33 An Evolved Fuel System 1
Contemplate for a moment the fuel system of a car. It is assembled from many parts like fuel lines, injectors, and pumps, and each is designed just for its particular function. Away from the engine, safe and secure, a volatile liquid fuel that every part of the system helps to regulate is sequestered in a sealed tank.
Various sensors make sure exactly the right amount of fuel is exposed to combustion. You can imagine how quickly and badly things would fail if this were not a tightly controlled system. And yet there is practically no chance that a properly maintained vehicle will catch fire. This is a wonder of engineering.
Combustion is only allowed to take place at the precise moment when the optimal air/fuel mixture is attained, called the stoichiometric point. Chips and sensors in your car want the right octane. Put the fuel used in race cars in your car and soon you’ll need an expensive repair. Add fuel with too much ethanol and this robust fuel system will eventually become damaged. Allow a spark plug to fire with a piston out of place and you will have pinging. There is some margin for error but in the larger sense this is a very finely tuned system. It is a system produced by armies of engineers and technicians who painstakingly designed and fabricated every component of that fuel system for its singular purpose.
This system was designed. The design has evolved over time but it hasn’t evolved the way any organism has. You won’t find a little useless vestigial carburetor in a vehicle with electronic fuel injection. Engineers can start from a clean sheet of paper on any component at any time...
And they can even scrap the whole system and make up a completely different fuel system. They are not limited in their options by inheritance.
The engineering of your digestive system wasn’t like that. That is the result of an eons-long, undirected evolutionary process. It is a product of compromise. It doesn’t have a separate tidy place to store its fuel from which to precisely pulse it out, only as much as needed at the moment. It can’t demand of you that you fill it only with a precisely formulated and standardized fuel. As a work of engineering, your digestive system is amazing. It can deal with fluxes and foul-ups in a way that a car never could. It is durable, forgiving, and efficient. All that it needs from you is a little consideration and care and it will do its job for many decades.
In Robb Wolf's book, The Paleo Solution, he talks about digestion. He uses three subheadings called “Normal State,” “Fasted State,” and “Overfed State.” In the “Overfed State” section he depicts a cascading metabolic meltdown with several “DEFCON” stages caused by excess carbs. He wants carbs to seem scary. What about the other macronutrients? Are they scary, too? He mentions proteins only to say that you simply can’t over-consume them. He doesn’t mention fats at all. Apparently he thinks you can’t overfeed on fats, either. But consume too much carbohydrate and you will produce palmitic acid, and very bad things will happen. His unstated but clear message is that we should keep an eye on our carbohydrate consumption because carbs are dangerous.
I presume this is the sort of study Wolf must have had in mind when he chose to single out carbs as the DEFCON macronutrient. I have to make that presumption because he doesn’t reference a particular study to support the scenario he describes. In this study using eight healthy subjects, the feeding of diets with the same number of calories but differing amounts of fat and carbs indicated that more carbs caused higher triglycerides. If we accept that we want triglycerides lower, then in this study, high fat seemed better than high carb.
But look closely at what happened here. The high-fat diet and the high-carb diet had the same ratio of starch to sugar and fiber content was kept low. Then look at the middle line. Subjects also received a continuous intravenous infusion of palmitic acid. Palmitic acid is what Thomas Dayspring was talking about when he said your body can convert carbs into saturated fat. Palmitic acid is a saturated fat and you don’t want it giving you lipemia after a meal. Obviously, the feeding conditions here were unusual, assuming that you don't usually pump palmitic acid into yourself intravenously. The authors acknowledged that their findings may have limited relevance to the long term consumption of low-fat diets. They used foods that were high in sugar and low in fiber. I don’t think research like this says much about healthy carbs.
Here is another example of carbs causing the production of palmitic acid, but notice this was very explicitly under conditions of overfeeding, or hyperalimentation, as it is called here. The subjects were given two and a half times more calories than they burned. Maybe if you eat more than double the food you should, then a problem will arise. Remember, Robb Wolf’s alarmism was under his “Overfed State” subheading.
These people had to endure forced feeding in this experiment as well, using intravenous methods in addition to a nasogastric feeding tube. This went on night and day. This is the major leagues of overfeeding. How else are you going to more than double a person’s normal food intake?
Those are indeed extreme conditions. Could Robb Wolf have been only warning us against taking part in experiments like that? Probably not. There is a more likely scenario under which the liver produces excess palmitate. That would be under the all-too-common condition of insulin resistance. This study made it clear that hyperinsulinemic obese subjects synthesized considerably more fat in their livers than healthy subjects when eating a high-carb diet. The experimental design was too complicated to explain here but this paper is free to download. Suffice it to say that they used real food and they did not overfeed anyone. Did Robb Wolf make it clear that he was only referring to people who already had a messed up metabolism? No, he didn’t.
What these researchers found was that these metabolically deranged people had three to four times the amount of de novo lipogenesis as healthy people. Moreover, that new fat was primarily produced from the simple sugars in their diets. They said the determining factor in the degree of fat synthesis was the proportion of sugars they were fed. Now we are not only talking about people who aren’t normal and healthy, but we aren’t talking about all carbs, either. We are looking at obese people consuming sugar, the nutritionally ignorant and vulnerable demographic preyed upon by the likes of Wolf.
As I said, this study was not about overfeeding. So why did their livers produce this fat from carbs? The researchers could only speculate. What you should take from this study is that Wolf has not given you an accurate view of how your fuel system works. He said that overfeeding on protein is improbable. However misleading that is about protein, in my opinion, he is being even more misleading about carbs. It is especially improbable that you will overfeed on healthy carbs, carbs that have fiber and water in them that will fill you up before overfeeding ever occurs.
