As a scientist, I did a self-experiment to compare a vegan diet with eating meat. Here’s what I found out

three years ago, I was briefly dating a primary school teacher who happened to be a part-time animal rights activist. The experience made me take a decision I’ve been living with ever since: veganism. Things didn’t work out with the primary school teacher, but my initial commitment\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ to veganism did last.

At times, I’ve wondered if I’m depriving myself of great pleasure or, as some studies have suggested, even risking my mental health. So, as a scientist, last year I concluded that I finally needed to study what effect this decision was having on me, and decide whether I should stick to veganism for life or give it up.

I didn’t have scientific grant funding to conduct the gold standard of a large randomised control trial, but I did have the time and inclination to conduct a study on myself, the results of which were recently published in Physiology and Behaviour.

I started, as many do, by taking part in Veganuary. On a daily basics, I recorded what I’d done that day and importantly how much I had enjoyed the food I’d eaten. Every week I was weighed, and my waist circumference measured. I also completed questionnaire measures of depression and anxiety symptoms every week.

During January, I led my normal vegan life but was particularly strict in checking whether food and drink was vegan. My diet looked like a lot of other vegan diets: chickpea curry (check), tofu stir-fry (check), lentil pasta (check). I was still eating out, and even enjoyed a weekend away. The latter was great, with the exception of a well-intended but very odd vegan hotel breakfast of stir-fried noodles.

In February, I stopped being vegan and repeated the same daily and weekly measures. During the non-vegan period I made a concerted effort to eat meals that were not vegan. I ditched oat milk for normal milk. I ate cheese, meat and fish rather than my usual diet of tofu, beans and pulses. As in January, I still ate out and happened to have another weekend trip away, this time to Spain. It was great, with the exception of a culinary experience never to be repeated – callos a la madrileña: blood sausage and tripe.

During both months, I diligently measured how often I was drinking alcohol, eating out and exercising, but luckily these things didn’t differ much. Then, after a “wash-out” period, in which I returned to my normal relaxed vegan lifestyle, I started phase two in August, changing the order of the vegan versus non-vegan periods and starting with two months of non-veganism. I didn’t measure anything on a daily basis, as I was worried this may be making me more conscious of my behaviour and potentially making me act more healthily. The idea that recording one’s own behaviour can influence subsequent behaviour is well established in psychology, and referred to as “self-monitoring”. It’s a tool that is used to help manage mental healthweight loss and increase adherence to medicine usage.

When December rolled round, I had finally finished my self-experiment.

As a scientist with a psychology background, I am used to looking at qualitative and quantitative data. Qualitative data refers to personal experiences in a study. When planning the study, I thought I might have an affirming experience or “defining moment” that made me commit to veganism for life, or to ditch it. That didn’t happen. But I did notice a few things.

First, as a non-vegan, some friends and family were keener to hang out with me when food was involved and expressed disappointment during the vegan periods of the study. When switching between non-vegan versus vegan study periods, I also noticed how veganism was acting as a red light to unnecessary eating. For instance, as a non-vegan, snacks, treats and desserts were available in abundance, and temptation turned into eating. But as a vegan, those temptations were very often removed. We’ve long known that vegan diets tend to be lower in saturated fat, but I hadn’t suspected this could be in part due to veganism preventing eating of it altogether.

The quantitative data was really clear cut. My body weight was lower when vegan and higher during non-veganism. After two months of non-veganism, I’d gained 1.6kg, then when switching to veganism for the next two months I lost 1.2kg. But my rated daily enjoyment of food was close to identical during vegan and non-vegan days. There was a similar story for my mental health. My weekly recordings of depression and anxiety symptoms were nearly identical during both study periods.

Self-experiments come with lots of caveats. Results come from a single participant, and can’t always be generalised. Another limitation of my study is that it was short. But, if my data could be generalised, they would predict that veganism may have a causal influence on body weight; that concerns over how much a person would enjoy a vegan diet might not ring true; and that a vegan diet probably doesn’t causally affect mental health.

When I read studies that show vegans are more likely to be X or Y compared with non-vegans, I am highly suspicious. Instead, vegans and non-vegans differ in lots of ways, and these differences will not be causal. Take gender as an example. Vegans are far more likely to be female than male. Do we conclude from this that veganism makes you female? Of course not.

And what did I decide about long-term veganism? For me, the likely benefits for my health, the environment and reducing animal suffering outweigh the minor inconveniences. As I write this, nine months after the experiment finished, I’m still a committed vegan.

  • Eric Robinson is a behavioural scientist and professor in psychology at the University of Liverpool. To read a longer version of this article go to The Conversation

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