In The Art and Science of Low Carbohydrate Living, authors Phinney and Volek take great care to make the point that eating high fat is critical to being able to tolerate the first few weeks of ketosis, as is being hardcore about restricting carbohydrate intake. "Yo-yoing" your carb intake is likely to prolong the period of adaptation.

Phinney has done a lot of research on ketogenic diets and athletic performance. Here he writes:

There are to date no studies that carefully examine the optimum length of this keto-adapataion period, but it is clearly longer than one week and likely well advanced within 3–4 weeks. The process does not appear to happen any faster in highly trained athletes than in overweight or untrained individuals. This adaptation process also appears to require consistent adherence to carbohydrate restriction, as people who intermittently consume carbohydrates while attempting a ketogenic diet report subjectively reduced exercise tolerance.

As far as how long it takes just to get into ketosis (not adaptation), not long at all. It's my understanding that no matter what kind of diet you eat, you'll go into ketosis during your sleep cycle, unless you're sleep-eating. So you should be ketotic pretty much right away, although not keto-adapted.

There's more about keto-adaptation here: http://paleohacks.com/questions/56190/yoyo-ketosis-and-bad-feelings/56192#56192

I'm sure you'll get many answers but for me, the longer I go between meals the easier it is to switch back and forth between burning glucose and burning fat (releasing and burning stored fat.)

You know you're in ketosis when you haven't eaten in at least 8 hours and you feel strong and high-energy (rather than weak and famished.) Nowadays I go into ketosis every night because I don't normally eat after 4 pm.

When I first started an ancestral eating program, I'd wake up in the weak-and-famished mode. I didn't do anything crazy, I just tried to wait an hour or two and then I'd eat a breakfast high in protein and fat, such as beef, bacon and eggs. I'd wait as long as I could before eating a second meal and would eat as much as I wanted.

By doing that, each morning I felt better and better and pretty soon it didn't matter if I ate breakfast or waited for lunch or even supper.

I too would like to know how to achieve ketosis.

I am told it is a brave new world where fat literally melts off, the opposite gender begins swoons at the very scent, and one always manages to find a parking spot!

Pray, share whatever knowledge you acquire in your quest that you might help others achieve this rare dove of a goal.

Be quick, Michelle, ere the insulin rob you of what little life you have left to find you buried in sepulchre by the sea, where mermaids sing (each to each), and your too, too sullied flesh festers over like a blister in the sun.

I can kick myself into ketosis if I work out in a semi-fasted state. By "semi-fasted" I mean having had a 100% fat pre-workout snack - usually a cup of coffee with cream and coconut oil. My workout is usually some type of high intensity intervals like sprints mixed with some weight lifting. I find that by the end of that kind of workout I am in ketosis, which I recognize by the acetone smell in my nostrils when I breathe through my nose.

It might take this kind of routine to kick your metabolism into a fat-burning one. I recommend trying HIIT training in a semi-fasted fats-only state to see if you can induce ketosis.

You can check to see if you are in Ketosis by buying Ketostix and testing. Once you are urinating ketones, your in, no need to constantly test yourself as the amount you excrete in urine changes pretty constantly.

Once in ketosis, remember, its not that eating dietary fat makes you burn fat, but rather the LACK of carbohydrate that has you burning fat. Therefore, to lose weight, while in ketosis, you must eat less calories overall than you burn.

If you eat more fat than you burn, you will gain fat, so shoot to eat less. Put another way, your only going to burn stored bodyfat AFTER you burn any dietary fat.

How much were you eating of other things during that time? You may simply have been lacking enough food or nutrients overall. If you fast, you can expect to feel bad or hungry for a couple of days if you're used to eating lots of carbs. Things should start to improve then, though ketone production continues increasing for several weeks to reach 'full ketosis'. However, you're in and out on ketosis all day, there's no magic trick to achieve this zen-like state.

We could spend a lot of time hacking your meal plans and activity levels and everything else, but to be honest the simplest test if you are interested is to go the water fast. Say once a week, starting with skipping meals, then going a whole day, then 2 or 3 if things are going ok. If you don't eat for a week and feel fine, then you know it's not carbs per se that were the issue. Some would consider a brutal experiment though, so if you don't have a good reason then why not stick with a nice level of carbs?

I started a zero carb intake and on my third day. My first day was bad. I didn't feel like myself. The second day was better. The third day, funny because I didn't feel hungry until after I ate. Breakfast was ok, just dinner which was a grilled chicken breast and a jalapeño pepper. After I ate this, I started feeling hungry. Been feeling a little tired but otherwise good!

