Paleo Diet and Paleolithic Diet Questions & Answers

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From what I've read, fructose stimulates hunger (causing you to want to eat more of it) and is processed by the liver directly into stored fat. That is not what my question is about, because those both make sense to me from an evolutionary standpoint: the plant wants its fruits to be eaten and seeds spread, and the body wants to store extra energy during times of plenty (when fruits are in season) for later when times are scarce.

Why, exactly, is fructose hepatotoxic? Is it because we are consuming it in such great quantities, greater than we ever would have encountered in natural, wild fruit? Or is there some sort of evolutionary benefit to either us or the plant? Is it a chemical defense, like capsaicin? Just curious.

flag	asked Jan 31 2011 at 13:31 Sgroh87 842●5●17

This question has been asked and answered in several other threads. – Stephen-Aegis Jan 31 2011 at 19:40

Mass quantities relative to what we do. – thhq Feb 16 2012 at 14:56

And thinking about it, being fat is a chemical defense against starvation. +1. – thhq Feb 16 2012 at 14:58

Weird, someone went through here and downvoted every answer that said or implied something bad about fructose. – Paul Feb 16 2012 at 16:52

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Wasn't me. Hello cliff? – thhq Feb 16 2012 at 17:18

pfw · Answer 1 · 2011-01-31 14:02:01Z UTC

If you are liver glycogen replete and continue to eat fructose in excess, your liver will attempt to convert it into fat to pass around the body. If you overeat fructose chronically, excess fat will begin to accumulate in your liver, causing non-alcoholic fatty liver disease.

This happens when you chug a lot of soda (or some other pure sugar "food") chronically, something which is entirely outside everything's evolutionary experience. If you are exercising constantly fructose can help you quickly replenish liver glycogen (a lot of those carb replenishment goos for endurance athletes are half or a third fructose for this reason), but most people aren't working at that level.

Incidentally, it's incorrect to say that "fructose is bad for you". Like all things, fructose is context sensitive and ranges from beneficial to benign to bad. If you eat it in excess, as you may if you are eating SAD without thinking about it, bad things can happen, but if you're incidentally consuming it as part of a healthy diet then it's probably not an issue.

Domer88 · Answer 2 · 2011-01-31 21:20:11Z UTC

Read this story:

link text

Hominids about 15M years ago developed a mutation in the way they metabolized fructose, which is why it goes straight to fat in humans today. At the time, it proferred an evolutionary advantage, perhaps because our ancestors were leaving the jungle and moving to the savanna, where fruit would be seasonal.

In any case, other mammals do not metabolize fruit the way we do. We pack it away into fat for a rainy day. Other mammals use it for immediate energy. Our strategy made perfect sense when fruit was only available at a few select times per year. But now, it's a recipe for disaster. Compound that with our relatively recent discovery of cane sugar and HFCS, and we are loading up on orders of magnitude more fructose than we were evolved to handle.

Philosopher · Answer 3 · 2011-01-31 18:58:09Z UTC

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HFCS "high fructose corn syrup" commonly called "fructose" the processed sugar contained in most sodas is really bad for your health for a number of reasons including the empty calories associated with soda consumption. Fructose in whole fruits is not bad for your health, unless you still need to lose weight or have metabolic syndrome. Fruits have been a main staple of primates and humans for millions of years and fruit is an essential component in almost any hunter-gatherer diet!

answered Jan 31 2011 at 18:58

Philosopher
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Fructose regardless of the source is the same. Eat too much fruit, and you will get too much fructose. Your liver doesn't care where it comes from. And HFCS has only slightly more fructose than sugar does, so the focus on HFCS at the expense of a broader focus on sugar is misguided. – Domer88 Jan 31 2011 at 20:26

Domer the problem is no one is able to get from fruit the huge amounts of HFCS that you get with sodas, if you drink them all day long. Also HFCS does contain a lot of glucose that is much more harmful than fructose. If you do not get fruits your diet is way different than the one of hunter gatherers! – Philosopher Jan 31 2011 at 21:21

