As we’ve seen above, animals lose a lot of energy and total protein when converting this to meat and dairy products.

But we also need to consider protein quality and provision of micronutrients – essential vitamins and minerals we need to function well. Some, but not all, plant-based products contain high-quality protein. Legumes, such as beans, peas, tofu and other soy products do. Cereals, on their own, don’t – although a complete protein profile can be achieved when mixing them with legumes in your diet.

Cereals are great at providing energy, and some protein but they’re missing many essential elements. They are a low-quality protein source. Protein is made up of building blocks called ‘amino acids’ – we need to make sure we’re getting enough of each of these individual amino acids.10 Cereals have an ‘incomplete’ amino acid profile meaning they are lacking in some of them.11 Cereals also lack a number of important micronutrients, such as calcium, iron and B-vitamins. In fact, vitamin B12 is one that you can only get from animal products, or from food supplements.

Individual animal products – meat, dairy, fish, eggs – do have a complete amino acid profile. Animals are effective in taking energy-dense but low-quality protein cereals, and converting them into high-quality protein sources. The downside is that they waste a lot of energy and total protein in the process.

The key point is that in switching to a vegan diet we cannot simply divert cereals from animal feed to human food. For proper nutrition, we will have to change the types of crops we grow. Not all crops provide low-quality protein – legumes such as peas, beans, lentils and products such as tofu have a good amino acid profile; when mixed with cereals in a person’s diet, it’s possible to get the full range of essential elements.12

There is also a lot of potential to mimic the animal conversion process in the lab – either through lab-grown meat or fermentation processes that make meat substitutes. These would allow us to reap the benefits of converting carbohydrates and sugars into high-quality protein without all of the waste that comes with it.