If he chooses to use a ketogenic diet, the simple sugars are a big no no. Dave preps countless competitors including Toney Freeman and Evan Centopani on low carb diets. Same with Disgusted. They work great and when done right , are not really that hard
Those guys are heavily juiced, I think that would make a low carb diet a hell of a lot easier, as you can still keep up your weight lifting. Theoretically, low carb/ketogenic diets are perfect for fat burning. I've given it 2 chances but with the same result everytime: no physical energy, lethargy, lack of mental energy....all leading to decreased gym performance and ultimately, muscle loss.
The bottom line is, there is nothing wrong with carbs on a diet, Yates was famous for still taking in massive amount of carbs on his diets and he got as shredded as anyone.