I had a lipid numbers similar to yours for years. Exercised regularly for more than 20 year - running 4-6 times per week. A handful of half-marathons and one marathon. Normal BMI. Resting heart rate in the low 50s. PCP was never concerned. Mother had a quadruple bypass at 62, which is young for a female, but I thought I was protected because (1) my PCP wasn't concerned and (2) the message that it's all lifestyle is so prominent and mine seemed pretty good. I got a CAC test and my score was in the 98th percentile for my age and gender. The CAC was prescribed because they found plaque in my iliac arteries in an x-ray. I can't say my diet had always been plant-based, but I had not eaten any (absolute zero) red meat in decades. All my meat consumption was lean chicken and turkey (white meat). I ate a reasonable number of servings of vegetables each day.

It's been about a year of trying to figure out what went wrong and I still can't be sure. The frustrating thing about this, is that it's so difficult to measure. I had a CT angiogram and it showed that there was no blockage greater than 50%. So I think I am in reasonable shape for now.

FWIW, here are the three things that I suspect may have been causal/related.

I have high lipoprotein(a). It's genetic. I gather some people now are taking drugs that reduce it, but I haven't discussed it yet with my cardiologist. If you reach a certain level above normal, it becomes a risk factor. In fact, my cardiologist gave me a letter to give my immediate family members stating the fact that it is a risk factor and they should consider getting tested.

I have poor blood glucose control. I read "Beat the Heart Attack Gene" and learned a lot. One thing it mentions is the link between diabetes and ASCVD. I wore a CGM for a while, and the peaks I was getting were WELL above normal. I was shocked. I had a two-hour glucose test and by that test I was pre-diabetic (though not by HBA1C or fasting glucose). I've made some dietary changes to try to bring that down, but it has been very challenging to keep down.

I suspect I was getting too much saturated fat. I always aimed to eat low fat. No fried foods. No red meat. No butter. No high fat foods ... But I never focused specifically on the types of fat and apparently saturated fat is particularly bad for some people. I worked with a heart health dietician and she said I should keep it less than 8gm per day, lower than her "standard" recommended level of saturated fat.

As I said, who knows. I don't think you ever can. Since the diagnosis, I've just tried to manage every variable that's associated with atherosclerosis. I also had my carotids and abdominal aorta checked. I imagine your level of plaque is too low to really be worried about that.

I would suggest reading "Beat the Heart Attack Gene". It was a nice combination of accessible but science-based. It's a good starting point, and then you can get more information on the issues it raises.

My score was clearly bad, so I'm not very familiar with how the lower scores break down. The CAC score is absolute, and I think you are in good shape. I wish I had taken a test at your age. (I am early 60s.) At first, I looked back and got frustrated that I worked so hard to stay healthy and still ended up with a high CAC. Now I just thank my lucky stars, because I believe it is what saved me from my mother's fate. She lived through the bypass, but I think her life still ended too early. The doctors never explained what happened to her, but alluded to the fact that some vessel probably just got clogged and they'd never know where it was. Who knows, but that is what I was told.

Good luck! As others have mentioned, lots of people life long, healthy, normal lives with much higher scores and diagnosed much later in life without the same runway you have to manage it.