tz12345

This is not exactly expert advice, as I’m not a medical professional myself. However, I do have several family members in the medical field, so your question is something we’ve discussed many times in the past.
The question of genetics vs. environment (in this case, lifestyle choices such as diet) is definitely a subject of debate. However, like you said, studies have shown that diet and activity levels ABSOLUTELY DO have an effect on health outcomes, as a general rule.
Keep in mind, as well, that in addition to preventing serious illness and early death R”L, living a healthy lifestyle also improves your everyday life, as you are less likely to develop chronic, long-term health issues that are also uncomfortable and inconvenient.
Another thing I would like to share is an anecdote about a relative of mine, who lived an extremely healthy lifestyle, never smoked a cigarette in his life, yet was diagnosed with Stage IV lung cancer, which ultimately killed him. You might say, what was the point of all his exercise and self-control if he died from lung cancer, of all things? I will tell you that he lived much longer and was able to fight much harder than the average person who is given that diagnosis. Since he was so fit at the time of his diagnosis, he was, with Hashem’s help, able to live for another two years (the doctors gave him two months!), marry off another daughter, and witness the birth of two more grandchildren.
There are many things in life we cannot control, and whether or not we will be healthy is one of them. However, we are still obligated to do our hishtadlus and guard our health – it is a mitzvah! – and daven that Hashem do the rest.