Myth 1: Fat makes you - fat(ter)

In my first post "The more I tried, the more I failed", I have stated three fundamental, but controversial statements of LCHF. I will explore them one by one. The first and the most important statement of LCHF is:

It is the carbohydrates, not fat, that make us fat.

When I told it to my friends, and tried to explain it to them a bit, they found it very difficult to accept. I think that in the end, some of them may have accepted it on the rational level, but I could see in their eyes that a part of them strongly felt that I should start being more careful at choosing my mushrooms on the local market.

But let's think about it a little. What happens in our body when we eat carbs and what when we eat fat?



Let's look at carbs first. When we eat carbohydrates (potatoes, rice, pasta, bread, sweets...), our body first breaks them down into their basic building blocks: glucose. Glucose is our fuel and all cells in our body can use it for energy. Most of the cells may also use other things as fuel, but more on that later. Carbs are easily and quickly digested and soon after eating them, a bunch of glucose enters our bloodstream. Our body responds by producing insulin - a hormone responsible to quickly push glucose from our bloodstream into our cells, which then use it as energy.

Unless we eat very small amounts of carbohydrates, the amount of glucose in our bloodstream is way over our energy requirements of that moment (that last bit of the sentence is important). Therefore, there is an excess of glucose which can't be immediately used by our cells. Our body starts storing this excess glucose for later use and insulin plays a major role here. There are three possible places for storage and they are used as stated in below order:

1. In our liver, as glycogen.
2. In our muscles, as glycogen.
3. In our fatty cells, as fat.

This means than only when our liver and muscles are full, the last place is fatty cells. This means that the very moment when liver and muscles are full of glycogen, all excessive glucose is immediately converted into fat. It is worth pointing out that the usage of stored energy follows the same order. First, we burn glycogen in liver and muscles, and only then we resort to burning fat.

But what happens, when we eat fat?

Similarly as complex carbohydrates, fats need to be broken down into smaller building blocks before they can enter our bloodstream. The concept is similar as with carbs, but it takes a whole different digestive process to do that. It also takes more time and a bit more energy. First, bits of large fat molecules are mixed with digestive fluids and packed together with a bit of protein and a bit of cholesterol into "packages" called chylomicrons. Chylomicrons then enter our lymphatic system and from there they get into the bloodstream. They go all the way to the capillaries into the proximity of all kinds of cells, where they are finally broken down into basic building blocks: fatty acids and glycerol. These can enter the cells, where they are used either as energy, or are reconstructed back into fat for later usage.

This means, that if our cells don't need any energy, eating fat also makes us fat. But, if our cells are not getting energy from glucose, fat is burned for energy instead.

Another that happens in the absence of glucose is ketosis. This is the process when our body starts using fatty acids for energy instead of glucose. It is triggered by a long physical activity or by starvation. Most types of cells in our body can absorb fatty acids and use them for energy, but our brain cells can't. That's why liver starts using fat to generate new compounds called ketone bodies, which are soluble in blood and can be used by brain for energy. Therefore, in the absence of glucose, we start using fat for energy and even brain gets their own dose of energy in the form of ketones. To be exact, while digesting fats, our body creates a little bit of glucose as well. It comes from glycerol, one of basic components of fats. There is not a lot of glucose created from fat and it is created very slowly, hence insulin rises minimally. This can be seen at above graphs which compares insulin levels in the period of 6 hours after eating fats (black dots) and carbohydrates (white squares). It is clear that when eating carbohydrates, glucose level doubled within the hour, which is followed by a rush of insulin, which, between 1 and 4 hours after meal, pushed glucose out. On the other hand, when eating fat, not much has been happening in terms of glucose and insulin variations.

A lot of low fat diets advise you to eat plenty of small meals and exercise regularly. And a lot of studies show that these diets work, IF (and that's a big if) you manage to follow them. Small meals decrease the spikes of carbohydrates and exercising is regularly depleting glycogen reserves, at the same time inducing part time ketosis. But, the problem of these diets is that eating 5 to 6 small meals for many months and exercising for 1-2 hours three times a week requires a big change in lifestyle. And even then, ketosis as the most desired state is constantly switched on and off. Many people fail. Not because diets don't work, but because they require a great sacrifice.

LCHF offers an interesting alternative over most diets. By pretty much completely eliminating carbohydrates out of nutrition, there are no glucose/insulin spikes (see above graph), which means that after the reserves are depleted and body enters ketosis, it stays there, even without physical activity. Because there is never any elevated insulin, fatty cells open up to release our own stored fat whenever there is lack of nutrition. Our bloodstream is full of ketones and with plenty of fat to digest, therefore we are not hungry all them time.

In conclusion, if we have a surplus of energy, carbs and fats both make us fat. But, it is much easier to create surplus with carbohydrates than with fat. Hence, if you eat when you are hungry and not overeat yourself completely, carbohydrates make you fat, but fat doesn't.