Most (read 2/3rds or more) of the food we eat should be plants. The rest can be meat products (if you eat meat) and other processed goodies if needbe.
The best way to have a plant based lifestyle is to ensure that the carbs you eat themselves are plants, rather than processed carbs (often white grains & foods with added sugar) that hold little to no nutrient value & over many years can wreck how your body handles blood sugar, even if you're "in shape"
Take a listen and see which plant carbs you can start subbing for meals!