A Carbohydrate is a Carbohydrate - or is it?

I said last week that I would explain about different sugars... I found the perfect explanation in the book Fat Chance, by Robert H. Lustig M.D.  Seeing as no one can explain it as perfectly as Dr. Lustig, I decided to leave it in his own words, but you will have to bear with me as it is a bit long.

"All carbohydrates are not created equal.  Just as there are different gradations of fats, there are different gradations of carbohydrates based on their metabolism.  To illustrate how this works, consider the following exercise involving the metabolism of three different carbohydrates of equal caloric value (120 calories): glucose, ethanol (grain alcohol), and fructose.

Glucose

Despite its absolute necessity for life, dietary glucose isn't perfect.  When it exists in nature without fructose, it's called "starch", and it truly does supply "empty calories", energy for either storage or burning.  But the Atkins, Paleo, and caloric-restriction adherents will all tell you that the glucose molecule has three metabolic downsides, all of which do damage over time and necessitate the limitation of its consumption.  To demonstrate this, let's consume 120 calories of glucose (e.g., one-half cup cooked white rice).  Twenty percent, or 24 calories, will enter the liver, whereas the rest will be metabolized by other organs in the body.  Here's what happens:

1. Glucose metabolism is insulin-dependent.  Consuming glucose raises the glucose level in the bloodstream, stimulating insulin release, which promotes energy storage into fat cells and causes weight gain.
2. The overwhelming majority of glucose in the liver will be directed toward forming glycogen, or liver starch, which is not harmful to the liver cell.  This also will keep the liver from releasing glucose into the blood, preventing diabetes.
3. A small amount of glucose will be metabolized by the liver mitochondria for energy.
4. Any excess glucose in the liver that is not shunted to glycogen and not metabolized by  the mitochondria for energy will instead be converted to triglycerides.  High triglyceride levels in the blood can promote development of cardiovascular disease.
5. Glucose can bind to proteins in the cell, which causes two problems:
• When glucose binds to proteins throughout the body, the proteins become less flexible, contributing to the aging process and causing organ dysfunction.
• Every time a glucose molecule binds to a protein, it releases a reactive oxygen species (ROS), which can cause tissue damage if not immediately mopped up by an antioxidant in the peroxisome.

Like all things, glucose in excess can be bad for you - especially when it lacks fiber, which limits the insulin response.  However, you would have to consume a lot of it and over a long period of time for glucose to have these detrimental effects.  In general, large amounts of glucose (starches such as pasta, white bread, rice, etc.) will cause you to gain pounds but it won't make you sick.  Rather, if over time you gain too much weight from glucose, the visceral fat that is formed will eventually take its toll on your health.  But when you consume the same number of calories as either ethanol or fructose, you get much more of a bang to your liver (more like a hand grenade), and it takes its toll much faster.

Ethanol (Grain Alcohol)

Ethanol is a naturally occurring by-product of carbohydrate metabolism, called fermentation.  Upon ingestion of 120 calories of ethanol (e.g., a 1.5 ounce shot of 80-proof hard spirits), 10 percent (12 calories) is metabolized within the stomach and intestine (called the first-pass effect) and 10 percent is metabolized by the brain and other organs.  The metabolism in the brain is what leads to the alcohol's intoxicating effects.  Approximately 96 calories reach the liver - four times more than with glucose.  And that's important, as the detrimental effects are dose-dependent.

1. After ethanol enters the liver in high dosages, it can promote ROS formation and cell damage.
2. In contrast to glucose, which went to glycogen, the ethanol goes straight to the mitochondria.
3. Any excess gets turned into fat by a process called de novo (new) lipogenesis (fat-making).  The lipid buildup can lead to liver insulin resistance and inflammation.
4. If this process continues, it can eventually cause alcoholic liver disease.  This is a surefire prescription for slow death or, at best, a liver transplant.
5. Alternatively, the lipid can exit the liver and take up residence in skeletal muscle, where it also induces insulin resistance and can cause heart disease.
6. Lastly, ethanol enhances its own consumption, by acting on the brain's reward pathway.  When this goes out of control, addiction sets in.