There are also studies demonstrating high-fat overfeeding, and the picture is even uglier there. Wolf doesn’t seem to know this research exists. At only 50% excess of calories, high fat feeding caused the production of not just palmitate but also glucose. Yes, after consuming excess fat, the liver produced more glucose. This was entirely predictable, as I’ll show you in my videos called “How to Become Insulin Resistant.” Their blood sugar rose only a little, but that was because they were producing so much insulin. Yes, Robb Wolf, overfeeding on fat is very bad as well, and that is more likely to do bad things to a healthy person than is overfeeding on healthy carbs.
Yes, palmitic acid is the main product of fat synthesis during overnutrition and it is something you should try to minimize.
Fat synthesis can happen because of fat, protein, or carbohydrate overnutrition, so excesses of any of these over time can cause you to enter an inflamed, insulin resistant state.
But let’s leave out the lab experiments with liquid and intravenous overfeeding for a moment. What is interesting to me is the question of which way normal people seem more likely to have these unwanted fats in their blood. In this epidemiological study of almost 2900 older people, researchers set out to correlate de novo lipogenesis with actual dietary practices.
Here I’ve shown you the results. Notice that the white bars, as I highlighted at the right, represent palmitic acid, which has a 16-carbon chain. Protein and alcohol intake both correlated with more palmitic acid in the blood than did carbs. In these measures of real people, the endogenously synthesized fat that Robb Wolf says is so problematic tends to be more of a problem for those who consume more protein, not more carbs. I would think his readers would be more concerned about what happens to normal people eating normal food. They might be surprised to learn that protein doesn’t deserve the free pass Wolf gave it.
The authors noted that the particular type of carb that was likely to blame for whatever excess carb-induced palmitate synthesis was taking place was fructose, not other sugars and not starch. You can be sure whole fruits weren’t the major source of that fructose for these people. When you see the phrase "large amounts of fructose," you should understand that this is a reference to processed foods and beverages.
This important study from 1998 made it obvious for us what sort of carbs cause our livers to synthesize fat. Lisa Hudgins used subjects described as normal, which you should understand to mean non-obese and non-diabetic. They were given contrasting diets of identical macronutrient composition. Everything was high-carb here. The variables she played around with were starch-to-sugar ratio and solid versus liquid.
There you see that macronutrients were indeed held constant across the diets.
This is a modified version of their graph so you can see what happened to palmitate production once the switch was made from a sugary liquid diet to a starchy solid diet. This graph should tell you all you need to know. Triglycerides plummeted when the carbs were solid rather than liquid and starch rather than sugar. We can choose a healthier state by choosing good carbs. There is no justification for alarmism about carbs in general.
Dietary fiber is proven to be effective in lowering triglycerides.
Starches, whole plant foods, and exercise are all effective at reducing triglycerides.
The glycemic index is one good yet imperfect tool for helping us measure the quality of carbs. This, I believe, is the first trial testing a low glycemic index approach, led by the inventor of the glycemic index, David Jenkins. With macronutrients mostly held constant, a lower glycemic index diet dropped LDL and triglycerides for subjects with problematic lipid profiles.
Paleo dieters, I draw your attention to the foods which were used to bring about this improvement – grain products and beans.
Here is an especially fascinating animal experiment. It used rats with impaired insulin production eating high- and low-GI diets and focused on the effects of carbs on body composition. A high-GI diet altered their fat mass and lean mass so that they were substantially fatter and worse off than the rats fed a low-GI diet. All carbs are not the same, Mr. Wolf. It's time you got a clue.
It is important to distinguish between good and bad carbs. In this paper on de novo lipogenesis, these authors noted that starch and fiber counteracted any tendency for triglycerides to rise after the consumption of carbs. Sugar is the problem here. In this respect I agree with John Yudkin. Refined sugar is indeed problematic, and it likely is an aggravating factor in heart disease for those with high cholesterol or insulin resistance.
With all this established, let’s not exaggerate the problems caused by sugar. In this study, diets were compared that had different sources of carbs. One diet was very high in sugar. The other diet was based on starches and had no sugar. The high-sugar diet did not affect triglycerides, insulin, or free fatty acids at all. The high-sugar diet only raised blood sugar. That isn’t good but notice that the meltdown Wolf might have expected from newly created palmitate just never happened. Why? Didn’t we just learn that sugar causes all these other problems?
While they were not very healthy, at least the subjects in this one had normal carbohydrate metabolism. Also, the diets were not extreme. There was no overfeeding. This is not to say refined sugar is good for you. Sugar just is not the source of all the problems that the low-carbers say it is.
In order to have significant de novo lipogenesis, we need refined sugar and lots of it, with a minimum of fiber and starch. This slide describes some of the experiments that have established this.
Please note that even carbs that are called whole grain can be relatively unhealthy because they are often highly processed, which causes them to have a high glycemic index and reduces the advantages of their fiber.
Think of the fiber and water in whole plant foods as the regulators of your evolved fuel system. They allow the different components in your natural fuel system to work at the pace and in the manner they work best.
You wouldn’t want your car’s fuel system dumping a whole bunch of excess fuel into your engine’s cylinders, if we pretend for a moment that that is possible. You would never expect a mechanical system to handle such abuse and you would probably want to keep a good distance from your car if you knew something like that was about to happen. You should realize that your digestion has conditions under which it works best as well, and if you don’t provide that, you should expect some sort of damage to result. Avoid overeating. Avoid excessively volatile fuels made from refined sugars. Think of them as the racing fuels that don’t belong in a normal vehicle. Don’t gunk up the system with saturated fat. Eat whole plant foods. Give every component of your fuel system a fair shot at doing its job the right way.
You may not be convinced by all this yet. You may want more evidence that the high-carb, whole plant food approach really does regulate the human fuel system properly. I’ll give you that evidence in Part II.