<  Previous: How our body works III

In the previous articles we briefly looked at carbohydrates, proteins and how they affect insulin levels in our body.

So let's start bringing dietary fat into the conversation. And we'll do it by looking at three studies.

INSULIN AND LIPOLYSIS

Let's remember our now classic graph and what we said in "How Our Body Works II"

• When insulin levels are high, the body stores glucose as fat to use as an energy source in the future.
• When insulin levels are low, the body uses this stored energy.

In 1996 it became a study on animals and humansduring which huge doses of glucose and insulin were given. Although the purpose of the research was to look at the flow of fatty acids to the mitochondria, we are interested in something else that was observed.

Fat oxidation was reduced by 43%. What we would call "fat burning" did not stop even under these supernatural doses of insulin and glucose. Only the rate slowed down. Let me make it a little clearer for those who lost.

As we said, homeostasis should be considered as a thermostat and not as a switch. In short, the processes of the body never stop. And to be even clearer, this means that as you can see from our graph, insulin and glucagon are constantly being secreted. They simply decrease or increase in their levels.

You keep gaining fat and you keep losing fat. The process of lipolysis does not stop and any other approach would be naive to say the least.

THE BODY DOES NOT WANT TO CONVERT CARBOHYDRATES INTO FAT

A catchy and provocative title, you can't say. After everything you've heard from diet gurus, celebrities, TV shows and the internet, here I come and tell you something like this.

And yet it is true. 1988 survey this time. After 3 days of a hypocaloric, low-carbohydrate diet, the people who took part gradually ate more and more over a week.

They started with 3600Kcal and at the end of the week, their daily calorie intake was 5000Kcal. The macronutrient partitioning of the diet was 11% protein, 3% fat, 86% carbohydrate.

Carbohydrates alone exceeded their daily calorie requirements. Pure madness. Shall we see what happened?

Remember, we start on the fourth day, the previous three were the diet. So we notice that although the carbohydrate intake is incredibly high, on the first day we also have high levels of carbohydrate oxidation.

From the next day until the end of the week we see a gradual increase in de novo lipogenesis, or in short, fatty acid synthesis. But this becomes significant after carbohydrate oxidation, which remains high. The body wants first of all to "burn" the carbohydrates and then the fat.

CARBOHYDRATES AND LIPOGENESIS

If the previous survey is not enough for you, let's move on to a third and final one. This is the "McDevitt RM, Bott SJ, Harding M, et al. De novo lipogenesis during controlled overfeeding with sucrose or glucose in lean and obese women. Am J Clin Nutr. 2001 Dec;74(6):737-46. DOI: 10.1093/ajcn/74.6.737".

Here the diet was 50% above the daily requirements of those taking part, while the macronutrient partitioning of the diet was 50% carbohydrate, 42% fat and 8% protein.

The results were dramatic, with de novo lipogenesis increasing dramatically.

But the thing is that of the 1398g of carbohydrates given (5592 calories!) 1280 (5120 calories) were oxidized, while of the total new 282g of fat, only 4 were due to de novo lipogenesis from the carbohydrates!

I think we have a clear picture now:

• The body doesn't want to turn carbohydrates into fat, and oxidizing them is a priority.
• In fact, when insulin levels are high, not only is glucose stored as fat, but also dietary fat.
• Although it is possible to build up fat from carbohydrates, this will occur under extreme conditions of overeating.
• Carbohydrate consumption and insulin secretion by the pancreas do not freeze the lipolysis process, but slow it down.

Don't tell me, it was good for an article, wasn't it? Didn't we bust a lot of myths and learn a lot of facts about how our bodies work?

So more next time!

Update 25/01/2019: New research finds that a low-fat diet, even if high in sugar and calories, can reduce liver fat, unlike a diet that is low in calories but high in fat. The reduction in liver fat is apparently due to the difference in de novo lipogenesis.
Surowska A, Jegatheesan P, Campos V, et al. Effects of Dietary Protein and Fat Content on Intrahepatocellular and Intramyocellular Lipids during a 6-Day Hypercaloric, High Sucrose Diet: a Randomized Controlled Trial in Normal Weight Healthy Subjects. nutrients. 2019 Jan 21;11(1). pii: E209. doi: 10.3390/nu11010209.