You may already be aware that fructose – the sugar found in everything from high fructose corn syrup and fruit juice to agave syrup and honey – is harmful when consumed in excess – which is exactly what many (if not most) Americans do.
However, you may be surprised to learn that fructose is, in many ways, very similar to alcohol in the damage that it can do to your body.
So while you may already be exercising caution by not overconsuming alcoholic beverages, it may be time to take a closer look at the equally potentially damaging effects associated with your intake of sodas, fruit juice and other fructose-sweetened foods and drinks as well.
Fructose’s Three Major Similarities to Alcohol
Unlike glucose, which can be used by virtually every cell in your body, fructose can only be metabolized by your liver, because your liver is the only organ that has the transporter for it.
Since all fructose gets shuttled to your liver, and, if you eat a typical Western-style diet, you consume high amounts of it, fructose ends up taxing and damaging your liver in the same way alcohol and other toxins do. In fact, fructose is virtually identical to alcohol with regard to the metabolic havoc it wreaks.
According to Dr. Lustig, Professor of Pediatrics in the Division of Endocrinology at the University of California, fructose is a “chronic, dose-dependent liver toxin.” And just like alcohol, fructose is metabolized directly into fat – not cellular energy, like glucose.
He discussed this topic in the video above, but after the video was produced his paper on the topic was published in the Journal of the Academy of Nutrition and Dietetics, Dr. Lustig explains the three similarities between fructose and its fermentation byproduct, ethanol (alcohol):
- Your liver’s metabolism of fructose is similar to alcohol, as they both serve as substrates for converting dietary carbohydrate into fat, which promotes insulin resistance, dyslipidemia (abnormal fat levels in the bloodstream), and fatty liver
- Fructose undergoes the Maillard reaction with proteins, leading to the formation of superoxide free radicals that can result in liver inflammation similar to acetaldehyde, an intermediary metabolite of ethanol
- By “stimulating the ‘hedonic pathway’ of the brain both directly and indirectly,” Dr. Lustig noted, “fructose creates habituation, and possibly dependence; also paralleling ethanol.”
Dr. Lustig concluded:
“Thus, fructose induces alterations in both hepatic [liver] metabolism and central nervous system energy signaling, leading to a ‘vicious cycle’ of excessive consumption and disease consistent with metabolic syndrome. On a societal level, the treatment of fructose as a commodity exhibits market similarities to ethanol. Analogous to ethanol, societal efforts to reduce fructose consumption will likely be necessary to combat the obesity epidemic.”
Fructose Versus Alcohol: The Dangerous Metabolic Cascade
After consuming an alcoholic beverage, 10 percent of the ethanol gets broken down by the stomach and intestine as a “first pass” effect, and another 10 percent is metabolized by your brain and other organs. The fact that ethanol is partially metabolized in your brain is the reason you experience that familiar “buzz.”
The remaining 80 percent hits your liver, where it must be broken down. This metabolic cascade can be summarized as follows:
- Your liver converts ethanol to aldehydes, which produce free radicals that damage proteins in your liver.
- Some of these aldehydes are converted to glucose, but a large amount of excess citrate is formed in the process, stimulating “junk chemicals” that result in free fatty acids (FFAs), VLDL (smaller, denser LDL (bad cholesterol) particles that stimulate arterial plaque formation) and triglycerides. A 120-calorie intake of ethanol produces VLDL that are transported to your fat cells and contribute to obesity or plaque formation. This is what leads to the dyslipidemia of alcoholism.
- The resulting lipids, together with the ethanol, upregulate enzymes that induce an inflammatory cascade, which in turn causes hepatic insulin resistance, liver inflammation and cirrhosis.
- Fat globules accumulate in your liver as well, which can lead to fatty liver disease.
- Free fatty acids (FFAs) leave your liver and cause your skeletal muscles to become insulin resistant. This is a worse form of insulin resistance than hepatic insulin resistance and can lead to type 2 diabetes.
- After a 120-calorie bolus dose of ethanol, a large fraction (about 40 calories) can contribute to disease.
In nearly every way, fructose is metabolized the same way as ethanol, creating the same cascade of damaging effects in your body. When you consume fructose, 100 percent of it goes directly to your liver to be metabolized. This is why it is a hepatotoxin when consumed excessively – it overloads your liver. Fructose metabolism creates the following adverse effects:
- Fructose is immediately converted by your liver to fructose-1-phosphate (F1P), depleting your liver cells of phosphates.
- The above process produces waste products in the form of uric acid. Uric acid blocks an enzyme that makes nitric oxide. Nitric oxide is your body’s natural blood pressure regulator, especially important for the full dilation of the lining of the arteries known as the endothelium. So when it is blocked, your arteries don’t fully dilate, creating a greater burden on your heart and raising your blood pressure – leading to chronic hypertension. Elevated uric acid levels can deposit into soft tissues causing painful inflammation, especially gout.
- Almost all of the F1P is turned into pyruvate, ending up as citrate, which results in de novo lipogenesis, the end products of which are FFAs, VLDLs, and triglycerides. The result – hyperlipidemia.
- Fructose stimulates g-3-p (activated glycerol), which is the crucial molecule for turning FFAs into triglycerides within your fat cells. The rate of deposition of fat into fat cells is dependent on the presence of g-3-p. The more g-3-p that is available, the more fat that is deposited. Fructose is the carbohydrate most efficiently converted into g-3-p. In other words, fructose is the most lipophilic (fat-producing) carbohydrate.
- FFAs are exported from your liver and taken up in skeletal muscle, causing skeletal muscle insulin resistance.
- Some of the FFAs stay in your liver, leading to fat droplet accumulation, hepatic insulin resistance and nonalcoholic fatty liver disease (NAFLD).
- Insulin resistance stresses your pancreas, which pumps out more insulin in response to rising blood sugar as your cells are unable to get the sugar out of your bloodstream, and this can progress to type 2 diabetes.
- As with a bolus dose of ethanol, a 120-calorie bolus of fructose results in a large fraction (again, about 40 calories) that directly contributes to disease.
You can see by comparing the metabolism of fructose with the metabolism of ethanol that they are very similar. In fact, when you compare the metabolism of 150 calories of soda with 150 calories of beer (a 12-ounce can of each), about 90 calories reach the liver in either case. Fructose causes most of the same toxic effects as ethanol because both come from sugar fermentation. Both ethanol metabolism and fructose metabolism lead to visceral adiposity (belly fat), insulin resistance and metabolic syndrome.