Why does stress make you fat?

Obesity is a huge health issue today.  Many estimates suggest that obesity and its associated complications are now the leading cause of death in the developed world.  But why are we so fat?

Are we simply eating too much because we are greedy, as many mainstream commentators would have us believe?  Or are we just eating too much of the wrong things, as the low-carb and low-fat camps would suggest?

One thing that many people sometimes skip over is that stress can have a role in making people fat.

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This is my fourth post in my series on stress.  Previously, I’ve written about what is stress? how does stress work? how does stress make us ill?  This post is about why stress makes you fat, and it’s not a particularly long post, because you can explain the fundamental principles fairly quickly.

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Stress and cortisol

Most people who demonstrate symptoms of chronic stress show higher levels of cortisol than normal people.  Most articles you will read about why stress makes you fat will therefore concentrate on the effects that high cortisol has on the body.

I am also going to use that working hypothesis today, in the full knowledge that it’s not quite correct.  Some people with chronic stress (particularly people suffering from post-traumatic stress disorder) suffer from abnormally low cortisol levels and yet still show the same metabolic effects as those will high cortisol.

Tomorrow, I’ll look at a very interesting study that why it doesn’t actually matter either way.

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What cortisol does

So high cortisol levels result from suffering chronic stress.  But what does high cortisol do to your body?  Let’s have a quick recap.  Cortisol has the following known effects:

• Mobilisation of all fuels by increasing the plasma concentrations of amino acids, glucose, glycerol and free fatty acids
• Catabolism of body proteins for energy to create glucose by gluconeogenesis and for tissue repair in damaged organs
• Increases the ability of vascular muscle to contract
• Assists in the ability of the body to withstand stress
• Inhibits inflammation and specific immune responses

From that list, you can probably pick out the problem for people whose cortisol levels are elevated above normal levels for extended periods of time.

If you said gluconeogenesis, you win a prize.

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Cortisol, gluconeogenesis and getting fat

Interestingly, it is only in the last 10 years that it was established for certain that cortisol causes increased gluconeogenesis in human beings.  Studies with rats had been done previously but it had been difficult to replicate them with human beings.

However, a study finally concluded that “cortisol administration in humans increases glucose production by stimulating gluconeogenesis.  Smaller increases in serum cortisol may contribute to the abnormal glucose metabolism known to occur in the metabolic syndrome.” Cortisol increases gluconeogenesis in humans: its role in the metabolic syndrome, Khani, Tayek, Clincal Science, 2001.

In other words, you can eat as low-carb as you like but if you are constantly stressed out, you might as well be munching cookies all day long.

But there’s more…

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Cortisol, testosterone and growth hormone

To add insult to injury, studies have found that not only does cortisol increase your glucose levels but it also decreases testosterone and growth hormone levels.  See stress related cortisol secretions in men: relationships with abdominal obesity and endocrine, metabolic and haemodynamic abnormalities,  Rosmond, Dallman and Bjorntorp, Journal of Clinical Endocrinology and Metabolism, 1998

In case you were wondering, low testosterone makes you fat.  See low serum testosterone as a predictor of visceral fat in Japanese-American Men, Tsai, Boyko, Leonetti and Fujimoto, International Journal of Obesity and other Metabolic Disorders, 2000

And I’m sure you won’t be surprised to hear that low growth hormone also makes you fat.  See growth hormone replacement in healthy older men improves body composition but not functional ability, Papadakis, Grady, Black, Tierney, Gretchen, Gooding, Schambelan and Grunfeld, Annals of Internal Medicine, 2004

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Sure, but we are talking about serious stress here, right?

Er, no.  Don’t let the nomenclature fool you.  Remember, the term “acute stress” refers to an inducement of the fight-or-flight response.  The term “chronic stress” sounds really horrible but actually all we are talking about is a stressor over which the individual has no control or influence and has to manage by using elevated cortisol levels.

The English civil service are not renowned for having a particularly stressful working life.  They have historically had very little threat to their job security compared to the private sector, are paid almost as well and receive huge pensions based on their final salaries.

In a famous study, often referred to as the Whitehall II study, Michael Marmot followed 10,308 men and women, aged 35-55, employed in 20 London civil service departments over 14 years.

The study found that “a dose-response relation was found between exposure to work stressors over 14 years and risk of the metabolic syndrome, independent of other relevant risk factors” and concluded that “stress at work is an important risk factor for the metabolic syndrome. The study provides evidence for the biological plausibility of the link between psychosocial stressors from everyday life and heart disease.”  See chronic stress at work and the metabolic syndrome, Chandola, Brunner and Marmot, British Medical Journal, 2006

At the risk of repeating myself, this is called “chronic stress” because it causes a chronic effect.  I would be the first to say that we should not be putting people in a situation at work that causes this to happen.  However, to believe that the English are whipping or beating their civil servants would be incorrect.  Unfortunately, this is simply poor management, unpleasant bosses and inflexible bureaucracy.

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Conclusion: stress makes you fat

These data are definitive.  You can dig up the studies and check them out if you like.  And you’ll find that if you put a study like the Whitehall II study next to a generic high-fat or hamburger-eating study, you’ll see that the stress study shows that the more stress you undergo, the fatter you get.  Your generic hamburger-eating study won’t show anything like that kind of correlation.