Personality, diet, attitude
I met a woman who ate a lot of foods like Cheezy puffs, boxed artificial mac & cheese... Very few veggies & fruits. She was literally scitzophrenic & psychotic. She had a terrible temper, stole, lied, made threats, used people... She had 4 kids & abandoned 3 of them. She was slightly overweight.
One of the nicest people I know, happens to eat very healthy foods.
My Mom's side of the family, which is quite kind, friendly, and holds good job positions, eats mostly healthy foods, but also eats plenty of icecream, pasteurized milk...
Same for my Father's side.
My family history involves a man who heavily abused alcohol, & was a cruel tyrant.
Food can make it very difficult for a person to be at peace, calm, relaxed, friendly, kind, and warm, but it's not the only factor. Environmental toxins may have an effect as well, but these external factors are not an excuse.
Some people may have to struggle harder than others to be nice. Some people may have such a inTOXICated body that it requires a great deal of effort just to not be mean, forget about being kind, while other people may have such health and bodily condition for them to be naturally inclined to make many intimate connections and enjoy serving others, and their struggle may be less, but the standard to which they will ultimately be held to, will be higher.
True religion is a major cause in instilling in humans a sense of shame, a conscience, a desire to put others first. It's role in a healthy society cannot be underestimated. Of course there are deceitful people in every crowd. Just look at what happened to Christ. Pretenders who seek power will use religion for their own means, and always have, but the reality of religion's life-giving sustenance can be obtained for individuals who are sincere, and seek it, from the holy texts, and through unbiased investigation.