Rebound weight gain refers to weight re-gained after loss on a diet.
When dieting was revived it was assumed if you reduced your calorie intake, drastically to lose say 50 lbs your body would use up that stored weight. Like having 50 shekels and spending them.
And that would be the end of that.
That expectation was shattered when it turned out folks kept re-gaining what they'd lost, sometimes more. For a while people repeated and repeated the experiment, only to find the same result.
At some point it this was acknowledged to be a facet of weight loss and the term rebound was born to indicate how the weight was like a boomerang. You threw it out and it came back. The battle then extended to how to keep that rebound from happening.
The strategy was stay on a diet for life,or lifestyle as its now known.
No one has satisfactorily explained why this initially and understandably unexpected fillip should occur. It makes even less sense than a lot of aspects of dieting and that's really saying something. The usual excuse is of course to blame dieters, it's because they "returned to their old habits".
After enduring often a lot of pain, discomfort and boredom of a diet, often with an appetite and hunger that has become depressed or impotent in despair of ever being satisfied. Why wouldn't people if they return to eating the foods they like, just not eat them but far less as they've shown they can do by losing the weight in the first place?
Because some equal and opposing force is set in motion by the restriction itself and that plays itself out eventually.
If you miss breakfast, you eat more at lunch, if you miss lunch as well, you eat more at dinner than you would have if you'd only missed breakfast.
The same for missing meals applies to missing lots of meals or the missing parts of many curtailed meals. If that sounds almost like the body's keeping some kind of tally of the missing grub/ weight then that shows up something else that's never answered.
The body can have a very long memory. Years ago this was discovered and even named, it's was called "retired athletes syndrome". After decades of intense physical activity often starting from early childhood, sportsmen and women can find that once their sporting career is over, their bodies start to try and make good all that 'missing; energy. A bit like the body regaining after a weight loss diet.
As you can imagine, this is put down the usual, they stopped exercising, they continued to eat what they ate when they were active. Again, why? They eat more because their use of their bodies demands more as they are using up more energy. If they cease to be active why would they continue indefinitely-adjustment period aside- to eat what their body no longer needs?
It all smacks of an excuse to explain the inexplicable, that something else is going on which doesn't fit the diet hypothesis model. The excuses of course do.
If post diet rebound was just spontaneous elective greed, why wouldn't amounts re-gained vary significantly be more individual? Why would they so often more or less the starting weight? Furthermore, it is the way the body adjusts itself during the process.
This is most clearly seen when the rebound is more or less immediate. The person is dragged quickly back to their starting point with a swiftness that can be breathtaking, in a fraction of the time it took to lose it. Yet when the body approaches the starting weight, it slows down sometimes gain comes to a virtual dead halt.
How can it keep doing that randomly?
Maintaining equilibrium is clearly the body's goal and it has nothing to do with intent or willpower or anything conscious. The pattern is too clear, too predictable, too repeatable to be put down to deliberate willfulness on the part of dieters.