Old:Plant-based

Plant-based food comes from plants rather than animals.

Reasons

More environmentally friendly, due to:

Eating food crops more directly, instead of feeding them to animals and eating the animals, which is inefficient.
Avoiding the methane emissions of cows.

Less animal cruelty:

Cows, chickens, and pigs suffer in factory farms, where conditions are far worse than the nice farms you see in children's storybooks. Factory farms exist to meet the high demand for meat, milk and eggs. The less we consume these products, the lower the demand, and the fewer animals suffer.

What to eat

There are countless possible plant-based diets. This page focuses on the nutritious ones.

Frugal diet

Even with today's inflation, it's possible to meet all your nutritional needs for less than $4/day. The key is to cook things from scratch, and focus on cheap raw ingredients:

($0.75/day) Grains: rice, pasta, cornmeal, oats, flour for baking
($1.00/day) Legumes: beans, lentils, dry split peas, soybeans
($0.75/day) Root vegetables: potatoes, carrots, onions
($0.50/day) Oils: canola or any other oil that happens to be cheap
($0.40/day) Miscellaneous: seasonings, yeast/bakingpowder, etc.

This diet also involves low-cost vitamin supplements:

($0.16/day) A "one-a-day" multivitamin that also includes minerals
($0.09/day) Calcium tablet
($0.07/day) Vitamin C tablet (...)( Technically, there is already enough vitamin C in the multivitamin, but we include the extra vitamin C for good measure, especially since the diet lacks fresh fruits. Officially, the daily requirement for vitamin C is only 90 mg/day, but some studies suggest there are additional benefits of consuming up to 500 mg/day: more resiliance against oxidative stress. Vitamin C is also essential to iron absorption if the iron is the plant-based form (i.e. the iron in lentils and beans). All you need is a small piece of the vitamin C tablet at every meal. )

Total cost:

($3.72/day) - Note: Prices are quick estimates. They may change, but the general principle remains: This diet is one of the cheapest possible ways to eat healthy.

There are a lot of misleading ideas about synthetic vitamins being "no good", but in this diet, they are essential. Read this to clear things up.

Some things to make with these ingredients:

Soups: from legumes, carrots, onions, and seasonings
Potatoes cooked with oil and seasonings. The easiest way to do this is in the microwave.
Breads: from flour, water, oil, yeast, seasonings, sometimes sugar. Can be stuffed with carrots and onions.
Seasoned beans and polenta (cornmeal)
Spiced lentils and rice, with chopped carrots

See example in nutrition calculator (...)( These examples in the calculator use the "raw" version of foods such as beans - not because you'd want to eat them raw (you can't!), but because it's easier to track the number of grams; packages of dry beans are usually measured in grams. And although the calculator has data available on boiled beans & vegetables, the data probably assumes that the water has been drained after cooking. Don't do that - the water has valuable nutrients (minerals). )

Including junk food

Of course if you eat only junk food (plant-based or not), you will miss essential nutrients and eventually suffer from health problems.

However, with a bit of thought, it's actually possible to create a healthy diet where:

Most of the calories come from junk food.
Most of the protein comes from legumes (beans, lentils, and/or split peas), which also provide fiber, vitamins and minerals.
Other vitamins & minerals come from root vegetables and a vitamin/mineral supplement.

This is similar to the frugal diet mentioned earlier, but with slightly less cheap and slightly less cooking.

See example in nutrition calculator

See example 2

Raw veganism

This involves more fresh fruits, nuts, and herbs. It tends to be more expensive - partly because of the resources required to keep food fresh. Switching to frozen fruits might be cheaper and actually be better for the environment (...)( despite the extra energy involved in refrigeration, the supply chain involves a lot less food waste overall ).

See example in nutrition calculator (...)( This isn't the best example so far. If you come up with something better, join the discussion. )

Terminology

Veganism is a lifestyle that avoids all animal products, both for food and non-food items. Note that the food part has a far greater impact on animals than non-food. ^{[QUANTIFICATION needed]}
Vegetarianism avoids only meat, and is ok with other animal products such as eggs or milk.