Every week my fiancé weighed me and measured my waist circumference. So that I couldn’t be influenced by any changes happening to my body weight, when we did this, I closed my eyes and was guided onto the scales (she may have been right about avoiding dating vegans after all). 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 that I tolerated while watching others enjoy a very non-vegan full English. Life rolled on and was enjoyable.
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.
A small proportion of the meals I ate still ended up being vegan by chance (about 15%), compared to 100% of my meals being vegan in the vegan study period. My palate did not change over night, I still enjoyed Indian food, Chinese and Italian. But the variety of options available grew as a result of stopping veganism for the month.
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 I wouldn’t want to repeat - callos a la madrileña. This is a stew popular in Madrid which includes blood sausage and some very unfortunate looking and smelling tripe.
Phase one of the experiment was now complete. During the two months that made up phase one I diligently measured how often I was drinking alcohol, eating out and exercising (in case for some reason I’d had a particularly unhealthy month) but luckily these things didn’t differ much at all between the two months.
After phase one of the experiment I then had a “wash out” period in which I returned to my normal relaxed vegan lifestyle, stopping taking daily and weekly measures. I did however weight myself to keep a record of this and chose to do it to give my fiancé a rest.
Then, in August, I started phase two and changed the order of the vegan vs non-vegan periods to account for this. Phase two started 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 than I would be otherwise. The idea that recording one’s own behaviour can influence subsequent behaviour is well established in psychology and referred to as “self-monitoring”.
Self-monitoring is a tool that is used to help manage mental health, weight loss and increase adherence to medicine usage.
During this period my fiancé did weigh and measure me every week and I recorded my mental health as in phase one of the experiment. After two months of veganism I reverted to two months of non-veganism from October. December rolled round and I had finally finished my self-experiment.
As a scientist from a psychology background, I am used to looking at both 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 committed me to veganism for life or to ditch veganism. 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 vs vegan study periods I also noticed how veganism was acting as a red light to unnecessary eating. For example, when I was slightly tempted by a snack, coffee shop treat or dessert as a non-vegan they were available in abundance and temptation turned into eating.
But as a vegan, those temptations were very often removed due to the complete lack of vegan options available or a meagre unappealing offering. 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 all together.
The quantitative data was really clear cut. My body weight responded consistently in response to vegan vs non-vegan study periods – it was lower when vegan and higher during non-veganism. During the two-month part of the study, 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. I looked at exercise and how much I was moving as potential explanations for these differences, but the data largely suggested that the differences in weight were caused by what I was eating.
The findings also revealed that those differences in body weight did not come at the expense of the pleasure I derived from eating. My rated daily enjoyment of food was close to identical during vegan days and non-vegan days. There was a similar story for my mental health. My weekly recording of depression and anxiety symptoms were close to identical during both study periods.
What does it all mean?
Self-experiments come with lots of caveats. Results come from a single participant and this of course makes you wonder whether the results can generalise to other people. Sometimes they will and sometimes they won’t. The results of Crandon’s self-experiment on vitamin c and scurvy clearly did generalise.
My results suggest that veganism may have a causal influence on my body weight. Another caveat and limitation of my study is that it was short. I therefore used my results to calculate what would be predicted to happen to my body weight if the experiment had carried on for longer.
I forecasted two scenarios for what would happen over a full year. A scenario where after the study I remained vegan and a scenario where I gave up veganism. The modelling exercise revealed that under the scenario of giving up veganism I would weight 6.4kg more at the end of 12 months, than if I stuck to veganism. This is a pretty big difference. My findings therefore hint that, in addition to environmental benefits, veganism may also help people maintain a healthy weight.
However, as I’m a fairly health conscious person and cook regularly, it may be the case that a less health conscious vegan that mainly gets by on processed burgers, fries and snacks would experiences less of a vegan-body weight benefit than I did.
I was pleasantly surprised that my derived pleasure from food did not differ between vegan and non-vegan study days. Concerns over how much a person would enjoy a vegan diet are a likely barrier to giving veganism a go and, based on my study data, these concerns might not ring true.
I’ve pondered whether veganism is likely to affect mental health and if my study was ever likely to detect such an effect or test it fairly, due to it being so short. But my best bet at the moment is that a vegan diet probably doesn’t causally affect mental health.
When I read studies that show vegans tend to be more likely to be X or Y compared to non-vegans, I am now highly suspect on how likely it is that veganism causes X or Y. X or Y could relate to anything, whether that’s physical or mental health. Instead, vegans and non-vegans differ in lots of ways and these differences will not be causal.
Take sex as an example. Vegans are far more likely to be female than male. Do we then conclude from this that veganism makes you more likely to be female? Of course not.
And what did I decide about long-term veganism? As I write this, nine months after the experiment finished, I’m still a committed vegan. For me, the likely benefits for my health, the environment and reducing animal suffering outweigh the minor inconveniences associated with being vegan.