Some of the key questions I cannot answer but I can explain what is happening, some of which will be good news others bad.
How much weight will you gain and how long will it take to lose it? This is hard to figure because of the way low carb diets effect the body. The purveyors of these are interested in repeat business, not the customers, something you will already understand, and to see why these are great for business and not for people using them I will explain what has happened to your body. Some good news before I thoroughly depress you in a moment is that you are doing some good stuff now.
Why do low carb diets make you lose weight?
Low carb is almost universally accompanied by high protein. Even if it isn't the body will resort to catabolising (or cannibalising) your lean muscle tissue, removing the waste from this takes a lot of water, producing instant weight loss. If it did have high protein you have a lot of excess that will be stored as lipoproteins (fat) or disposed of as urea in your urine, taking more water with it.
In the weight stakes water and fat are in a different class, so dropping water will make you drop weight fast, hence instant success.
Where's the catch?
Loads of them.
Starting with an assumption that you are on a high protein diet, excess proteins are converted to lipoprotein where possible to be stored along with other fats. This means you can have lost weight and gained fat.
Water balance cannot remain below ideal indefinitely. The body will redress the balance putting the water your body desperately needs back. So the water you lost is back, and if eating more protein you have gained fat, so weight is up. This is where the business works so well by getting people yoyo dieting themselves to death or bad health.
Lean mass loss. The body catabolises it's lean mass to produce energy. This helps you lose weight in the short term by destroying the heavy muscle, but long term you are losing tissue that burns more energy than simply carrying fat around. This also impairs your abilities meaning you can't train as effectively to burn energy through training.
Final one for this list. The human animal is designed for a diet high in complex carbs aka starch, so much so it bases it's metabolism in part on the amount of carbs entering the body. So lower carbs means you burn less energy, and to add a final insult the body assumes it's starving so is less likely to allow metabolism of fats.
What happens next?
The body will force you to end extreme low carb diets, there are no exceptions because the alternative is literally death, as a few using the Aitkens diet have proven. The effect of this is massive and the final piece of the puzzle needed to send most back to the low carb life again.
The body sees the end of starvation as a time when it needs to store more fat to ensure it survives the next time of shortage, which is why yoyo dieters get heavier over time.
The metabolism remains low as a precaution while the body sends out more desire to shovel in food.
Appetite increases to constantly be just ahead of the intake, meaning you can be totally full and still hungry. The appetite will remain unless brought under control.
The balance
The part too few people know and diet companies spend a fortune repressing is that we are designed to have complex carbs as our main calorific source. The figures of an ideal are carbs 60-65% of calories (with max 5% of this being sugars), 25% fats, 17.5% proteins. This is flexible and some find the standard doesn't suit them well so adjust to their own needs. Mine is closer to 70% carbs because I burn energy at an absurd rate and need it readily available.
When wanting a weight loss diet the proportions don't change the amounts change across the board. So dropping from 1,400 calories to 1,300 doesn't mean cutting out 100 calories of carbs it means around 60-65 calories of carbs 25 of fat 17.5 of protein. Sorry I know this last will have appeared condescending but this point is where most go badly wrong and I would rather risk insult than someone missing the point.
What can you do?
Most important part first. Accept what has happened and move forward. Kicking yourself for the mistake won't help in any way. You did it, we've all made errors on diet at some time. Just view this as a blow you have to recover from and leave it behind you.
Get your diet into sensible balance. I don't care what the foods are, that is personal taste, but the carb, fat, protein balance is important.
Find out roughly how much energy you are burning. There are a wealth of calorie calculators online, some on fitness.com if I recall, use one to get an idea of how many you are using as a guide.
Set a realistic deficit. You have just come out of a long starvation mode, while getting your body back to normal you will need to be eating roughly what you need. I would aim for a couple of hundred calorie deficit at first and increase it to 500 to 1,000 over time. You shouldn't feel lethargic or tired due to lack of energy, that risks not getting the metabolism going again.
Remember the math. 1 pound of fat = 3,500 calories, so losing a pound of fat a week = 500 calories a day deficit, 2 = 1,000 calories deficit over 1/2 the average calorie needs of an adult, that is impressive, not disappointing. If you are losing weight and don't see space for a deficit be aware this could easily be water. Or lean mass if training well.
Day by day you could gain or lose a few pounds easily. Take a trend over time for accuracy.
Set long term goals realistically. 1 or 2 pounds a week of fat loss is good going, so set your targets based on these volumes. Also remember the lighter you are the less energy you burn, so the lighter you get the less food you will need to be eating to lose weight.
End game. When you get to your preferred weight find out how much food you need to maintain that, remember it will be less than when you were heavier. Stick to this on balance.
There's not a lot of good news there. But there is one here. The fact you have made this mistake and come to find out what you should do now puts you among the smarter dieters. Now if you add patience you can undo the damage and get back on track nicely.
Keep us updated, we like to see people doing well. We have all had long journeys with ups and downs so don't worry if some updates aren't positive.
