What is insulin sensitivity and how does it affect the body?

Conversations about insulin too often can feel like they're all about diabetes, and while those are important conversations to have, insulin itself exists in all of our bodies well beyond the context of that chronic condition.

This hormone plays an important role in our health and our weight, and understanding what it does, its relationship to our blood sugar levels, and the difference between insulin sensitivity and insulin resistance can be really important in understanding how we gain weight and lose it, when we are at risk of certain health conditions, including diabetes, and the importance of managing stress and sleep in maintaining our overall health.

So here, we'll take a look at what insulin sensitivity is, how you may develop insulin resistance, and what you can do to improve your insulin sensitivity and maintain a healthy weight.  

What is insulin sensitivity?

Insulin is a vital hormone that your body produces in your pancreas to control your blood sugar levels. It does this by moving excess sugar, also known as glucose, from your bloodstream and into your cells, where it can be stored and later used for energy [1]. 

When we talk about insulin sensitivity, we’re talking about how sensitive your body is to insulin and how much of the hormone it needs to control your blood glucose levels. This varies from person-to-person, and is impacted by several factors both in and out of your control [2].  

What factors affect insulin sensitivity?

When it comes to insulin sensitivity, there are a number of factors at play that can impact how your body reacts to and resists this hormone. These factors include:  

• Having a family history of diabetes or a personal history of gestational diabetes

• Being over the age of 35 (although younger people can still develop insulin resistance)

• Excess weight affecting growth hormone secretion, abnormal fat distribution, or a large waist or neck circumference

• Race and ethnicity
• Not being physically active and having a poor diet

• Smoking or being exposed to secondhand smoke

• Certain medical conditions, such as high blood pressure, hormonal disorders such as polycystic ovary syndrome (PCOS) cushing's syndrome, acromegaly, sleep apnea, or having had some viral diseases such as COVID-19

• Taking certain medications over time, such as glucocorticoids, antipsychotics, or some HIV treatments [3]

While some of these factors are in your control, many, such as your age, your family history, or your race, are not. If you face one or more of these factors, you are at a higher risk of developing insulin resistance syndrome, and it's important to have regular check-ups with your doctor to monitor your blood sugar levels [3]. 

What are the symptoms of low insulin sensitivity?

If you looked at the risk factors above and saw yourself checking a few boxes, the next question feels like it's inevitably going to be, well, what are the symptoms of insulin sensitivity, and how do I know if I have it?

Unfortunately, it's an easier question to ask than it is to answer, as low insulin sensitivity doesn't generally have any symptoms, particularly if your pancreas is still producing the hormone. That said, low insulin sensitivity can lead to prediabetes, and that does have symptoms which you can monitor, including:  

• Tiredness, particularly after eating  
• Increased hunger 
• Increased thirst 
• Weight gain
• Passing urine more often than you previously needed to  
• Blurred vision 
• Cuts and wounds are healing unusually slowly, and 
• Frequent infections, including urinary tract infections (UTIs), skin infections and yeast infections such as thrush [4]

If you have any of these symptoms, you may be insulin-resistant, and you should speak to your doctor or a medical professional.  

Are there symptoms of high insulin sensitivity?

High insulin sensitivity is, generally speaking, a good thing. It means that your body responds and reacts as it’s supposed to to insulin, and can use it effectively in regulating blood sugar levels. That said, there are times when high insulin sensitivity can be dangerous.  

In particular, for people with type 1 diabetes, high insulin sensitivity can increase the risk of hypoglycemia. Similarly, studies have repeatedly shown that physical activity and exercise has insulin sensitising effects that can also present a higher risk of hypoglycemia for people on insulin and other medications that can induce hypoglycemia. The insulin-sensitising effects in these cases can sometimes last for up to 48 hours, so it’s important to monitor for symptoms, which include:  

• Hunger 

• Exhaustion or physical weakness 

• Blurred vision 

• Dizziness 

• Anxiety or irritability 

• Sweating and shaking 

• Tingling lips 

• Heart palpitations; and

• Confusion. 

In severe cases of low blood sugar, you may also experience fainting, seizures or fits [4]. If you experience anything like this, it's important to get your blood sugar levels stable again through consuming something sugary, such as fruit juice, jelly beans, or glucose tablets.

How is insulin sensitivity diagnosed?

Many health care professionals actually don’t test for insulin sensitivity, in no small part, because it can be difficult to determine when a patient has no symptoms, and the pancreas is still producing insulin.  

They’re more likely to test and diagnose if they believe you might have severe insulin resistance or be prediabetic. To do that, your doctor will discuss your medical history with you, make note of your risk factors, particularly if you’re over the age of 35, overweight or obese, or have other risk factors for prediabetes and type 2 diabetes, perform a physical exam, and likely suggest blood tests. 

These blood tests will measure your blood glucose level to determine if it’s higher than normal. They can do this through two different types of tests:  

• The A1C Test, which shows your average blood glucose level over the past 3 months. This test will diagnose you with prediabetes if your A1C results are between 5.7% and 6.4%, placing them outside the healthy range.  

• The Fasting Plasma Glucose (FPG) Test, which shows your blood glucose level at the time of the test. This test will diagnose you with prediabetes if your FPG results are between 100 and 125 mg/dL (milligrams per deciliter).  

