Insulin Therapy and Weight Gain

  • Mysaa Ahmed Master of Public Health - MPH, Public Health, Alneelain University
  • Saba Amber BSc, Manchester Metropolitan University, UK
  • Ellen Rogers MSc in Advanced Biological Sciences, University of Exeter

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What is insulin, and how does it work?

Insulin is a hormone produced by our bodies to regulate blood sugar (glucose) levels. It is produced by beta cells in the pancreas and stored in the pancreas until it is needed. After eating, insulin is released into the bloodstream, where it allows glucose in the blood to move into your cells, where it is used as a source of energy or converted into fat for long-term storage.

Diabetes is a disease in which your body can’t make or release enough insulin (type 1 diabetes), or where the insulin made by your body becomes ineffective (type 2 diabetes). Patients with diabetes are recommended to use insulin therapy (or injections) to control their blood sugar levels.

Insulin comes as a medication called human insulin as it is made to exactly resemble the insulin made by our bodies. It is recommended for all patients with type 1 diabetes as well as some patients with type 2 or other types of diabetes, such as gestational diabetes.

There are many conditions that can affect your body’s ability to produce and release insulin, such as:

  • Gestational diabetes: diabetes that begins during pregnancy, and most of the time disappears after giving birth.
  • Prediabetes: when your body can’t use insulin properly (insulin resistance), but its blood sugar levels do not reach high enough levels to be classified as type 2 diabetes.
  • Type 1 diabetes: when your pancreas can’t make insulin, or it doesn’t make enough to control your blood sugar.
  • Type 2 diabetes:  when your pancreas makes ineffective insulin or the body can’t use the insulin as it should.
  • Metabolic syndrome: (insulin resistance syndrome), is a group of health conditions that increase an individual’s risk of developing heart conditions and diabetes. Insulin resistance means the cells can’t use the glucose in your blood as a source of energy.

 There are different types of human insulin offered to diabetics. The main types are:1

  • Rapid-acting insulin: starts working within five to 20 minutes, peaks about an hour or two after the injection and is effective for between three and five hours.
  • Regular (short-acting) insulin: starts working 30 to 45 minutes after injection, peaks about two to four hours after the injection, and is effective for between five and eight hours.
  • Intermediate-acting insulin: starts working two hours after injection, peaks between four and 12 hours after the injection, and it keeps working from 14 to 24 hours.
  • Long-lasting insulin: it takes about an hour for this type to start working, but it peaks between three and 14 hours after injection and can work for up to a day. 
  • Ultra long-acting insulin: starts working about an hour after injection. This type of insulin doesn’t ‘peak’, and can maintain the same level of efficiency for up to two days. 

Side effects of insulin therapy

You should speak with your healthcare provider or your pharmacist about the proper use of insulin to avoid side effects, but it is important to know the side effects that could happen, including the following:2

  • Redness, swelling and irritation at the side of the injection
  • Constipation
  • Weight gain
  • Hypos: low blood glucose level (hypoglycemia), which can cause you to feel dizzy, confused, or irritated. Hypoglycemia is a serious side effect that can lead to serious complications if not dealt with quickly, which is why it is important for diabetics to regularly check their blood sugar levels and consume quick-acting carbohydrates if needed. 

How does insulin cause weight gain?

Taking insulin to manage high blood glucose has been associated with weight gain. It is thought that patients taking insulin therapy often eat more carbohydrates out of fear of becoming hypoglycaemic. Consuming more calories and glucose than your body needs leads to excess glucose being converted into fat for future use. Furthermore, insulin therapy reduces glycosuria (the presence of glucose in urine) so less excess glucose is excreted. 

