Why do low-carb diets work? The insulin hypothesis

(versión en español: pinchar aquí)

If what you say about insulin is true, how can health authorities recommend to base on carbs more than half of our food intake? How can grain be the basement on the food pyramid?

That’s the question a friend of mine asked me this morning. My answer: «Low-carb diets do work and are healthy, according to scientific studies. And it is so even if the «insulin hypothesis» were wrong. «

Insulin hypothesis

This theory says that carbs raise blood sugar levels, which causes an increase of blood insulin levels in order to reduce the glucose levels. Insulin is the main hormone involved in the regulation of fat breakdown: if the level of insulin is low, fat is released from the adipocyte, if the level is high fat is stored. Low-carb diets keep the levels of glucose and insulin low, thus allowing our body to burn the stored fat and lose weight or maintain it.

Which foods raise glucose and insulin? Carbohydrates. Proteins also raise insulin, but it is «irrelevant» in the sense that we don’t want to play with our protein intake: we need a minimum but we shouldn’t eat too much. If the amount of protein is fixed, the question is, what else do we eat? Carbs or fat?

Of course this is a simplification, because the human body is very complex, but explanations for people like me, who are not experts in these matters, should leave the details aside and go to the basics.

Is that so? Is really insulin the hormone that makes us fat? The following figure (see origin) shows the effect of insulin concentration in a fat cell (adipocyte): when insulin levels increase the rate of conversion of glucose into fat increases (white dots), while the rate of release of fat (black dots, lipolysis) decreases.

F1largeThat is, if the concentration of insulin rises, the adipocyte absorbs more fat and releases less fat, i.e. gets fat. Are we misinterpreting the graph? I do not think so; the text of the article reads as follows:

These dual actions are illustrated in Fig. 1, where insulin’s well recognized action in stimulating lipogenesis from glucose (in rat adipocytes) is illustrated. What perhaps is less well known is insulin’s simultaneous inhibitory action on lipolysis.

Nobody doubts that insulin inhibits the «fat burning» process.

«The great medical disconnect»

If our cells get fat by an excess of insulin, and saying that we get fat is the same as saying that our cells get fat, how can they tell us that the cause of gaining weight is that we eat more calories than we spend? That’s what Gary Taubes and Peter Attia call «the great medical disconnect»:

«This is not controversial—if you go to an endocrinology textbook and look up what makes a fat cell fat, it’ll tell you all the ways insulin does it. Then you look up obesity, and it’ll say people get fat because they eat too much and exercise too little. There’s a complete disconnect between the fundamental science and the cause of human obesity.» Gary Taubes

Think about it: how does an adipocyte know we are eating too much and doing little exercise so it can decide to store fat instead of releasing it? Who tells him that? How does he do it? Does it know by magic? No. Fat cells in our body don’t receive that information: they receive the signal to accumulate fat, i.e. the rise in insulin levels.


In summary, assume that the blood insulin levels of a person throughout the day are shown in the following figure:


As long as the insulin level is low (zone highlighted in yellow), we are burning fat, but when the level is high (after breakfast, lunch and dinner) we are storing fat. Low-carb diets reduce the insulin spikes we see in the graph, maximizing the time insulin is low.

Answering the initial question: how can it be that the official diet recommendations base our eating on carbs, knowing the effect insulin has on our body? It is because of the fear of fat, the invention of stupid and zealots vegetarians and scientists (all of that mixed most of the time). Once the dogma «fat is bad» was imposed we had to eat more grains. And don’t forget who says we have to base our diet on grains: the United States Department of Agriculture (see). And the rest of the world following sheep-like their dogmas.

But let’s not forget the essential: carbs-based diets have skyrocketed the rates of obesity and diabetes worldwide, and it’s been scientifically proven that low-carb diets work and are healthy. Does it really matter if the insulin hypothesis is true?

Further reading:

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