Losing weight can be a challenging task. Many people struggle to achieve their ideal body shape but once they succeed in their weight loss attempts, they discover that it is not easy to maintain long term weight loss. You might be wondering, why is it so challenging?
There are several reasons why it is difficult to keep off those extra pounds, but one in particular stands out and it refers to the body's regulatory mechanism to maintain a constant weight. This phenomenon is also known as the “set point theory” and it explains why most diets fail over time. There is hope, however, as there are solutions to fight it!
What does the "set point theory" really mean?
Just as we have a "temperature set point" in our brains that keeps us at a relatively constant body temperature, we have a "weight set point" as well.
According to research studies there is a complex set of factors involved in keeping us at a stable body weight. These include our genetic predisposition, hormones, and most importantly our brain. It turns out that human bodies have evolved to survive under conditions of starvation because our ancestors lived through periods of scarcity. This process is called evolutionary adaptation. Fat stores are our body's biological mechanism to defend us against hunger. Our body has developed over time a complex system of adaptive mechanisms that include hormone and chemical connections that link the brain with the rest of the body to maintain stability. These regulatory mechanisms control our drive to eat and our energy expenditure.
Although we humans can use our brains to make conscious decisions, most of our actions are carried out by an unconscious mind that operates independently from our conscious thoughts. When it comes to our body's level of stored fats, it is our brain that takes control. Our body weight regulatory system works as follows:
1) When we gain weight, the excess fat signals the brain (via hormones) that our energy stores have increased. Hormones are just like "car shuttles". Each one is unique. Their main purpose is to carry and deliver information from one place in the body to another. When they reach the brain, they instruct it to increase the energy expenditure and to decrease appetite resulting in less food intake. Over time this brings the body down to its "set point".
2) In the case of intentional weight loss, the opposite happens. Our body's biological response to negative energy balance (ie. less food intake) is to signal our brain to slow down metabolism and to increase hunger, which in turn leads us to eat extra calories, resulting in future weight gain bringing our body mass index to its "set point".
Today, most of us live in an environment where there is food available at any time. We eat very different kinds of food compared to what our ancestors ate. We have access to ultra-processed foods, western diet, we're exposed to stress, and to sleep deprivation. Some medications we take may result in additional weight gain as well.
The environment we live in, often leads over time to a slow and steady increase of our "fat mass set point" and eventually to obesity. Losing weight and keeping it down, requires lowering "the set point". To do so, we must first understand how this process works.
What controls our body weight?
Three main "control centers" together regulate our body weight.
The first "weight control center" is our fat tissue, otherwise known as adipose tissue. We used to believe that fat tissue was just a storage place for excess calories. However, recent research has shown that fat cells are quite active because they produce hormones that regulate our hunger, appetite, inflammation, and energy balance. These hormones play an essential role in controlling our body weight and alterations in their levels can lead to changes in body fat distribution and may result in obesity.
To understand how this process works, let's take the example of a hormone called "leptin". This hormone travels throughout the bloodstream to reach the "hypothalamus", a part of our brain that controls hunger and satiety. Increasing levels of leptin instruct centers in the brain to decrease our appetite leading to less food intake, increased metabolism and energy expenditure. In other words, when fat stores are full, leptin tells our body to stop eating by increasing feelings of fullness after eating. It is our body's natural appetite suppressant. It also plays a key role in controlling our metabolism.
Let's take another example. "Adiponectin" is a hormone, released in the blood by our fat cells. It is meant to control inflammation and energy expenditure. Abnormal levels of this hormone have been associated with type 2 diabetes, heart disease, high blood pressure, fatty liver and extra weight.
Our second "weight control center" is the gastrointestinal tract. When our stomach is empty, it releases a hormone called "ghrelin" also known as the "hunger hormone" which informs our brain it's time to eat. When "ghrelin" levels are high, we feel very hungry and we indulge in eating more food. And, the larger the size of our stomach, the more "ghrelin" we have circulating in our body.