Weight gain on insulin therapy may also be related to the fact that insulin is a hormonal regulator of appetite. As such, high levels of insulin can increase hunger and elevate your appetite, resulting in you eating more calories than your body needs. Therefore, finding proper ways to control your weight while you are on insulin therapy is very important.3,4

Weight control during insulin therapy

Maintaining a healthy diet and staying physically active are key to controlling your weight and avoiding obesity and its health consequences, Here are a few tips that can help you achieve that: 

  1. Keep track of your calories: plan healthy meals that contain fewer calories, but have the right amount of protein, fat, carbohydrates, vegetables and fruits. Talk to your doctor or dietician about your meals and how to plan them right.
  2. Don’t skip meals: skipping meals usually leads to bad diet choices and taking in more calories than you need for the next meal. It can also lower your blood glucose level and cause unwanted side effects if you don’t adjust your insulin dose.
  3. Exercise: being physically active burns calories and helps your body to use insulin more efficiently. It is crucial to consult with your physician first to determine the level of physical activities that match your insulin intake, it is also important to keep your glucometer and a snack nearby because exercises can cause your blood sugar to drop.
  4. Take your insulin only as instructed: don’t skip or reduce your insulin dose without talking to your doctor, complications of high blood sugar are very serious, and can be fatal if not treated urgently.
  5. Ask your healthcare provider about alternatives: some diabetes treatments like metformin can help regulate your blood glucose level and reduce your insulin dose. Ask your provider if they can be part of your treatment plan.


Insulin is the key hormone for blood glucose regulation. It allows glucose to enter the cells to be used as a source of energy for different cellular functions, or be converted into fat for later use. Insulin also plays a significant role in metabolism and can affect your appetite and food cravings. All these factors can explain why some people gain weight whilst on insulin therapy. 

Consuming healthy balanced meals and keeping active physically are key to avoiding gaining extra weight while you are taking insulin. You can also speak with your GP about other alternatives and medications that can be used with insulin to control weight gain and avoid obesity. It is vital to always talk to your healthcare provider and get all the information you need about how to take your medications right, and the necessary precautions to avoid all the side effects.


  1. Does insulin cause you to gain belly fat?

Insulin can lead to an overall weight gain, but it doesn’t specifically cause fat deposition in the belly area.

  1. Does increasing insulin help you lose weight?

Increasing insulin levels in the body can lead to you putting on extra weight due to its role in fat storage, metabolism, cravings and an overall increase in appetite and food intake.

  1. Which insulin does not cause weight gain?

The long-acting insulin when combined with other oral antidiabetic medications like metformin can cause less weight gain than other types of insulin.5


  1. CDC. Centers for Disease Control and Prevention. 2021 [cited 2024 Jan 16]. Types of insulin. Available from:
  2. Benefits and side-effects of insulin – NDSS [Internet]. [cited 2024 Jan 18]. Available from:
  3. Russell-Jones D, Khan R. Insulin-associated weight gain in diabetes--causes, effects and coping strategies. Diabetes Obes Metab. 2007 Nov;9(6):799–812.
  4. Heller S. Weight gain during insulin therapy in patients with type 2 diabetes mellitus. Diabetes Research and Clinical Practice [Internet]. 2004 Sep 1 [cited 2024 Jan 18];65:S23–7. Available from:
  5. Davies MJ, Derezinski T, Pedersen CB, Clauson P. Reduced weight gain with insulin detemir compared to NPH insulin is not explained by a reduction in hypoglycemia. Diabetes Technol Ther. 2008 Aug;10(4):273–7.

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Mysaa Ahmed

Master of Public Health - MPH, Public Health, Alneelain University

Advanced Post Graduate Diploma in Clinical Research and Medical Writing, Health Research, James Lind Institute

I’m a dedicated and passionate medical writer, with experience in public health and dentistry and an interest in implementation research, health promotion and community development. I thrive on bridging the gap between research findings and real-world applications, and communicating complex healthcare information and ensuring it reaches all community members effectively. presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
Klarity is a citizen-centric health data management platform that enables citizens to securely access, control and share their own health data. Klarity Health Library aims to provide clear and evidence-based health and wellness related informative articles. 
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