But I've heard you can permanently lower your body's weight set point?

Excerpt from Show Me blog post on the topic:

“When we restrict calorie intake the body has a way to manage it, but it costs.

The energy deficit has to be addressed by filling the deficit from within the body itself. Most biological systems are run to an overdrive level with certain key clamps put on the system to keep it at an optimal state.

It is biologically more energy-intensive and risky to try to run a system right to 100% all the time than to run the system to 200% and just use a few hormones or enzymes to clamp it down to 100%. 

Our bodies are probably quite literally built to burn off excess energy in our sleep if there are any unneeded excesses.

But restrict your calories and now all of the limiting hormones like leptin, ghrelin and insulin and others are left scrambling because you have just dumped the entire metabolic system to well below its 100% functional level. Leptin is a clamping hormone. With nothing to clamp down on, it plummets in our blood streams and this creates a cascade of shut downs throughout the body.

We have evolved to overeat and maintain weight easily, in our sleep no less. We have evolved to survive some environmentally imposed under-eating as well, but not with the same ease and not without some heavy-duty damage for which we must account.

Some lizards can indeed drop their tails, when threatened, as a way to avoid a predator.“The loss of the tail (called autotomy)…is stressful to the lizard, especially if that lizard stores critical fat deposits in the tail, such as leopard geckos. Not only do they need to spend energy healing the stump and regrowing the tail, but the loss of fat may occur at a critical time, such as during gestation or a period of low food availability.” [M. Kaplan, 2002]

Think of dieting as autotomy for humans.”

You will read all manner of incorrect garbage in the mainstream press about how you can change your weight set point permanently using diet or exercise, or both. The only way that a weight set point is permanently adjusted is by restricting calorie intake in perpetuity (and usually at increasing levels as you age— autotomy for humans, remember?) or removing parts of the brain, as has been unequivocally proven with animal studies.

We thankfully have not resorted to removing parts of human brains just yet as a way to stay thin, but given our adoption of stomach mutilations (various gastric-bypass surgeries) perhaps I should not speak too soon.