One of the biggest challenges in successful weight management is prevention of weight regain after weight loss. Studies show that most often, people regain weight after intentional weight loss, with many people regaining most or all of their lost weight over time (and then some, in some cases).
There are two major drivers of weight regain:
1. Many powerful changes in hunger and fullness hormones happen with weight loss, which drive us to eat and regain weight.
2. Our energy burn (called ‘energy expenditure’) drops – more than we might expect.
Today, we are going to focus on #2 above. (stay tuned for much more on #1 another day!)
So, just how much does our energy burn drop with weight loss?
Well, it turns out that we are geared towards retaining energy and downregulating metabolism in the face of weight loss, as a strong defence mechanism genetically engineered to protect our weight to survive times of famine. This happens thanks to a decrease in thyroid hormone levels, decrease in sympathetic nervous system tone, an increase in skeletal muscle efficiency, and other changes as well. While we do expect a proportional decrease in energy burn simply due to the weight loss itself, the decrease in energy burn is actually much more than that, thanks to these changes.
Here’s an example: When a person loses 10% of their body weight, one might think that their daily energy burn (called Total Energy Expenditure or TEE) would also drop by 10%, reflecting 10% less body mass that needs daily care and energy, and 10% less body mass for the person to physically carry around in a day. In fact, studies show that the total energy burn of this person will actually drop by 20-25%, – in other words – to 10-15% less than what would be predicted.
Said another way, it will take 300-400 fewer calories per day to maintain the 10% loss in body weight, compared to a person of the same body shape, size, and weight, who hasn’t lost 10% of their weight.
This decrease in total energy expenditure may not persist forever – the POUNDS LOST study suggested that the TEE comes back up to expected baseline after 2 years (though others have suggested that the reduced energy burn lasts as long as 7 years or more). Some research has also suggested that the drop in energy expenditure may be less with a low carb diet, higher with a low glycemic index diet, and the highest on a low fat diet (my speculation on this is that this may be related to higher protein intake in the low carb diet – it takes more calories to burn and digest protein compared to carbs compared to fat).
Because of this reduction in energy burn with weight loss, as well as the powerful hormone changes that happen to drive hunger, it is very difficult to maintain weight loss. Fortunately, the American National Weight Control Registry has provided some useful information regarding habits that help keep the weight off (though these are not easy either) – check it out!