I’ve begun to intentionally take more calories as fat for a week or so now, mainly from several varieties of nuts: black walnuts, pistachios, almonds, cashews, peanuts, some olive oil, but also (very) small amounts of butter, small amounts of fat in red meat (mostly lean), and just a little cheese.
Along with somewhat higher protein intake: Hammer Whey as baseline, king salmon, lean grass fed beef, some chicken, a few grasshoppers, road kill, and so on. OK, I’m kidding on the last two.
The differential means reducing carbohydrates in general, though I do eat a wide variety of fruit for its vitamins and minerals (fresh, whole). Lowering carbohydrate intake is a concern for heavy training, but there are hints that my energy production on rides is increasingly aerobic (fat burning), as I mentioned in New Personal Best on Tunitas Creek.
It makes no sense to me to rule out any food as entirely “bad” (“zero intake” sounds like bad science and bad psychology and context dropping to me). Well, I might say high fructose soft drinks, but even that (Mountain Dew) has proven itself as useful in long endurance events. What is really a turn-off is the dogma of Food Preachers: a complex and personal machine like one’s own body has certain signals on what it wants and what degrades it. One has to pay attention to the good and bad signals. No study is going to change that any time soon, just as studies of drugs clearly show efficacy or non-efficacy on a genetic basis at times. And of course, moderation and variety make the most sense of all.
Still, that leaves the question of primary and secondary foods. From what I can tell for myself, a moderate amount of carbohydrates is enough, fat at ~40% of calories (mostly nuts and similar) is probably a good thing and protein intake of several types is probably better than any “high this” or “high that” diet, perhaps best termed the “I have an agenda diet”—again noting that personal physiology quite probably factors in significantly.