We already discussed New Year’s resolutions a couple of weeks ago, but weight loss is such an overwhelmingly popular subject this time of year that it’s worth discussing twice this month.
The classic understanding of how weight change works is pretty simple: a calorie excess leads to weight gain, a calorie deficit leads to weight loss. That’s generally a true statement, but anyone who has tried to lose weight – and keep it off – knows that it’s a much more complicated process than that.
One of the things that makes weight loss complicated is something called the theory of a body weight “set-point”.
This refers to the body’s tendency to want to maintain – maybe a better word is “defend” – a weight that it is familiar with and comfortable at. There appears to be a “target” weight range – usually a range of about ten pounds – that each person’s body is genetically programmed towards. Many researchers believe we are born with a set-point weight that we should reach and maintain in adulthood if all other things are equal.
The problem is this: most of the factors in our lives aren’t “equal” when it comes to maintaining body weight. Most things in our world are far more likely to lead to weight gain than weight loss. Calorie-dense foods are easily accessible and cheap. This was not the case for most of humanity’s existence. Physical activity is no longer a routine part of most of our lives. Many of us have gym memberships now, as we need to set aside time to get the activity that was once an unavoidable daily aspect of the lives of hunter-gatherers and farmers. Roombas vacuum for us. Dishwashers have replaced washing dishes by hand. We don’t even have to walk through a store to purchase items we want – Amazon will deliver to your doorstep. You can functionally live 95% or more of your daily life from your driver’s seat, office chair, couch, and bed. This and more is why many researchers refer to our modern society as an inherently “obesogenic” environment.
Over time, a set-point weight can be overridden. Weight gain occurs over months, years, and decades, until that person decides to lose weight. That should be easy, right? After all, for someone with obesity, their body once had a set-point weight that was much lower than their current weight.
Unfortunately, set-points can change. In what is likely an evolutionary adaptation to ward off starvation – which was much more common during the thousands of years that our genetics were established than it is now – our body can change its set-point weight. Specifically, it can increase.
To borrow an analogy from a very informative TED Talk on the subject, this process works a lot like a thermostat. Your brain regulates things like hunger and fullness, as well as makes small adjustments to metabolism. As long as most things are consistent, weight will be as well. In a house, a thermostat can make adjustments to keep the temperature consistent even as the temperature outside changes.
But what happens if you leave the front door open on a frigid January night? You can bet your furnace will struggle to keep up. This is what it’s like for our brain when we constantly have a surplus of energy in the body. Eventually the weight will change. Unfortunately, in our bodies, eventually the setting on the thermostat will too.
Once our body re-programs its set-point to a higher weight, weight loss becomes more difficult. Even more difficult is maintaining the lower body weight over time. Our brain and body will work to re-gain lost weight by manipulating hunger and fullness hormones. A well-known study on participants in The Biggest Loser reality show found that participants who had lost large amounts of weight dealt with slower metabolisms – even when their new body weight was accounted for – as well as dramatic deficiencies in the hormone leptin, known as the primary “fullness hormone” in our digestive system. In other words, they were hungry all the time with a slow metabolism – a perfect recipe for weight re-gain, which occurred for most of them.
Research conducted by Rudy Leibel at Columbia University found similar effects, finding that someone who had recently lost weight is likely to have a 15-20% lower metabolism than someone of the same (but stable) weight.
To put this in perspective let’s compare two hypothetical people, both male. Person A is six feet tall and weighs 200 pounds. He has lost 40 pounds over the past six months. Person B is also six feet tall and weighs 200 pounds, but has been at that weight for his entire adult life. They have the same body composition. Person A would likely need to have an intake 15-20% lower than Person B to maintain the same weight. In other words, Person A would need to consistently consume 400-500 fewer calories than Person B to maintain weight, while dealing with higher levels of hunger the entire time. Check out this interview with Rudy Leibel for a more detailed explanation of how all of this happens in the body.
It’s not entirely clear if set-point weight can eventually be reset to a lower level, but it appears likely. There isn’t a definitive answer for if, how, and how long it takes for this to happen, however.
All of this may seem quite discouraging, but there are many people who have successfully lost weight and kept it off over time. The National Weight Control Registry is evidence of this. But long-term weight loss is difficult, and it might help to understand that sometimes your own biology might be an obstacle to reaching your goals.