To begin, not eating is surprisingly the way to get healthy, not eating provides more benefit to health than eating. Malnutrition is not healthy. In nations that eat too much and nations that are malnutrition are both deleterious to heath and longevity. The more money you have the longer you will likely live and this is down to placebo which plays a significant role in health and longevity.

However, let's discuss diet. The vegan diet is by far the best diet.

The vegan diet is the wholefood diet, comprised of low sugar fruits and vegetables, nuts and legumes and medicinal plants and herbs as they arrive with minimal processing, not strictly such as extra virgin olive oil to season salads and similar. They are not faux animals products, nor are they sugar sweets. They are not rice, bread, coke and fries. The vegan diet is incomplete, and vegans must be enterprising to complete the vegan diet.

Vegans cannot source Vitamin B12 from the plant sources. The efforts to resolve these issues are...

1. Take a Vitamin B12 or a B-Complex pill supplement
2. There are exotic forms of B12 in plants, e.g. the water lentil. Such low B12 plant source would need to be re-engineered to produce more B12. Water lentils could be in a spice powder seasoning format.

Vegan is probably the hardest diet to do correctly, a mineral and vitamin supplement could be beneficial until you hone in the diet to get complete nutrition from vegan sources.

Getting enough proteins and the full list of amino acids also takes skill. We do not have an answer for the protein conundrum as yet, and one or two eggs a day may be beneficial. The large scale production of vegan protein could come by using genetically modified yeast and bacteria, such as from solar foods. No murine studies have yet been performed. Either the bacteria is consumed or the bacteria produce amino acids as a byproduct.

Researchers have found that the bacteria P. pastoris, in particular, is the most effective and commonly used for genetically engineering high-quality collagen.

To produce collagen, four human genes that code for collagen are added to the genetic structure of the microbes. Once the genes are in place, the yeast or bacteria then start to produce building blocks of human collagen. Pepsin, a digestive enzyme, is added to help structure the building blocks into collagen molecules with the exact structure of human collagen.

Once this process is complete, you have yourself vegan proteins!

The process is discussed here... https://link.springer.com/article/10.1007/s00253-005-0180-x

Completing the vegan diet means no animal products and the associated environmental and health benefits.