A New Hypothesis of Obesity
As I suggested in my last post, you should watch the embedded video to study up for this post. In case you didn’t watch the video, or if you came to this post without having seen the previous one, I’ll embed the video below. I hate to do so, because the way YouTube shows the video caught me in an expression or whatever that makes me look 400 years old when the reality is that I’m only 300 years old. (If you would like to see how old I look in person, I’m speaking at Low-Carb Denver 2020. It’s not just for docs. Come by and say Hi. I would love to meet you.)
Let me explain a little about this video. I gave this talk at the big Low-Carb summit in Breckinridge, CO almost two years ago. I was given 30 minutes for the presentation, and I ran over. I had gone through the thing a few times before presenting, but for some reason, when I got going on the talk it went long by about 10-12 minutes. The organizer of the conference was in the front row going nuts.
Which I understand. I hate it when speakers go over, and I usually make it a point not to. When presenters go over their allotted time, they end up throwing the whole schedule off, and the people who get shafted are the attendees, because invariably the time is made up by cutting into the break time or lunch time or bar time at the end. I realized I was going to run over about halfway through, and so I picked up the pace. Had I not, the thing would have run over a lot longer.
Wasn’t that fun?
I’ve agonized over how to present all this more understandably. But it’s tough, because is complex biochemistry. After some reflection, I’ve decided to present it from the final result backwards to the precipitating cause. So, here goes.
How we get fat
This is going to sound simplistic, but we get fat by increasing the amount of fat in the fat cells.* What drives fat into the fat cells? Insulin. If the fat cells are sensitive to insulin, insulin will drive the processes that move fat into those cells. If the cells are insulin resistant, then the fat is turned away.
We’ve come to think of insulin resistance is a bad thing–and body wide, it surely is–but maybe it is part of the system that regulates how much fat gets into the fat cells. And maybe the shifting from insulin sensitivity to insulin resistance is a gateway controlling the amount of fat entering and staying in the fat cells.
I say maybe as this entire idea is hypothetical, not a proven fact. But the underlying physiology and biochemistry are pretty damn compelling.
If the insulin resistance is the gateway, what is the switch for the gateway? It could be ROS, which stands for reactive oxygen species, which is the scientific term for free radicals. As it turns out, free radicals are not the monsters they’ve been made out to be, at least not in all situations. It’s well known that ROS (which we’ll call them from now on) are signaling molecules. And they are an integral part of our immune system as well as contributors to many physiological functions.
ROS released from the mitochondria (the sausage-shaped organelles within the cells responsible for producing 85-90 percent of the energy required for life) accumulate and are converted to hydrogen peroxide, which then (also acting as a signaling molecule) induces insulin resistance in that cell.
How and why are the ROS that stimulate insulin resistance released from the mitochondria?
Well, this is where it gets a bit complicated, so hang in there
The energy of life
The currency of life is called adenosine triphosphate, aka ATP. Almost all of the billions of chemical reactions required to sustain life require energy to drive them and would never happen without it. ATP is that energy source. ATP breaks down and releases the energy needed to catalyze these life-maintaining reactions. Since these chemical reactions are happening constantly, we need a ready source of ATP to provide the needed energy. Fortunately, we are constantly synthesizing this ATP in our mitochondria. In fact, we produce about our own body weight in ATP every single day. Ponder that for a minute. If you weigh 160 pounds, your mitochondria produce about 160 pounds of ATP each and every day to power all your ongoing chemical reactions.
ATP is produced primarily via a process called oxidative phosphorylation. This is a term describing the addition of a phosphate group (a specific chemical structure) to a molecule of adenosine diphosphate, ADP. The molecule ADP has two phosphate groups hooked on to it; when a third phosphate group is hooked on, ADP becomes ATP. The DIphospate becomes TRIphospate. It goes from two to three phosphate groups. The bond that attaches the third phosphate group onto the other two is a high-energy bond. When that bond is broken to release energy to fuel a chemical reaction, the ATP loses the phosphate group and becomes ADP again, which is ready to be recycled back to ATP.
