Cortisol. Is it bad for weight loss?
That’s the question posed by one Muscle Evo reader this week.
“I’ve read that too much exercise can increase my cortisol levels and put the brakes on weight loss,” he wrote. “Is this true?”
Cortisol does have the potential to affect your rate of weight loss. But it’s not as simple as saying that when cortisol goes up, your rate of weight loss goes down.
Nor is it the case that suppressing cortisol — as the people trying to sell you cortisol blocking supplements would have you believe — will help you lose weight.
First up, what is cortisol? And what effect does it have on weight loss?
Cortisol and Weight Loss
Cortisol is a hormone produced by your adrenal glands. One of its main functions is to increase the flow of glucose, protein and fat out of your tissues and into the circulation.
Cortisol levels tend to rise sharply in the morning when you wake up, peak about 30 minutes later, before declining over the course of the day. It’s also released in response to physical or emotional stress.
Cortisol has firmly established itself as one of the “villains” in the hormonal world of goodies and baddies. But actually, it isn’t. In the right amount and at the right time, cortisol has several benefits for anyone wanting more muscle and less fat.
Firstly, cortisol has anti-inflammatory properties. It doesn’t cause inflammation, but rises in response to inflammation. This gives it an important role to play in repairing muscle damage after exercise (one reason why I don’t think so-called “cortisol blocking” supplements are a great idea).
One other benefit of cortisol is that it has a lipolytic effect, which means that it accelerates the rate at which stored fat is released from fat cells.
It’s a different story, however, when cortisol levels are raised for long periods, which is often due to constant physiological and/or psychological stress. And a large calorie deficit, created by excessive amounts of exercise and a very restrictive diet, definitely falls into the “physiological stress” category.
One of the problems associated with persistently high cortisol levels is water retention.
This extra water can obscure your results, making it appear as though your rate of fat loss has stalled. All that happens is that water replaces some of the fat that’s been lost, so your weight on the scales stays the same.
“When you train a lot you release a lot of cortisol,” explains Leigh Peele in Starve Mode. “Cortisol makes your body go puffy with water.”
“Another important thing to keep in mind is that rest and food are the only things that help blunt cortisol once increased. Specifically, carbohydrates. Imagine what a lot of aggressive training and no carbs is going to do to the body.
“I have seen athletes and dieters increase ten pounds and upward in a low caloric deficit because they began extreme training with no carbohydrates,” adds Leigh. “Understand the increase in edema and retention (of water) makes you look different. It isn’t fat, but it sure can look like it.”
That’s often the reason why some people whose weight loss has stalled seem to lose fat very quickly when they “cheat” on their diet. Cortisol levels drop, retained water is lost, and they end up several pounds lighter.
A prolonged elevation in cortisol isn’t great news for your muscles either. Cortisol inhibits protein synthesis, promotes protein breakdown, as well as countering the effects of other anabolic hormones, testosterone in particular.
Cortisol does have the potential to cause weight gain, but that’s mainly via the effect it has on your appetite.
Cortisol makes your brain less sensitive to the effects of leptin, blunting its satiating signal. This can leave you feeling a lot hungrier than normal. Cortisol also tends to stimulate your appetite, particularly for foods that are high in starch, sugar or fat.
The problem is made worse in people who secrete large amounts of cortisol in response to stress (known as cortisol hypersecreters). They are the ones who tend to eat more as a way of dealing with that stress.
Given a choice of foods to eat, they will usually pick the stuff that’s high in fat and sugar, mainly because these foods help to calm the body’s response to chronic stress.
There is also a link between stress-induced cortisol secretion and abdominal fat.
In scientific lingo, visceral fat cells are more “metabolically active” than subcutaneous fat cells. Not only are they more sensitive to the effects of circulating cortisol than fat cells in other parts of your body, they also have more receptors that respond to cortisol by activating enzymes that store fat.
So if you are a cortisol hypersecreter, there’s a good chance that you’re going to crave high sugar or high fat “comfort food” whenever your level of stress starts to boil over. Not only that, but many of the extra calories you eat during a stress-induced binge are going to be stored in your belly.
Of course, not everyone responds to stress in the same way.
Expose a group of people to the same source of stress, and not everyone will secrete the same amount of cortisol. This is partially due to variations in psychology. One person may find an event particularly stressful, while another reacts in a very different way.
When the source of stress is removed, their cortisol levels will return to normal at varying speeds, mainly because of physiological differences in the rate at which the body breaks down cortisol.
There are also plenty of people who lose weight when they’re exposed to stress, primarily because they seem to lose their appetite and eat less. Roughly 6 out of 10 people will respond to stress by eating more. The rest become hypophagic, which means that they eat less.
I don’t want to create the impression that a rise in cortisol levels somehow makes weight gain inevitable, because that certainly isn’t the case.
A good example of how resilient your body can be, even when exposed to a “multi-stressor” environment, comes from an intriguing study of US Army Rangers taking part in an 8-week training course.
Not only were the soldiers consuming an extremely low-calorie diet (one meal per day in some cases), they were exposed to extremes of hot and cold weather. Each day involved patrols in hostile terrain with loaded rucksacks weighing over 70 pounds. A typical night’s sleep lasted less than four hours.
As you might expect, the soldiers lost both fat and muscle. Those who completed the training lost 22 pounds in weight. Of this, 13 pounds came from fat, and 9 pounds came from lean tissue.
Cortisol levels also rose over the course of the study. Testosterone approached castrate levels. But this didn’t stop the men losing fat.
To quote the researchers directly:
“Cortisol levels increased significantly from initial values by week 4 in group 1 and week 6 in group 2; the rise occurred as a similarly low body fat was achieved, indicated by mean sum of skinfold thicknesses (roughly 28 millimeters). The highest cortisol level (950 μmol/l) was measured in the individual who lost the greatest amount of body weight (23% of initial body weight) and began the course with minimal fat reserves (7% body fat).”
Much the same results were shown in a case study of a drug-free competitive bodybuilder preparing for a contest.
In the first three months of dieting, his body fat levels dropped from 14.8 to 8.9%. That’s despite the fact that cortisol levels more than doubled over the same period.
For the next three months, cortisol remained at twice the baseline level. Yet our man was still able to cut his body fat levels in half, hitting 4.5% body fat by the end of the study.
In both studies, cortisol did not stop fat being lost. Nor did it lead to fat being gained in the absence of a calorie surplus.
Combining massive amounts of exercise with an extremely restrictive diet in a frantic attempt to lose as much fat as you can in as little time as possible is not a great idea.
But cutting out exercise completely because you’ve read a bunch of “scare stories” about what it’s going to do to you is also a mistake. The truth can be found somewhere in the middle.
SEE ALSO: THE FLAT BELLY CHEAT SHEET
If you want less flab and more muscle when you look down at your abs (or where they should be), check out The Flat Belly Cheat Sheet.
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ABOUT THE AUTHORChristian Finn is the nation’s leading authority on science-based, joint-friendly ways to build muscle. A former "trainer to the trainers," he holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.