No, the mono diet isn't what you eat when you have "mono" also known as mononucleosis, the kissing disease, and Epstein-Barr.
Although if you have mono, you might feel so poorly you only eat one food. And that is the mono diet.
What is the mono diet?
The mono diet is eating only one food per meal. So, breakfast might be an apple. It could be multiple apples as long as all of your items are the same food. You wouldn't be able to have an apple with peanut butter.
Depending on how strictly you follow the mono diet, you wouldn’t even be able to eat peanut butter by itself. Most peanut butters are not just made from peanuts. They have oil and sugar added. Sometimes they have salt. Some peanut butters also have fillers, emulsifiers, or other additives.
What is the theory behind the mono diet?
The theory is that early man only ate one food per meal.