The Link Between Cortisol, Metabolism, and Weight Gain
In recent decades, much research has linked chronic stress to weight gain and obesity.
Cortisol plays an important role in metabolism, leading researchers to hypothesize that constantly high levels of cortisol may contribute to weight gain.
Some animal studies have shown that too much cortisol can promote the accumulation of belly fat. And researchers know that humans and lab animals tend to opt for energy-dense foods when under constant stress, leading some to suggest that chronically high cortisol levels also may play a role in making us crave high-calorie comfort foods.
But scientific studies in humans have turned up mixed results on the relationship between high cortisol and weight gain, with some studies finding a link and others not.
A 2018 review of scientific and medical studies found that not all people with obesity have high cortisol.
 But the researchers concluded that ongoing stress may contribute to or maintain obesity in those who have high exposure to cortisol or are more sensitive to it.
Many of these older studies measured cortisol levels in blood, urine, or saliva. While these bodily fluids can serve as good markers for daily fluctuations in cortisol levels and help doctors assess when too much or too little cortisol is being produced, some scientists have argued that they may not provide the most accurate picture of long-term cortisol exposure.
In a large 2017 study of more than 2,500 British adults, researchers measured cortisol concentrations in hair. They found that people with higher hair cortisol levels over a four-year period were more likely to be obese — and to stay obese — than people with lower levels. However, the researchers noted that it was not clear if the elevated cortisol was linked to a cause of obesity or was just a related issue. The authors also said that hair cortisol may be a better marker of long-term cortisol exposure — and chronic stress — than cortisol levels measured in blood, urine, or saliva.
Another study involving 2,499 people in Brazil tested the link between hair cortisol levels and the body. The researchers also found that higher cortisol levels had a connection to higher body weight.
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