It requires energy to add this third phosphate group onto ADP to make it ATP. Where does this energy come from?
In short, it comes from the breakdown of the food we eat. What we refer to as our metabolism breaks down the chemical bonds of the foods we eat and uses the energy released to drive the conversion of ADP to ATP.
The electron transport chain, Part 1
The electron transport chain is composed of five molecular complexes and a kind of complicated traffic interchange called the CoQ couple. These five complexes are called, simply enough, Complexes I, II, III, IV, and V, they are usually denoted by Roman Numerals (don’t ask me why). They are strung out along the inner mitochondrial membrane, which is extremely important, but not that important in your developing an understanding of this process, so I’m not going to go into it. Just know that there is a membrane with space on both sides that contain the Complexes I through V and the CoQ couple.
When the metabolic processes that are initiated when we eat (or when we don’t and are breaking down stored fat and/or stored glucose/glycogen) tear apart the molecules making up the food we eat, the carbon chains making up the fats and sugars are stripped of their hydrogens and oxygens, and the energy stored in these foods is released as high-energy electrons. These electrons are grabbed by high-energy-electron-transport molecules and are carted to the electron transport chain. This is similar to picking up coal or wood and carrying it to a furnace to be burned. These high-energy-electron-transport molecules tote the electrons to different parts of the electron transport chain and dump them there.
Some specific electron carriers dump the electrons in Complex I, while others dump them into Complex II. To make it even more complicated, some electron carriers dump their electrons into a structure (also in the membrane) called the electron transport flavoprotein, ETF. The ETF is not often shown in graphics of the electron transport chain, but it is there and is important to our theory.
All these structures then send their electrons through the CoQ couple, which is where the magic happens. But before we get to that, let’s look at how the process produces ATP.
The high-energy-electrons that are dumped into the various complexes and the ETF are eventually shuttled down the line from one complex to the next, much like a bucket brigade. As each complex hands off an electron to the next in line, a bit of energy is released. This released energy powers the pumping of hydrogen ions (called H+) across the membrane.
As more food (or stored fat or sugar) is broken down, more high-energy-electrons are fed into the complexes and handed off down the line. So, more energy pumps H+ across the membrane. As the pumping continues and the H+ increases on one side, the pressure on that side builds. (It’s not really pressure, per se, as in the air pressure in a tire, but it’s both chemical and electrical pressure.
When more H+ are on one side of the membrane, there is a difference in concentration of hydrogen and a difference in the electrical charge due to the positive or + charge on the hydrogen. Consequently, there are two different forces pushing on the membrane: a chemical concentration one and an electrical one. The pressure difference across the membrane is called the chemiosmotic gradient, a term you can immediately forget.)
When there is an inequality of pressure across a membrane, there is a force trying to equalize the pressure. Just like in a tire filled with air, the air wants to get out to equalize with the air in the atmosphere, but the rubber of the tire prevents it. If you puncture the tire, the air rushes out until the pressure inside the tire is equal to the pressure outside, an unfortunate situation we call a flat tire.
Same situation exists across the membrane in the mitochondria, except, like the air blowing through the puncture in the inflated tire, this pressure is released by the H+ zipping through Complex V. Complex V is like a tiny turbine. As the H+ go through it, they provide the energy to turn the turbine, which adds a phosphate group to an ADP converting it to an ATP and releasing it to go out and work to drive chemical reactions.
When your body metabolizes your food (or when your body turns to stored reserves), the fats and sugar are sent down different pathways. The glucose (sugar) goes into the Krebs cycle, also called the TCA cycle and a couple of other names just to keep it confusing for medical students who are trying to learn about it.
Fats are broken down via a process called beta-oxidation, which chops the fats into two carbon segments, then feeds them into the Krebs cycle.
As glucose and fats are processed through the Krebs cycle, high-energy electrons are removed and attached to high-energy-electron carriers to be transported to the electron transport chain.
