Part 9: …Especially Fructose
One piece of advice that you wouldn’t imagine to be controversial, at least, is to minimize your intake of sugar. But even here, the mainstream voice can surprise: the American Diabetes Association still to this day says that for diabetics, “Sucrose-containing foods can be substituted for other carbohydrates in the meal plan or, if added to the meal plan, covered with insulin or other glucose-lowering medications.” And since the ADA wants everyone, even diabetics, to get at least 130g of carbohydrates (about 520 calories) every day, why, hell, go ahead and have a soda!
Why would they feed extra sugar to someone whose body has impaired blood sugar control? It seems ludicrous, and in fact, I think it’s terrible advice. But to understand, at least in part, how this situation arose, we have to talk about fructose and the glycemic index.
The glycemic index is a measure of the effect a food has on blood glucose levels. The scale is defined such that a solution of glucose itself (which, as you can imagine, raises blood glucose levels substantially) is assigned a value of 100. A food that only raises blood glucose levels half as much would have a value of 50, and so on. Dieters are often advised to avoid foods with a glycemic index higher than 55.
Here’s a short table listing the glycemic index of a few foods, just to illustrate the idea. Lower is better. You can take these values as ‘very approximate’, since I pulled them from a random web site.
glucose 100 baked potato 95 refined white flour 85 table sugar (sucrose) 70 banana (ripe) 60 banana (unripe) 45 carrot juice 40 carrot (raw) 30 fructose 20 asparagus 15 beef 0
Americans eat a lot of sugar, and about 1/2 of it is fructose (a kind of sugar found in fruit), either as table sugar (sucrose, which is 50% fructose, 50% glucose), or as high-fructose corn syrup, (HFCS, or HFCS-55, which is 55% fructose, 45% glucose).
Hey, and fructose was in the table above, nestled snugly down there with the vegetables. It has almost no effect (at least in the short term) on blood glucose or insulin levels. This led, in the 1980’s, to its promotion as a ‘healthy’ sugar, and table sugar, being half fructose, looked pretty attractive (for a sugar), especially compared to baked potatoes and bread made from refined white flour. In The New England Journal of Medicine, diabetologist John Bantle wrote, “We see no reason for diabetics to be denied foods containing sucrose.”
Sounds great! But mark the sequel:
Unlike glucose (70% of which is taken up by the body’s cells before ever encountering the liver), fructose is not immediately usable by the body; it must be metabolized in the liver, which converts it to triglycerides (”fructose-induced lipogenesis”). Now, this is bad enough — high triglyceride levels are a far better predictor of cardiovascular disease than total cholesterol — but it gets worse:
…fructose apparently blocks both the metabolism of glucose in the liver and the synthesis of glucose into glycogen, the form in which the liver stores glucose locally for later use. As a result, the pancreas secretes more insulin to overcome this glucose traffic-jam at the liver, and this in turn induces the muscles to compensate by becoming more insulin resistant. The research on this fructose-induced insulin resistance was done on laboratory animals, but it confirmed what Reiser at the USDA had observed in humans and published in 1981: given sufficient time, high-fructose diets can induce high insulin levels, high blood sugar, and insulin resistance, even though in the short term fructose has little effect on either blood sugar or insulin and so a very low glycemic index. It has also been known since the 1960s that fructose elevates blood pressure more than an equivalent amount of glucose does, a phenomenon called fructose-induced hypertension.
Because sucrose and high-fructose corn syrup (HFCS-55) are both effectively half glucose and half fructose, they offer the worst of both sugars. The fructose will stimulate the liver to produce triglycerides, while the glucose will stimulate insulin secretion. And the glucose-induced insulin response in turn will prompt the liver to secrete even more triglycerides than it would from the fructose alone, while the insulin will also elevate blood pressure apart from the effect of fructose…
The effect of fructose on the formation of advanced glycation end-products — AGEs, the haphazard glomming together of proteins in cells and tissues — is worrisome as well. Most of the research on AGE accumulation in humans has focused on the influence of glucose, because it is the dominant sugar in the blood. Glucose, however, is the least reactive of all sugars, the one least likely to attach itself without an enzyme to a nearby protein, which is the first step in the formation of AGEs. As it turns out, however, fructose is significantly more reactive in the bloodstream than glucose, and perhaps ten times more effective than glucose at inducing the cross-linking of proteins that leads to the cellular junk of advanced glycation end-products. Fructose also leads to the formation of AGEs and cross-linked proteins that seem more resistant to the body’s disposal mechanisms than those created by glucose. It also increases markedly the oxidation of LDL particles, which appears to be a necessary step in atherosclerosis.
…from Good Calories, Bad Calories (Knopf, 2007), by Gary Taubes, p. 200-201
The above is especially alarming considering that our national per-capita consumption of sugars has increased from a stable historical mean of 110-120 pounds per year from the 1920’s (or even the 1950’s) up to almost 150 pounds per year (almost half a pound a day!), with virtually all of the increase due to high-fructose corn syrup (e.g. soda pop, Snapple, ice cream, candy, low-fat yogurt, salad dressings, you name it).
As for me, I’ve cut back my consumption of all kinds of sugars…especially on added fructose.
To be continued…