What Role Does Insulin Play in Weight Loss?

There are many reasons why a keto diet is great for weight loss, but what role does the hormone insulin play?

2-Jan 2022, by Lee Sandwith

What Role Does Insulin Play in Weight Loss?

The topic of hormones and insulin come up time and time again when it comes to weight loss, but what does the research say?

Investigating the Carbohydrate Insulin Model of Obesity

There are many reasons to consider switching to a ketogenic but the main reason the diet has become so popular is due to how effective the diet is for weight loss.

If you’re new to keto, you might be wondering how it works, so in this article that’s exactly what we’re going to cover.

To get going, let’s get back to basics and explain a few things in simple terms.

What is a Keto Diet?

The word keto is derived from the word ketosis which is a metabolic state where the body switches its main fuel source from glucose to ketones.

When glucose levels are depleted, the body accesses its fat stores and it breaks them down into fatty acids in the liver.

These fatty acids are then converted into molecules called ketone bodies which are used by the body for fuel.

Another term for ketosis is “ketogenesis” which basically means “generates ketones”.

There are three main ketone bodies: acetoacetate, acetone and beta-hydroxybutyrate (BhB).

From a metabolic standpoint, you're classed as being in the state of ketosis if your blood levels of BhB are above 0.5 mmol per litre.

There are four key ways that you can get into ketosis:

1. Keeping carbs very low in the diet
2. Fasting
3. Vigorous exercise
4. Exogenous ketone supplements

All of these methods are interesting; however, obviously the first one pertains to “diet” given that the thing being modified is carbohydrate.

In order to trigger the process of ketogenesis, we typically need to aim for a carbohydrate intake of less than 20-50g net carbs. When people achieve this, they are said to be “in ketosis”.

Net carbs = total carbs – fibre - polyols

You're in ketosis if your blood levels of BhB are above 0.5 mmol per litre.

The technical term for driving the process of ketogenesis through diet is called nutritional ketosis.

The keto diet, therefore, is one which encourages the body to switch its main fuel source from glucose to ketones through the process of ketogenesis.

“Keto”, “keto diet” and “ketogenic diet” all mean the same thing.

The best way to think about ketogenesis is that it is a secondary backup energy system which evolved over time to allow humans to survive and thrive during times of food scarcity.

In evolutionary terms, we were designed to be in ketosis on a regular basis and it has only been in modern times that we started to rely on carbs as our main source of energy.

It is that excess of carbs that is thought to be one of the main causes of many of the non-communicable diseases so common today, especially type 2 diabetes and obesity.

Keto has become so popular today because switching your main fuel source from carbs to fat has real potential to help reverse many of these conditions.

So Why is Keto So Effective for Weight Loss?

There are many reasons that the keto diet is thought to be so effective for weight loss, the main ones being as follows:

  • Lower insulin
  • Reduced appetite
  • Dietary restriction
  • Promotes behavioural changes
  • Ability to more easily incorporate fasting

If you have spent some time researching keto on the internet, there’s no doubt that the topic of insulin is front and centre.

However, opinions are very much divided about this in the scientific community, and it’s actually quite a controversial topic.

At one end of the spectrum, there’s a view that insulin is the key driver of weight gain and at the other, it’s all about Calories In v Calories Out (CICO).

Insulin and Weight Loss?

Insulin is a hormone released by the pancreas when blood glucose levels rise. It stabilizes blood glucose levels, has a number of important functions and plays a major role in metabolism.

For example, insulin helps glucose reach important tissues where it is used for energy and it is involved in the regulation of the macromolecules, such as protein, carbs and fat.

Insulin is also thought to play a critical role in body weight management, as one of the main functions of insulin is to store excess energy.

This is why insulin is sometimes referred to as a storage hormone.

While glucose is used by several tissues, it is the activity in the liver that is most important for weight management.

Insulin promotes the uptake of glucose from the blood into the liver where glucose is either converted into glycogen for storage in the muscles or into triglycerides which are stored as adipose tissue. Insulin is required for and facilitates both of these processes.

The pancreas also secretes another important hormone called glucagon which has the opposite effect of insulin. While insulin promotes the storage of excess energy, glucagon’s role is to break down things in the body to provide energy. Another role of insulin is to suppress the function of glucagon.

The Carbohydrate Insulin Model of Obesity (CIM)

The Carbohydrate Insulin Model of Obesity, or CIM as it has become known, is one advocated by the famous author Gary Taubes.

In a nutshell, CIM proposes that obesity is primarily caused by the consumption of high-glycemic carbs which produces hormonal changes which promote increased adipose tissue, exacerbated hunger and lower energy expenditure (Ludwig 2018).

This reduces levels of circulating glucose and free fatty acids, shunts fat into fat cells, and makes us fat, hungry, and sluggish.

According to CIM, high calorie intake and low calorie expenditure are a result of expanding fat tissue, not its cause.

But what does that mean for calories?

Do calories matter on keto?

Primarily due to the CIM, a question that comes up time and time again is: do calories matter on keto?

The answer to that is simple: of course they do.

The calories in calories out (CICO) the model is very simple. If you consume more calories than you burn you’ll gain weight, if you consume less calories than you burn, you’ll lose weight.

This model has been the accepted energy balance model for decades, and what many people misunderstand is that the CIM model still agrees with CICO, even though they are seen as two vehemently opposing models.

The main issue with CIM is that Taubes, and other low-carb proponents such as Dr. Jason Fung, have gone as far as to publicly state that it is not possible to gain weight at all if insulin levels are low.

