It’s often suggested that in order to lose weight, you need to eat less calories than you expend. In other words, calories in versus calories out= weight loss or weight gain. While in theory this is true, it’s an overly simplistic view. Many people eat less calories than they expend but their weight remains stable. This is because of metabolic adaptations that occur in response to a negative energy balance (consuming less calories than expending). Read on to find out more.
In response to consuming less calories than are expended, something called “adaptive thermogenesis” can occur. This is a decrease in energy expenditure that can’t just be explained by a decreased body weight. This occurs as the body makes changes to reduce the gap between energy intake and expenditure by becoming more efficient. In other words, the predicted equation of energy balance being equal to energy intake minus energy expenditure doesn’t work because energy intake influences energy expenditure.
The reasons for this adaptive thermogenesis isn’t fully understood but reduced sympathetic system output, thyroid levels and insulin secretion can all be contributing factors. Some other reasons for this reduced energy expenditure is the reduced thermic effect of feeding, which is the energy needed to digest and store the food we eat. Those who have a negative energy balance have reduced energy expenditure after eating food so that their overall daily energy expenditure is reduced There is also some research to suggest there is a reduction in non-planned physical activity with negative energy balance (AKA becoming more sedentary) and an increase in muscular efficiency, which means less energy expended with exercise. All of these factors mean that less calories are required on a daily basis as we reduce our calorie intake.
With a negative energy balance, there is not only a decreased energy expenditure, but also metabolic responses that drive us to eat more. For instance, leptin is a hormone that decreases appetite. When calories are restricted, leptin levels decrease and as a result, appetite increases. Similarly, ghrelin is a hormone that causes hunger. When calories are restricted, ghrelin levels rise, and so does hunger. People blame a lack of willpower for causing them to “fall off their diet.” However, willpower isn’t the real issue, but rather, biology. There are underlying physiological changes in hormone levels that drive us to eat more.
So what do we do? First, don’t overly focus on calories. Calorie counting is not only tedious but also very inaccurate. There is also no point in counting calories when we can’t accurately know how many calories we need per day as this is influenced by so many factors. Second, re-evaluate your need for achieving a certain weight goal. Each person has a unique body weight range, where their body weight likes to sit (for more on that, click here). While we can work hard to drive it below this range, staying here is not usually sustainable long term because our body’s biology is fighting this with the physiological changes mentioned above. Focus on making balanced and healthy lifestyle changes, and trust that your body will fall at the weight that it’s meant to be at.
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