Earlier this week, I was asked whether fruit is bad for you because it has fructose.

Answer: no, absolutely not. As a general rule, nothing that God made is unhealthy across the board. There are certain circumstances under which eating too much fruit might be a bad idea (for instance, a patient with intestinal candidiasis, or insulin resistance), though. In those cases, limiting fruit to 1-2 pieces per day and going with the ones lower in sugar is wise until the condition is reversed.

But when extracted from fruit and used as a sweetener for other things, fructose by itself is definitely not healthy. Here’s why.

It’s Unregulated

When you ingest glucose (or a carb that can be broken down into glucose), it enters a ten-step biochemical process called glycolysis as one of three cycles to convert the glucose into your body’s energy currency, called ATP. At step 5 of glycolyss, your body gets to decide, based on its current needs, whether the glucose should be sent to storage (where it’ll end up as body fat) or whether it should be used as energy.

Fructose, however, enters glycolysis just after this regulatory step. Instead of continuing through glycolysis for energy production, it goes straight to storage (fat).

Because it bypasses the regulatory step, your body never asks itself the question, “Do I need energy right now or am I full?”

Leptin: the “I’m Full Now” Hormone

Leptin is a hormone secreted by adipose tissue (fat cells) that tells you you’re full. (Its opposite hormone is called ghrelin, which tells you you’re hungry.  You can remember this because the word ghrelin sounds like a stomach growling.) When your body detects that you have plenty of glucose (via insulin, see below) and your energy capacity is high (ie. you have adequate ATP), leptin will send the signal, “Stop eating, we have enough right now!”

But fructose doesn’t trigger insulin, and therefore it doesn’t trigger leptin. So you keep eating, gaining the extra as fat.

Insulin Resistance and Fructose

Because fructose doesn’t trigger insulin, you’d think this would make it less likely to cause insulin resistance than too much glucose might do. However, high fructose consumption is strongly associated with development of insulin resistance in animals, and the data suggests the same process occurs in humans. This may be because fructose turns into fat in the liver more readily than does glucose, and NAFLD (Non-Alcoholic Fatty Liver Disease) is strongly correlated with insulin resistance. It may be because fructose consumption leads to central obesity (since it goes straight to storage), and central obesity leads to insulin resistance. The process isn’t fully understood, but the connections are certainly there.

Fruit vs Fruit Juice

In the context of a piece of fruit, fructose is not bad for you. There’s not that much of it, relative to the fiber and all the nutrients you’re getting in the fruit. (If you eat nothing but fruit, though, you can potentially set yourself up for candidiasis or nutrient deficiencies.)

Fruit juice (or fruit concentrate), however, is the fruit with none of the fiber, which slows the release of the fructose into your bloodstream — so it’s a whopping dose of sugar all rushing into storage at once. Likewise, products “sweetened with fruit juice” may sound natural, but they are not healthy. They’re not as bad as, say, aspartame, but you’re not doing yourself any favors… especially if you’re trying to lose weight and reverse insulin resistance.

The Take-Home Message:

  • Eat fruit, just eat more veggies.
  • Skip anything sweetened with fruit juice… or at least consume it as sparingly as you would regular sugar.
  • Agave, natural sounding though it seems, is actually 90% fructose. You’re better off choosing honey.
  • Minimize fruit juices as beverages, or dilute them with water.

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