• Marcus Baxby

The Insulin Hypothesis and Low Carb Diets - A Basic Guide

Updated: Apr 28

You may have heard that low carb diets are the best way to lose fat, maintain health and generally win at life. This is false.


Unfortunately, there is still a large band of zealots who believe this to be true, and who will defend their stance to the hilt, even in the face of contrary evidence.


The underlying argument / reasoning for the evangelisation of low carb diets is known as the Insulin hypothesis.


Here's the truth - this hypothesis has been tested, time and time again, and been disproven time and time again, but in spite of this, there are still many who are 'loyal' to the idea that low carb is superior, for everyone, to every other diet.


Now - if you've heard about the insulin hypothesis, you may have been drawn in by the lofty positions of some of its proponents, many of whom are Doctors, and/or are endorsed by celebrities or athletes.


If you haven't, I'll save you some time - energy balance, not carbs or insulin, is the Principle behind all fat loss.


If you eat and drink more than you use, you will gain weight. If you use more than you eat and drink, you will lose weight.


The reason that people are 'loyal' to low carb is invariably that it is the method that has worked for them. A method, let's remember, that has helped them to create an energy deficit (adhering to the Principle of Energy Balance), and thus lose weight and/or improve their health.


Here are a few warning signs that a person may be a low-carb zealot:


‘Not all calories are created equal’

‘Sugar is addictive and is the cause of the obesity crisis’

‘Carbs spike insulin which causes fat storage/traps fat in cells - we should avoid spiking insulin’

'Most people are insulin resistant because of eating carbs'

‘Carbs make people hungry and cause over-eating’

‘People lose more weight on low carb’


So let’s tackle these one by one:


‘Not all calories are created equal’

What people are generally referring to is nutrient density. Yes - certain foods contain more nutrients than others. These micronutrients are excellent for overall health, and that’s why we encourage eating a variety of whole foods. However, in terms of calories, the calorie is a unit of measurement - when it comes to weight loss, it has been proven time and time again that energy balance is the underlying principle, and that, regardless of the ‘quality’ of the diet, a calorie deficit will produce weight loss. [Calories are King] A famous example of this is the Twinkie Diet, which while perhaps not optimal for health in the long term, elicited fat loss due to energy deficit, and thus improved health markers in the short term.


‘Sugar is addictive’

Sugar does not create a physiological dependency in the same way as certain drugs. However, there are such things as hyper palatable foods, which are frequently combinations of sugar and fat, and which are notoriously difficult to stop eating.

This is a separate topic, which will be discussed in another post, but suffice to say that sugar is not addictive!


'Carbs spike insulin which stops fat burning/causes fat storage/traps fat in cells - we should avoid spiking insulin' This is an incomplete understanding of the role of insulin. The human body will always seek homeostasis - ie. a constant internal environment. An easy example is body temperature - a healthy body maintains its temperature by either making or releasing heat to keep it at around 37 degrees.

The relationship between glucose and insulin is similar. At a very basic level, chronically high blood glucose is toxic. Insulin is a hormone released to counter-act blood glucose, and bring it back to normal levels. When insulin is released, nutrients (including protein, carbs and fats), are pushed into cells. The release of insulin temporarily halts the use of fat as a fuel source, because it temporarily increases the use of carbohydrate as a fuel source (to get rid of the glucose in the blood).

Once this carbohydrate has been used, the body returns to homeostasis, and to normal levels of fat and carbohydrate usage.

Only in a chronic energy surplus (i.e. eating more than you are using) will fat be stored as body fat.


'Most people are insulin resistant because of eating carbs' Insulin is only elevated very temporarily (after eating), and quickly returns to normal in healthy individuals. The repeated eating of carbohydrates (and corresponding release of insulin) doesn't cause fat gain or cause the pancreas to 'wear out' or release more insulin to cause insulin resitance or diabetes.

Diabetes is a separate topic that will be discussed on a separate post, but again, energy balance, lack of movement and unhealthy lifestyle is the primary cause.


‘Carbs make people hungry and cause over-eating’

The insulin hypothesis says that because insulin is being raised and bringing blood glucose down, low blood glucose then causes hunger. In fact, blood glucose is just being brought down to 'normal' levels, and the scientific studies have shown that there is no relationship between the insulin response of a food, and feelings of fullness.

We have mentioned before about hyper-pallatable foods that contain carbs and fats, and this is likely where the 'over-eating' concept arises.

'People lose more weight on low-carb'

At face value - this one seems to have some truth to it. Low carb diets do often elicit more weight loss.


One reason is that water is stored with carbohydrates - therefore once carbohydrates are cut out from the diet, and stored carbohydrates are used in the body, people lose weight due to also storing less water. Quick weight loss on low carb is therefore often due to water, not body fat.

In addition, telling someone to eat low carb quite often lowers calories by default (they remove high-calorie foods and/or hyper-palatable foods such as bread, pizza, biscuits, crisps etc), increases volume of the diet, and increases protein, which we know is very satiating and leads people to eat less (see protein blog post).


A low carb diet may therefore be easier for people to adhere to within a calorie deficit when they are not measuring calories directly.


This is why telling people to cut out carbs often 'works' in the short term, but very often people don't know what to do once the carb-cutting period is over, and tend to put weight back on.


When studies match the calorie and protein content of diets that are low-carb, low-fat and any combination of carbs and fats, it is clear that there is no difference in fat loss. This has been studied so many times that it is now unequivocal - energy balance (calories in vs calories out) is the Principle to which all diets adhere. If you eat less than you use, you will lose fat.

Take home points:

Being a Doctor doesn't automatically mean that you are correct about nutrition.

Low carb zealots are numerous, and misinformed.

Calories are King [one of our Core Principles] - Energy Balance, not carbohydrates, makes the difference for fat loss (and the associated health benefits).

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Knutsford, Cheshire, England, United Kingdom

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