I’m a scientist who went on a vegan diet for a month – this is how healthy I was after On the face of it, I appeared to be the poster-boy for healthy vegan living

I am, and always have been, an honest-to-god ‘meatatarian’. All manner of vertebrate species, roasted, BBQ’d, cured, tartared… you name it, I love it. So when the producers of BBC2’s Trust Me I’m A Doctor (where I am one of the presenters) asked me to go on a vegan diet for a month, it gave me pause for thought. But glancing down at my 45-year-old and slightly wobbly belly, I saw an opportunity and agreed.

Veganism as a diet is easy enough to understand. You just have to avoid consuming anything animal based, including dairy and eggs. In contrast, the reasons motivating people to become vegan are complex. To some, it is a philosophy rooted in ethics; while others are driven by the environmental impact of the meat industry. Many, however, choose a vegan diet for health reasons, which was the angle I was tasked with investigating.

Vegan food is not necessarily healthy

I planned for my vegan month with military precision. I read vegan cookbooks and reached out to ‘cheffie’ friends for advice about how to obtain ‘umami’ flavour without using meat (I can now do magic with Miso). What I realised was that vegan food was not necessarily ‘healthy’. I could have, for instance, spent the entire month eating crisps, cookies, and any number of other vegan confectionary items. I even found a ‘bacon-flavoured’ snack, that claimed to have no artificial flavouring, but yet was certified to be vegan (go figure). Because I did not want to go vegan for a month and gain weight, I made the decision to stick with a ‘plant-based’ and whole-foods approach instead.

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In addition, there were also well-catalogued issues with micronutrient deficiencies in vegan diets to consider; in particular vitamin B12, which is found largely in animal-based products, as well as iodine. Vitamin B12 is fat soluble, so I figured I had enough stored around my belly to easily last me the month; and I happened to like seaweed, which is rich in iodine. Hence I made the decision not to take supplements. I was weighed and had some limited blood biochemistry measurements (glucose and cholesterol levels, and micronutrients) performed before and after.

A difficult first week

The first week did not go smoothly. There was a disastrously sloppy quinoa concoction (blame the cook and not the quinoa), and an unhappy liaison with some oat-milk ‘crème fraiche’. Before anyone yells at me, it didn’t taste bad, it just didn’t taste like crème fraiche. And that was when I had my epiphany. When I prepared a dish that was meant to have dairy or meat, and replaced it with something else, such as swapping the mince beef for lentils in a cottage pie, then I missed the meat. Whereas if I made something that was never designed to have meat to begin with, then there was nothing to miss, and life became easier.

So what happened at the end of the month? Well, I had no micronutrient deficiencies, but I did end my vegan experience 10 pounds lighter, with a 12 per cent drop in my blood cholesterol levels. Wow – on the face of it, I appeared to be the poster-boy for healthy vegan living!

Why I lost 10 pounds

But here is where the (vegan) meat-balls meet the sauce. Why did I lose weight? Was it because of the vegan diet per se? No. Plant-based foods (as opposed to crisps) are simply less calorically dense than meat or dairy. So even though I ate as much as I wanted during my meals, I was still absorbing fewer calories than if I had been eating animal-based food. I have just written a book called ‘Gene Eating’ where I look into the truth behind most of the popular diets (including ‘plant-based’) that are available. The bottom-line is the only way to lose weight is to eat less then you burn. The trick is to find an effective and sustainable way to do so that suits your own individual biology. For me, going vegan was clearly an effective way to absorb fewer calories, and hence lose weight. Other approaches will similarly suit other people.

What affects cholesterol

How about my cholesterol levels? Well, part of the drop could be explained by my weight loss, and part of it by the removal of saturated fat from my diet. But (and it is a big but) I would probably have seen the same effect had I switched to a pescetarian diet (fish are rich in unsaturated fats) such as a Mediterranian diet. Importantly, many people’s cholesterol levels, because of their genetics, are not actually influenced by their diet at all. For some people, dietary changes (particularly reducing saturated fats) would lower their cholesterol. For others, however – depending on their genes – medication would be the only route.

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I have, however, changed my eating behaviour as a result of this experiment. While I missed meat too much to give it up entirely, I have become a ‘flexitarian’, whereby I am vegan during weekday lunches and at least twice a week in the evenings. I have probably cut my meat intake by 40 per cent. For me, this dietary change seems sustainable, and I have, thus far, managed to maintain the lighter me for the past 10 months. I’m lactose intolerant which means I can have cheese (which is lower in lactose than milk), but cannot drink a lot of milk. So dairy was never a big thing for me.

So is it healthy to be vegan? As long as it is done properly and the deficiencies in B12, iodine, as well as iron and calcium, are met (by supplementation if necessary), then it is certainly a healthy way to live. It is, however, a choice that some of us are privileged enough to be able to make. It isn’t, by any stretch, the only way to eat healthily.

Gene Eating: The science of obesity and the truth about diets by Dr Giles Yeo is published by Seven Dials at £14.99