With regard to the human brain we can provide general advice about how to promote brain health across the lifespan. When we were cavemen and cavewomen we ate one good fat for every bad fat. Today, we eat about 15 bad fats for every good fat. This is important because our brains are composed of about 60% fat and the lipid substance helps to facilitate information processing.
Thinking live a cave person might be a good exercise when thinking about what to eat. We should try and eat plants/vegetables, nuts, beans, fruit, fish, and lean game such as chicken. We should try to reduce processed foods, red meat, trans fatty acids, soda and foods high in sugar. We should strive to eat less than more and use utensils more often as it might help to less consumption of food and a healthier consumption of foods.
It is also important to realize that foods are supposed to be pleasurable and that an occasional piece of cake, pie, ice cream, etc will not cause major damage to the system. This is particularly true when one follows some of the general advice above.
I personally have begun a study of my own diet with increased intake of fruits and vegetables, reduction in processed fats, removal of soda from the diet, and increased fish and lean chicken. It is not uncommon for me to now have fruit in the am and day with a salad (olive oil and vinegar are good for the brain), and a piece of fish or chicken at night. I have been relatively consistent though I fail now and then. I am observing change in body mass and in psychology including energy and mental alertness.
Stay tuned and I will provide you an update in the near future!