There are two types of high-energy-electron-transport molecules that carry these electrons. They are called FADH2 and NADH. It’s a function of where in the Krebs cycle these electrons are handed off as to which of the two carriers grabs them. For each turn of the Krebs cycle three NADH are used and one FADH2. (NADH and FADH2 are the abbreviations of the names of these molecules. You don’t need to know their actual names for our purposes. Hell, I’m so used to using their initials that I can’t even remember their real names without looking them up.)
As mentioned above the process of beta-oxidation involves lopping two-carbon segments of fat off at a time and sending them to the Krebs cycle. The process of chopping these fats involves four steps. During the first step, an electron is thrown off and is captured by FADH2. During the third step, another is thrown off and grabbed by NADH. For purposes of this discussion, the first of the four steps is the important one, because it varies depending upon whether the fat is saturated or unsaturated. The more unsaturated the fat, the less FADH2 is generated, which is crucial to the generation of ROS, which determine the amount of insulin resistance. And, ultimately, the amount of fat stored in the fat cell.
Why are fewer electrons thrown off, requiring fewer FADH2 to carry them, from unsaturated fats than saturated fats in the first step of beta-oxidation? Because in the first step, a double bond is inserted into a saturated fat going through the process. (See red circle in graphic below.) This double-bond addition strips off an electron that is captured and transported to the ETF in the electron transport chain by FADH2. Unlike a saturated fat, an unsaturated fat already has one or more double bonds, so it basically misses this step and no high-energy electron is released. For every double bond in an unsaturated fat, one fewer electron is released and one fewer FADH2 is sent on its way as compared to a saturated fat of the same length. So the greater the unsaturation of the fat, the greater the difference in the production of FADH2, which, as we shall see, is consequential in the storage of fat in the fat cells.
Let’s bear this in mind as we go back to the electron transport chain.
Electron transport chain, Part 2
The first complex in the electron transport chain is Complex I. NADH thrown off from beta-oxidation and the Krebs cycle enters the electron transport chain through Complex I. FADH2 enters via two different pathways. The FADH2 generated in the Krebs cycle enters via Complex II, which is actually part of the Krebs cycle that resides in the membrane. FADH2 generated by beta oxidation enters through EFT, which is also embedded in the membrane. This is the crucial step in understanding the difference between the effects of saturated versus unsaturated fat on the development of insulin resistance. Here’s why.
Complex I and Complex II and ETF all feed their electrons into the CoQ couple. After going through the CoQ couple, the electrons are handed off to Complex III, which hands them off to Complex IV, pumping H+ across the membrane all the while. The final complex, Complex V (also called ATP synthase, just to keep things complicated), is the turbine described above (and shown in an animation in my video presentation) that churns out the ATP as the H+ flow back through in an effort to equalize ‘pressure’ on both sides of the membrane.
Since electrons are coming into the CoQ couple from multiple directions (Complex I, Complex II, and ETF), it is like an intersection of streets. If traffic is moving, then everyone gets through the intersection with little delay. If, however, it is rush hour on the Friday before a long weekend, traffic can back up, and it can take forever to get through.
We’ve all had the experience of driving somewhere and hitting such a traffic backup. Most of the drivers of the cars wait patiently and inch their way through the long line of traffic until they make it through the intersection and are on their way. In these situations, however, there are always impatient drivers who tire of the wait, say Screw it, pull out of the line and make a U-turn and head back up the road in the opposite way to find a faster route.
The same thing happens with electrons getting backed up going through the CoQ couple. Most of them make it through to Complex III, but if the electron traffic is congested enough, some of them turn around and go back through Complex I backwards. When this happens, it is called, logically enough, reverse electron transport (RET), which is a major part of our hypothesis.
When electrons go backwards in Complex I, the complex releases them as free radicals, ROS.
These ROS then are a signal that the cell is full (which makes sense given that the CoQ Couple is jammed up with electron traffic. The ROS end up as hydrogen peroxide and increase localized insulin resistance, which turns fat and glucose away. And now we’re back to where we started in the earlier part of this essay.
