The FDA considers bitter kola generally safe to eat, but classifies it similarly to essential oils. That means there’s not much information available about serving sizes or nutritional data. However, a 2013 study found that bitter kola was high in the following nutrients:

Carbohydrates
Fat
Protein
The study same study also found that bitter kola had high levels of:

Vitamin C
Calcium
Potassium
Iron
Caffeine