Increasing healthful foods with anti-oxidants or phytonutrients will help. In addition to blackberries, there are blueberries and many other fresh fruits, as well as leafy greens and fresh vegetables in general.
Decreasing unhealthful foods also helps. This includes animal products (meat, dairy, eggs) as well as processed foods. Grains like wheat (and flour) ought to be avoided in favor of starchy vegetables like sweet potatoes, yams, and winter squashes.