct effect on present or future insurance claims. They're a business and they can, should and will protect their bottom line: money. No one should take that personally, even though health insurance deals with something very personal.
Yes they should lower the person's premium if they can change their bad habits into a new one. They should also be promoting more health instead of medications all the time. They should allow for homeopathic treatments also under the persons plan. They should set a program up to pay the person for changing their lives around because changing the bad habits of unhealthy foods is quite hard for some people to change. They should charge the companies that are putting unhealthy food out even more money for their employees health insurance.
Yes, an insurance company could lower a claimant's premium if he or she switches to a healthy lifestyle after being diagnosed with cardiovascular disease, because the person could be a lower risk. The job of insurance is to manage risk. If a person is less of a risk than they were before, they could have a lower rate.
I do not think that an insurance company can lower their premium just because a customer decides to switch to a healthier lifestyle after being diagnosed with cardiovascular disease. I think that after they are diagnosed, the risk has already been documented regardless and there is no proof that the healthier lifestyle can help.