The link between intermittent fasting and insulin resistance

Written by Trey Reck

Medically reviewed by Louise Bula, RD

Published on November 7, 2023 | Updated on March 28, 2024

Your body is incredible. 

It works constantly to keep you alive and functioning. Your hormones — chemical messengers that coordinate bodily functions by carrying signals through the blood to the organs, muscles, tissues, and cells — play a huge role in this. 

There are over 50 different hormones in the human body, and in the context of weight loss or gain, insulin is thought to be one of the most significant. 

Insulin controls the amount of sugar in your blood. When insulin levels peak too high too often, the result can be insulin resistance, a condition which, left unchecked, can lead to weight gain, type 2 diabetes, and heart problems. 

So, does intermittent fasting help with insulin resistance? Is intermittent fasting even good for those with insulin resistance? 

Let’s explore the connection between intermittent fasting and insulin resistance to find out.  

How insulin works

Your body needs glucose (sugar) for energy, but your cells can’t absorb glucose directly. That’s where insulin comes in.[5] Here’s how it works. 

When you eat, your body turns the carbohydrates in your food into glucose. Your blood sugar rises, signaling your pancreas to release insulin. 

Insulin acts like a kind of shuttle bus, helping glucose enter your muscle, fat, and liver cells. Once there, it’s used for energy or stored for when your blood sugar runs low. 

This process keeps your blood sugar levels balanced and within a healthy range, stopping them from getting too high (hypoglycemia) or too low (hypoglycemia).[1] 

What is insulin resistance?

Insulin resistance is when your body no longer responds to insulin [6], so your cells can’t take in glucose, and your blood sugar levels stay elevated as a result. 

Your pancreas continues to release insulin to try and reduce your blood sugar to a healthy level. But, if it can’t overcome the resistance, the cells in the pancreas that produce insulin can eventually wear out.

How does insulin resistance develop?

Insulin resistance can develop from several causes. 

Carrying extra body weight

Carrying extra body weight, particularly around your stomach, can increase the likelihood of insulin resistance. Fat cells release inflammatory molecules (like cytokines and adipokines), which trigger inflammation and stop insulin from effectively communicating with your cells.[7] Higher levels of free fatty acids in the blood can also reduce insulin’s ability to drive glucose into your muscle and liver cells.

What you eat

Eating high-carbohydrate foods, particularly those high in refined sugar, leads to a rapid rise in blood sugar levels, resulting in a surge in insulin production.[8] When this happens too frequently, cells may suppress their insulin receptors and become less responsive to insulin’s signals.

Chronic stress

Stress triggers the release of stress hormones [9], like cortisol and adrenaline, which can increase blood sugar levels and decrease glucose uptake. Chronic (i.e., long-term) stress means this happens often, resulting in insulin resistance, just like in the example above. High cortisol levels can also lead to increased belly fat, which compounds the issue.[10]

Lack of physical activity

Regular exercise makes your muscle cells more responsive to insulin.[11] But when you’re not active, your muscles don’t use glucose effectively. So, being too sedentary means your cells can become less sensitive to insulin’s attempts to get glucose into them.

Poor sleep

Not getting enough quality sleep can disrupt your natural circadian rhythms, which changes how effectively your body processes blood sugar. Research suggests that irregular sleep affects the hormones involved in blood sugar control, leading to higher fasting glucose levels and lower insulin sensitivity. 

Intermittent fasting, as we’ll see, can be a real help with several of these factors. If you’re already eager to give it a go,  take our SIMPLE quiz, and we’ll help you kick off your intermittent fasting journey!

Insulin resistance symptoms

If you had insulin resistance, how would you know? These are the symptoms to look out for:

Constant hunger

Feeling hungry regularly — even shortly after eating a meal — can be a sign that your cells aren’t absorbing enough glucose and your body is sending the signal that it needs more. 

Extreme thirst

If you notice you’re drinking a lot more water than usual, it could be because your kidneys are working harder to remove excess sugar from your bloodstream.

