Humans are natural omnivores
Broadly accurate as biology, and it settles nothing ethically. Being able to do something is not an obligation to do it.
Our bodies were shaped over millions of years by eating meat alongside plants, and it shows in our teeth, our guts, and how readily we absorb nutrients like B12, iron and complete protein from animal foods. Eating animals is not some cultural aberration to be corrected but part of what humans are, as much a part of our nature as the predation of any other omnivore. A diet that cuts out half of what our biology was built for treats a basic feature of being human as a moral failing, and that gets things backwards.
Humans are dietary generalists. We digest and derive nutrition from both plant and animal foods, and populations have historically eaten widely varying proportions of each depending on what was available. There is little point disputing this.
The conclusion does not follow from it. Capability describes the range of things we can do, not which of them we should. We are also capable of a great many things we have decided against on reflection. Once the alternatives exist and are adequate (which the dietetic bodies affirm) the question becomes an ethical one, and the physiology has already said everything it can say.
- Humans evolved eating meat: it's in our DNA
Different wording, same argument. The response above answers all of them.
Moving from a description of how things are to a claim about how they ought to be, without supplying the moral premise that would connect the two. Identified by David Hume.
How it applies here: A fact about human physiology is offered as a conclusion about what we should eat, with no premise supplied to connect the capacity to the entitlement.
Treating 'natural' as evidence of 'good', or 'unnatural' as evidence of 'bad'. Whether something occurs in nature tells you nothing about whether it is beneficial or right: hemlock, malaria and infant mortality are all perfectly natural.
How it applies here: Treats the natural or evolved condition as the standard of what is acceptable, which it is not in any other domain of medicine or ethics.