Probably the sudden spike in blood sugar from carbs. Your blood sugar was lower the rest of the day, so the carbs all at one feels like if you are three sugary candy bars in a row.

I've had a lot of success with OMAD for weight loss and improved attention, but it's a lot more protein and fats and veggies. And I make sure the starches I eat are slow-digesting like pasta, not fast-digesting like bread or any sugary desserts.

Were you supplementing with electrolytes while fasting? Don’t have any studies at hand right now, but fasting apparently causes you to quickly lose fluid and electrolytes.

I recently started doing 5:2 fasting and noticed on the day after fasting that I tend to get bouts of pretty bad orthostatic hypotension. Supplementing with a zero-calorie electrolyte on fasting days and the day after helped mitigate this.

I haven't had that experience, but I usually do longer fasts.

My go to for this would be electrolyte levels, which can vary heavily depending on water intake, diet, exercise, supplementation, etc.

Here's some journal articles I found based on a quick search.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1364615/ https://pubmed.ncbi.nlm.nih.gov/8777833/ https://link.springer.com/article/10.1007/s002280050682

Be interested to hear if something in one of those pops out at you.

Interesting, increased heart rate after eating is not uncommon [1]. Could be a sudden influx of glucose after fasting kicking a lot metabolic functions into gear.

[1] https://www.healthtoday.com/be-healthy/heart-health/why-does...

I lost 15kg by tracking calories and eating one meal a day in the evening. The rest of the day was filled with coffee and an apple for lunch.

I've pretty much stuck to one meal a day now. Lunch is still something light, like a protein bar or an apple. The only time I really eat breakfast now is if I'm on holiday and it's included...