Introduction
For the past 4 weeks I have been eating a vegan diet, and have taken a blood test both before and after.
I averaged around 1800kcal/day and expected 2kg 
weight loss, however in the end only lost 0.5kg. This was much less than expected, and so it seems it may have actually inhibited it.
The diet was fairly balanced, it included fresh fruit, some vegetables, kidney beans, chickpeas, seaweed (nori), hemp seeds, but it did also include some processed food (frozen vegan pizza, vegan curries), fortified almond milk and vegan protein powder.
Direct link to results: https://blog.rickyhewitt.dev/wp-content/uploads/2020/07/thriva-after-vegan.png
Blood results
Unbound Tesosterone
0.311nmol/L to 0.2893nmol/L (NORMAL)
(slight DECREASE, but still within normal range)
Total Testosterone
16.3nmol/L to 14.63nmol/L (NORMAL)
(slight DECREASE, but still within normal range)
Iron
25.99umol/L to 20.3 (NORMAL)
(DECREASE, still within normal range, however a drop of almost 6 points a month would lead to low levels within 3 more months)
Vitamin B12 (active)
85.4pmol/L to 111pmol/L (NORMAL)
(INCREASE, likely increased due to supplementation of B12 as advised)
Folate
20.9nmol/L to 11.5nmol/L (NORMAL before, borderline insuffcient now)
(DECREASE by almost half, concerning as it would be insuffcient within 1 more month)
LDL (bad) Cholesterol
2.66mmol/L to 2.3mmol/L (NORMAL)
(DECREASE)
Non-HDL Cholosterol
3.34mmol/L to 2.89mmol/L (NORMAL)
(DECREASE)
HDL (good) Cholesterol
0.75mmol/L to 0.61mmol/L (LOW)
(DECREASE, which is bad as it is GOOD Cholesterol and is currently within a low/insufficient range)
Total Cholesterol
4.09mmol/L to 3.5mmol/L (OPTIMAL)
(DECREASE)
Triglycerides
1.49mmol/L to 1.27mmol (NORMAL)
(slight DECREASE)
Liver (total protein)
80g/L to 67g/L (NORMAL, however borderline LOW now)
(DECREASE, which is slightly concerning as I was supplementing 50-75g of vegan protein powder most days, despite this I would be classed as ‘Low’ within another month)
Vitamin D
72.4nmol/L to 54nmol/L (NORMAL before, borderline INSUFFICIENT now)
(DECREASE, despite 1000IU supplementation most days, which is concerning because if I continued it would have been insufficient)
There’s a whole bunch of others that I won’t include because they’re not as relevant or have smaller changes.
Conclusion
Some of the results are somewhat strange, for instance Vitamin B 12 has increased, despite the fact for most people going vegan it would usually decrease!
The drop in Vitamin D and Iron are both slightly concerning and if they continued to drop at the same rate then in my case it would have eventually lead to a deficiency. Even worse — I was supplementing 1000IU of Vitamin D most days, yet still had a significant drop.
Based on my results, if I were going to advise the vegan diet (or try it again) I would recommend being careful about your Iron & Vitamin D intake, and not eat any vegan junk foods, and keep it 100% wholefood.
In my case I will be trying a low carb/keto diet next and will also have a comparison for that. For now I think a vegan diet is not for me, however I wouldn’t rule out trying again someday with a 100% wholefood diet.