I have found a strange thing happens when I talk to nutritionists about the fate of carbohydrates in the human body. Professors, who shall be nameless, appear unable to admit how basic human physiology works. For example, they may concede a few steps here and there, but they will never, ever, admit to the following chain that I have described below.
1: Carbohydrates, such as fruit and vegetables, bread, pasta… and, of course, less complex sugars – such as the stuff we sprinkle on cornflakes, that we call ‘sugar’, are all turned into simple sugars in the human digestive tract before entering the bloodstream.
2: If you keep eating carbohydrate the resultant simple sugars will, at first, be stored. The human body can pack away around 1,500 calories of sugar. However, once this limit is reached, the liver will turn the rest into fat.
3: The fat that is made in the liver is palmitic acid
4: The next step is that three palmitic acid molecules are attached to a glycerol molecule, to form a triglyceride.
5: These triglycerides will then be packed into Very Low Density Lipoproteins (VLDL) and released into the bloodstream. [Beware of confusion here. For VLDLs are also called triglycerides although, of course, they are not. VLDLs contain triglycerides but they are not the same thing – even if they are called the same thing].
6: When VLDLs reach fat cells (adipose tissue), the triglyceride is stripped out and absorbed into fat cells. Which means that VLDLs gradually shrink.
7: Once a VLDL has lost a large amount of triglyceride it becomes a new, smaller, lipoprotein, which is often referred to as ‘bad cholesterol’ a.k.a. LDL (Low Density Lipoprotein).
8: LDL is taken out of the circulation, primarily, by the liver. Some LDLs are removed from the circulation by other cells around the body that need the cholesterol contained in them.
9: As can be seen, the only source of LDL is VLDL.
Here a couple of quotes from Wikipedia to confirm at least a couple of these steps:
Lipogenesis is the process by which acetyl-CoA is converted to fatty acids. The former is an intermediate stage in metabolism of simple sugars, such as glucose, a source of energy of living organisms. Through lipogenesis and subsequent triglyceride synthesis, the energy can be efficiently stored in the form of fats.
Lipogenesis encompasses both the process of fatty acid synthesis and triglyceride synthesis (where fatty acids are esterified with glycerol to form fats). The products are secreted from the liver in the form of very-low-density lipoproteins (VLDL). VLDL are secreted directly into blood, where they mature and function to deliver the endogenously derived lipids to peripheral tissues. https://en.wikipedia.org/wiki/Lipogenesis
Excess carbohydrates in the body are converted to palmitic acid. Palmitic acid is the first fatty acid produced during fatty acid synthesis and the precursor to longer fatty acids. As a consequence, palmitic acid is a major body component of animals. In humans, one analysis found it to comprise 21–30% (molar) of human depot fat and it is a major, but highly variable, lipid component of human breast milk. https://en.wikipedia.org/wiki/Palmitic_acid
I am half tempted to leave the blog here and let you think about what all of that means for a while. However, I feel the need to make a couple of other points, in no particular order. First, I would like you to think about this fact. The form of fatty acid that the liver chooses to synthesize from sugar(s) is palmitic acid, a saturated fat. Palmitic acid is also the major component of breast milk.
Yet, despite this, we are told that saturated fats are uniquely unhealthy, and eating them leads to heart disease. Indeed, within to the very same Wikipedia article on palmitic acid we learn that: ‘According to the World Health Organization, evidence is “convincing” that consumption of palmitic acid increases risk of developing cardiovascular diseases.’
It seems that we are being asked to believe that the body naturally synthesizes a substance, palmitic acid, that actively damages our health. Not only that, but mothers choose to synthesize exactly the same form of fatty acid in their breast milk, which then increase the chances of their offspring developing cardiovascular disease.
Now just how likely does this seem…exactly? We have evolved to kill ourselves from heart disease? As Spock may have said, ‘its evolution Jim, but not as we know it.’ You would think that if polyunsaturated fats were healthy, this is what the human body might choose to make. But no, we eat super healthy fruit and vegetables and then our body, in a unique and ironic twist of fate, converts them into death dealing saturated fatty acids.
Not only that, but just to rub salt into the wounds, once the liver has synthesized these death dealing fatty acid molecules it then chooses to pack them into VLDLs which have the cheek to shrink down into LDL a.k.a. ‘cholesterol’ and these also kill us with heart disease (allegedly).
Of course, if you actually eat saturated fat, this gets nowhere near the liver. It is digested, packed into chylomicrons, and these very large lipoproteins enter the bloodstream directly through the thoracic duct. Which is a secret passage from the gut that opens out in one of the veins in your neck. When chylomicrons encounter fat cells, the fats/triglycerides are sucked out, and the chylomicron shrinks down to virtually nothing. Chylomicrons, however, do not convert to LDL and have nothing whatsoever to do with heart disease – even according to those who think saturated fat in the diet is deadly.
Yet, despite this knowledge we are continuously told, in all seriousness, that eating saturated fat raises our LDL levels and causes us to die prematurely of heart disease. [You may have noticed that cholesterol has hardly entered this discussion at any point.] When people ask me why I don’t believe in the diet/heart hypothesis, I tend to shrug and move the conversation on.
However, if I am feeling a bit stroppy I tend to reply that ‘Even if you were to believe that a raised LDL levels causes heart disease, the current diet/heart hypothesis does not, and cannot make any sense from a biological or physiological perspective.’ If you were actually looking for a substance that really could raise LDL/cholesterol levels it would have to be carbohydrates a.k.a. sugars. After all the only source of LDL is VLDL, and it is eating too much sugar that raises VLDL levels.
In short, how can it not be that carbohydrates raise LDL levels? This is what a basic understanding of lipid physiology tells us must be true. Yet, people write papers on this phenomenon in a tone of almost stunned surprise. Here for example is a paper called ‘The Effect of Dietary Carbohydrate on Triglyceride Metabolism in Humans’:
When the content of dietary carbohydrate is elevated above the level typically consumed (>55% of energy), blood concentrations of triglycerides rise. This phenomenon, known as carbohydrate-induced hypertriglyceridemia, is paradoxical because the increase in dietary carbohydrate usually comes at the expense of dietary fat. Thus, when the content of the carbohydrate in the diet is increased, fat in the diet is reduced, but the content of fat (triglycerides) in the blood rises. http://jn.nutrition.org/content/131/10/2772S.full#fn-1
This author, writing for the Journal of Nutrition, finds it paradoxical that… increased dietary carbohydrate usually comes at the expense of dietary fat….but the content of fat (triglycerides) in the blood rises. Well, what did they think would happen? That carbohydrates would turn into fairies at the bottom of the garden?
Once the liver and muscles are full of sugar (stored as glycogen – a polymer of glucose) the body can do absolutely nothing else with it, but turn it into fat – through the processes I have described earlier. This is basic, incontrovertible science.
Most people who are interested in the potential benefits of the low carb high fat diet (LCHF), have tended to look at it from the perspective of helping with controlling diabetes, and promoting weight loss. I came at the LCHF diet from my own perspective, which is heart disease.
When you understand the science you find yourself looking at the diet heart hypothesis (fat in the diet raises LDL levels, which causes heart disease) and thinking. This does not make any sense at all. Yet, such is the determination of the nutritional experts to defend their position that they never, ever, talk about ‘what happens to the carbs?’
What happens to the carbs is that they are all turned into saturated fat. This then raises VLDL levels and these, in turn becomes LDL. Yet eating carbs is supposed to be healthy, and eating saturated fat is unhealthy. Go figure.
The world of nutrition is, I am afraid, nuts.