Thus, for the same number of calories, ethanol is more likely than glucose to cause chronic disease.

Fructose

Fructose is never found alone in nature.  Rather, it is always partnered with its more benign sister molecule, glucose.  They both have the same chemical composition (C6H12O6), but they are hardly the same.  Fructose is much worse.  Let's start with the Maillard, or "browning", reaction.  This is the same reaction that turns hemoglobin in your red blood cells into hemoglobin A1c (HbA1c), the lab test that doctors follow to determine how high a diabetic patient's blood sugar has risen over time...

... There are dozens of studies that now implicate fructose as a major player in causing metabolic syndrome.  In fact, it's metabolized a lot like ethanol.  Let's now consume 120 calories of sucrose (60g of glucose, 60 of fructose) - for example, an 8 ounce glass of orange juice.  (As I mentioned before, juice is just as bad as soda, if not worse.)  The 60 calories of glucose do the same 20-80 split, so 12 calories of glucose will enter the liver.  But, unlike with glucose, which can be metabolized by all organs, the liver is the primary site of fructose metabolism (although the kidney has the capacity to metabolize a few calories in rare cases).  Give or take, the whole 60 calories of fructose end up in the liver.  So, the liver gets a 72-calories dose, triple the amount as with glucose alone.

The unique metabolism of fructose can induce each of the phenomena associated with metabolic syndrome:

1. Triple the dose means the liver needs triple the energy to metabolize this combo versus glucose alone, depleting the liver cell of adenosine triphosphate (or ATP, the vital chemical that conveys energy within cells).  ATP depletion leads to the generation of the waste product uric acid.  Uric acid causes gout and increases blood pressure.
2. The fructose does not go to glycogen.  It goes straight to the mitochondria.  Excess acetyl-CoA is formed, exceeding the mitochondria's ability to metabolize it.
3. The excess acetyl-CoA leaves the mitochondria and gets metabolized into fat, which can promote heart disease.
4. Fructose activates a liver enzyme, which is the bridge between liver metabolism and inflammation.  This inactivates a key messenger of insulin action, leading to liver insulin resistance.
5. The lack of insulin effect in the liver means that there is no method to keep the glucose down, so the blood glucose rises, which can eventually lead to diabetes.
6. The liver insulin resistance means the pancreas has to release extra insulin, which can force extra energy into fat cells, leading to obesity.  And the fat cells that fill up most are the visceral fat, the bad kind associated with metabolic disease.
7. The high insulin can also drive the growth of many cancers.
8. The high insulin blocks leptin signaling, giving the hypothalamus the false sense of "starvation", and causing you to eat more.
9. Fructose may also contribute to breakdown of the intestinal barrier.  Normally the intestine prevents bacteria from entering the bloodstream.  This intestinal breakdown may lead to a breach in the walls of the intestine.  The result is a "leaky gut", which could increase the body's exposure to inflammation and more ROS.  This worsens insulin resistance and drives the insulin levels even higher.
10. Fructose undergoes the Maillard (browning) reaction 7 times faster than glucose, which can damage cells directly.  Although the experiments are in their infancy, preliminary results suggest that in a susceptible environment, fructose can accelerate aging and the development of cancer.
11. The data on fructose and dementia in humans are currently correlative and indirect.  However, the data on insulin resistance and dementia show clear causation.  African Americans and Latinos are the biggest fructose consumers and those with the highest waist circumference (a marker for insulin resistance).  Coincidentally, they also have the highest risk for dementia."

I hope this information helps you to make wiser choices in your diet.

I can help you improve your health.  If you would like to make an appointment with me either in person or via Skype, just send me an email to lucycarr@socialnutrition.com