Insulin, Glucagon, and Fat Metabolism



by Jeff Cyr and Esmée La Fleur

Imagine you had a vehicle that would have two fuel tanks available to it. One would be a fuel tank of 10 gallons of gasoline. The other would be a fuel tank of 200 gallons of diesel. Your vehicle is capable of using both fuel sources. With the flip of a switch, you can change from one fuel source to the other.

Now imagine you are taking this vehicle on a cross country trip. Your tank of gasoline with 10 gallons of gasoline will allow you to travel 300 miles before having to stop and refuel. But, if you could simply flip the switch and and start using the 200 gallon tank of diesel, you could travel 6000 miles without needing to stop and refuel.

Like this vehicle, your body has the the ability to run on two different fuel sources: glucose (glycogen) or fat. If you eat a carbohydrate-based diet, you are only have access to stored glycogen (small gasoline tank) for energy. But if you eat a fat based diet, you now have access to stored body fat (large diesel tank) for energy.

Some people with good metabolic flexibility are able to go back and forth between these two fuel sources fairly easily, but people who are metabolically impaired like folks with type 2 diabetes or insulin resistance, cannot do this. When you have become metabolically inflexible, it is much more difficult to flip the switch that allows you to burn body fat.

Your liver stores 60-100 grams of glycogen and your muscles store 300-350 grams of glycogen. So, when you are dependent on glycogen (small gasoline tank) for energy, you have roughly 2000 stored calories available for use. This is not very much. However, most people have about 60,000 stored calories in the form of body fat (large diesel tank). When you are able to access your body fat, you have an almost endless supply of steady energy.

The thing that determines which fuel tank you can use is the balance between the hormones insulin and glucagon. If there is too much insulin being produced, as occurs in type 2 diabetics and people who are insulin resistant, you will only have access to glycogen (small gasoline tank) for energy. This is because insulin effectively locks the door to your stored body fat, making it inaccessible.However, the hormone glucagon is the key that will unlock that door, giving you access to stored body fat (large diesel tank) for energy any time you need it.

In order for you to be able to switch fuel tanks – going from glycogen (gasoline) to fat (diesel) – you have to lower your insulin levels. This can be a challenge for people with type 2 diabetes or insulin resistance because their body is literally flooded with insulin. The only way to reduce insulin levels is through diet and fasting.

There are three macronutrients for us to choose from: carbohydrate, protein, and fat.

Carbohydrate causes the pancreas to release insulin, while simultaneously preventing the pancreas from releasing glucagon. Therefore, if you eat a carbohydrate-dominant diet, you produce more insulin than glucagon, and this keeps your fat stores locked up tight.

A diet that is very low-to-no carbohydrate, moderate protein, and very high fat, will produce a lower level of total insulin, as well as a lower ratio of insulin to glucagon. This is because protein produces equal amounts of insulin and glucagon, while fat produces neither insulin nor glucagon.

So, when you eat a Low Carb or Zero Carb diet, you produce less insulin and more glucagon which gives you access to your stored body fat (large diesel tank) for energy, instead of being stuck with only your glucose (glycogen) storage tank (small gasoline tank). This means that you do not have to stop and re-fuel as often. It also means that you can lower your body fat percentage easier if this is one of your goals.

When you change your macronutrient ratios in favor of fat first and foremost, and protein secondarily, you will decrease the insulin and increase the glucagon produced in your body. This is the key that will allow you to unlock the door to your fat stores (large diesel tank) and use them for energy.

However, in order for this to happen, you must also limit your consumption of protein. Too much protein can keep insulin high, especially in people who are very insulin resistant. You can be quite insulin resistant without being a type 2 diabetic. In fact, Dr. Joseph Kraft, author of Diabetes Epidemic & You, recently found that 80% of people with normal blood glucose levels were – in fact – insulin resistant to one degree or another. So, the odds that you are insulin resistant is very, very high.

Eating a Zero Carb diet that is high in protein can prevent weight loss in people who are insulin resistant. The level of protein you can eat without raising your insulin depends on your level of insulin resistance. The more insulin resistant you are, the less protein you can eat without raising your insulin. Therefore, some people will have much more leeway than others in how much protein they can safely consume.

A person’s minimum protein requirement is 1 gm per kilogram of your healthy weight. That is what is need to replace and repair essential body tissues, hormones, and functions. How much more you can eat than this is best determined by testing you morning fasting blood glucose levels.

If your blood glucose is higher than 90 mg/dL (5.0 mmol/L) after an overnight 12 hour fast, then you may be eating too much protein for your particular metabolism. Many people can eat twice their minimum requirements without problems, but the only way to know your limit is to test yourself with a blood glucose meter.

In summary, if you want to lose body fat and have access to an almost unlimited source of energy, you need to lessen or completely remove carbohydrates (which will reduce insulin), include adequate protein (which will increase glucagon), and consume lots of fat (which is metabolically neutral and does not produce either insulin or glucagon). This will allow you to free yourself from a dependence on glycogen (small gasoline tank) for energy, and give you the ability to run on fat (large diesel tank) without having to re-fuel at frequent intervals.

If you run your engine (metabolism) on fat (large diesel tank), your vehicle (body) will operate more smoothly and will get a lot more miles to the gallon than it can ever get with glycogen (small gasoline tank).

11 thoughts on “Insulin, Glucagon, and Fat Metabolism

  1. Thanks so much for offering the great analogy with the gas versus diesel tanks. I do have a question, however, with what you write about the protein requirement of 1g/1kg. Would this number then be the daily protein allowance? Also, what do you mean by healthy weight? My current weight is not healthy for my height. (OK, I had two questions, instead of one.) So maybe the protein ratio would be too high. I want to transition my body to be a lean, mean, diesel-burning machine. I’ve been doing LCHF for nigh on four months with nary a visible loss of fat. Maybe I’ve had my ratios wrong, that is, too much protein and not enough fat. Lately I’ve been adding more fat, but I am looking forward to your concise answers. Thanks again!


    • Hi Jasmine, I wrote a companion piece to this article today to address your very questions, as you are not the only one who has asked them. I have asked several members of Principia Carnivora to review it for feedback and then I will publish it. So hopefully it will be out tomorrow.


  2. Pingback: Optimal Protein on a Zero Carb Diet | Eat Meat. Drink Water.

  3. Great post, Esmee & Jeff. I think your readers will really like a similar post I wrote a while back in a series I did on fuel partitioning. I also used the gas tank analogy, but in a slightly different angle, and went into a little more detail. (Some people might want to read it for that very reason, while others would purposely *not* read it, hehheh.) Either way, I’ll share the link for those who are interested:

    There’s also some interesting stuff about why killing yourself in the gym for hours and hours a day isn’t a magical path to fat loss.

    Liked by 1 person

  4. I enjoy the articles you post. I also write on related matters and appreciate the attention you give to details, something that, in my opinion, is not common enough these days. Anyway, I’ve written quite a bit about diabetes, and about glucose and fat metabolism. You and some of your readers might be interested. Here are two of them:


  5. “This is because protein produces equal amounts of insulin and glucagon, while fat produces neither insulin nor glucagon.

    So, when you eat a Low Carb or Zero Carb diet, you produce less insulin and more glucagon ”
    Does the first statement not contradict the second statement?


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