11
Jan
12

Sucrose shenanigans

Apparently I want to write about sugar metabolism and insulin these days.  Okay.

So the last time I dumped a bunch of ScienceDaily links on this here blog, I noted that a number of authors had pointed the Finger of Opprobrium at sucrose (table sugar, a compound of glucose and fructose) as damningly as at high-fructose corn syrup (a solution of glucose and fructose).  I wondered if there was a metabolic difference between the two besides “sucrose needs a sucrase enzyme of some sort before it can be metabolized”.  Being very much not a biology nerd, I have no idea how important this is, and I suspect the answer is “maybe a little, maybe a lot; it kind of depends”.

Well, lookey here:

The first study showed that male rats given water sweetened with high-fructose corn syrup in addition to a standard diet of rat chow gained much more weight than male rats that received water sweetened with table sugar, or sucrose, in conjunction with the standard diet. The concentration of sugar in the sucrose solution was the same as is found in some commercial soft drinks, while the high-fructose corn syrup solution was half as concentrated as most sodas.

Whoa!  If this is indicative, the extra fructose — or maybe the extra enzyme needed in the metabolic pathway for sucrose — is a big fuckin’ deal.  But then:

The critical differences in appetite, metabolism and gene expression that underlie this phenomenon are yet to be discovered, but may relate to the fact that excess fructose is being metabolized to produce fat, while glucose is largely being processed for energy or stored as a carbohydrate, called glycogen, in the liver and muscles.

I was under the impression that the liver metabolized fructose preferentially to produce glycogen (although I’m also under the impression that it needs a 1:1 ratio of glucose to fructose to do it), so this claim makes little sense to me on its face.  I suppose it’s possible that the sucrase requirement throttles uptake, but since sucrase does its thing in the duodenum rather than in the liver proper I’m awfully skeptical about that.  If I’m right about the 1:1 ratio for glycogen formation, I could imagine that the left-over fructose from 42:55 HFCS would immediately get turned into triglycerides and somehow fuck up liver function, whereas the 50:50 sucrose would keep churning out glycogen until the rats’ muscles had been packed full of the stuff, but I have very low confidence in that explanation.

On the other hand, I have very low confidence in this counterpoint paper in general:

So here’s what these folks did: They took a bunch of people and gave them something to drink before lunch.  Then they monitored how much those people ate at lunch.  From there, they drew conclusions about the various drinks’ propensities to cause obesity.

“Some companies have made a sincere effort to put sucrose back in soda,” said Dr. Adam Drewnowski, director of the Nutritional Sciences Program at the University of Washington and the senior author of the study. “But there is no direct link between the type of sweetener and obesity. As far as appetite is concerned, cane and corn sugars in beverages are much the same.”

Colour me skeptical.

Here’s the setup:

The Seattle investigators provided subjects with a beverage mid-morning, then tracked hunger, appetite and thirst for two hours, and then gave the study participants lunch. Cola beverages sweetened with sucrose or with two different types of high-fructose corn syrup were compared to an aspartame-sweetened diet cola, milk (1 percent fat), and to a no-beverage control group. Lunch consisted of a wide variety of savory and sweet foods, accompanied only by plain water. Each participant went through separate tests for each type of beverage over the span of several weeks.

[…] Participants ate somewhat less at lunch after drinking any of the caloric beverages, but only partially compensated for the calories they consumed in the beverage. People who drank any of the caloric beverages — whether cane-sweetened cola, one of the high-fructose sweetened colas, or 1 percent milk — consumed more total calories that day when both the beverage and lunch were taken into account. Researchers found no differences in how the four caloric beverages affected appetite and food intake.

Look, sucrose provokes an insulin response.  So does HFCS.  So does milk.  Insulin suppresses appetite.  The novelty here, if anything, is that a single beverage of each type — normalized for calorie content, I presume — provokes roughly the same insulin response after two hours.  What about after ten minutes?  Meh, that can’t possibly be important to people who buy combo meals at fast-food joints, because they all drink their Coke first and get to their burger and fries one hundred and twenty minutes later.

“In terms of suppressing your appetite, a calorie from high-fructose corn syrup seems to be no different than a calorie from table sugar or a calorie from milk,” explained [researcher Pablo] Monsivais.

If you’re drinking it once, two hours before a meal, yeah.  How exactly does this merit sweeping claims about the role of HFCS in obesity?

This study was supported by grants from the National Institute of Dental and Craniofacial Research at the National Institutes of Health, the American Beverage Association, and the Corn Refiners Association.

Oh, that’s how.  Okay then.

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