How much meat should we eat?

Only one plant — one — delivers vitamin D and that is a mushroom. It gets worse — only mushrooms exposed to sunlight do. Mushrooms are famous for growing without sun, so their scope for topping up vitamin D levels is not impressive.

These examples are just the most striking ones. Zinc, iron, copper, selenium, vitamin A and others are all critical for everyday health, and plants have them. Sort of. They do not have them in abundance, particularly bulk sources of calories, such as potatoes and wheat. Plants acquire minerals from the soil they grew in, and much arable land is light on them. Many people who eat plants exclusively are at risk of being deficient in minerals. Popeye would have needed a lot of spinach if that was his only source of iron. This is the point being skated over when enthusiasts say plants have everything you need. Yes, they do, but not easily or abundantly or even adequately.

In my view, this insight answers the question with which I started. Animal food is a far richer and more concentrated source of many essential micronutrients than plants are. Saying plants have everything you need is misleading.

It helps to appreciate that an animal’s function in the food chain is to concentrate things. The trace mineral levels of grass are often limited too — just like food plants for humans — but the animal’s tissues reflect what it ate and accumulated over a long time.

Similar arguments arise with the essential amino acids we struggle to make enough of in our tissues, such as taurine, which doesn’t come in plants.

People who live entirely plant-based must manage their intake with these insights. Simply taking the steak from the plate and eating the baked potato and the coleslaw doesn’t work. Without animal food, a diet must be actively manipulated with rich and varied plants — lots of legumes and nuts, for instance — essential minerals and vitamins in a pill, and blood tests of iron and red cells from time to time. Strict veganism is particularly problematic for children, pregnant women and the elderly.

In the end, the proof of the tofu pudding is in the eating, which means longevity studies. Are vegans healthier and living longer? The question is tricky because people motivated enough to micro-manage their diet will likely do other healthful things such as exercise and drink modestly. The effect of diet alone is challenging to capture. Also, most research lumps vegans in with vegetarians, who still eat dairy and eggs.

Further complicating things, research compares meat abstainers with everyone else, most of whom eat far too much of the stuff. It doesn’t pin down the narrow flexitarian cohort who eat meat only occasionally, which is what I am arguing for. Most observational studies suggest that vegans and vegetarians are healthier than the average but do not necessarily live longer. In my view, the confounding factors just described make it difficult to say whether that tells us anything useful about the place of meat and eggs or not.

Personally, I turn to the Blue Zones. There are pockets of long-lived people around the globe — and many books analyzing their lifestyles which, in key respects, are remarkably consistent. Tight families, regular exercise, life-long work, small meals, beans and nuts and herbs and green leaves all add up to centenarian lifespans, and so does meat. Ikaria in Greece, Okinawa in Japan, Sardinia in Italy, and the Nicoya Peninsula in Costa Rica all maintain a place for it. Meat from scrawny healthy specimens that walked in the sunshine and grazed wild grass and herbs, eggs laid in the dust by feral chickens, fish from inshore nets eaten by coastal people. All in modest proportions, just occasionally.

(The fifth Blue Zone — Loma Linda in California — appears to be the exception because of its vegetarianism, but dairy, fish and eggs still figure, once again, and crucially, in frugal quantities.)

So, forego animal protein if the ethics bother you. But if you seek health and long life from the consensus of the ages, then keep it restrained and seek an animal that lived and ate naturally — an egg here, a lamb chop there, sardines next week. In my view, that is Mother Nature’s sweet spot.

‘If a diet doesn’t deliver something essential – even just one item – it can’t be what we evolved to eat’