Here is a healthy plan that I am currently on.
The plan has 3 components:
1) Free foods, which you eat as many as you like: Fruit, vegetables, meat substitutes (tofu, quorn), fat-free dairy and eggs. You can also choose to eat either unlimited lean meat, or unlimited potato, pulses and cereals (oats, rice, etc.)
2) A treat, like chocolate, sugary or fatty foods, or some alcohol - if you allow yourself one small portion, you can be healthy without denying yourself
3) Healthy foods which are high calorie: Bread, processed breakfast cereals, nuts and seeds, oil, dairy products, processed soy and cereal products (like soy and rice milks, non-dairy cheese)
Obviously, you can tailor this plan to your personal preferences (e.g. if you are vegetarian, or allergic to something). For optimum health it is best to try and eat a wide variety of foods that encompass your vitamin needs.
To lose weight you eat 2 portions of the high calorie Healthy foods every day, and to maintain your weight eat 3 portions. To gain weight, try to eat more of these kinds of foods. This way you will gain weight without making yourself ill on junk food
