Yes, Mike, through a standard DNA test such as 23andme or through a physician if one wanted to better understand APOE status and risk for Alzheimer's disease. Those with an APOE 4 allele are at much greater risk, which is were most of the interest in APOE status springs from. The less than 1% of us who are 2/2 have the lowest dementia risk but evidence is emerging that we may be more vulnerable to metabolic disorders and diabetes.
Finding 2/2 participants is really difficult and there are almost no studies available with an adequate sample size to have predictive power for APOE 2 folks... you need to test over 1000 people to get 100 2/2's -- very expensive! We still need to extrapolate from genetic knock-in animal studies, mostly mouse. Thankfully findings in mice don't immediately generalize to humans as they've found a bunch of issues in mice that have the 2 allele, if they translated directly to people I'd be f***ed.
As a disclaimer, I don't endorse the diet recommendations above, but I do find them interesting. I've known for a very long time that I respond poorly to simple carbs, since my teens actually, and I've come to believe this is influenced by my apoe status. I really like fatty fish and dense, slow release, energy sources -- the older I get the more I lean this way.