In Bhagwad Gita, wherever there is a mention about food, it is about eater and the food itself (4-30, 6-16/17,9-27,1-52). This suggests that he gives importance to human's predominant nature and temperament than food itself. In 17th chapter too, he discussed in detail, sattvik, rajasik and tamasik nature of a man and not the food. Had it been about a food and food habits, he would have gone into great details with examples. Sattvik person first think about food's impact on भूतसमुदाय (Body, senses, intellect and mind) and then eat it. So goes the verse 17.8 - explains impact first and then type of food selected by sattvik person. Rajasik person first eats the food and then thinks about adverse effects. So goes the verse 17.9 - God first explained food selected by rajasik person and then the adverse effects. In 17.10, he did not even mentioned ill-effects of tamasik food. This shows that tamasik person does not think at all! Tamas means zombie state. No thought processes at all! Out of delusion, tamasik person eats like an animal, and behaves like a beast. So, based on this description, it is clear that, it is not food that decides your nature but it is your nature that selects food and maintains your particular nature. If we want to change anyone's nature, we will first have to work on their nature i.e. स्वभाव. No easy task to alter human nature. This process starts very early in life. Before birth. This is the reason I emphasis more often on two institution most 1) Marriage 2) Parenting - Child development. Future depends on these two social norms. We must protect them. When they are of sattvik nature, we can pray mother nature to gift Sattvik generations. It is difficult to mold, already molded clay pot (Tamasik nature of grown up adults). And if you try, very hard, you may break the equilibrium. If you really are interested in building healthy future, work on children. Prepare Sattvik nature in them. Nurture them accordingly.