A Fat Chance (Part THREE): The Nitty Gritty Science of the Metabolism of Fat

(written with the assistance of Dr. Richard Feinman)

Notice: This is the third article in an ongoing series. Make sure to check out the first and second parts before reading this one, and check out the last article in the series afterward!

• • A Fat Chance (Part ONE): Introduction
  • A Fat Chance (Part TWO): How and Why I Eat so Much Fat!
  • A Fat Chance (Part THREE): The Nitty Gritty Science of the Metabolism of Fat
  • A Fat Chance (Part FOUR): Fat, the Neuroprotector!

It seems so intuitive that eating fat makes one fat. This perception is indeed a common one, and is what I had been culturally influenced to believe throughout my life. In order for foods that any animal ingests to be stored as visceral fat (fat surrounding organs) or adipose tissue (body tissue containing stored fat), certain metabolic conversions need to take place. Our current perception of fat being the number one culprit of poor health in the USA has not only failed to reduce our weight, but this perception has also failed to reduce the number of heart attacks, strokes, cases of diabetes, insulin sensitivity, autism, Alzheimer’s, and hundreds of other mental and chronic diseases 7. I am not saying that a lack of fat is the cause of these chronic diseases. I am only pointing out that this disseminated perception, as well as the official USDA recommendations, do not seem to be working. So what have biochemistry textbooks told us about the metabolism of fat and fat storage?

I am not a biochemist, but in my quest to understand the human metabolism of fat, I had the opportunity to speak with Dr. Richard Feinman, a professor of cell biology at SUNY in Brooklyn, NY. Jimmy Moore had forwarded a complex metabolic question of mine to Dr. Feinman and told him to take a look at my website. I am so fortunate that Dr. Feinman then offered to help me to write this post. Over the months that we have been passing emails back and forth, I have grown fond of his self described down-to-earth and brutally honest demeanor. Dr. Feinman always attributes this approach to growing up in Brooklyn. Perhaps the reason that I appreciate this disposition is because, for 8 years, I called his hometown my own home as well.

It has been incredible working with them both, and despite my initial errors, Dr. Feinman expressed that I only missed the target a few times. Additionally, the misconceptions that I had turned out to be enlightening opportunities for me, as he was kind enough to take the time to clarify the areas that I was confused about. Hopefully this explanation will be equally enlightening for you.

It is now my understanding that the most prevalent pathway that results in the storage of fat occurs when glucose levels are high in the bloodstream (high blood sugar). If the body is functioning normally, when blood sugar is high, insulin is produced, which tells the body to store the extra glucose as glycogen. Glycogen is stored in the liver and muscles first, but there is a limit to how much glycogen the muscles and liver can store. After the glycogen stores of the liver and muscles are full, glycogen is then stored as visceral fat or adipose tissue that first accumulates around the belly. This is a fat storage that we have all observed or are familiar with personally. In fact, glycogen is being stored in both of these manners all of the time. The rapid rise in blood sugar caused by a high carbohydrate and sugar diet leads to fat storage using this pathway 8.

Sugar and carbohydrates raise blood sugar faster than any other nutrients that humans eat because they are broken down into glucose, which is what is measured in blood sugar, in ONE metabolic step 9. It is not as simple as putting the calories in consumed fat into storage fat. The diagrams of metabolic pathways in a biochemistry text can be compared to any regular map. For example, if I were to use a map to plan a trip from my home in Austin, TX to visit Dr. Feinman in Brooklyn, NY, there are many routes that I could take to get there. Analogously, there is a possibility of different routes being chosen for metabolism. Metabolic maps explain POSSIBLE ways to get from point A to point B, but they do not show you where the traffic lights are, where the heavy traffic is, where road closures and detours are, etc. In other words, metabolism is not your simple chemical reaction where A+B=C. (See this post on Dr. Feinman’s blog: Introduction to Metabolism. The Black Box of Life.)

The main traffic cop in metabolism is the hormone insulin. If there is a lot of insulin (which occurs when blood sugar is elevated), fatty acid traffic is directed into fat storage. When insulin levels increase, more traffic cops are around to tell the extra sugar to be stored as fat. This was an important concept for me to understand because more insulin is not usually produced by ingesting fats, but the amount of this hormone is most certainly elevated from sugars and carbohydrates 10, 22.

In an online nutrition course that I recently took, the instructor said “your body CAN convert fat and protein into glucose, but it would PREFER not to.” I remember thinking, “how do we determine what the body PREFERS to do? Does the body also PREFER not to exercise? My body almost always PREFERS not to get up in the morning.” It seems that she must have meant that the path of least resistance is the conversion of carbohydrates and sugar into glucose. This conversion is indeed the path of least resistance for the body to create glucose, which also makes it the easiest way for the body to end up with high blood sugar, leading to glycerol storage as fatty tissue 11.

Dr. Robert Atkins brought the idea of fueling the body with fat rather than carbohydrates to the mainstream with the Atkins diet. This approach seemed to over simplify metabolism by only encouraging people to eat a high fat/low carb diet. Dr. Atkins recognized that ATP, the compound that gives us energy, could be generated without carbs, and many people following his diet  began to fuel themselves using only meat and animal fats: many people opted to eat no vegetables because even fibrous, non-starchy vegetables contain a fair amount of carbohydrates.

Humans are omnivores, not carnivores, and the human gut contains about ten times as many bacterial cells than there are human cells in our entire body 19. This microbiome, as it is called, feed almost entirely on dietary fiber and carbohydrates (prebiotics). I do not eliminate either of these because I think that eliminating, or drastically limiting, any food that humans have been consuming for the entirety of our evolutionary history is not at all wise. Grains and dairy, on the other hand, are thought to have only been a substantial part of our species diet for about 7.5% of the existence of homosapiens (1,500 out of 200,000 years). That being said, I do eat some grains, and I certainly eat dairy in the form of butter, but I do not see a problem with drastically limiting both dairy and grains because they are both foods that our species survived and thrived without for over 90% of our existence 12.

Essentially, sugar and carbohydrates are more frequently and rapidly stored as fat than is consumed fat. Additionally, the process of burning adipose and visceral fat is more rapid when the body does not have sugars and carbohydrates to use as fuel. Finally, carbohydrates do not seem to be all bad. I highly caution against any dietary practice that eliminates or drastically limits foods that humans have been consuming for the majority of our evolution… so listen to your mother and “eat your veggies too!”

Get the Guide to Fats and Oils from the How to Feed a Brain book!

Go to part four, where I will share what I have learned about how and why fat is protective to the brain.

Read our article on Which Fats Are Healthy Fats