Does intermittent fasting mess with hormones?

Does intermittent fasting mess with hormones?

Weight loss. Extra energy. Clearer skin. Intermittent fasting experts have promised all of these benefits and more. But is it really as good as it sounds? Before you jump on board, take a look at how intermittent fasting affects your hormones and how to do it without sacrificing hormone health.

The lowdown on intermittent fasting

Intermittent fasting (IF) may seem new, but it’s taken from an old concept. Our ancestors had daily periods of fasting, especially when food was scarce or unavailable. These days, however, food sources are plentiful. Now, intermittent fasting has become a mental practice along with a way of eating. It offers the potential to lower inflammation and possibly reduce your risk for certain conditions, like diabetes. People even report that their thoughts seem clearer and their brain function has improved as a result of intermittent fasting.

How hormones respond to intermittent fasting

Though it may decrease insulin, intermittent fasting can also raise adrenaline and cortisol in some people. These two hormones play a vital role in many essential functions, like metabolism, muscle inflammation, and memory. However, over time and in certain individuals, increased cortisol can lead to cortisol dysregulation, or, some sources say, adrenal fatigue.

Your body makes cortisol from cholesterol, but if levels stay high for too long, it will eventually use progesterone, a sex hormone, to keep up with demand. Eventually, high cortisol can cause side effects like decreased sex hormones (progesterone), muscle weakness, headaches, weight gain, and insomnia. It can also affect the amount of thyroid stimulating hormone (TSH) you make, which can further slow your metabolism.

Some forms of intermittent fasting may prompt severe calorie restriction, if you’re not careful. Having too much of a calorie deficit for too long can negatively impact estrogen and luteinizing hormone in some women, which may cause irregular or absent cycles.

The intermittent fasting methods safest for your hormones

Still want to try intermittent fasting? Here are a few examples of common IF methods and how to modify them to protect your hormone health.


Most people who use intermittent fasting go with 16:8. In a 24-hour span, you hold off on food for a full 16 hours and aim to get your daily calorie requirements in an 8-hour window. Why is this method so popular? For nearly half of your 16-hour fast, you’re (ideally) sleeping. To reach the full fasting window, you’d just postpone eating until your midday meal.

How to modify the 16:8

Instead of fasting for a full 16 hours, go with a maximum of 14 to 15 hours. In your 9 to 10 hours of eating, make sure your body’s getting enough of the nutrients and calories it needs—healthy fats, protein, and complex carbs. Overall, you shouldn’t have much of a calorie deficit with this method, and that’s good news for your hormones.

Circadian rhythm

If you love breakfast right when you wake up, you’re in luck. Your body naturally associates sunlight with its energy expenditure. The circadian rhythm diet matches up your eating habits to your “body clock,” or natural rise and fall of cortisol.

To try out the circadian rhythm method, put twelve hours between your last meal of the day and the first. So, if you eat a small dinner at 5 p.m., you’re done until 5 a.m. the next day—and that early meal should be the biggest, so you can get most of your calories before 3 p.m.

How to modify the circadian rhythm diet

Because your caloric intake stays relatively unchanged, modifications aren’t needed for the circadian rhythm diet.

Intermittent fasting methods you should think twice about


Naturally eat small a few days and more others? The 5:2 method may look good to you. For 2 (non-consecutive) days of each week, you consume 500 calories in each of those 24-hour periods. The other 5 days, you stay in your normal calorie range.

How to modify the 5:2

Our ultimate take on this one? There are better (and safer) options. But, if you really want to give this a go, talk with your doc first. To help your hormones, make sure you consume more calories than you ordinarily would on the 5 days you’re eating. Over-restriction creates a stress state for the body, and that can increase cortisol, exacerbate thyroid issues, and decrease sex hormones.


Eat-stop-eat asks that you pick 1 or 2 days per week and fast for the entire 24-hour period of each. On the other days, it allows you to eat like you ordinarily do.

How to modify eat-stop-eat

Many experts won’t give a thumbs-up to this one—at least not for women. With the amount fasting eat-stop-eat requires, it’s hard to consume enough calories on eat days to compensate. Like we mentioned regarding the 5:2, excessive calorie reduction isn’t good for your hormones.

Start with small steps and go slow

Phasing intermittent fasting into your life can be a rewarding experience. Science points to a long list of potential benefits, from promoting heart and brain health to increased weight loss and optimum cholesterol levels. But it’s not for everyone, which is why it’s a good idea to double-check with your doctor before starting, so you can go over your medical history and goals. Even if your provider gives you the green light, let yourself warm up to the concept of fasting by installing a few small fasting windows every few days and seeing how you respond.
Zach Mathews
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