Why Does Insulin Cause Weight Gain? (A Beginner’s Guide)

fact-checked and medically reviewed article

Obesity is not a caloric imbalance. It’s a hormonal imbalance. And insulin is its primary regulator. Therefore, learn how insulin causes weight gain and what you can do about it.

Why Insulin Is Important

In my opinion, why insulin is so important can be best explained through the example of metabolic syndrome – a term used to unify severe health risks of the present.

The risk criteria for metabolic syndrome are:

  • High blood glucose
  • Hypertension
  • Low HDL (high-density lipoprotein, the “good cholesterol”)
  • High triglycerides
  • Central obesity

All these factors significantly contribute to modern metabolic diseases, such as (Herman et al. 20171; Orgel et al. 20142; Ferreira et al. 20183; Athauda et al. 20164):

  • Type 2 diabetes
  • Cancer
  • Strokes
  • Heart attacks
  • Other cardiovascular diseases
  • Alzheimer’s disease
  • Parkinson’s disease

Indeed, metabolic syndrome’s risk factors all share a common root cause – hyperinsulinemia or persistently high insulin levels . And often, they are accelerated through insulin resistance.

Hence, insulin and insulin resistance is at the heart of mortality in Western society.

Insulin causes not only weight gain, but also many diseases

The Role of Insulin in Weight Gain

Insulin is a hormone present in most biological life – from insects to humans. Hormones are chemical messengers targeting specific cells.

In humans, insulin’s primary role is to regulate nutrient storage (Mercola 20175).

Consequently, it helps to store energy gained in times of abundance for times of food scarcity. The storage hormone encourages fat accumulation and signals cells to take up glucose from the bloodstream.

Hormones deliver their message by binding to a cell’s receptor. With this in mind, insulin functions in the body as a key opening the cell by matching its lock – the receptor. Once insulin opens the door, glucose can enter the cell.

A rise in blood sugar levels is triggering insulin production and release from the pancreas.

Then, after the stomach and intestine have broken them down into smaller parts, different macronutrients have different effects on blood glucose and insulin levels.

Amino acids from proteins have a minimal impact on blood sugar while elevating insulin. On the contrary, fatty acids have minimal effects on both blood glucose and insulin.

Sugars from carbohydrates, which are chains of sugars, are significantly spiking blood glucose as well as insulin levels (Fung 20166).

On the other hand, insufficient insulin can cause glucose to build up in the blood.

For example, that’s the case when the immune system mistakenly destroys the insulin-producing cells in the pancreas (an autoimmune condition), which results in type 1 diabetes.

At mealtimes, consumed carbohydrates are causing excess blood sugar, since the bloodstream only contains about 4 grams of glucose at any point in time.

Therefore, insulin functions in the body as a messenger and helps to get the majority of sugar out of the blood.

Carbohydrates, Insulin, and Weight Gain

Something has to happen with heaps of blood sugar at mealtimes. The liver is converting excess carbohydrates into a readily available storage resource called glycogen through a process called “glycogenesis.”

Hence that’s the body’s preferred fuel for short-term energy expenditure.

But there is limited space for glycogen in the liver. Another process called “de novo lipogenesis” is started in case glycogen stores are full.

The definition of de novo lipogenesis is the conversion of excess carbohydrates into body fat.

In contrast to glycogen, body fat is a long-term type of energy storage. It can be stored in unlimited amounts but is harder to access. Glycogen, on the other hand, can quickly provide glucose to your body.

And here’s the challenge before you can access stored body fat, you need to empty about 1500 to 2000 calories of glycogen stored in your liver and skeletal muscles, where glycogen is stored (Volek et al. 20117).

Hence glycogen stores are acting as a battery with limited duration. They may not last long, but carbohydrates in foods are recharging glycogen stores daily.

As long as your glycogen stores are not empty, insulin can cause weight gain

Consequently, the body doesn’t tap into its emergency storage of fat in times of food scarcity.

It doesn’t break down body fat for energy in case you follow a Western pattern diet (WPD) or standard American diet (SAD). Maybe it’s called SAD for a reason.

Additionally, insulin supports the preservation of fat. It inhibits the enzyme hormone-sensitive lipase (HSL), which is responsible for mobilizing stored body fat (Meijssen et al. 20018).

