The Process of Digestion

When you ingest carbohydrates, they are broken down into glucose within the small intestine. This glucose is then released into the bloodstream via blood vessels. Next, let’s briefly explore how fats enter the bloodstream.

After consuming fats, they travel to the small intestine. However, fats do not enter the bloodstream directly through blood vessels due to the size of chylomicrons (which are lipoproteins primarily composed of triglycerides and cholesterol). Instead, these chylomicrons enter lymphatic vessels known as lacteals. These lacteals eventually drain into veins near the left and right thoracic duct, and from there, the fats are pumped into the bloodstream via the heart.

Why Combining Carbs and Fats Is a Bad Idea

Now that we have a basic understanding of how glucose and fats travel into the bloodstream, the question remains: why is it advisable to avoid eating carbohydrates and fats in the same meal? The answer lies in insulin!

Indeed, I’m being serious. Insulin is the key reason why combining large amounts of fats and carbohydrates in a single meal is not a good idea. As previously mentioned, when carbohydrates are consumed, insulin is released from the beta cells in the pancreas. This insulin binds to cell receptors, allowing the cells to "open up" because they require glucose for energy! Consequently, as blood glucose levels decrease, the fats from that creamy pasta are also circulating in the bloodstream alongside the glucose. So, what happens when insulin binds to the cells? Naturally, glucose and other nutrients enter the cells, but what else?

Fat!

Exactly! For those curious about how fats and sugars/carbohydrates make their way into fat cells, let’s dive a bit deeper into the science.

A Closer Look at Chylomicrons

Recall that chylomicrons are lipoproteins made up of a protein/phospholipid coating that carries cholesterol and triglycerides throughout the bloodstream. Upon entering the bloodstream, HDL (high-density lipoprotein) donates two crucial proteins: apo-C2 and apo-E.

The apo-C2 protein binds to lipoprotein lipases present in blood vessels. These lipases break down triglycerides into glycerol and free fatty acids. These free fatty acids then enter fat cells (adipocytes), and the glucose in the bloodstream also enters these cells due to the presence of insulin and GLUT-4 receptors.

The Transformation Process

Once inside the adipocytes, glucose can undergo glycolysis—the initial stage of cellular respiration, where glucose is converted into two pyruvates. This process leads to the formation of dihydroxyacetone phosphate, which can subsequently be converted into glycerol. This glycerol can then transform into glycerol-3-phosphate.

At this point, you have fatty acids from the fats consumed and glycerol-3-phosphate from the carbohydrates. These components can combine within the adipocytes to form triglycerides or fat, facilitated by acyl-transferase enzymes.

The Bottom Line

There’s so much more science behind this, but it’s fascinating to realize that all this is happening within us! This is why I firmly believe that what you eat truly matters. It makes sense, right? For example, I would likely accumulate more fat inside my cells if I consumed 1000 calories primarily from carbohydrates and fats compared to 1000 calories from mostly proteins and fats.

Even if the caloric intake is the same, the types of food consumed still have significant implications. Consuming the same number of calories in two different meals can lead to differing effects on fat accumulation—one meal could contribute to more fat gain (carbohydrates and fats) while another (proteins and fats or a different combination) might not.

If you want to learn more about the impacts of different food combinations, check out these videos:

This video delves into why mixing fats and carbs can hinder weight loss, presenting the top rule for achieving your diet goals.

In this video, Dr. Berg explores the effects of food combinations, specifically the differences between fat with carbs and fat with protein.