"Slow metabolizers" refers to individuals with a slower rate of metabolism. It means their bodies take longer to process and break down substances such as medications or certain foods. Full definition
It turns out that your «cardiac twitch» is related to your caffeine metabolism — slow metabolizers of caffeine have a higher risk of heart attacks if they drink more than two cups of coffee per day; however, fast metabolizers have a reduced risk of a heart attack if they have at least a cup of coffee a day. (mindbodygreen.com)
As quite counter intuitively carb tolerant people are slow metabolizers which will also influence optimal meal timing and meal frequency. (strengthsensei.com)
The same amount of caffeine will tend to have more stimulating effect on slow metabolizers than on fast metabolizers. (forums.phoenixrising.me)