After we eat, food travels down to the small bowel which secretes a hormone called "GLP-1 (glucagon-like peptide-1)" to be released. Clinical studies show that GLP-1 (glucagon-like peptide-1) has a positive impact on various organ systems throughout our entire body. Among its most important functions, it helps us digest food by telling our pancreas to release insulin, and in doing so it helps to lower the blood sugar levels. It also informs our brain that we have had enough food to eat, thus lowering our hunger levels and caloric intake. Researchers have discovered medications called GLP-1 agonists (e.g. liraglutide or semaglutide) that simulate the effects of this hormone. Not only do they help with control of diabetes but they can also help with treatment of obesity.
Other hormones released from the gut such as "GIP" (glucose dependent insulinotropic polypeptide) and "amylin" have important functions and are currently being studied as possible treatments of obesity.
The third and perhaps the most important biological control center is our brain. We can think of our brain as the central railway hub where different destinations connect. External factors (such as our environment) and biological factors (such as body fat levels and hormones) come together in this central hub which exerts biological control over our body. The hypothalamus, the nucleus accumbens (localized in the striatal region of our brain) and the prefrontal cortex are the three brain centers that work together to control our hunger, fullness, and our desire to eat.
"The nucleus accumbens" is an area of our brain that responds to dopamine, the “feel-good” neurochemical. Dopamine gives a sense of pleasure and motivation and is part of our reward system. Research studies demonstrated that overweight individuals have differences in this area of the brain that controls pleasure. They detected here fewer dopamine receptors. This means that people with excess weight may indulge in emotional eating as a way to compensate for less activation of these brain centers. Perhaps this represents another mechanism of evolutionary adaptation and these brain circuits may have developed to make sure that we received pleasure from food to help us survive.
To conclude, the brain integrates all the inputs from peripheral signals originating throughout our body and from external factors such as the environment we live in. The brain exerts active regulation of all the biological mechanisms involved in our caloric intake and our metabolic response which results in our body weight regulation.
Can my body weight set point change?
As described above, there is a very complex mechanism of metabolic adaptation that regulates the balance between energy intake and expenditure culminating in the control of body weight. It involves hormones, neurotransmitters, and even environmental factors. Not all of these factors are within our control!
As we lose fat, our metabolic rate slows down, which means we require less calorie intake to stay alive. Our appetite increases. This is our body’s natural way to return to its "normal" weight.
It would be a logical and reasonable assumption that losing fat gradually might help our brain adapt to a new "set point" as opposed to using fad diets to lose weight fast. However, there isn't enough evidence to support this hypothesis yet.
There is some good news! There are solutions to keep the weight down despite having a higher weight set point. A research proven strategy is to develop healthy habits such as frequent exercise, healthy eating and daily weighing. One clinical study published in the New England Journal of Medicine demonstrated that people who manage to maintain long term weight loss have higher physical activity levels and weigh themselves more often. Adopting a new mindset towards eating and an active lifestyle can help us stay healthy and achieve our goal weight.
Another scientifically proven method to lower the body mass "set point" is by use of medications. Many research studies show that people who are excessively overweight also have abnormal weight regulating hormone levels, and even their brain is wired differently. Medications that simulate the effect of the body's natural hormones will help achieve and maintain weight loss while at the same time having multiple other health benefits. Long term use of these medications may be needed for the treatment of obesity, similar to treatment strategies of other chronic conditions such as hypertension, chronic kidney disease, diabetes and many others.
You may wonder what happens when we stop these medications? A study published in JAMA in 2021 indicates that stopping the weight control medications, in this case GLP-1 agonist (Semaglutide), leads to weight regain. This is believed to be due to a reset in the body weight "set point" to its previous level.
The body weight set point is our survival mechanism to maintain current weight in response to any weight changes. It explains why many people struggle to keep off the extra pounds. It also explains why some people seem to naturally maintain a healthy body composition without much effort.
The science behind this theory is still evolving but we have learned there are ways to control obesity such as adopting a new mindset around food and developing new healthy lifestyle habits. We can intentionally reduce our calories. We can choose to exercise to expend more energy. And we now have medications to help us achieve and maintain successful weight loss with the final goal of maintaining good health.