Food in all Kenya's hotels and lodges is generally of a high standard and service is excellent. Many quality restaurants abound in Nairobi and at the coast. Indian Italian Brazilian German Chinese Japanese as well as specialty Meat Carveries and seafood restaurants are all are to be found.
City street hot-food vendors are safe fresh and tasty. Ask for Muhogo.
If in Mombasa try Bollywood for Indian vegetarian dishes and/or Roberto's for Italian. In Nairobi Misono - a Japanese Restaraunt is a good choice.
Standards may not be so certain however at the lower end of the scale and much depends on the quality of the accommodation used and the price you pay.
If you are a back-packer and eat every meal you are offered anywhere in the tropics you risk tummy bugs. Be selective. Possible hazards range from minor bouts of travelers' diarrhea to dysentery and more serious parasitic diseases that may ruin your trip so precautions are worthwhile.
Always choose food that has been freshly and thoroughly cooked served hot and avoid doubtful buffet food or anything that has been reheated or left exposed to flies.
Do not be afraid to reject food you consider unsafe or to ask for something to be prepared specially or to skip a meal.