The electrons that end up clogging the CoQ Couple are carried by the FADH2 coming from beta-oxidation of fat through ETF. More FADH2 means more electrons means more of a traffic jam. Which drives electrons backwards via RET through Complex 1 and pops them off as ROS, driving localized insulin resistance and preventing more fat being moved into the fat cells.
What drives more FADH2 through ETF? Saturated fat.
What drives less through? Polyunsaturated fat (PUFA).
Why does it matter? That’s the question that goes to the heart of the hypothesis.
If you want to keep your fat cells from expanding beyond a certain level, and you want yourself to keep from expanding along with them (i.e., getting fat), then you want to block entry of fat into the fat cells. Which is what localized insulin resistance does. And this localized insulin resistance is driven by FADH2. And what makes more FADH2? Saturated fat. What makes less? PUFA.
The obesity epidemic
For decades the level of obesity in the United States stayed pretty level. All of a sudden in about 1980 the rate of obesity began to rise. And it hasn’t stopped since.
You can get all kinds of answers from people. If you look at the statistics, you’ll see that caloric intake has increased by about 240-250 calories per capita per day. If you break this down and look at the macronutrient content of this caloric increase, you find that protein has increased a tiny bit, fat has gone up a little, while the majority of the caloric increase comes from carbohydrate.
So, there you have your answer. More carbohydrate is making us fatter. Seems pretty logical, but…
We can’t just say that the fact that we are eating more carbs is making us fat. Reason demands that we ask the question: Why? Why after decades of consistent carb intake, did we suddenly start eating more carbs in 1980?
Did carbs suddenly become tastier in 1980? Did Snack food and junk food first arrive on the scene in 1980? Did people just spontaneously start stuffing their faces with carbs in 1980? Or did something else happen?
Let’s take a look at protein intake. It rose slightly, but didn’t really change in quality.
How about fat?
Fat intake increased a little since 1980. If you look at the change in the type of fat we ate starting in 1980, you see an enormous difference. Although total fat didn’t change much, the amount of PUFA in the diet skyrocketed, while the amount of saturated fat fell.
So, maybe the type of fat has something to do with it. My early hypothesis was that PUFA somehow drove the increase in obesity and maybe the fall off of saturated fat intake contributed.
In other words, maybe PUFA is driving the obesity epidemic while saturated fat is protective. So, I started looking for a biochemical or physiological mechanism that could explain this.
I came across the work of Peter Dombromylskyj, (see his Proton Series in his Hyperlipid blog) who had gone back the basic biochemistry of fat metabolism and noticed that saturated fat increased the production of FADH2 while PUFA decreased it. So, the ratio of the two, the FADH2/NADH ratio, may act as a switch to control the storage of fat. As the ratio goes up—more FADH2 to NADH—the storage of fat goes down.
If this were true, then it would help explain the enormous increase in obesity since around 1980. Since then—thanks to the widespread fear of saturated fat—we’ve all been reducing saturated fat and replacing it with PUFA.
By advocating the substitution of PUFA, provided mainly in the form of industrial seed oils, for saturated fat, which we have all eaten for millennia, in a misguided attempt to reduce the rate of heart disease, the nutritional authorities unwittingly set us up for the massive obesity epidemic we’re now in the midst of.
A diet high in PUFA, by the decrease in production of FADH2, inhibits the rate of RET, allowing the fat cells to continue to take up calories beyond a certain set point. Adding saturated fat increases the RET and signals that the fat cells are full.
While the fat cells are open for stuffing, both fat and glucose go in. Since PUFA brings this about, PUFA ends up acting as a sort of supercharged carb in that it continues to flood into the fat cells like glucose, but it has over twice as many calories per gram as glucose.
Could explain a lot.
Before I end, I want to propose an experiment. Maybe someone out there has the contacts to get it going.
