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How does intermittent fasting help with insulin resistance?

Insulin resistance is a risk factor for many diseases. Intermittent fasting can improve insulin resistance.
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Hormones are very powerful regulators of your weight. If you want to lose weight without permanently struggling and constantly feeling hungry, you have to bring your hormones into balance.

The most crucial hormone in this context is insulin. Insulin resistance is an underlying cause of weight gain.

Written by
Sarah Neidler, PhD
Freelance Science and Medical Writer

We discuss today how intermittent fasting can help you improve insulin resistance.

But let’s start with the basics.

What is insulin?

You probably know insulin as a blood sugar-lowering hormone. Many people with type 2 diabetes take insulin to control their blood sugar. But insulin has many more functions. Primarily, it is a storage hormone (1)

When you eat something, your blood sugar rises. The pancreas then secretes insulin to lower your blood sugar. Muscle cells take sugar from the blood for immediate use. But the muscles and liver can also store sugar (as glycogen) for later use.

Because high blood sugar is harmful, it is crucial that muscle and liver cells take up sugar from food as fast as possible. For this reason, fat gets stored away in fat cells for later use as long as insulin is elevated.

As soon as blood sugar levels return to the normal range, insulin also returns to normal. Now, the stored energy can be accessed. The body first uses its stored sugar. This helps to keep the blood sugar stable in between meals. The more sugar storage gets depleted, the more fat is released from the fat cells. 

So, a healthy person always goes through cycles of storing energy and using stored energy:

Meal → Blood sugar and insulin go up → What is not immediately needed is stored for later use → Blood sugar and insulin return to normal → Energy stores are used until the next meal.

What is insulin resistance?

High blood sugar.

Insulin resistance means that the cells don’t appropriately respond to insulin anymore. Muscle cells refuse to take up sugar when insulin tells them to do so. At an advanced stage, even fat cells can refuse to take up fatty acids from the blood.

Because high blood sugar is harmful, the pancreas responds by producing more insulin. The high levels of insulin force the cells to take up sugar even though they don’t “want” to. Unfortunately, high insulin levels make insulin resistance worse–it is a vicious cycle.

But the pancreas cannot produce unlimited amounts of insulin. At some point, the need for insulin (due to advanced insulin resistance) is higher than what the pancreas can supply. As a consequence, the blood sugar rises beyond healthy levels–even between meals. 

As you probably know, high blood sugar is the primary symptom of type 2 diabetes. So, insulin resistance is the cause of diabetes (2). But you can be insulin resistant for many years before diabetes develops.

What causes insulin resistance?

Many factors can contribute to insulin resistance. Certain genetic predispositions can promote its development. Also, lifestyle factors such as a lack of exercise and sleep, and too much stress can lead to insulin resistance.

But in most cases, eating habits are driving insulin resistance.

Remember that healthy people always go through cycles of energy storage and energy usage. When you eat, your body is storing energy. And it takes a while before your body starts to use this energy.

What do you think happens to all the energy when you constantly eat–without taking longer breaks between meals? You’ve probably already guessed: Your body is storing energy all the time but has hardly any opportunity to use it. 

When cells get overloaded with energy, they try to protect themselves by becoming insulin resistant. And because insulin resistance is accompanied by high levels of the storage hormone insulin, it makes it difficult to access our energy storage. Having no access to our energy storage means that we become hungry very soon after a meal. 

So we eat despite having plenty of stored energy. A simpler way to say this is: overeating causes insulin resistance, and insulin resistance, in turn, causes overeating. It’s a vicious cycle.

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Why is insulin resistance harmful?

Insulin resistance is associated with most modern chronic diseases. People with insulin resistance have a high risk of cardiovascular disease, dementia, cancer, autoimmune conditions, PCOS, and inflammatory diseases (3).

Insulin resistance is associated with weight gain, but this is only a minor problem. The real problem is that the body’s energy storage areas are chuck-full, and the body doesn’t know where to store the excess energy. 

When the liver’s glycogen storage areas are overflowing, it starts to convert glucose into fat. This fat can be stored in fat cells, but their capacity to store fat is also limited. (How much fat fat cells can store is unique to each individual. For this reason, some people gain a lot of weight, while others stay slim despite overeating.)

Once fat cells refuse to take up more fat, the fat has to be stored in the liver. 

The liver has many functions in sugar and fat metabolism. Fat in the liver interferes with these functions. For this reason, fatty liver leads to unhealthy cholesterol levels (high LDL–the “bad” cholesterol and low HDL–the “good” cholesterol), elevated blood lipids, and also indirectly to high blood sugar.

A fatty liver is reversible in the early stages. But too much fat in the liver leads to scarring of liver tissue (cirrhosis of the liver), which is hard to reverse and can even lead to liver failure.

Insulin resistance also has a role to play in obesity, read more about it here.

