How Should I Transition Out Of My Diet... My Keto Diet.
Part 1: Returning To Maintenance
First and foremost, it's important to know that while calculators such as the ones provided by MyFitnessPal are very general. Unfortunately, they don't have the ability to understand that you've been dieting for the past few months. So, while 2020 calories may be "maintenance" for your height, weight, composition and activity level, it's certainly not the correct amount for your situation.
If you're basing your weight loss (or maintenance) off of calories, it's imperative that you find your actual maintenance intake by counting calories and watching your weight fluctuation for a few days. If your weight stays the same, then you've found your "current maintenance," which I'm almost certain will be different than the MyFitnessPal Calculator.
Second, in terms of reverse dieting, you're certainly correct about that increase (1520 to 2020) being a bit too large to do over night. However, it's important we touch on the different methods of reverse dieting.
Method 1: Slow reverse dieting
While slowly increasing calories (<50 kcal at a time) can potentially allow for better control, I believe it's a bit too slow. Consider that for most people, 50 calories over or under maintenance won't make a difference. That's literally fewer calories than eating an extra oreo.
While having moderate increases in calories might be great for monitoring weight changes, It's a bit too slow. Not to mention, if you're only increasing calories by 50 or so every week, you'll remain at a "deficit" for a very long time, which could reduce your responsiveness in the gym.
Method 2: Fast reverse dieting
In this case, you're increasing immediately back up to your original "maintenance calories intake." This is wrong in my eyes for a few reasons.
First, this isn't your maintenance anymore. With such a drastic change of body weight and a strong reduction of calories for some time, you're metabolic rate decreases, otherwise known as adaptive thermogenesis. So, if you automatically jump up to your original "maintenance" it's likely that you're actually in a surplus.
Second, if you immediately jump up to higher calories (significantly higher) you don't have the ability to adjust before weight gain occurs. You could accidentally consume 5-10,000 extra calories in a matter of a week (overall) and not even know it.
Method 3: Moderate Reverse Dieting
I suggest using the same methods that would be used for weight loss. After finding your "current maintenance," increase that amount by 20%. During this increase, monitor weight daily to understand how you're responding. If you haven't gained any weight, increase by another 10-20% based on your response.
By using this method, you can make small adjustments while increasing calories meaningfully, yet not so much that you accidentally get fat as a result.
Don't immediately increase calories in their entirety but also don't increase at the pace of snail. Start with a 20% increase of calories (or an extra meal of protein, veggies and a light carb). Weigh yourself daily and increase calories further based on how your weight and performance in the gym changes.
Part 2: Switching Macros
As far as switching macros are concerned, your first consideration should of course be calories. However, I think it's important to not ignore the potential of switching macros here. If you were normally consuming carbs and simply wanted to increase or decrease, it wouldn't be a big deal. However, since you've essentially been keto for sometime, special care should be taken when switching to a higher carb approach.
First, you've been consuming little to no carbohydrates for some time. To all of sudden increase carbs drastically won't only upset your gastrointestinal system, but could also lead to unwanted fat gain. The reason for this is largely because you're simply not accustomed to the high carb intake anymore. Not to mention, your body is likely optimized for metabolizing fat rather than a large amount of carbohydrate.
Essentially, this is the possibility: You're in nutritional ketosis, primarily using ketones (metabolized fat) as energy. Now all of a sudden, you consume a large amount of carbohydrate. So, does the body immediately switch to metabolizing carbohydrate? Well, sort of.
Obviously the body needs to metabolize the food you eat, but it's more so of what happens once the byproduct of that metabolism (carbohydrates now become glucose in the blood). Does that glucose get used? Probably not, since you're body has been primarily using ketones as energy. Now you have both high blood glucose and high levels of fatty acids in the blood (which is similar to what occurs with metabolic syndrome and type 2 diabetes.
Now let it be known I'm not saying this will happen to you, just that it's a possibility. I mean is it hard to believe that they body may have difficulty digesting and using large amounts of a macronutrient that you haven't consumed for months?
I would suggest along with your slow increase calories to slowly reduce the level of fat you're consuming, while slowly increasing carbs. Here's an example of how I would slowly transition out of your macro distribution:
If you're transitioning out of keto, it makes sense to reduce fat and increase carbs in steps, rather than all at once. Since you've been avoiding carbs for some time, increasing them by over 100% immediately can cause gastrointestinal distress and may even lead to unwanted fat build up. Overall, it just makes sense to slowly change macros rather than all at once.
Overall, if you're transitioning out of a diet or even also transitioning out of a high fat diet, I suggest modestly, yet meaningfully adjust your food intake. Do so sequentially while closely monitoring your weight.
If you increase carbs and total calories drastically from the start, you risk unwanted weight gain that you won't be able to remove. If you take things too slow, you could waste weeks or months due to continuing your calorie deficit. In both of these situations (which happen to be the same situation) taking the moderate approach is likely the superior option.