Here’s a post I found on reddit.com about calorie counting on a Keto diet:
“Counting calories is useful in the beginning for informational purposes. Many people who attempt a ketogenic (low carb high fat) diet end up actually consuming a low carb high protein diet. It can be really difficult to get the fat content of your meals up to the right level ( I.e. at least 50%+ of calories, ideally 65%, up to 80% in some cases.) this is why calorie counting is important – it is a reality check on your macronutrient ratios and you can adjust your meals accordingly (I.e. pump up the fat content by adding a certain amount of butter or oil.) As you start to lose weight, it’s also important because you will learn your “sweet spot” for weight loss – many people find that below a certain calorie threshold they have diminishing weight loss returns.
Don’t be surprised if you lose more than 2 lbs per week. I’ve been eating a ketogenic diet at weight maintenance levels for years (for health/metabolic anomaly) reasons and recently decided to lose some weight that I’d gained a few years ago when I tried eating a ”normal” diet. To start losing weight, I made no changes to my weight maintenance diet except make sure I exercised every morning, cut out unplanned snacks, and limited my ‘desserts’ (cheese, panna cotta, low carb cheesecake) to 2-3 a week. With just these small changes, I’ve lost almost 4% of my body weight (6 lbs) in 9 days. Be prepared for huge (and scary) weight loss once you’re chugging along. If you feel you’re losing too fast, eat more! This is another reason why calorie counting is helpful in the early stages – if you find you’re still losing 1/2 lb per day on a 1500 calorie diet weeks into ketosis, you may want to up your calories to avoid saggy skin or other complications of too -rapid weight loss…”
Then, in answer to this question: “my question rather is should I be restricting my calorie count each day to what a traditional calorie deficit says I need to lose weight?” Reply: “I wouldn’t, if I were you. I’d give it a couple weeks and then take a look at your weight loss and your daily calories averaged over the course of a week and make broad adjustments if you think they are necessary, i.e. if you aren’t losing enough weight or are consuming way too few calories (a common problem when your appetite disappears.)
The problem is that the BMR calculators and calorie deficit calculations are not always predictive of what actually happens on a ketogenic diet. I eat ketogenically all the time and typically eat 300-1000 calories more than the BMR calculators say I need. For the past ten days, I have been actively ‘dieting’ and tracking my calories. I have not been running a calorie deficit according to the BMR calculators out there (even with exercise factored in), nor am I particularly active person that would have reason to have a high BMR than expected. Yet in 10 days I have lost eight pounds by making small tweaks to my normal diet (reducing snacking, limiting sugar alcohols, drinking more water and taking vitamin supplements) – and this loss can’t be attributed to water weight from burning up glycogen, since I already ate a ketogenic diet before and therefore have very little excess glycogen. So, according to this data, I’ve been running a calorie deficit of 2800 calories per day and have a BMR of 4300. Yeah right! (I am 5’4″, female, was 165.4 lbs 10 days ago, and am not a particularly active or muscular person.) These sort of wonky calculations are common, especially at the beginning of weight loss.
TL;DR – My advice would be to track but not restrict calories until you have enough data to review your weight loss and how many calories you’re consuming, and then make broad adjustments to your strategy rather than nitpicking the calories on individual days (as that can get very tiring very fast.) If you find your weight loss is to slow or slowing, that’s the time you might want to pay more attention to calorie deficit calculations.”