I find it takes me about 2 weeks the first time to hit it. And yes, going keto drives you insane - I shaln't ever be doing it again.

You can use keto sticks (urinalysis) to check, but its very very hit-and-miss. I don't know if this was true of others - but I could always tell because my pee would smell like mayonaisse :| Not great.

Just stick to paleo - I've lost just as much weight on this without even trying to limit calories.

My experience...

For best results cut out 100% of carbs from your diet. I'm talking if the box/bag/container says "0.5 carbs," don't buy it. If you stick with straight chicken, beef, bacon, and fish only with diet zero carb soda, diet green tea, and water -you will lose weight INCREDIBLY fast. I lost 30 lbs in 3 weeks (21 days) following that method (NEVER CHEATING). If you introduce carbs into your body it decreases the effects if the Ketosis/Atkins. This is the only diet that I found that works for me for instant results. BTW you can eat as much meat as you want. Seriously, go nuts (if you're hungry), it will all get passed through you and you will burn fat like crazy.

I need to lose weight quickly!! Im on my second day of low carbs and feel pretty good. should I cut out cheeses and veggies and just eat meat for a few weeks to get a good jump start? please advise thank you

I'm on day 8 of a zero carb diet, I'm literally living off pure whey protein shakes and eggs and tuna. I was 11 and half stone and I've lost 7lbs in 8 days. However, I've had 2 days in the past weeks where I've felt sick and I'm tired, aching muscles and bad mood swings. From what people say I'm in ketosis and it's hell up to now but I'm desperate to lose another stone. I'm feeling so tempted to give up but I'm hanging on another week or so to see if there are any more gains and if so I'll stick with it. Just hope the mood swings go, this diet is mentally challenging!I personally believe to lose weight you need zero carbs in order for your body to burn it's fat rather than carb stores.

I have been in ketosis twice, and I usually get there by doing a near-100% fast (maybe with some coffee, artificial sweetener, and creamer). In my opinion, it requires about 3 days' worth of caloric restriction to achieve it. So I can either fast completely for 3 days, or work out very hard for 2 days (roughly 1000 cal/day of workout) to achieve ketosis (in my case, it requires 6000 cal of total caloric restriction, period.) I have never eaten fat and protein to get into ketosis.

You can tell you're in ketosis because you aren't hungry at all and you smell weird - even to yourself. I find, however, that going from the 3rd to 4th day can sometimes be impossibly hard, so I have to play games with my schedule to avoid locations (such as home) where it's easy to break the ketogenic fasting, and snack on carbs, and maybe on the 3rd day go to an extra workout to get into the ketosis state right before bedtime, before my willpower is overcome by the discomfort.

Some body builders inject insulin to metabolize all their glucose and enter ketosis faster. A more natural and safer way to promote ketosis is to take Leucine - see http://forum.bodybuilding.com/showthread.php?t=113801571

When I entered ketosis it was because I abstained from all carbs and ate the proper proteins and fats diligently. I lost an insane amount of weight and was a stickler with hydration (water and tea). I actually did not experience any mood swings although it was difficult to sleep well. I easily fixed that with a sleep aid per a doctors advice. I guess if you did see a doctor you could also ask for a mood stabilizer if it was really bad. The only other "drawback" was a person close to me noticed a 'smell'. Additionally I was cold quite a bit. I didn't really care because the overall feeling of health and my physical apperance was satisfying enough to stick with it. Additionally while in ketosis my skin became the most suple it had ever been. Eventually, due to self sabatoging ways I let up and went back to being a glutten! Know this, after what I discovered, I look forward to re-entering the carb restricted life soon. It was the only thing close to "magic" that I have tried. But this leads to the main problem: as astongishing and great as it is to go into ketosis and have the benefits you can just was easily see it dissapear. Don't stay far away or else you will find yourself back at square one or even worse.

Can someone tell me how long this "smell" lasts in ketosis? Everyone on this forum mentions it so what do you do about it?

I am on day 8 of ketosis, and I feel great. I havent consumed many carbs at all, but gave myself 2 carb desert last night, it was delicious...:-) But after day 3 i was in full blown ketosis and went through the withdraws of sugar, migrane for a whold day, but now I feel great!! lost 6 pounds and I am not hungry but make myself eat. I do have the Diet dr.pepper, taste pretty good lots of fluids. I am on a roll and determined, ....good luck to all