But that’s where prolonged and intermittent fasting, and a low-carb high-fat diet or ketogenic diet, are aiming. If you want to get actionable details on how to tap into body fat for energy, have a look at my FREE PDF Guide.

Why Does Insulin Cause Weight Gain?

Insulin is the primary storage hormone. Hence, any food consumption leads to insulin release.

It then acts as a messenger for sugar and fat storage. Contrarily, in the absence of food, the high levels of insulin drop to enable the burning of sugar and later fat for energy.

As explained above, the average person is seldom tapping into body fat for energy. But that only explains why insulin isn’t good for weight loss.

In the case of glycogen stores (your short-term battery) in the liver are full, it generates new fat.

Therefore your excess carbohydrates will be stored as newly synthesized fat around organs (visceral fat), below your skin (subcutaneous fat), or directly in the liver (fatty liver).

Nature built us for periods of feeding and fasting. The human body is meant to switch between the use of readily available and long-term stored energy.

Likewise, you might have heard that we are only losing weight during a night’s sleep.

But over the last decades, we have completely repressed that we can go more than eight hours without eating persistently. Ad campaigns educated us with garbage, like having six meals a day to lose weight.

The results are excessively high levels of insulin, induced by the imbalance between feeding and fasting. As a crucial regulator of body weight, insulin causes weight gain.

In essence, we have a perfect recipe for an obesity epidemic (Fung 20169).

Insulin and Body Set Weight

Hormones are chemical messengers regulating almost everything. For example, they regulate hunger, satiety, thirst, body temperature, and body weight.

The region of the brain responsible for the regulation of those essential processes is called the hypothalamus.

With this in mind, a defining ability of the human body is the adaption to change called “homeostasis.”

Therefore the hypothalamus is tightly regulating body temperature around a stable level. That’s usually about 36°C or 98°F.

Similarly, the same principle of homeostasis applies to body weight. Hence, it isn’t high caloric intake or lack of exercise that causes weight gain.

However, the food industry is trying to tell us so because the calorie approach justifies low-quality food.

Instead, a hormonal imbalance is setting body weight to an unhealthy level. Given that, the hypothalamus commands the body to increase fat mass using available calories.

The hypothalamus is located above the pituitary gland in the brain

As a result, the body is short of energy and craves for increased caloric intake.

Consequently, the hypothalamus increases the hunger hormone ghrelin and decreases the satiety hormones peptide YY, cholecystokinin, and leptin.

Restricting calories to counteract the body’s effort to increase fat mass doesn’t work out long-term. In that case, the basal metabolism is down-regulated to satisfy the higher priority goal of gaining body fat.

That doesn’t necessarily mean that one is gaining weight under caloric restriction, but likely fat for the sacrifice of muscle mass. Nevertheless, the resulting lowered metabolic rate is also known as Jojo-effect.

For this reason, overeating and lack of physical activity are symptoms of obesity rather than its causes.

However, it takes time to alter body set weight since the body’s principle of homeostasis maintains a stable weight. Hence excess insulin causes weight gain sneakily – pound by pound, year by year.

How does Insulin Cause Weight Gain?

We now know that insulin functions in the body as the primary regulator of energy storage and energy balance. With this in mind, we can add the hypothesis that it’s also the critical regulator of body weight in the brain.

That means insulin also functions in the body by triggering the hypothalamus to up-regulate weight.

As a result, appetite rises, and we want to eat. Like many other things, the brain centrally controls weight gain through the nervous system.

In this case, the function of the hypothalamus uses hormones to execute regulations through the endocrine system. We do not consciously regulate essential body functions like heart rate, breathing, or basal metabolic rate.

Furthermore, hormones regulate anything related to metabolism. In the body weight set point theory, insulin and weight gain are in a cause-and-effect relationship since it’s the triggering messenger.

Insulin is the primary regulator of body set weight in the brain

Given that, people with high insulin levels should gain weight easier.

And studies have found this aspect of the body weight set point theory to be correct. Not only do obese patients insulin levels after an overnight fast, but they also react with stronger insulin responses (Tentolouris et al. 200810).

On top of that, insulin levels remain high in obese subjects after a meal for a prolonged time, while in lean subjects, they quickly drop back to a healthy range.

Moreover, there is a strong correlation between high fasting insulin levels, waist to hip ratio, BMI, and obesity (Ferrannini et al. 199711). But is the relationship causal too?