What are the signs of insulin resistance?

Because high insulin levels block the energy stores, insulin resistance results in constant hunger, even shortly after eating. And because insulin lowers blood sugar, people with insulin resistance often experience symptoms of low blood sugar, such as weakness and dizziness. 

Weight gain, especially in the belly area, is also a common symptom of insulin resistance. 

Moreover, insulin resistance leads to the so-called metabolic syndrome. The metabolic syndrome has the following symptoms (4):

  • Enlarged waist circumference: ≥ 102 cm in men and ≥ 88 cm in women
  • High blood pressure: systolic blood pressure ≥ 130 mmHg, diastolic blood pressure ≥ 85 mmHg
  • Elevated triglycerides (blood lipids): ≥ 150 mg/dl
  • Low HDL-cholesterol: < 40 mg/dL in men and < 50 mg/dL in women
  • High fasting blood sugar: ≥ 100 mg/dL

Metabolic syndrome is diagnosed when at least three of these symptoms are present.

How to reverse insulin resistance?

The good news is that insulin resistance can be reversed. 

Intermittent fasting is very powerful in improving insulin resistance–within a few weeks.

Studies show that intermittent fasting can improve all signs of insulin resistance. It:

  • lowers blood pressure (5), 
  • facilitates weight loss (especially in the belly area)(6),
  • improves cholesterol (7),
  • lowers triglycerides (8),
  • reduces oxidative stress (a consequence of insulin resistance)(9),
  • improves blood sugar regulation,
  • helps to get the appetite under control (10).

Why is intermittent fasting so effective in lowering insulin resistance?

By extending the time between meals, you give your body the opportunity to access energy storage areas. Once your stored energy (especially glycogen) gets regularly depleted, insulin resistance improves.

Intermittent fasting breaks the vicious cycle: increasing the time between meals allows you to access your stored energy → hunger fades → insulin resistance improves.

The downside is that insulin resistance makes fasting more difficult. If you have signs of insulin resistance, you should slowly increase the time between meals when starting with intermittent fasting. For instance, you could start fasting for 12 hours, then proceed to 13 hours, then 14, and so on. Depending on the degree of your insulin resistance, it may take a few weeks or even months before you are able to fast for 16 hours (16/8-fasting). 

Bottom line

Many women struggle with their weight and other health issues without realizing that their problems are caused by insulin resistance. Luckily, insulin resistance can be reversed, and intermittent fasting is one of the powerful tools to help achieve this.

If you’re struggling with intermittent fasting because of insulin resistance, don’t worry. We are here to help. Just join our intermittent fasting community for women only.

Intermittent fasting has many other health benefits you may want to know about, read about them here.


1. Petersen MC, Shulman GI. Mechanisms of Insulin Action and Insulin Resistance. Physiol Rev. Oct 1 2018;98(4):2133-2223. doi:10.1152/physrev.00063.2017

2. Taylor R. Insulin resistance and type 2 diabetes. Diabetes. Apr 2012;61(4):778-9. doi:10.2337/db12-0073

3. Rao G. Insulin resistance syndrome. Am Fam Physician. Mar 15 2001;63(6):1159-63, 1165-6.

4. Huang PL. A comprehensive definition for metabolic syndrome. Dis Model Mech. May-Jun 2009;2(5-6):231-7. doi:10.1242/dmm.001180

5. Wilkinson MJ, Manoogian ENC, Zadourian A, et al. Ten-Hour Time-Restricted Eating Reduces Weight, Blood Pressure, and Atherogenic Lipids in Patients with Metabolic Syndrome. Cell Metab. Jan 7 2020;31(1):92-104 e5. doi:10.1016/j.cmet.2019.11.004

6. Anton SD, Lee SA, Donahoo WT, et al. The Effects of Time Restricted Feeding on Overweight, Older Adults: A Pilot Study. Nutrients. Jun 30 2019;11(7)doi:10.3390/nu11071500

7. Adlouni A, Ghalim N, Benslimane A, Lecerf JM, Saile R. Fasting during Ramadan induces a marked increase in high-density lipoprotein cholesterol and decrease in low-density lipoprotein cholesterol. Ann Nutr Metab. 1997;41(4):242-9. doi:10.1159/000177999

8. Harvie MN, Pegington M, Mattson MP, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International Journal of Obesity. 2011;35(5):714-727. doi:10.1038/ijo.2010.171

9. Johnson JB, Summer W, Cutler RG, et al. Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radic Biol Med. Mar 1 2007;42(5):665-74. doi:10.1016/j.freeradbiomed.2006.12.005

10. Ravussin E, Beyl RA, Poggiogalle E, Hsia DS, Peterson CM. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans. Obesity (Silver Spring). Aug 2019;27(8):1244-1254. doi:10.1002/oby.22518

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