Keto Lie #5: Fat is a ‘free food’ because it doesn’t elicit an insulin response

The Carbohydrate – Insulin Hypothesis is one of the cornerstone beliefs of many who subscribe to low carb and keto diets. 

The theory is that because carbohydrates raise insulin the most and insulin is related to fat storage, eating more carbohydrates will lead to more fat storage on your body. Hence, dietary fat should be used as the primary energy source because it doesn’t impact blood sugar or insulin levels, so is effectively a ‘free food’.

Will more insulin make you fat?

Essentially, the Carbohydrate-Insulin Hypothesis says:

eat more carbohydrates -> make more insulin -> get fatter

Dr David Ludwig states that ‘insulin is like Miracle-Gro for your fat cells‘ and Dr Jason Fung says ‘I can make you fat.  I can make anybody fat.  I just need to give you enough insulin’. 

This theory is partially correct.  If someone injects excessive amounts of exogenous insulin, their liver will hold their stored energy back, the energy in their blood will decrease, and they will get extremely hungry and be compelled to eat more, and hence eat an excessive amount of food and thus gain fat.  

However, this ‘fun fact’ is completely irrelevant for the 98.5% of the population that has a working pancreas. 

So, unless you are injecting insulin to manage your Type 1 Diabetes or advanced Type 2 Diabetes, this is completely irrelevant!  It would be illegal for someone to go around jabbing you with a needle to inject you with insulin throughout the day.  They would be deemed a dangerous public nuisance and locked up. 

Your body is super-efficient.  It does not produce more of anything than it needs to.  Your pancreas will not release any more insulin than is required to keep your stored energy in storage, while food is coming in via your mouth. 

As shown in the chart below, total insulin demand across the day is positively correlated with your body mass index (BMI).  While correlation does not necessarily mean causation, it appears that your insulin requirement across the day is driven by the amount of energy that your body is holding in storage. 

Basal vs bolus insulin

People with Type 1 Diabetes know that they need to use basal insulin (to keep their blood sugars stable when they don’t eat) as well as bolus insulin (for their food). 

For people on a standard high-carb diet, basal insulin makes up around 50% of their total daily insulin, while the rest is injected to manage their meals.  However, for people on a low-carb or keto diet, basal insulin can make up as much as 90% of their total daily insulin requirements. 

So, unless you can switch off your insulin pump or choose not to take your injections and let your blood sugars run high, the only way to reduce the insulin produced by your pancreas is to focus on eating higher satiety foods that will enable you to consume less energy without having to exert unsustainable levels of willpower.

We don’t really understand the long-term insulin response to food

It is true that your pancreas produces more insulin in the short term in response to carbohydrates, followed by protein and then fat (note: fructose and fibre tend to have a negative impact).  See What affects your blood sugar and insulin (other than carbs)? for more details.

The data that we have from the Food Insulin Index testing suggest that fat has about 10% of the insulin response compared to carbs.  However, it’s critical to keep in mind that these insulin tests are only done over the first 2 hours after eating. 

We know very little about the long-term insulin response to the food we eat beyond 2 hours.  It appears that fat still elicits a significant insulin response in the fullness of time.

To illustrate, the chart below (from A plant-based, low-fat diet decreases ad libitum energy intake compared to an animal-based, ketogenic diet: An inpatient randomised controlled trial) shows how blood sugars respond differently to a 75% carbohydrate (PBLF (green line) = plant-based low-fat) vs a 75% fat (ABLC (red line) = animal-based low carb) diet.  Blood glucose rises quickly in response to low-fat foods, whereas they increase slowly with low-carb foods.  However, for both extremes, after 2 hours, blood sugars are still elevated above the baseline. 

Blood sugars and insulin rise and fall more quickly in response to a high-carb meal compared to a high-fat meal.  While it’s likely that less insulin is produced in response to fat compared to carbohydrates, calorie-for-calorie in the fullness of time, the insulin response to fat is still significant.  There’s a lot going on beyond the 2 hours that we have measurements for.  Hence, we can’t assume that there is a negligible insulin response to high-fat foods. 

I know anecdotally, from watching Moni’s closed-loop pump system, that a large steak will require continual insulin for up to 10 hours as it digests and is metabolised.  If she ever happens to eat something with carbs and fat together, her insulin requirements will be elevated for more than a day, with more insulin required to keep blood sugars suppressed.  There’s a lot going on beyond the 2 hours that we have measurements for.  Hence, we can’t assume that there is a negligible insulin response to high-fat foods. 

Oxidative priority

A little-known fact when it comes to nutrition and metabolism is that the order your body burns fuels is inversely proportional to the capacity your body has to store those fuels.  This is known as oxidative priority or oxidative hierarchy

The table below shows the relative priority that alcohol, ketones, glucose and fat are used in your body (adapted from Oxidative Priority, Meal Frequency, and the Energy Economy of Food and Activity: Implications for Longevity, Obesity, and Cardiometabolic Disease by Cronise et al., 2017). 

 AlcoholKetonesExcess proteinGlucoseFatty acidsBody fat
UseEnergyEnergyEnergy & excretionEnergyEnergyStorage
Capacity (calories)20201200 – 200015040,000 – 500,000
Thermic effect15%3%20 – 35%5 – 15%3 – 15%3 – 15%

We have minimal capacity to store alcohol, ketones and excess protein (i.e. beyond what you require for muscle protein synthesis and all your other critical bodily functions).  Your body raises insulin to abruptly shut off the release of stored energy until it disposes of these fuels. 

Your body has some capacity to store glucose, but not a lot, so we also see a more aggressive insulin response to carbohydrates.  However, your body is more than happy to hold fat in your adipose tissue (i.e. your butt, tummy or muffin top).  Hence, the insulin response for fat is less acute. 