Although it might sound controversial, there is a well-known disorder able to prove that high levels of insulin cause weight gain and low levels of insulin lead to weight loss.

It’s type 1 diabetes – an autoimmune disease characterized by the absence of insulin.

Insulin and Weight Loss

Let’s quickly compare the two main types of diabetes, type 1 vs. type 2. In many ways, those related disorders are opponents of one another.

The human body’s friendly fire eradicating the insulin-secreting cells in the pancreas for unknown reasons is what causes type 1 diabetes.

Given that the immune system’s own antibodies induce the disorder, it’s an autoimmune disease.

Conversely, type 2 diabetes is a lifestyle and dietary disease. If food choices frequently lead to high blood sugar, the body reacts with hyperinsulinemia.

This excessive insulin secretion leads to the underlying force of type 2 diabetes – insulin resistance.

Due to the elimination of the insulin-producing cells, you can’t reverse type 1 diabetes naturally. But you can reverse type 2 diabetes naturally through diet since it’s a very severe state of insulin resistance (Fung 201812).

Nevertheless, history shows that humanity has been aware for decades that type 1 diabetes literally can melt flesh away. Its weight loss characteristics caused absolute fatality before insulin could be manufactured.

Without insulin treatment, type 1 diabetics lose weight no matter how many calories they ingest. Therefore, low levels of insulin evidentially cause weight loss.

Diabetes treatment proves that insulin does cause weight gain

Exogenous Insulin and Weight Gain

Let’s have a look at the life-saving treatment of diabetes type 1 – insulin injection. If insulin is a primary body set weight regulator, giving insulin to people must induce weight gain.

In a study published in Diabetes Care, researchers compared the conventional treatment of type 1 diabetes to intensive therapy.

Standard treatment is limited to 1-2 insulin injections daily, while intensive treatment of type 1 diabetes means multiple injections daily.

The findings of the scientists showed significantly more weight gain in the intensive treatment group of type 1 diabetes patients.

Those patients gained 4.75 kilograms more on average than their conventional treatment counterparts.

Additionally, intensive treatment of type 1 diabetes was more likely to result in an increased waist/hip ratio and obesity  (White et al. 200113).

Moreover, in a randomized controlled trial at the Oxford Centre for Diabetes, Endocrinology, and Metabolism, researchers compared different insulin treatments of type 2 diabetes patients.

They separated subjects into three groups from low over medium to high dosage of exogenous insulin.

And the results were as expected (Holmann et al. 200714):

  • Low dosage group – 1.9 kilograms or 4.2 pounds weight gain on average
  • Medium dosage group – 4.7 kilograms or 10.4 pounds weight gain on average
  • High dosage group – 5.7 kilograms or 12.5 pounds weight gain on average

Correspondingly, this is also what most doctors can agree upon based on their experience. The more insulin they give for diabetes treatment, the higher is the weight gain of patients.

Hence, the evidence stresses it out – insulin causes weight gain.

After all, our bodies do not expose the critical physiological factor of fat accumulation to conscious regulation through caloric intake and exercise.

Although the topic might be more complicated than we thought, overweight isn’t a caloric imbalance. It’s a hormonal imbalance (Lustig 200115).

Leptin and Insulin Resistance

Closely aligned with hunger and appetite, the hypothalamus also functions as a switching point that tightly regulates body fat. It does so by using the satiety hormone leptin, which increases with body fat.

Hence, leptin acts as a natural counterpart to insulin. While insulin is a hormone encouraging fat storage, leptin triggers the reduction of body fat (Benoit et al. 200416).

The higher leptin levels, the smaller the appetite and cravings. On the other hand, high insulin levels inhibit leptin secretion (Lustig et al. 200417).

Usually, both fasting leptin and insulin levels are high in obese subjects. Consequently, that indicates insulin and leptin resistance.

Moreover, also the response to food intake in obese people causes different effects. While leptin levels are rising in lean people, they are falling in overweight subjects.

Given that their brains do not get the signal of being full, obese people are less likely to stop eating.

Hence, overweight people are starving while carrying hundreds of thousands of excess calories with them, which they also can’t excess due to persistently high insulin levels.

Furthermore, constant exposure to high leptin levels can cause leptin resistance in the brain.

This kind of self-regulation shows a similarity to insulin resistance, which is commonly associated with leptin resistance (Martin et al. 200818).

