More on fructose

no added sugar

UPDATE: April 23, 2019 new podcast on this topic

The word “fructose” sends some self-appointed nutritionistas into a frenzy.  They read something on the internet, and they’re convinced fructose is poison, even though they understand little about human metabolism.  It’s a great justification for high protein/high meat diets, without any of that annoying healthy fruit.  Is it really poison, the cause of every human ill?  If so, how did early humans ever survive, eating all that fruit?

The amount of sugar consumed in fruit is small compared to the doses people get from sugar-sweetened foods and beverages.  Fructose is half of table sugar, and roughly half of high fructose corn syrup.  Honey has a higher proportion of fructose.  Pure fructose is hard to find, so blaming health problem only on fructose is tricky.  A study that will be published later this year tried to do just that.

For two weeks, subjects were fed diets with 25% of calories from either pure glucose or pure fructose or high fructose corn syrup (roughly half fructose and half glucose).  This is a high level of added sugar, but probably not unusual for many people.  If the person consumed 2000 calories/day, this represents about 125 grams, or 500 calories of added sugar.  You can easily get that much from 3 cans of soda pop every day.  Certainly plenty of people consume that much soda pop regularly, and maybe eat more sugar from other sources like candy, desserts, pastries and sweetened coffee drinks.

The researchers report that subjects on the fructose or HFCS diets, but not the glucose diet, had increased LDL cholesterol, triglycerides and other markers for heart disease risk.  Some of this effect can be traced to how fructose is metabolized in the liver, where excess fructose is turned into fat.

The key word is “excess”.  I posed a food scenario to Dr Lauri Byerley of Louisiana State University, who has written about fructose metabolism (registration required).

A 9 year old child eats one of these snacks:

  1. apple and cup of milk
  2. Snickers bar and can of soda pop

Both snacks have some fructose, although clearly the second one is much higher in added sugar, and has little nutritional value compared to the first one.  How would the child’s metabolism handle these?

The first snack has no added sugar, but has a natural sugar content of about 31 grams, of which about 11 grams are from fructose in the apple.  The second snack has 62 grams of total sugar, all added sugar, and 26 of those are fructose.  Does the higher fructose load in the second snack automatically cause problems?  As Dr. Byerley points out, not necessarily.  It really depends on a lot of other factors:

  • Is the child at a healthy weight or overweight
  • Is the child active or sedentary
  • What else is the child eating that day?
  • Is the child chronically eating excess calories, or usually eating the right amount for energy needs?

Obviously, the apple-milk snack has a lower total sugar load, so for a healthy, active child, those naturally occurring sugars would likely be burned for energy needs.  The candy bar snack is another matter, if the child is sedentary and already overweight and eating excess calories.  Fructose that’s not converted to energy is turned into fat.

Getting back to the original question: is the hysteria over fructose valid?  It depends.  As Dr. Byerley noted, it’s not possible to predict for sure how fructose is metabolized, because that metabolism depends on so many other factors at the time.  Research into this puzzle is needed, but these studies are hard to design.  I haven’t read the actual study mentioned above, but it seems to suggest that something about fructose, in very high doses, has an adverse effect on heart disease risk factors.

Speaking of fruit, if you ate a medium apple, an orange and a medium banana in one day, you’d get about 20 grams of fructose, no added sugar.  You’d also get plenty of fiber, vitamins and minerals.   If you ate that Snickers bar/soda pop snack, you’d get 26 grams of fructose, and a total of 62 grams of added sugar.  Nothing else.

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