Because fat has a lower thermic effect compared to the other fuels, it is much easier to store.  While protein and carbs are difficult to convert to fat for storage, it’s much easier for dietary fat to be stored as body fat.  So any fat that’s leftover (i.e. once you’ve burned through the alcohol, carbs and excess protein) is easily stored as fat on your body.

Your pancreas raises insulin to shut off the release of stored energy while it burns off the fuels that it doesn’t want to store.  The reason that we don’t see much of a rise in insulin in response to fat is that your body is more than happy to store it for later use!   

You can’t turn off your insulin!

Amongst people with Type 1 Diabetes, there is a dangerous practice called diabulimia, where they intentionally underdose their insulin to allow their blood sugars to run high to lose weight.  Their stored energy will flow into their bloodstream and leads to dangerously high blood sugars, ketones and free fatty acids in the blood (and potentially the life-threatening state known as Diabetic Ketoacidosis) as well as horrific levels of muscle wastage. 

When my wife Monica was first diagnosed with Type 1 Diabetes, she was losing 0.5 kg per day!  She would have wasted away and died in only a few days without injected insulin.  I’m explaining this horrific process because this is essentially what people who believe in the Carbohydrate-Insulin Hypothesis think will happen to them when they reduce the carbohydrates in their diet.  This is simply not the case.  They don’t really understand what they are hoping for.  Uncontrolled Type 1 Diabetes is a truly terrible disease, and you can’t inflict it on yourself by avoiding carbs and/or protein! 

To understand how much insulin is required for the different macronutrients in the fullness of time, the experiment I would love to see done is to have a large number of people with Type 1 Diabetes track their food meticulously, both on a high- and low-carb diet and correlate their total daily dose of insulin with their calorie, protein, fat and carbohydrate intake.  If anyone can get that data to me, I would love to analyse it.  Until then, we won’t know precisely how much insulin is required across the day for the different macronutrients. 

What we do know is:

  • the limited insulin data that we have only considered the first 2 hours, so the full insulin demand of our food is still very poorly understood, especially for fat, which has a slower and longer insulin response after eating;
  • because your body has to burn off carbs and excess protein, your body releases more insulin to shut off the release of stored body fat while you use up the fuels that it can’t store much of.  Meanwhile, it is easy to store fat, and you have a lot of room to store it, so the insulin response after eating it is much lower;
  • most of the insulin produced by your pancreas is required to hold your fat in storage, so the best way to reduce insulin is to find a way of eating that allows you to eat less without excessive self-restraint. 

How to reduce your insulin levels across the day

While we don’t have data for the long-term response to the different macronutrients, I do have data for Monica’s total daily insulin dose for the past 10 years. 

This chart shows how her insulin requirements have changed as we progressed from a standard higher-carb diet followed by low-carb, then low insulin load.  However, the lowest insulin requirements were when she participated in our Nutritional Optimisation Masterclass

The chart below shows Monica’s insulin dose in the period leading up to and during the first Nutritional Optimisation Masterclass that we did together, with her daily insulin demand dropping from the high twenties to the teens. 

To be clear, Type 1 Diabetes cannot be cured or reversed.  Monica’s pancreas still produces no insulin.  However, the insulin she needs to take has been vastly reduced by optimising both her food choices and reducing her body fat levels. 

During the Masterclass, Monica was able to lose 7.5 kg or 10.7% of her body weight during the 6-week challenge.  These photos show us both before and after 6 weeks. 

The main difference from Monica’s previous diet was a reduction in her intake of nuts, cheese and cream, which are useful to help stabilise blood sugars, but not necessarily for fat loss or reducing insulin across the day. 

Although high-fat foods cause a slower and more stable insulin response, they still affect insulin requirements across the whole day.   While low-carb foods like nuts, cheese and cream can be an excellent way for people managing diabetes to obtain adequate energy while maintaining stable blood sugars, they also appear to trigger a long-term insulin response.

Reducing those foods improves satiety, reduces overall energy intake, which lowers insulin across the day and allows body fat to be used.

Anecdotally, I’ve heard from a number of other people with Type 1 Diabetes who saw their daily insulin requirements dramatically increase and their insulin sensitivity drop when they jumped on the high-fat keto trend.  Allison Herschede, a co-founder of the Type 1 Grit Facebook Group, found her total daily dose of insulin doubled on a 90% fat ketogenic diet. 

Allison said, ‘It was like injecting water.  I realised the only time I had high ketone levels was when I was insulin resistant.  The only time I ever had high ketones was when I was on 90% fat’.  During her high-fat keto experimentation, her HbA1c went up to 8% but has now returned to 4.8% after following our nutrient-dense, high-satiety meals. 

Focusing on nutrient-dense, higher satiety foods tends to reduce overall insulin requirements across the day, not just immediately after meals.  By focusing on nutrient density, you are also able to get the nutrients you need with fewer calories, improve satiety and eat less!

What is really happening?

So rather than:

eat more carbohydrates -> make more insulin -> get fatter

what appears to be driving obesity is:

low satiety nutrient-poor foods -> increased cravings and appetite -> increased energy intake -> fat storage -> increased daily insulin

Reducing the processed carbs in your diet will help stabilise your blood sugars (i.e. symptom management).  But if you want to lower your insulin requirements, reverse Type 2 Diabetes and attack energy toxicity (the root cause of most of our metabolic disease), you should prioritise nutrient-dense, high-satiety foods and meals that will enable you to reduce your insulin levels across the whole day.

The real solution to managing Type 2 Diabetes, blood sugar, insulin levels and avoiding the myriad of complications of metabolic syndrome is:

high-satiety nutrient-dense foods and meals -> decreased cravings and appetite -> decreased energy intake -> fat loss -> optimised insulin levels

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