Does Metformin Cause Weight Gain?

Metformin is a biguanide. Besides the fact that it’s the most widespread type 2 diabetes and insulin resistance medication, it’s also the most powerful of its class.

Biguanides work by blocking glucose production in the liver. By impairing gluconeogenesis, it doesn’t elevate insulin levels. For this reason, metformin doesn’t support hypoglycemia and weight gain.

With this in mind, metformin also isn’t worsening diabetes and obesity. Nevertheless, it’s also not fighting those diseases or weight gain. Hence, metformin is weight neutral (Fung et al. 201819).

Although metformin doesn’t cause weight gain, it comes with the most common problem of medication.

Metformin is just targeting the symptom, not the root cause.

Since it can’t fight the root cause of the diseases, hyperinsulinemia, metformin also can’t reverse insulin resistance or type 2 diabetes.

Therefore, metformin is big business for big pharma, because it doesn’t take away the illness, but impairs its development.

Once you’ve started taking it, you almost can’t stop using metformin.

And the effective dosage of the drug needs to be increased over time, again and again.

In conclusion, it needs diet and lifestyle changes to reverse insulin resistance, obesity, and type 2 diabetes sustainably.


Although the storage hormone is vital, too much insulin can cause serious side effects – above all, weight gain.

Since the conventional view that a high-carbohydrate and low-fat diet is healthy, favors hyperinsulinemia and insulin resistance, we are already facing severe health issues.

Because insulin prevents weight loss and helps store body fat more efficiently, obesity is slowly but surely on its way to become a pandemic.

But what is even more alarming is that the modern diseases that make up the lion’s share of the mortality rates in the western world are mainly due to high insulin levels.

Frequently Aksed Questions (FAQ)

How can I avoid gaining weight on insulin?

There are two major things to avoid gaining weight on insulin:
• A low-carb, high-fat diet to avoid high blood sugar and excess insulin secretion
• Intermittent fasting, since frequent eating maximizes body fat storage due to insulin

How does insulin make you gain weight?

Insulin is the primary storage hormone. It acts as a trigger for sugar and fat storage while blocking the ability to burn body fat for energy.

Does insulin cause belly fat?

Insulin promotes the storage of excess carbohydrates as fat around organs (visceral fat), below your skin (subcutaneous fat), or directly in the liver (fatty liver).

Can high insulin levels cause weight gain?

Countless studies regarding intensive insulin treatment confirm that high insulin levels evidentially cause weight gain.

Does metformin cause weight gain and bloating?

Metformin neither causes weight gain nor weight loss. It’s weight neutral.



1Herman ME, O’Keefe JH, Bell DSH, Schwartz SS. Insulin Therapy Increases Cardiovascular Risk in Type 2 Diabetes. Prog Cardiovasc Dis. 2017 Nov – Dec;60(3):422-434. doi: 10.1016/j.pcad.2017.09.001. Epub 2017 Sep 25. Review. PubMed PMID: 28958751.

2Orgel E, Mittelman SD. The links between insulin resistance, diabetes, and cancer. Curr Diab Rep. 2013 Apr;13(2):213-22. doi: 10.1007/s11892-012-0356-6. Review. PubMed PMID: 23271574; PubMed Central PMCID: PMC3595327.

3Ferreira LSS, Fernandes CS, Vieira MNN, De Felice FG. Insulin Resistance in Alzheimer’s Disease. Front Neurosci. 2018;12:830. doi: 10.3389/fnins.2018.00830. eCollection 2018. Review. PubMed PMID: 30542257; PubMed Central PMCID: PMC6277874.

4Athauda D, Foltynie T. Insulin resistance and Parkinson’s disease: A new target for disease modification?. Prog Neurobiol. 2016 Oct – Nov;145-146:98-120. doi: 10.1016/j.pneurobio.2016.10.001. Epub 2016 Oct 3. Review. PubMed PMID: 27713036.

5Mercola J. Fat for Fuel: A Revolutionary Diet to Combat Cancer, Boost Brain Power, and Increase Your Energy. Carlsbad, CA: Hay House Publishing, 2017.

6Fung J. The Obesity Code: Unlocking the Secrets of Weight Loss. Vancouver: Greystone Books, 2016.