Your healthcare provider may also use an Oral Glucose Tolerance Test to diagnose prediabetes, but these aren’t easy to give, are more time-consuming and cost more than other tests, so it’s less common as a part of the diagnostic process than the blood tests above.  

If you have risk factors for type 2 diabetes but your diagnosis is negative for prediabetes, you may be retested at least every three years. If your diagnosis is positive, you have a high risk of developing type 2 diabetes within 5 to 10 years, and you should be tested for it annually. Luckily, though, there are steps you can take to prevent or reverse insulin resistance [3].  

How is insulin sensitivity managed?

Insulin sensitivity is a spectrum that ranges from high insulin sensitivity to low insulin sensitivity and insulin resistance, and how you manage it ultimately depends on the needs of your body and the risk factors you have.  

Treating high insulin sensitivity 

If you have high insulin sensitivity, you shouldn’t need to manage it unless you also have type 1 diabetes and are at risk of going hypoglycaemic. If you are, you should follow your doctor's treatment plan and check your blood sugar levels, and if they are below 4mmol/L, you should:  

1. Eat or drink something like a small glass of juice or a sugary drink, 4 large jelly babies, 2 tubes of glucose gel, or 5 glucose or dextrose tablets

2. After 10-15 minutes, check your blood sugar levels

1. If it’s still below 4mmol/L, repeat steps 1 and 2 

Once your symptoms have improved and your blood sugar is back up over 4mmol/L, you should eat something that will maintain the higher blood sugar levels, such as a sandwich or your next meal [4].  

Treating low insulin sensitivity 

While you can't reverse the clock or change your genetic makeup, it is also possible to improve insulin resistance if you have a low sensitivity to the hormone or if your body doesn't produce enough insulin to manage your blood sugar.

Lifestyle changes in particular have been known to influence insulin sensitivity, with dietary factors, physical activity aand weight loss all being known to affect insulin levels and promote better health. So, to manage insulin sensitivity and reduce insulin resistance, try:

• To move your body more and get more physical activity into your day-to-day life: Exercise has been proven to make your body more insulin sensitive and to build muscle that can absorb blood glucose. On top of that, physical activity actually allows glucose to enter muscle cells without needing insulin to act as an intermediary, reducing the need and dependence on the hormone for energy. While the latter doesn’t necessarily improve insulin sensitivity itself, it still helps to improve your blood glucose control, and can help to shed excess body fat, which has other health benefits such as reducing the risk of heart disease and other health conditions. 

• Eating healthy: While no single diet has been proven to be the most effective at addressing low insulin sensitivity, studies have found that eating foods that are low in healthy fat and high in processed carbohydrates and saturated fat can produce insulin resistance and negatively impact your blood sugar levels. These foods also impact your hdl cholesterol level, which has shown a link to insulin resistance. As a result, eating a balanced diet full of healthy foods with plenty of fibre, lean protein and healthy fats can help to address your insulin sensitivity [5].  

• Losing weight: Weight loss has also been proven to enhance insulin sensitivity as it reduces the effects of nonalcoholic fatty liver disease and inflammation, fatty acid mobilisation and supports the body’s metabolic system. This lowers the risk of developing diabetes and other metabolic syndromes associated with excess weight [6].  

• To get enough sleep: Sleep plays a vital role in managing blood glucose levels, and while it won't cure insulin resistance, getting the recommended minimum of 7 hours each night can support your body to not just maintain insulin sensitivity, but improve it over time [7]. It can also improve other health outcomes, reducing the risk of cardiovascular diseases, metabolic disorders and other chronic diseases.

Can you prevent insulin sensitivity?

While there are some factors at play when it comes to insulin sensitivity that are out of your control, such as age, race, family history, and medical conditions, you can look after your body and reduce some of the lifestyle factors that can cause low insulin sensitivity and diabetes.

Getting enough exercise, eating a healthy diet rich in fibre, lean proteins and healthy fats, managing stress, getting enough sleep, and maintaining a healthy weight are all steps you can take to reduce your personal risk of low insulin sensitivity.  

If you feel you have an increased risk of diabetes, are showing signs of insulin resistance, or have weight-related health problems, the Juniper Programme can support you to not only lose the excess fat but also build strength, monitor your health, and help you make lifestyle changes that are sustainable and have you looking and feeling your best.

What is the difference between insulin sensitivity and insulin resistance?

It’s important to remember that insulin sensitivity is a spectrum. In that sense, high insulin sensitivity is generally an indicator of good health, whereas low insulin sensitivity – which is also known as insulin resistance – is an indicator that you may be prediabetic and at risk of developing type 2 diabetes.

When you hear the term people with insulin resistance as a result, what you’re hearing is actually people with low insulin sensitivity, and includes all that we have discussed here today.  

Biomarkers, longevity, and insulin sensitivity

Insulin sensitivity is also an important metabolic biomarker linked to longevity and healthy ageing.

Alongside markers like cholesterol, inflammation, and blood pressure, insulin sensitivity reflects how efficiently the body manages energy over time. Poor insulin sensitivity is associated with accelerated biological ageing and a higher risk of chronic conditions such as cardiovascular disease and neurodegenerative disorders.

Supporting insulin sensitivity through consistent lifestyle habits can help preserve metabolic flexibility, reduce long-term disease risk, and promote healthier ageing across the lifespan.

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