How is sucrose broken down by the body, in comparison to unbound fructose and glucose?

Answered on August 19, 2014
Created June 28, 2013 at 8:45 PM

I've always been a little confused about this. I hope one of you nutritional science nuts can shed some light on this.

I've seen many fructose/sucrose/glucose related questions on Paleohacks, and inevitably someone mentions that sucrose is simply 50% each fructose and glucose and therefore eating sucrose is 50% as bad as eating fructose. Okay, got that, but it ignores the bond between the sugars.

How is sucrose broken down by the body as compared to unbound fructose and glucose? Is it broken down any differently, is the bond between the sugars another factor in how our bodies metabolize it, or is it all the same in the end? Is sucrose really any better/worse/different than fructose on its own?

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on June 28, 2013
at 09:22 PM

Most sucrose we eat is hydrolyzed to glucose and fructose by the enzyme sucrase in the small intestines, although some (likely a small amount) of sucrose will be hydrolyzed in the presence of the acidic medium of our stomach.

Personally, I don't think it's fair to say the health effects of a certain amount of sucrose will be comparable to the effects of the amount of fructose contained therein for a few reasons.

Most studies indicting fructose use fructose only, but fructose alone can be hard to absorb in the digestive tract (fructose malabsorption is a common issue), which can lead to gut issues, which can lead to lots of health problems. The presence of glucose is known to aid the absorption of fructose by stimulating the sugar transporter GLUT2, so it seems likely sucrose might help ameliorate these negative effects.

Fructose alone also doesn't really stimulate insulin, but sucrose does, almost as much as just glucose. Since insulin is thought to help regulate appetite and glycation detoxification (via glyoxalase 1), sucrose again seems like it would be safer than fructose and likely on par with just glucose.

I looked for evaluations of sucrose versus glucose or starch in controlled human trials here and found far less damning evidence like there is with fructose vs. glucose, although starch seems to come out a bit ahead. Either way, it made me doubt sucrose was comparable to the sum of its parts.

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