I was directed to this article (i warn you - it's super long) during a discussion about metabolism and obesity. If you've ever lost weight but had trouble keeping it off, or exercised but didn't see the results you expected, this might shed some light on things.

A physician in Australia conducted a study where participants were obese men and women. They were placed on extremely low calorie diets until they lost around 30lbs and then worked to maintain the new weight.

A full year after significant weight loss, these men and women remained in what could be described as a biologically altered state. Their still-plump bodies were acting as if they were starving and were working overtime to regain the pounds they lost. For instance, a gastric hormone called ghrelin, often dubbed the "hunger hormone," was about 20 percent higher than at the start of the study. Another hormone associated with suppressing hunger, peptide YY, was also abnormally low. Levels of leptin, a hormone that suppresses hunger and increases metabolism, also remained lower than expected. A cocktail of other hormones associated with hunger and metabolism all remained significantly changed compared to pre-dieting levels. It was almost as if weight loss had put their bodies into a unique metabolic state, a sort of post-dieting syndrome that set them apart from people who hadn't tried to lose weight in the first place.

Motherfucker!

In a study done at Columbia University,

Muscle biopsies taken before, during and after weight loss show that once a person drops weight, their muscle fibers undergo a transformation, making them more like highly efficient "slow twitch" muscle fibers. A result is that after losing weight, your muscles burn 20 to 25 percent fewer calories during everyday activity and moderate aerobic exercise than those of a person who is naturally at the same weight. ... Another way that the body seems to fight weight loss is by altering the way the brain responds to food...[T]he body, in order to get back to its pre-diet weight, induces cravings by making the person feel more excited about food and giving him or her less willpower to resist a high-calorie treat.

Which is to say your body is an asshole that's actively working against you. Things brings us to "decision fatigue", which comes with another super long article and deserves a post of its own (which i will get to). However, i will tell you about the part of the article that talks about decision fatigue and its impact on dieters - the brain converts glucose to energy. The energy fuels our willpower. Willpower enables us to resist temptation. When you're on a diet, you restrict your caloric intake and consequently, your glucose intake, effectively reducing your willpower.

The discoveries about glucose help explain why dieting is a uniquely difficult test of self-control -- and why even people with phenomenally strong willpower in the rest of their lives can have such a hard time losing weight. They start out the day with virtuous intentions, resisting croissants at breakfast and dessert at lunch, but each act of resistance further lowers their willpower. As their willpower weakens late in the day, they need to replenish it. But to resupply that energy, they need to give the body glucose. They're trapped in a nutritional catch-22:

1. In order not to eat, a dieter needs willpower.

2. In order to have willpower, a dieter needs to eat.

This reminds me of when i used to do 3-day fasts. Day 1 was easy peasy. Day 2 was unbearable. I never made it to Day 3.

So, i thought, your body has to eventually go back to working normally, right? It's just in starvation mode now because it's been so used to getting more food for so long, but it'll adapt to the new status quo in a year or two. Shows what i know.

How long this state lasts isn't known, but preliminary research at Columbia suggests that for as many as six years after weight loss, the body continues to defend the old, higher weight by burning off far fewer calories than would be expected. The problem could persist indefinitely.

Well...hrm....i guess, if, uh, there's an apocalypse and food becomes scarce.....people with slower metabolisms will be better off...yeah...