Meaning, a high carb diet is REQUIRED for weight gain, and a low-carb diet is REQUIRED for weight loss.

So, hang on a minute here!

Obviously this claim has been seriously baulked at in the scientific community as it flies in the face of the CICO model altogether.

In my own personal experience, I really struggle to maintain weight on keto and, in fact, I do much better on a high carb diet and counting calories when it comes to getting lean.

Also, if this this were true, everyone who follows a keto diet would be very lean, which we know is not the case.

Obviously the idea that it’s all about insulin, and calories don’t matter, is hard to reconcile with decades of research into metabolism for decades.

But anyone who works with individuals knows that there are cases where a calorie deficit does not work, so there is definitely something going on where the CICO model doesn’t fit.


This leaves us with two very opposing views on insulin.

In the Calories in Calorie Out camp, people believe that it’s all about getting the energy balance right and that people just need to be more disciplined.

In the CIM camp, people believe CICO doesn’t work and that insulin is the only factor.

These are two very extreme view points, but could there be a meeting in middle somewhere?

Personally, I very much believe in CICO as it is backed by decades of research and it has worked for me personally and millions worldwide. It just makes sense.

But I have also worked with people who have been achieving a strict calorie deficit and still not lost weight. Now, either these people are completely lying to themselves, or there is something else going on for some people.

Whether that thing is insulin or not is still yet to be decided, but with all research, it’s best to keep an open mind with as there is always plenty of research supporting both sides of the argument.

CICO versus Counting Calories

Personally I feel that people in the keto community might well be getting confused between CICO and “counting calories”.

Many people have tried the CICO model and failed, but as soon as they switch to keto, they have major success.

And because they are counting carbs instead of calories, they believe that CICO does not work, but what they really mean is “counting calories” doesn’t work.

A simple thought experiment proves that you still need to treat the calories in calories out model with respect as there’s obviously a threshold where excess calories will still result in weight gain.

For example, if you’re only burning 1,000 calories of energy per day, but you’re consuming 10,000 calories worth of energy, your body will need to do SOMETHING with that 9,000 calories of excess energy.

What else could be going on?

Whether insulin in “the” thing in terms of weight loss is a moot point as what’s clinically clear is that keto works.

One of the major benefits of switching to low-carb is how it reprograms your body when it comes to satiation and ultimately it simply does not feel like you’re on a “diet”.

Let me explain why.

When your main fuel source is carbs, because glucose is metabolised quickly, you experience the feeling of hunger regularly throughout the day. Everyone is familiar with glucose highs and lows.

Now, that can be managed if you choose complex carbs such as wholewheat breads, pasta and rice instead of simple carbs such as refined sugar, white breads and pasta, BUT carbs are still sugars.

The more complex carbs are essentially just longer molecules of sugar, so whilst you may delay the onset of hunger by selecting more complex carbs, the hunger is still coming.

And the thing with the hunger for carbs, the body essentially CRAVES another glucose hit and it can be quite a painful feeling. This is why sugar addiction is sometimes compared to addiction to hard drugs.

Eventually, as you become more adapted to keto, you will feel much less hungry and will regain control of your appetite.

Because of this, you will rarely overeat and you’ll be able to easily incorporate fasting into your lifestyle.

Moreover, the vast majority of people also clean up their diets, switching from unhealthy processed foods to clean, quality wholefoods.

This behavioural reprogramming is why keto is so great for weight loss. Your body will more naturally regulate appetite so you do not need to count calories and you will rarely overeat because the feeling of hunger is different.

On top of that, fatty foods are also delicious so you can continue to really enjoy your meals.

It is for these reasons that keto is referred to as a way of eating or a lifestyle change rather than a diet. This is why it is so successful - it is not a diet; but rather a longer-term lifestyle choice.

Final word

Personally I believe that the sweet spot in terms of weight loss is having a handle on your calories and eating proper wholefoods, regardless of your carb intake.

If this doesn’t work for you, then switching to keto is a great option which has a high chance of success.

If you’ve tried everything and never succeeded, I would highly recommend giving keto a go.

About the Author

Lee Sandwith holds a Masters Degree in Clinical Nutrition and is a registered nutritionist with the Association for Nutrition. You can book a free 30 minute consultation with Lee here.


  • Ludwig DS, Ebbeling CB. The Carbohydrate-Insulin Model of Obesity: Beyond "Calories In, Calories Out". JAMA Intern Med. 2018 Aug 1;178(8):1098-1103. doi: 10.1001/jamainternmed.2018.2933. PMID: 29971406; PMCID: PMC6082688.
  • Ludwig DS, Majzoub JA, Al-Zahrani A, Dallal GE, Blanco I, Roberts SB. High glycemic index foods, overeating, and obesity. Pediatrics. 1999 Mar;103(3):E26. doi: 10.1542/peds.103.3.e26. PMID: 10049982.
  • Hall KD, Guyenet SJ, Leibel RL. The Carbohydrate-Insulin Model of Obesity Is Difficult to Reconcile With Current Evidence. JAMA Intern Med. 2018 Aug 1;178(8):1103-1105. doi: 10.1001/jamainternmed.2018.2920. PMID: 29971320.
  • Speakman JR, Hall KD. Carbohydrates, insulin, and obesity. Science. 2021 May 7;372(6542):577-578. doi: 10.1126/science.aav0448. PMID: 33958466.

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