Back in the old pre-let’s-all-quit-eating-foods-of-animal-origin days, McDonald’s fries were cooked in beef tallow. Since the CSPI and other groups of slow-witted dolts came down on them, they’ve switched to cooking them in vegetable oil. Vegetable oil doesn’t flavor them in the same way beef tallow does, so they had to do all kinds of food-technology wizardry to make them taste the same. Some people still don’t think they taste the same. Listen to this podcast by Malcolm Gladwell, who got to eat some McDonald’s fries cooked the old way.
Vegetable oils are primarily PUFA whereas beef tallow is primarily saturated fat and mono-unsaturated fat with a little (a very little) PUFA thrown in.
If we could recruit, say, 30 people who would agree to eat McDonald’s fries till they were full, we could do a nice study. We would use them as their own controls. We would randomize them into two groups. One group would eat McDonald’s fries cooked in vegetable oil until full, while the other group would eat the fries cooked in beef tallow. We would measure the amounts of fries eaten by those in each group and record it. Then, a couple of weeks later, we would reverse the situation. Those who had eaten the beef-tallow cooked fries the first time, would eat until full of the vegetable cooked one. And vice versa.
If this FADH2/NADH ratio hypothesis is valid, then it would be expected that the subjects would have eaten less of the fries cooked in beef tallow and more of those cooked in vegetable oil.
Any readers out there have a contact at McDonald’s who could help us out here? I will totally volunteer my time to oversee the experiment.
In the next post, I’ll introduce you to someone who has sort of done this experiment on himself. And tell you the results. And give you many, many links you can go through to learn more and maybe try it yourself.
*The fat mass can also increase by increasing the number of fat cells, but I don’t want to complicate the issue with that right now. It’s already complex enough.)
Just in case you haven’t had enough, here are a few references you can take a look at. And, finally, if you scroll down below the references, you’ll find a way to get what I think are three of the best of these three papers.
Fisher-Wellman, K. H. & Neufer, P. D. (2012). Linking mitochondrial bioenergetics to insulin resistance via redox biology. Trends Endocrinol Metab, 23(3), 142-153.
Guarás, A. et al (2016) The CoQH2/CoQ ration serves as a sensor of respiratory chain efficiency. Cell Reports 15, 1-13.
Persiyantseva, NA (2013) Mitochondrial H2O2 as an enable signal for triggering autophosphorylation of insulin receptors in neurons. J Mol Signal 8(1) 11.
Pomytkin, IA. (2012) H2O2 Signalling pathway: A possible bridge between insulin receptor and mitochondria. Curr Neuropharmacol 10(4) 311-320.
Sato, K. et al (1995). Insulin, ketone bodies, and mitochondrial energy transduction. FASEB J, 9(8), 651-658.
Scialò, F. et al (2016) Mitochondrial ROS produced by reverse electron transport extend animal lifespan. Cell Metab, 12;23(4), 725-734.
Speijer, D. (2011). Oxygen radicals shaping evolution: why fatty acid catabolism leads to peroxisomes while neurons do without it: FADH(2)/NADH flux ratios determining mitochondrial radical formation were crucial for the eukaryotic invention of peroxisomes and catabolic tissue differentiation. Bioessays, 33(2), 88-94.
Speijer, D. (2014). How the mitochondrion was shaped by radical differences in substrates: what carnitine shuttles and uncoupling tell us about mitochondrial evolution in response to ROS. Bioessays, 36(7), 634-643.
Speijer, D. et al (2014). How to deal with oxygen radicals stemming from mitochondrial fatty acid oxidation. Philos Trans R Soc Lond B Biol Sci, 369(1646), 20130446.
Speijer, D. (2019) Can all major ROS forming sites of the respiratory chain be activated by high FADH(2)/NADH ratios?: Ancient evolutionary constraints determine mitochondrial ROS formation. Bioessays, 41(1), e1800180.
Stein, L. R., & Imai, S. (2012). The dynamic regulation of NAD metabolism in mitochondria. Trends Endocrinol Metab, 23(9), 420-428.
If you’re interested in learning more about all this, I’ve put together a packet of three papers I’ll be happy to email you. Put in your email address and click the button below, and you’ll have them in 10 seconds.