The Stress Factor: Why It’s Not as Simple as Calories in vs. Calories Out

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Contrary to what most people believe, long-term weight loss is not simply about cutting a few calories here and there. It sounds like it should be that straightforward, but it’s not. This has been proven in countless studies and by the countless tears of unsuccessful dieters desperately counting their calories.

We pretend to live in a world where nutrition demands scientifically rigorous proof that prescribed treatments are effective. So where are the studies that show that cutting calories results in long-term weight loss?

In fact, the past 60 years of intensive research have shown, time and time again, that caloric restriction does not work. Why? Because weight is under complete hormonal control. These hormones – including insulin, ghrelin, leptin, and cortisol – are potent “weight regulators” that hold the key to managing your weight. It is therefore entirely possible to feel like you are doing everything right, living a “healthy” life by exercising and eating well, but still notice the weight creeping up.

Let’s take a closer look at cortisol.

The Role of Cortisol

Cortisol is otherwise known as the stress hormone. It coordinates the body’s fight or flight response along with the sympathetic nervous system. Not surprisingly, this hormone is produced in response to stress. In Paleolithic times, this stress was often physical, such a being chased by a predator. In this case, the release of cortisol was essential in preparing our ancestors to fight or or flee that predator.

To achieve that, cortisol has different effects on the body:

  • It increases alertness and decreases the need for sleep.
  • It substantially enhances glucose availability, therefore providing energy for the muscles.
  • It redirects all available energy towards surviving the coming stressful period, curtailing non-essential metabolic activities.
  • Growth, digestion, and other long-term issues are temporarily restricted.
  • It activates the breakdown of proteins and their conversion to glucose. In a fasted state, cortisol has several mechanisms to increase glucose in the body.

In short, cortisol prepares the body for action. It moves energy out of stores and into readily available forms, such as glucose. Thanks to the release of cortisol and its effects, our Paleolithic ancestor was now ready for vigorous physical exertion (fight or flight), using up the abundant supply of glucose. Shortly thereafter, when the danger had passed, the cortisol levels decreased, returning to low levels and allowing the body to recover. Designed for these short bursts of stress, the body is well adapted to the short-term increase in cortisol and glucose.

Modern-Day Stressors

The situation is quite different for long-term psychological stress. For example, problems at work, marital issues, sleep deprivation, and arguments with children are all serious stressors, and ones that are unlikely to be experienced for only a very short period of time.

So, what happens then? In modern times, chronic, non-physical stressors increase cortisol. Under circumstances of chronically raised cortisol levels, the body accumulates central (visceral) fat.

One particular study demonstrated that cortisol increases with self-perceived stress levels – your own perception that the situation you are in is stressful vs. being actually chased by a tiger. This stress-related increase in cortisol consistently showed a strong relationship to both increased glucose and increased insulin levels. Since insulin is the major driver of obesity, it should be no surprise that it was also related to both BMI and abdominal obesity.

Psychological Stress and Weight Gain

Does excess cortisol lead to weight gain? Certainly, the evidence suggests so.

This link between chronic cortisol production and obesity is observed in certain diseases, such as Cushing’s Disease or Cushing’s Syndrome, characterized by excessive cortisol production, the hallmark of which is weight gain. Conversely, a condition known as Addison’s Disease, characterized by an underproduction of cortisol, is associated with low body weight.

A similar link is observed when administering synthetic forms of oral cortisol (hydrocortisone or prednisolone for example). These medications, which are commonly used to treat many chronic inflammatory conditions, are associated with fat deposition and weight gain.

Fundamentally, this effect is also observed in a population experiencing chronic stress, where excess cortisol leads to weight gain.

In a random sample from North Glasgow, Scotland, cortisol-excretion rates were strongly correlated to Body Mass Index (BMI) and waist measurements. In other words, higher cortisol levels were seen in heavier people. Importantly, cortisol-related weight gain particularly deposits fat in the abdomen, which results in an increased waist/hip ratio (WHR).

Lifestyle Factors

It is important, at this stage, to touch on the subject of sleep. The most important thing to note is that sleep deprivation causes stress. Even a single day of sleep deprivation can cause cortisol levels to increase by 100 percent. A meta-analysis of 696 studies published in 2008 showed that short sleep duration increased the risk of obesity by 55 percent in adults and 89 percent in children.

Researchers found that, for every hour of sleep deprivation, a person’s BMI rose by 0.35 kg/m2.

Unfortunately, stress may also cause sleep deprivation. Increased cortisol often causes insomnia due to the activation of the sympathetic fight or flight system, creating a classic vicious cycle.

Reducing stress is difficult, but it is vitally important. Stress relief is an active process. There are many time-tested methods to try, including mindfulness meditation, yoga, massage therapy, and exercise. Studies on mindfulness intervention observed the use of yoga, guided meditations, and group discussion to successfully reduce cortisol and abdominal fat.


Dr Nasr Al-Jafari is a Dubai-based Family Medicine Consultant and Functional Medicine Practitioner. He graduated from The University of Nottingham and completed his consultant training at The University of Manchester, UK. He has pioneered the use of obesity theory in the UAE for weight loss and type 2 diabetes reversal at DNA Health Medical Center where he is Medical Director.