Carbs. Fast Food. Supersized meals. Junk food. Eating too much, exercising too little. Genes. You’ve heard all about the role these factors play in the rise of obesity. So you’ve cut down on carbs, ramped up your exercise program, tailored your meals to suit your genes, and cooked meals at home. Yet you just get fatter. And sicker.

Here is the main reason why, in my opinion and that of many obesity researchers, Americans are so much fatter and so much sicker than the rest of the industrialized world.

Stress.

No, I’m not just talking about deadlines and annoying in-laws. I’m talking about something more fundamental—pervasive, unrelenting, soul-crushing, daily stress. According to an on-going study on stress in America conducted by the American Psychological Association, stress has become the new normal for life in the USA. Americans are more stressed and more unhappy than our counterparts in other countries. According to Columbia University's First World Happiness Report, the United States does not even make the top 10 in happiness rankings, logging in at number 11, behind Denmark, Finland, Norway, the Netherlands, Canada, Switzerland, Sweden, New Zealand, Australia, and Ireland. And our level of happiness has remained about the same for decades. As Paul Rosch, a clinical professor of medicine and psychiatry at New York Medical College and president of the non-profit American Institute of Stress in Yonkers, N.Y., succinctly puts it, "We have more or less accepted it as a way of life..."

To put this in more concrete terms, take a look at this graph from Food Service Warehouse:

What is apparent from the graph is that, although Americans eat more calories than anyone in the world, we do not eat substantially more than our 1st world counterparts in Europe. We consume only about 100 calories more per day than the French or Italians. Yet we are much, much fatter and sicker. Over a third of Americans (38%) are obese, but only about 20% of the French and 16% of Italians are, as you can see on this interactive graph from the International Association for the Study of Obesity.

When people hear that stress causes weight gain, they usually interpret it this way: People get stressed, so they eat more food (particularly sugary, fatty “comfort” food) to cope with their stress, and the extra calories cause them to gain weight. While there is some truth to this, what most people don’t realize is that stress alone can cause us to put on fat by altering many metabolic functions. In other words, a stressed person will put on more fat than a non-stressed person even when both eat the same number of calories.

How Chronic Stress Makes Us Fat and Sick

According to exercise scientists Christine Maglione-Garves and colleagues at the University of New Mexico, when stress is chronic, a cascade of hormonal pathways are activated that release large amounts of cortisol—a stress hormone--from the adrenals. Cortisol directly effects fat storage and weight gain in stressed individuals. It enhances lipogenesis (fat creation), break down of tissues, and suppression of the immune system. All of the things that make us fat and sick.

But high levels of cortisol also change our body shape dramatically by shifting fat to the abdomen from cells from the blood stream and other parts of the body. The fat that is created by high levels of cortisol is also more toxic than plain old subcutaneous fat (the normal fat under your skin). All fat cells contain an enzyme that converts inactive cortisone to active cortisol. But the gene that activates this conversion process is expressed more in obesity, particularly in deep abdominal fat cells. In fact, monkeys fed an American diet get fat -- but those under chronic stress put on much more belly fat than less-stressed monkeys. So it is almost as though toxic fat colonizes your abdomen, creating more of itself through the cortisol pathway that looks like this:

Stress -> Cortisol -> Enzyme activation -> More, larger fat cells + more cortisol receptors.

This shift of fat toward the abdomen happens not just to overweight people but to normal weight people as well. A study published in 2000 found that slender women who have high cortisol also were found to have more abdominal fat than their less-stressed counterparts, indicating a definite causal link between cortisol and increased storage of abdominal fat. People who have diseases associated with extreme exposure to cortisol, such as Cushing's disease, also have excessive amounts of visceral fat. This is why Dr. Oz commented in First for Women “I can usually tell if someone is stressed out or not just by looking at their belly size.” 

The Negative Health Effects of Chronic Stress Don’t Stop With Weight Gain

High levels of cortisol also cause high blood pressure, high cholesterol, and elevated glucose levels, laying the foundation for the development of cardiovascular disease, stroke, and diabetes—all of which have risen dramatically among Americans over the past few decades. According to the Centers for Disease Control, nearly 800,000 people die in the U. S. each year from cardiovascular disease, accounting for 1 in 3 deaths and more than $300 billion in direct medical costs and lost productivity. And statins are the leading prescription drugs sold in the U.S.

So how does chronic stress bring about this constellation of risk factors for heart disease?