7Volek JS, Phinney SE, Kossoff E, Eberstein J, Moore J. The Art and Science of Low Carbohydrate Living: An Expert Guide to Making the Life-Saving Benefits of Carbohydrate Restriction Sustainable and Enjoyable. Lexington, KY: Beyond Obesity, 2011.

8Meijssen S, Cabezas MC, Ballieux CG, Derksen RJ, Bilecen S, Erkelens DW. Insulin mediated inhibition of hormone sensitive lipase activity in vivo in relation to endogenous catecholamines in healthy subjects. J Clin Endocrinol Metab. 2001 Sep;86(9):4193-7. doi: 10.1210/jcem.86.9.7794. PubMed PMID: 11549649.

9Fung J. The Obesity Code: Unlocking the Secrets of Weight Loss. Vancouver: Greystone Books, 2016.


10Tentolouris N, Pavlatos S, Kokkinos A, Perrea D, Pagoni S, Katsilambros N. Diet-induced thermogenesis and substrate oxidation are not different between lean and obese women after two different isocaloric meals, one rich in protein and one rich in fat. Metabolism. 2008 Mar;57(3):313-20. doi: 10.1016/j.metabol.2007.10.004. PubMed PMID: 18249201.

11Ferrannini E, Natali A, Bell P, Cavallo-Perin P, Lalic N, Mingrone G. Insulin resistance and hypersecretion in obesity. European Group for the Study of Insulin Resistance (EGIR). J Clin Invest. 1997 Sep 1;100(5):1166-73. doi: 10.1172/JCI119628. PubMed PMID: 9303923; PubMed Central PMCID: PMC508292.

12Fung, J. The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended. Vancouver: Victory Belt Publishing, 2018.

13Influence of intensive diabetes treatment on body weight and composition of adults with type 1 diabetes in the Diabetes Control and Complications Trial. Diabetes Care. 2001 Oct;24(10):1711-21. doi: 10.2337/diacare.24.10.1711. PubMed PMID: 11574431; PubMed Central PMCID: PMC2663516.

14Holman RR, Thorne KI, Farmer AJ, Davies MJ, Keenan JF, Paul S, Levy JC. Addition of biphasic, prandial, or basal insulin to oral therapy in type 2 diabetes. N Engl J Med. 2007 Oct 25;357(17):1716-30. doi: 10.1056/NEJMoa075392. Epub 2007 Sep 21. PubMed PMID: 17890232.

15Lustig RH. The neuroendocrinology of childhood obesity. Pediatr Clin North Am. 2001 Aug;48(4):909-30. doi: 10.1016/s0031-3955(05)70348-5. Review. PubMed PMID: 11494643.


16Benoit SC, Clegg DJ, Seeley RJ, Woods SC. Insulin and leptin as adiposity signals. Recent Prog Horm Res. 2004;59:267-85. doi: 10.1210/rp.59.1.267. Review. PubMed PMID: 14749506.

17Lustig RH, Sen S, Soberman JE, Velasquez-Mieyer PA. Obesity, leptin resistance, and the effects of insulin reduction. Int J Obes Relat Metab Disord. 2004 Oct;28(10):1344-8. doi: 10.1038/sj.ijo.0802753. PubMed PMID: 15314628.

18Martin SS, Qasim A, Reilly MP. Leptin resistance: a possible interface of inflammation and metabolism in obesity-related cardiovascular disease. J Am Coll Cardiol. 2008 Oct 7;52(15):1201-10. doi: 10.1016/j.jacc.2008.05.060. Review. PubMed PMID: 18926322; PubMed Central PMCID: PMC4556270.

19Fung J, Teicholz N. The Diabetes Code: Prevent and Reverse Type 2 Diabetes Naturally. Vancouver: Greystone Books, 2018.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

This Post Has 2 Comments

  1. Andrew

    “Type 1 diabetics lose weight no matter how many calories they ingest” do they really? What’s your source for these claims and how is that supposed to work? How would you biologically explain that? What happened to the first law of thermodynamics?

    1. Hi Andrew,

    2. There are lots of studies confirming fatality of type 1 diabetes without treatment (example)
    3. The human body is not a closed system like a combustion engine. Therefore, you cannot apply the first law of thermodynamics
    4. Instead, it’s an open, dynamic system where the biological principle of homeostasis can be applied
    5. In short, if you buy the cheapest fuel, you will pay the price with your health.


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