mega weight loss

[JAMIE9999]

Lost 5.5 lbs. this week despite going over my daily intake by 4400 calories (i know, i over did it) one day this week.  How the heck did that happen?

[WendyB]

Its impossible to explain why are bodies do things.

You might gain next week to the huge loss. Its happened to me before.

[Dominique]

Weight loss (or gain) can come from water, fat or lean mass (e.g. muscles), usually in that order. Your mega loss most likely came primarily from water. In order to lose 5.5 lbs of fat in a week, you would need an average daily deficit of 2750 calories. Several factors can cause water loss (or gain). For instance, if you cut sharply your carbs (as when switching to a low-carb diet, or a ketogenic diet), you will lose a lot of water (because with each gram of carb stored in your glycogen stores comes about 3 grams of water). OTOH, if you eat very salty food, this will usually cause extra water retention.

Assuming you have a lot of weight to lose, you would want to have a longer-term approach. A useful tool for this is a free web-based service called TrendWeight, that you can link your Fitbit account to: if you enter your weigh-ins in Fitbit (or use the Fitbit Aria smartscale, or another smartscale like Withings or Weigh Gurus, that can automatically sync your weigh-ins to your Fitbit account), TrendWeight will be able to pull that data from it and show you where you weight really is going, regardless of the daily fluctuations.

[A_Lurker]

@JAMIE9999- I did over 6 months of daily weighing combined with detailed calorie counting.  I never did find an A to B relationship.  As @Dominique has said, sometimes it's water.  If you're female and still menstruating you can retain a lot of water before your period, and then you'll see t drop.  I found early on that undereating followed by overeating could show a weight gain followed by a loss.  There's a theory floating around called flexible dieting where you try and fool your body by doing exactly that (low days/high days staggered).  I also use trendweight.com as it's more important to see the overall trend rather than the specific numbers.