For one month I'll buy you as many energy gels and ho-hos as you need to maintain the exact caloric intake that you normally eat with your balanced diet, that's all you can eat because calories in equal calories out. At the end of the month we'll weigh you and check your resting heart rate.
The next month we'll repeat that, letting you eat your daily caloric intake in only the 73% lean beef you find at the grocery store. You can add mayo to the burger for "flavor". This month we'll weigh you and check your cholesterol, time to exhaustion, etc.
The next month we'll stir it up, you can drink your exact daily caloric intake all month for an entire month in high fructose corn syrup, which I'll buy you by the bottle. This month we'll drive by corn fields and see if you throw up.
If you can maintain your fitness and weight for those 3 months with that diet, I'll gladly say I'm wrong and I'll give you a month's supply of moon pies, but only a month's supply at your exact daily caloric intake.