Wednesday, August 31, 2011

Fat Metabolism for Better Health

After summarizing years of research into carbohydrate structure and metabolism, I had occasion to turn back to fat metabolism this week after running into a very knowledgeable Paleo enthusiast.

I discovered a couple of interesting branches of research on the Google Safaris that followed. One suggests that it is not caloric restriction in general that promotes longevity, but restriction of protein, and the other, restriction of carbohydrate. Both of these findings have been published in just the last 5 years.

What was more interesting to me though, was to understand how fat, or fatty acids in particular - as opposed to the glycerol that's also part of triglycerides - is actually metabolized by cells (Cellular Uptake of Fatty Acids), both adipose cells that store fat, and muscle cells that power the large skeletal muscles, through a pathway that requires zero insulin.

Also of interest is that 18 of the 20 amino acids in proteins can be converted to glucose via gluconeogenesis, and are the major source of energy in large skeletal muscles when catabolic muscle destruction takes place. When you eat too much protein, or incomplete protein, it's burned as carbs. By contrast, only the glycerin part of triglycerides can be converted to glucose.

Here's the exciting thing for cyclists and other endurance athletes. Fatty acids, which supply up to half of total energy needed for endurance athletes, have a completely separate, and parallel metabolic pathway from glucose, and can transition through the cell wall and into the cell mitochondria WITHOUT the aid of insulin. The implications of this are so far-reaching that I am still coming to grips with it. But already a few things are clear.

First, super-surges in strength almost certainly occur when energy demands are fed both through fatty acids AND high glucose levels while insulin levels are very high. This condition  would occur after 5-10 minutes of relative rest, say to 50-60% of max HR, when liver glycogen, and ride fuel digestion products, have been added together to create high blood glucose levels, and then the 6-minute insulin release cycle starts by dumping huge amounts of insulin into the blood. If this were to occur when maximal fatty acids are available to the muscle cell, and sufficient oxygen is available, the muscle cells have as much fuel and oxidizer as they can ever hope to use.

Second, this explains why so many are suffering with metabolic syndrome, obesity, and type II diabetes. When you eat either carbs, or protein (via gluconeogenesis) your body cannot immediately use, you use the carbohydrate, small intestine, insulin pathway to fuel the cell's mitochondria. Worse, there is some good evidence from research at UCSF that insulin is the primary cause of aging via the "Grim Reaper" gene.

When  you eat, or use fat stored in adipose tissue, only the small percentage of the triglycerides that is glycerol can be converted to glucose, and digested via the aqueous environment of the small intestine. Almost all of the energy in fat, in the form of fatty acids, is digested into the bloodstream by the liver with the help of bile salts, and those fatty acids are available to the cell directly, in a completely separate pathway, where insulin plays no role. Fatty acids are always a ready fuel, ready to go, delivered by their own private digestion pathway, and they never become toxic like glucose does in hyperglycemia.

Since the energy density of fatty acids is much greater than glucose, and elevated fatty acid levels are not toxic like glucose, the fat-based energy cycle doesn't have to be as tightly controlled as the glucose-based cycle. The glucose-based cycle is regulated against excess by adipose tissue mopping up glucose when there is no immediate demand from muscle, so sedentary consumption of carbs must result in storing fat to prevent hyperglycemia. The required speed of adipose mitigation of glucose levels depends of the GI of the carb.

By contrast the liver digests fat into the bloodstream, pulls it back out when VLDLs get too high, can convert stored glycogen into glucose, can convert fat's glycerin to glucose, and can absorb up to 2,000 calories worth of glucose in the form of glycogen. In short, it's a much more complete and flexible organ for regulating energy levels than is the pancreas, but you have to give it some fat to work with.

The push to move people to high carb, low fat diets has led us to run almost an entirely insulin-driven metabolism, both for powering muscle, and for storing fat. This is in contrast to our historical diet of mostly fat and protein driven diets. As a result our pancreases are dangerously overworked for most of our lives, are failing in many people, and the muscle and fat cells in our bodies are forced to consume glucose and insulin instead of primarily fatty acids - with only small amounts of glucose from liver glycogen, converted amino acids, and glycerine to support exclusively glucose-fueled organs like the brain. Wild swings in energy levels has created an epidemic of ADD, ADHD, and other behavioral problems in the "bargain".

In short, we're trying to run a marathon on one leg!  It just doesn't work.

I'm always cautious when incorporating new information in my daily life, but I have been eating more omelets and have switched from skim milk to 1%. The effect on hunger is amazing. Tentatively, I intend to save carbs to fuel rides, and move more and more towards fat as part of the nutrient rich diet that I eat off the bike, sans carbo loading, and recovery.

On a personal note, I'm just stunned at the utter stupidity of the nutritionists who suggested this, or somehow believed a low fat diet was going to work out well. As Robert H. Lustig, MD, UCSF Professor of Pediatrics in the Division of Endocrinology in this excellent video shows, there were some strong dissenters from the stampede to carbs and away from fats.


When the entire population of the US is 25lbs heavier than they were 25 yrs ago, and we have an epidemic of childhood obesity in 6 month old children, it's hard to argue that obesity is caused by lazy slobs who just can't be bothered to get off their butts and exercise. Something more profound is going on, and this video lays it out pretty well.

Give your pancreas a rest. Eat some fat, and live a longer and healthier life.


Anonymous said...

Another great research you have done. Cool, thanks for sharing. Thomas and I both were stunned when we cut away the bread, flours and wheats and fast carbs and started eating fatty things as nuts and eggs. Good fat is GOOD and won't harm at all. But eat a thick slice of bread and woom...there it sits on your hips...LOL.

But eating some fast carbs after your workouts is totally ok and you need to if you are an endurance athlete. Eating the right things at the right time is key:-) I'm curious to see how your food change will change your life! Keep us posted!

Grey Beard said...

Good to hear that Stephanie. I'm a little embarrassed that it's taken me this long to get back to fat. I started out promoting it and got roundly shouted down at my bike club, so decided to try conventional wisdom first. I'm sure, as you say, it's the balance that is going to be critical.

The key point of this research is...

The level of glucose in the blood has to be regulated very tightly, because high levels of glucose in the blood are toxic and damage many, or maybe all of the organs in the body. Thus, when there is not a ready use for carbs, such as at least moderate exercise, the fat cells get tasked with mopping up the excess glucose to avoid toxic levels. Fatty acids in the blood don't have this problem!


Fat in the bloodstream is not toxic, and is not primarily regulated by insulin and adipose tissues, but by the liver. The liver digests fats into the bloodstream, and also pulls them back out if they get too high.

Thus, fats are not only much denser energy, but also don't need to be regulated tightly to avoid toxic effects.

The liver also converts fat's glycerin into glucose, and stores slow carb's glucose as glycogen, which are both processed to produce glucose on demand to maintain a healthy level of blood sugar. Thus the liver is a much more fleible and complete regulator of energy than the small intestine/pancreas/insulin pathway is.

In short, put your liver in charge of managing energy levels by eating fats, instead of your pancreas by eating carbs, and live a much healthier, more even-keeled life.

Gotta Run..Gotta Ride said...

As soon as we learn that some fats are good for us it opens up an entire new door to understanding what is not so good for us.

It always comes back to proper exercise and diet. Takes some work in the beginning but quickly becomes a way of life.