Persistent fatigue

When your cells don’t use glucose effectively, your energy levels can dip, leading to persistent fatigue and low energy throughout the day.

Needing to pee a LOT

Having too much sugar in your blood means your kidneys have to work harder to get rid of it … and you take a lot of trips to the bathroom as a result.

Unexplained weight gain

Having insulin resistance means your pancreas will produce more insulin to try and resolve the problem and help glucose get into your cells. This elevated insulin level can lead to more calories being stored as fat.

Tingling sensations

Insulin resistance can lead to nerve damage (a condition known as neuropathy) in your hands and feet, which you’ll initially experience as tingling sensations.

Increased risk of infection

When your blood sugar levels aren’t well managed, it can compromise your immune system, leaving you more susceptible to infections and illnesses.

If you’re experiencing any of these symptoms and are concerned you might have insulin resistance, speak to your doctor.

The dangers of insulin resistance

Insulin resistance is pretty serious business. Left untreated, it can lead to a number of significant health challenges.

Type 2 diabetes 

Persistent insulin resistance can ultimately result in type 2 diabetes, which in turn can lead to other serious health complications.[2]

Cardiovascular disease

Insulin resistance is associated with an increased risk of heart disease. It can lead to high blood pressure, unhealthy cholesterol levels, and the development of atherosclerosis (hardening of the arteries), which can result in heart attacks and strokes.[12]

Obesity

Insulin resistance often promotes weight gain, particularly around the belly, which can lead to obesity. Obesity, in turn, further exacerbates insulin resistance, creating a vicious cycle.[13]

Polycystic ovary syndrome (PCOS) 

Many people with PCOS have insulin resistance. This can lead to hormonal imbalances, irregular periods, and difficulties with fertility.

Non-alcoholic fatty liver disease (NAFLD) 

Insulin resistance can lead to the accumulation of fat in the liver, resulting in NAFLD. This condition can progress to more severe liver damage if left unmanaged.[14]

Kidney disease

Long-term insulin resistance can damage the blood vessels in the kidneys, potentially leading to kidney disease or even kidney failure.[15]

Neuropathy 

As mentioned earlier, insulin resistance can contribute to nerve damage, leading to neuropathy, which can cause pain, numbness, and potentially long-term tissue damage.[16]

Vision problems

High blood sugar levels related to insulin resistance can harm the blood vessels in the eyes, leading to diabetic retinopathy, which can result in vision problems or even blindness.[16]

Cancer

Some research suggests a link between insulin resistance and an increased risk of certain cancers, including breast [17], colon [18], and pancreatic cancer.[19]

Autoimmune disorders

Insulin resistance may be associated with autoimmune conditions, such as rheumatoid arthritis and lupus.[20,21]

Chronic inflammation

Insulin resistance can cause chronic inflammation (also known as oxidative stress) throughout the body, contributing to a range of health issues.

Intermittent fasting and insulin

Intermittent fasting is an eating plan that involves alternating periods of fasting and eating. Each day, you have a period of time where you eat and a period of time where you don’t. This regular period of not eating is how intermittent fasting can positively impact your insulin levels. 

Every time you eat, your blood sugar rises, and your body has to balance it by releasing insulin. When you overeat frequently, your caloric intake is regularly too high, or you eat too many refined carbohydrate foods, your blood sugar control system can get overwhelmed and stop working properly. 

Intermittent fasting gives your body a daily break from its blood sugar management responsibilities. When you don’t eat, your pancreas doesn’t have to produce and release insulin because there’s no blood sugar to manage. 

If this already has you curious to see the health benefits for yourself, take our SIMPLE quiz to get started. We’ll recommend the right fasting schedule for you and make sure you have all the tools, information, and support you need to get started safely and start getting results quickly!

How can intermittent fasting reduce insulin resistance?

