There was a bunch of little stuff. I don't think it was as bad as the flu, but it was somewhat uncomfortable.
The initial symptom was wanting to eat all of the time, even if I wasn't hungry. My brain was convinced that I had to spend huge chunks of my time chewing on something flavorful.
So I sliced off some very flavorful cheese and nibbled little tiny pieces during the morning. That seemed to work. Note that I avoided all artificial sweeteners. There's some danger there that I felt I should avoid.
Eating a bunch of cheese leads to constipation. Some fiber every morning fixed that.
There were a few other things. My energy level dropped right off, then came back. Now I have much more energy than when I started. I had a little bit of brain fog, but it was manageable.
The biggest thing I've found about keto is that my personality changes. I am much more relaxed and sedate than I used to be -- more on an even keel. That's not necessarily a benefit. It was just unexpected.
ADD: The crazy thing about keto, as opposed to just IF, is that you have to be really OCD about what you eat. Manufacturers sneak carbs into everything. A food journal was critical for me -- and it was something I felt I didn't have to do, since I already knew so much about nutrition! Good thing my SO talked me into doing one.
It's insane. You go buy beans, and there's rice flour in it. You buy salmon, and there's sugar in it. It's beyond ridiculous, and explains so much about rising levels of obesity. Anything even vaguely processed has a lot of unnecessary carbs added, for one reason or another.
I've had it. A few days of very low carb intake leave me feeling very low-energy, foggy, and crabby. It's more of an issue if I'm also too calorie restricted, so if your goal is weight loss, I'd recommend starting Keto first with a similar number of calories to your existing diet, then restricting calories once you're past the adjustment phase.
I had it the first time I switched my diet. Headache, low energy, mild body-ache.
I'm currently a non-strict keto-er, which means I'm really just a high-fat, low carb eater. I think consensus on 'keto-flu' is really just that when you're flushing all the glycogen, it's taking with it a lot of water, and it's upsetting your sodium/potassium levels, I don't really know. I just know that I don't suffer from it when I transition from periods of moderate carbs back to low carbs.
It should be over in two days. Carb withdrawl makes you a little more tired. After that, you should even out -- no more crashes and highs -- to a constant level of good focus and energy. You do need to bump your fat and protein intake, first to avoid the addiction eating by actually being full, and second to provide energy. After a couple days you switch to burning fat instead of burning sugars.
For me it was very similar to the early stages of a bad flu. Tired, headaches, body aches, irritable, and mild nausea for about 5 days. I've heard that MCT oil can ease the transition a bit, but be careful because too much can cause stomach cramps and violent diarrhea. (I've never been able to handle more than one tablespoon at a time.)
I'm 6 weeks into a keto diet, haven't been over 20g of carbs a day throughout. Sleep is much deeper, but I feel I need to sleep longer.
First few weeks (in particular) I had to drop my weight amounts in the gym and found (fighting in) martial arts I tired quicker. Helped this with BCAAs and cream in my coffee prior to exercise (prior to this, my first meal wouldn't be until ~2pm and I'd exercise in the morning fasted). I suspect MCT oil would also help? Also struggled with low blood pressure/headrush when standing up quickly. Helped this with dioralyte and increasing my salt intake. Other than that, it's been good.
Pretty amazing diet really. Far, far leaner, no energy dip in the afternoon, and I'm far less bloated and uncomfortable. Although that's possibly because my diet seems to be a bit more FODMAP friendly. Interesting experiment, either way.
Keto is not exactly compatible with anaerobic exercise. If you're lifting or performing a mix of aerobic and anaerobic (e.g. running / sprinting intervals), your muscles still need some glucose. I'd suggest checking out the cycling ketogenic diet (carb cycling) - it will allow you to refuel your muscles' glycogen stores, allowing anaerobic exercise (weight lifting, etc) while maintaining ketosis 99% of the time (staying lean). Also check out alpha lipoic acid supplements, it will increase the ratio of glucose provided to your muscles vs fat storage during your carb load. Go get ripped :)
Keto and IF can be very dangerous if you don't know what you're doing. I'd suggest getting regular blood testing with your doctor while adjusting and figuring out your routine and meal plans.