Many hunter gatherer groups do not actively seek fruit or consume it regularly. – Stephen-Aegis Feb 9 2011 at 23:09

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Regardless of the feabibility of consuming large amounts of fructose from various sources, we have got to stop fetishizing where fructose comes from. Once it leaves the stomach and enters the bloodstream, heading straight for the liver, your body could care less whether it came from an apple, was cleaved from a sugar molecule, or was processed in an Iowa HFCS factory. – Domer88 Feb 10 2011 at 12:57

+1 for eating one whole fruit, which is different from drinking it from a glass containing 10 fruits and no fiber. – thhq Feb 16 2012 at 13:26

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Travis Culp · Answer 4 · 2011-01-31 18:44:21Z UTC

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Though technically a monosaccharide, practically speaking, we may as well think of fructose as a lipogenesis hormone. Talking about fructose as any other "carb" is far too simplistic.

answered Jan 31 2011 at 18:44

Travis Culp♦
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Both fructose and fat are foods and both are needed to produce triglycerides. Why do you selectively condemn the fructose? Ad libitum eating of both is a problem. And ad libitum eating of glucose (starches and sugars) promotes triglyceride formation at the adipose, so it is no less harmful. – thhq Feb 16 2012 at 13:16

Stancel · Answer 5 · 2011-01-31 19:56:54Z UTC

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HFCS is comparable in fructose:glucose ratio to sucrose and honey, both "natural" sweeteners considered healthier than HFCS. It is also comparable in Glycemic Index. If there is a problem with HFCS, it may be toxic processing, not the fructose.

answered Jan 31 2011 at 19:56

Stancel
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Fructose unprocessed still shows the exact same physical effects in the liver, how exactly is that toxic processing. – Stephen-Aegis Feb 9 2011 at 23:10

Paul · Answer 6 · 2012-02-16 10:00:52Z UTC

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I just want to make sure that everyone knows that a good portion of one of Dr. Harris's most recent posts gives his position on fructose. It's here. I would suggest reading the whole thing, not just the section marked "fructose," in order to get the context. Sorry if someone's mentioned this on another thread, recently I haven't been reading paleohacks as obsessively as usual.

edited Feb 16 2012 at 10:00

answered Feb 2 2011 at 3:16

Paul
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Uh...you should probably return to obsessiveness. Speaking of, in case you haven't checked out Patrik's paleo baby link, the blogger made this cool post...thepaleochild.com/2011/01/… – Kamal♦ Feb 2 2011 at 6:12

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WCC Paul ♦, you need to update your link. – Wcc Kamal Stabby fan Feb 16 2012 at 2:36

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The old PaNu links usually redirect, but I think this one didn't because he revised it and so the link changed. – Paul Feb 16 2012 at 10:01

Thanks for updating the link WCC Paul , because I actually do want to read it. – Wcc Kamal Stabby fan Feb 16 2012 at 21:00

losterman · Answer 7 · 2011-02-09 21:43:49Z UTC

Are you asking about the biochemistry of why it's bad? If you want to know the nitty gritty, watch this lecture, it's amazing: http://www.youtube.com/watch?v=dBnniua6-oM

But in brief, it's a toxin--by definition--because the liver is the only organ that can deal with fructose (in contrast to glucose, which can be used by any cell in the body).

Fructose in fruit is not actually good for you. The only reason that it's okay to eat fruit is that fruit contains a healthy dose of fiber along with the fructose, which prevents some of the fructose from being absorbed during digestion. Fructose in moderation won't kill you, but it's not, strictly speaking, "healthy."

Also, just FYI, you can order powdered dextrose (which is pure glucose--I recommend http://www.barryfarm.com/) to use as an alternative sweetener. It's still sugar, but it won't fry your liver.

Fructose is bad for you - why?

7 Answers