When did discussing food at a dinner party become as contentious as airing your religious or political beliefs?

These days, to a vegan or vegetarian, hearing someone talk about the benefits of eating liver seems as blatantly offensive as praising the Prime Minister to an ardent Corbynista.

As a nutritionist, I put it down to the fact that there are so many new diets and food crazes, people are more confused, fearful and, dare I say it, competitive about food than ever before.

Ten years ago, no one ever asked me which diet they should sign up to. Today I am continually hearing ‘should I go keto (a diet of 70 per cent fat) or paleo (the ‘caveman’ diet)?’

I tell them it really isn’t one size fits all but, that said, some things are universally inadvisable: sugar, too much caffeine and processed foods.

And then there is a firmly held belief of mine that’s a little more controversial.

Nutritionist Magdalena Wszelaki, believes vegetarian diets are not a healthy choice. She revealed the importance of listening to your body (file image)

I always advise people not to consider avoiding meat. I just don’t see a vegetarian diet as a healthy choice — let alone veganism, which means eschewing all meat, fish, eggs, dairy and even honey.

I was disappointed, but not at all surprised, to see evidence this week that more and more young women are lacking in vital nutrients as a result of their restrictive diets.

A report based on data from Public Health England’s national diet and nutrition survey found that the average woman doesn’t get enough of seven out of eight key minerals — and those in their 20s and 30s were worst off.

Men did slightly better, falling short on five of the eight nutrients on average, perhaps because men are less likely to follow the current craze for cutting out meat and dairy products.

My views on this issue are unlikely to be well received, I know. The number of vegans in Britain has tripled in the past ten years, to more than half a million. The NHS says more than 1.2 million people are vegetarian. And you only have to read any health blogger’s social media posts to see that avoiding meat, and often dairy, has become the latest form of nutritional one-upmanship.

But over the past decade I have worked with more than 2,000 women and the truth is, I have seen only a tiny percentage of them enjoy good long-term health while they were on a vegan or vegetarian diet.

Time and again, they feel great for the first year or two but then find themselves sliding into fatigue, depression and frequent colds. Many experience hair loss and weight gain. Often they develop problems with low thyroid function.

This pattern fascinates me — and I see it so often, it really is impossible to dismiss. So I asked the 2,800 members of my online support group about their experiences with giving up meat.

Some 70 per cent of those who had been vegan or vegetarian for more than two years admitted their health hadn’t changed, or had actually got worse, during that time. Many said they felt great for the first year but not afterwards.

Magdalena says many women ignore their bodies warning signals in order to follow idealized versions of what's deemed 'healthy' (file image)

Personally, I have never tried vegetarianism for long — my body naturally craves meat and I have learnt to accept what it’s telling me. But many women want so badly to fit in with an idealised version of what’s deemed ‘healthy’, that they ignore the warning signals their bodies are giving them.

The list of health problems caused by vegetarianism goes on and on. Over and over again, I have seen vegan and vegetarian clients experience significant health improvement after adding even small amounts of animal proteins back into their diets.

Take my friend Alex Jamieson, a long-time vegan, natural foods chef and respected health expert, who featured in the famous film about living on processed food, Super Size Me.

To the dismay of her large vegan following, after years of unexplained ill-health she started to feel well again very quickly after introducing a small amount of animal protein back into her diet.

So, what’s really going on?

The reason why going veggie seems to work so well initially is that, at the start, people tend to move away from convenience foods and eat more wholesome meals. That’s wonderful, as far as it goes.

Magdalena claims some vitamins and nutrients can be difficult to get from non-animal sources and using supplements aren't as easy to process (file image)

But it’s easy to get lazy. You can live off highly processed Pringles and Diet Coke and be vegan. Veggies and vegans can also eat highly inflammatory foods — gluten, soy, eggs and corn, for example — which experts believe can trigger digestive problems and a host of other illneses.

I’m not saying we should eat bacon every day. But in the long term, no matter how healthily you eat, there’s no denying that some vitamins and nutrients are very difficult to get from non-animal sources.

Vegans tend to be very low in vitamins A and D, for example. The best sources of these vitamins — which are vital for hormonal balance, strong bones and good mental health — are fish, meat and liver.

Vegetarians can get them from dairy but if you’re allergic, or avoiding it in deference to the latest healthy-eating trend, that goes out the window.

Can’t you just take supplements? Well, yes, but for many people nutrients from supplements are not as easy to process as those found in food — and they are expensive, too.

Magdalena says vegetarians often experience B12 and zinc deficiencies which can cause health problems (file image)

You also tend to see vitamin B12 and zinc deficiencies in vegetarians. Zinc is vital for the immune system and protecting the gut, while being deficient in both B12 and zinc contributes to an even bigger problem.

These days, most of us know we need healthy Omega-3 fats for brain health, cholesterol management and glowing skin. Veggies tend to get their Omega-3 fats from chia seeds and walnuts, as opposed to the oily fish on which meat-eaters rely.

But what many people don’t realise is that these plant-based foods contain Omega-3 in a form the body cannot easily process without two key nutrients: B12 and zinc.

Simply put, their bodies can’t properly use the nutrients they are taking in because of the lack of variety — and animal products — in their diet.

People sometimes joke that vegetarians and vegans are always depressed and gloomy, and this could be why. Omega-3 is linked to mental agility, stable moods and the balance of neurotransmitters in the brain.

What is really terrible in all this is the way many vegetarians vilify meat-eating. I have learnt from experience that demonising any natural food is not the key to good health and will serve only to make people feel bad about themselves.

Instead, each individual needs to learn to listen carefully to their own body.

Magdalena urges people trying vegetarian diets to stop when they reach a point where it no longer serves them (file image)

Eggs are a good example of something that can be very beneficial or just the opposite.

I had a client who used to be one of the top managers in Silicon Valley in the U.S. A vegetarian who ate dairy, she suffered such bad mood swings that her job was on the line and her husband of three years had started divorce proceedings.

I asked her to try an elimination diet, cutting out everything that could possibly be affecting her mood. That included eggs and dairy — and it changed her life: when she reintroduced dairy, she says, it turned her into a rage-filled monster who wanted to kill her husband.

But this story, while shocking, absolutely does not mean that everyone should stop eating eggs. It all comes down to bio-individuality — how we are all different in our genetic make-up and chemical composition.

We are slowly beginning to understand more about this mysterious area of science. For example, we now know there is a gene that controls how we metabolise fats: that’s why one person will see weight melt away while another is pudgy, sluggish and depressed.

So if you’re determined to go vegetarian, give it a try, by all means, but stop at the point where it no longer serves you — and, mark my words, that day will come.

Cooking For Hormone Balance, by Magdalena Wszelaki, is out now.