It may surprise you to learn that only 25% of the cholesterol in your body comes from what you eat. The other 75% is created in your very own liver via an enzyme called HMG CoA reductase. (Statins inhibit this enzyme, thereby inhibiting production of cholesterol. They also inhibit production of vitally important co-enzyme Q10.)

Now here is the interesting part: Insulin increases the production of LDL cholesterol.

In fact, insulin and leptin resistance shift LDL particles from large harmless fluffy ones to small, dense, and dangerous ones.

Now the final piece of the puzzle: What increases insulin levels? Three primary factors: Carbohydrate consumption (which you already knew), sleep debt, and chronic stress. So chronic stress bumps your insulin levels, interferes with hormones that normally signal that you’re full after you eat, and raises your bad cholesterol levels.

Why Dieting Dooms Us to Failure

If you are suffering from obesity, high cholesterol, metabolic syndrome, and high blood pressure, your doctor (and virtually everyone else around you) will begin sternly lecturing you about losing weight. Simple, right? Eat less, exercise more!

Well, unfortunately, this simplistic exhortation overlooks the true cause of your health woes, and instead places the blame squarely on your already over-burdened shoulders. As you struggle unsuccessfully to reduce your weight, you will be lectured about your apparent gluttony, laziness, and lack of willpower. Your protestations that you are already trying desperately to lose weight will be met with smirks and frank incredulity. But here is why your efforts are failing.

Cortisol, sad to say, also increases appetite, as well as cravings for sugary and fatty foods.

It interferes with satiety regulating hormones such as leptin and PYY so that when you eat these foods, it is difficult to stop because you don’t feel sated.

Stress also leads to the release of neuropeptide Y which stimulates abdominal fat formation and metabolic syndrome. 

And that is why draconian diets and diets that restrict single macronutrients (low fat or low carbohydrate diets) usually backfire. They do not address high circulating cortisol levels, so they do not normalize satiety feedback from the gastrointestinal tract to the brain. Because you don’t feel sated but instead feel even more stressed from all the dieting, it is usually impossible for people to stick to these regimens.

This yo-yo dieting and weight loss failure is not particular to weak-willed humans. When stressed and unstressed rats were given free access to normal rat chow and sugar water, the stressed ones will eat less healthy food, preferring instead to glug down the sugar water. (How do you stress a rat? Keep it in a confined space for several hours a day.) Not surprisingly, the stressed rats began accumulating belly fat. But then an interesting thing happened: Their cortisol levels began dropping. Dr. Mary Dallman, the lead author of this fascinating series of studies, explained the results this way: Gaining belly fat may be the body's coping mechanism for turning off the stress response. So your “stress eating” is not simply a dysfunctional coping mechanism learned from your parents, nor is it a psychological craving for love that is wrongfully addressed with food, nor any other explanations you may have heard. It is plainly and simply a short-term biologically-based coping mechanism that is disastrous in the long run.

In the long run, chronic stress will overwhelm this short term coping mechanism, as a series of studies conducted by Dr. Carol Shively, PhD of Wake Forest University on monkeys clearly show. She fed female monkeys a high fat “American style” diet, and compared various health indices of monkeys on top of the social hierarchy with those on the bottom rung. The results were sobering.

Monkeys on the bottom rung were more likely to put on belly fat than the high-ranking monkeys, despite eating the same fat-laden diet. They also showed more abdominal fat, more fat wrapped around organs, and more instances of metabolic syndrome. They were as likely as male monkeys to get heart disease, with large amounts of plaque clogging their arteries. All of this came from high levels of cortisol creating toxic abdominal fat. And all that cortisol came from living the stressed life that is “normal” on the bottom of a rigid social hierarchy.

What Is The Answer?

As this article plainly shows, we are not going to get thinner or healthier by simply cutting carbs, cutting calories, or increasing our exercise level. The body has numerous mechanisms, perfected over evolutionary time, to subvert these well-reasoned efforts to lose weight

But we might just have a fighting chance if we reduce our stress levels. Accomplishing that requires understanding why—despite living in one of the richest countries in the world--we are so stressed. That is the topic of Part 2. In Part 3, we'll see how calorie dense, nutritionally, poor and utterly tasteless American food contributes to the obesity crisis.

Copyright Denise Dellarosa Cummins, PhD, June 14, 2013

Dr. Cummins is the author of Good Thinking (Cambridge University Press, 2012) and a Fellow of the Association for Psychological Science.

About the Author

Denise Dellarosa Cummins, Ph.D.

Denise Dellarosa Cummins, Ph.D., is the author of Good Thinking, The Historical Foundations of Cognitive Science, and Evolution of Mind.

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