Basic guide to diets..

Strap in folks.. this is going to be a long one. A better blogger would parse this out into several posts, but it is my blog, so buckle up.
I have tried pretty much every diet out there that has been pitched for performance. As well I have advised clients and friends on fitness, and have credible data from them on most diets. They all have strengths and weaknesses for performance, compliance, and fat/weight management.
Lets jump in the deep end.

Vegetarianism: This is going to ruffle a few feathers. Vegetarianism is not generally an effective performance diet. It isn't really intended to be. Most people don't decide to become vegetarians or vegans in order to perform better at a sport. That said, one CAN perform well with a vegetarian diet particularly in endurance sports. When I rowed it was quite effective. Rebuilding muscle glycogen on a high carbohydrate plant based diet happens quite readily. You're generally hungry all the time. I found eating all the time also helped with recovery. However, this diet is particularly weak when one is trying to gain muscle mass beyond your body's comfortable range. I was a vegetarian for over a decade, and I got fairly strong (bench press over 350 with terrible levers for bench press, and hang clean and strict pressing 275), but it was hard. I had to force feed, I had to drink all manner of protein isolates, and milk pretty much constantly.
 Inactive folks can do ok on this diet, but processed foods (mmm french fries) do qualify as 'vegetarian' as a weight loss strategy it only goes as far as the rest of their diet. This is the biggest weakness of this diet. Excluding animal products, and including only plant products in no way informs performance or body composition. One could eat ice cream, french fries, and doritos, or one could have a smoothie for breakfast, a beet salad with feta, and a protein shake for lunch, and roasted vegetables for dinner. Both qualify as "vegetarian" but would have drastically divergent effects on performance and body composition. One still has to diet on top of this diet. Compliance within a vegetarian diet is generally a matter of morals and what motivated the individual to take on this diet initially. Overall I never recommend vegetarianism to folks, but it is easy to work within.

Zone: The zone.. does anyone remember this one? So much measurement, so many maths. Good grief. If you could hit your macros, pretty much everyone does pretty well.. You start to see problems when you're not dealing with generalists. People on the extreme ends of the spectrum of strength and endurance start to have.. not problems with performance, but have problems hitting their numbers. This is where the zone dies a slow and painful death. I have rarely dealt with a client who could consistently stay in "the zone." Eventually folks either just eat the same meals every day, or they get fed up with the zone.

Ketogenic:  The first four weeks of this year I went completely low/no carb. Only fibrous vegetables, daily carb intake was less than 30 grams. It was rough at first. The third through fifth days were downright painful. My brain felt like a starving symbiote. Compliance on this diet can be murder. The first week you feel worse and worse every morning, but after the first couple weeks, it was just another strict diet. It is strict; it is hard to eat out, it is hard to cook for others, it's just hard. I know a good number of folks who have tried a ketogenic diet and failed to even get off the blocks.
I dropped some weight, performed ok in the gym. I'm not training particularly hard these days, but I could perform in the gym without too much issue. The really interesting thing about this diet was that once I came off of it, my appetite was dialed down, and my sense of satiety had the volume turned up. Interestingly I've continued to lose body fat after. So the performance question is still open, but body composition improvements on the ketogenic diet are outstanding, IF you can stay on it for more than a couple weeks.

Paleo: My experience is that the Paleo diet is the best balance of performance, composition, and compliance. There are a lot of people who like to poke at the Paleo diet. They get stuck on two things: 1) You can't actually eat the same foods as Paleolithic people. 2) Paleolithic people died young. People who make these criticisms simply have not read the actual books that Robb Wolf and Dr. Lauren Cordain wrote explaining the diet in detail. If you haven't read the source material, you aren't qualified to make a criticism of a thing. If you scoff and think these things, then read the damn book. Otherwise, I don't understand what the issue people take with "eat some meat and green veggies" it's not complicated, and in my experience it works and it works well, and people (generally) are able to stick with it.

Here's the real deal with the efficacy of these diets: the stricter the diet, the margin of compliance is so narrow that when a bag of carrots is a "cheat" then eating a slice of pizza feels like a week in Vegas spending your retirement fund on hookers and blow. It gives you a pathway, a guide to understand something that is so fundamental to our existence. I think these kinds of diets have value for those reasons. Conversely, one needs to take the long view. Weeks and weeks of compliance are not scrubbed out by a single piece of cake. That is an overall net positive. Too many people focus on individual instances of non-compliance a loss rather than the net of the week or month.
The crux of all of this is the balance of satiety and energy. If you feel like you're sated, if you have enough energy, and you're meeting your goals of performance and body composition then you're probably on a good diet for you. If you feel constantly run down or you're always feeling deprived, even if you're on top of your performance and composition goals you're on an untenable track. It doesn't matter. Eventually you're going down, either to binge, or you're headed down the path to an eating disorder. If you're just suffering, you're on a bad diet (for the long term). You need to find a baseline diet that works generally for you. One that will maintain your body composition, one that will allow you to perform in your preferred arena, and one where your food is easy. Then you have a default position to return so that you can try making adjustments. Far too many folks move so many variables at the same time that they have no idea what is or is not working for them. If you have a baseline workout program, baseline diet, baseline recovery program.. then you can move one or two variables and see what is working for you. If you move all of these at the same time you simply have no clue what is influencing your performance or body composition.
Similarly if you're not tracking some metric of performance, then you simply don't know. You don't have to use your weight. Use a belt length, use pictures, use a 2 mile run, take measurements with a piece of string without any numbers on it. You only need retaliative measurements, but you need to measure.
If you're not happy with your performance, and body composition, put together a plan, and try things for 4-8 weeks. That seems to be the window to get through withdrawal, and see noticeable differences. I have seen a number of folks perform equally well on widely variant diets. Try stuff, work hard, find out what works for you.

Mahalo.