Complex sentence: There has been an increased popularity of the yellow-fleshed type of sweet potato, due to nutritionists have been promoting the idea that it provides increased levels of vitamin A, which is currently lacking in the Kenyan diet.
Split into simpler sentences: There has been an increased popularity of the yellow-fleshed type of sweet potato. The nutritionists have been promoting a change to this yellow-fleshed type of sweet potato because it provides increased levels of vitamin A, which is currently lacking in the Kenyan diet.