The effect of intermittent fasting on insulin sensitivity has been debated for several years.[22] 

A 2018 study investigating the connection between insulin resistance and intermittent fasting suggested fasting could play a role in reversing insulin resistance.[23]

Another study found that in adults living with type 2 diabetes, TRE resulted in 18% reduction in HbA1c, 15% reduction in fasting glucose levels, and a 14% reduction in insulin resistance.[24] 

Several studies suggest that fasting is just as effective as traditional calorie restriction diets in helping people lose weight and reduce the risk of developing type 2 diabetes.[25]

Best intermittent fasting schedules to reduce insulin resistance

A 2018 study showed that the 18:6 fasting protocol (fasting for 18 hours and eating within a six-hour window daily) improved insulin sensitivity in men with prediabetes.[22] This review showed intermittent fasting improved insulin sensitivity regardless of fasting schedule.[26] 

There is no one-size-fits-all when it comes to intermittent fasting — the best intermittent fasting schedule for reducing blood sugar is the schedule that works for you! 

Is intermittent fasting safe? 

If you are thinking of trying intermittent fasting for insulin resistance, check whether it’s safe for you before you start. For some people, getting the go-ahead from their doctor is imperative. This means you if you:

• have a medical condition
• take prescription medications
• are extremely active
• are pregnant, breastfeeding, or trying to conceive
• have a body mass index (BMI) < 18.5
• have (or are at risk of having) an eating disorder or have a history of one
• are under 18 years old, or are 80 years old or more

If it’s safe for you to try, know that some intermittent fasting schedules are safer than others: 

• We recommend fasting for a few hours daily (known as TRE, or time-restricted eating) and keeping your fasts to an 18-hour limit. 
• We don’t recommend fasting schedules like alternate day fasting, 5:2, Eat Stop Eat, water fasting, or dry fasting. 

SIMPLE’s expert opinion and final thoughts

So, does fasting help with insulin resistance? Yes, it can. 

Intermittent fasting gives your blood-sugar-management machinery a break every day and, in doing so, helps it work more efficiently and effectively. While some bodily processes can just keep cranking day in and day out, like breathing (that guy never switches off, huh!), others benefit from some periodic rest and recovery. Your body’s gotta last you the rest of your life, so a little daily maintenance never hurts. 

If you’re concerned that you might have insulin resistance and you want to try intermittent fasting for diabetes prevention purposes, speak with your doctor. Get the green light, then take our SIMPLE quiz to hit the ground running. We’ll help you stay focused, teach you how not to feel hungry when fasting, and guide you to develop nutrition habits that make you feel your best.

Frequently asked questions about intermittent fasting and insulin resistance

How long does it take intermittent fasting to fix insulin resistance?

Intermittent fasting isn’t a “fix” for insulin resistance. It can help, however. Studies show that intermittent fasting can reduce blood sugar and insulin resistance by 3% to 6% over 8 to 12 weeks in prediabetic individuals.[25] 

What happens to your body when you fast for 16 hours?

During a 16-hour fast, your body enters a state of fasting metabolism.[27] Initially, it depletes stored glycogen for energy, then shifts to burning stored fat for fuel. Insulin levels drop, promoting fat breakdown. Autophagy, a cellular cleansing process, may also occur. All of this can aid weight loss and improve metabolic health (and interestingly, it seems that intermittent fasting does not slow metabolism).

What is a quick fix for insulin resistance?

There is no quick fix for insulin resistance, as it often develops over time due to various risk factors. However, lifestyle changes — like eating a balanced diet (which could include low glycemic index foods), intermittent fasting, getting regular exercise, managing stress, and getting adequate sleep — can improve insulin sensitivity and help manage insulin resistance in the long term.[28]

Should you do intermittent fasting if you’re prediabetic?

Intermittent fasting can be effective in managing and preventing prediabetes.[29] However, intermittent fasting may not work for everyone, so talk to your doctor before trying it. 

Does starvation decrease insulin?

Yes, prolonged starvation can decrease insulin levels in the body.[30] As the body depletes its glycogen stores and relies on fat for energy, insulin production decreases to conserve glucose for essential functions. However, this is an extreme state and not a recommended approach for managing insulin levels.

Written by Trey Reck

Medically reviewed by Louise Bula, RD

Published on | Updated on March 28, 2024