Wednesday, March 31, 2010

Paleo Basics: Fructose Fact Vs. Fiction

In response to my post on the Kitavan diet, which includes plenty of fruit and likely 36g of fructose daily, "gn" asked me if I think it plausible to suppose that human ethnic groups differ in ability to deal with fructose loads, so that daily fruit won't harm dark-skinned Kitavans living in tropical climate (constant summer) for hundreds of generations, but will harm people of European descent whose ancestors had fructose supply only in late summer and fall seasons.

From this question, which I will address below,  I get the impression that the Lustig lecture embedded above has led many to believe that daily ingestion of fructose in any quantity has toxic effects, such as non-alcoholic-fatty-liver-syndrome (NAFLS), particularly to people of European descent.

Unfortunately, Lustig's lecture contains misleading hyperbole or exaggeration (e.g. within the first five minutes he says "The Japanese diet is all carbs and no fat, and the Atkins diet is all fat and no carbs" and later he claims that Japanese eat no sugar, a falsehood) and doesn't give important details about research on fructose metabolism. The main problem lies in a failure to define the dose of fructose required to produce the adverse effects. Let's take a look at some of the research to see what people have missed.

Fructose Research

Le et al investigated the effect of fructose overconsumption on blood lipids and ectopic lipid deposition in healthy subjects with and without a family history of type 2 diabetes.   In this study they found that fructose overconsumption  "increased ectopic lipid deposition in liver and muscle and fasting VLDL-triacylglycerols and decreased hepatic insulin sensitivity" and the effect appeared greater in offspring of parents who had type 2 diabetes.

To get this effect, they used a hypercaloric high-fructose diet supplying 3.5g fructose per kg of fat free mass, amounting to more than 35% of energy intake.  For a lean individual like myself, that would require putting down more than 222g/888kcal of fructose daily while also consuming more calories than I expend.   This is an unrealistic intake of fructose for a person eating a whole foods diet.  It would require consuming more than 444g of table sugar, 12 non-diet sodas, or about 18 medium size apples or bananas.

For another example, Ackerman et al studied fructose-induced fatty liver disease in rats.  To induce FLD in the rats, they used a diet consisting of 60% fructose by weight, which supplied all the carbohydrate in the diet.  Humans do not typically consume diets in which fructose is the sole carbohydrate and the major macronutrient by weight.

Brown et al looked at the effect of fructose on blood pressure in young healthy people.  They had 15 volunteers drink a 500ml  beverage containing a single dose of 60g fructose or glucose.  Both sugars produced an increase in heart rate, and the fructose dose produced an elevation in blood pressure that persisted for at least 2 hours.  To get a single dose of 60g fructose from sucrose (table sugar) would required ingesting about 120g sugar in one sitting--or, 157g of high-fructose corn syrup, or more than 4 apples or 4 bananas.  This says nothing about the effects of consuming the more typical 15g fructose per serving found in a serving of soda, let alone eating whole fruits, which contain other components (e.g. potassium) that tend to reduce blood pressure.  For my n=1 experiment, I have routinely eaten 3-4 pieces or servings (cups) of fruit in a day for more than 10 years in a row and my blood pressure remains at 110/60.

Swarbrick et al claimed to show that consumption of fructose-sweetened beverages increases postprandial triglycerides and fasting apoB concentrations, and suggest that long-term consumption of diets high in fructose could lead to an increased risk of CVD.  To produce their results, they fed study subjects diets providing 25% of total energy as fructose.  For a 2000 kcalorie diet, that is 500 kcalories or 125g of fructose.  Again, this would require consuming a total of 250g of sugar from sucrose or high-fructose corn syrup, i.e. more than 6 non-diet sodas, or at least 10 pieces or cups of fruit in a day. 

As John White noted in the American Journal of Clinical Nutrition, in the typical U.S. diet, fructose contributes about 200–250 kcal/d, which amounts to about 7–8% of the current 2700-kcal/d per capita total calorie intake, a much smaller intake than used in these experiments, so they provide no evidence that typical intakes of fructose induce fatty liver disease.  He added:

"Although examples of pure fructose causing metabolic upset at high concentrations abound, especially when fed as the sole carbohydrate source, there is no evidence that the common fructose-glucose sweeteners do the same. Thus, studies using extreme carbohydrate diets may be useful for probing biochemical pathways, but they have no relevance to the human diet or to current consumption."
I could go on but instead I will refer you to an excellent critical review of Lustig's lecture by Alan Aragon:  The bitter truth about fructose alarmism.  After reviewing 19 papers on the effects of dietary fructose disputing some of the anti-fructose claims made by Lustig, and finding Lustig's presentation lacking, Alan comments:

"So, what’s the upper safe limit of fructose per day (all sources considered)? Again, this depends on a number of variables, not the least of which are an individual’s physical activity level and lean body mass.Currently in the literature is a liberal camp reporting that fructose intakes up to 90 grams per day have a beneficial effect on HbA(1c), and  no significant effects are seen for fasting triacylglycerol or body weight with intakes up to 100 grams per day in adults [15]. The conservative camp suggests that the safe range is much less than this; roughly 25-40 grams per day [19].  Figuring that both sides are biased, the middle figure between the two camps is roughly 50 grams for active adults."  
Back To The Original Question

As I noted above, "gn" asked me if I find it plausible that Europeans have less tolerance for fructose than Kitavans.  Short answer: No.  Long answer:  All of the above studies were done on people of European descent, illustrating that Europeans have a quite high tolerance for fructose.  Further, fructose tolerance developed millions of years ago in the African primate lineage from which we all hale, due to primate consumption of fruit as a dietary staple.  When humans moved out of Africa about 50 thousand years ago, they would have lost fructose tolerance only if maintaining it proved a disadvantage in northern climates.  In other words, they would have lost fructose tolerance only if maintaining it resulted in death before reproduction.

I can't imagine a scenario in which the environment would select against fructose tolerance, i.e. in which maintenance of fructose tolerance despite a fructose-poor environment, would cause a person to lose fertility or die before having a chance to reproduce.  I also can't imagine a scenario in which the environment (seasonal variations in supply of fructose) would select for fructose-intolerance, i.e. favor the reproduction of fructose-intolerant individuals.  On the contrary, seasonal supply of fructose would continue to select for those who could eat naturally large amounts of fructose (i.e. fruits) when seasonally available, because those people maintaining the deeply ingrained primate ability to metabolize fructose would even in the north have a greater total available food supply than fructose-intolerant individuals.

I routinely eat three to five servings of fruits daily, i.e. 30 to 50g of fructose, and have done so most days for the past 10 years that I have eaten a practically paleo diet.  My ethnic background consists of Hungarian, French, and German.   My last blood profile showed my total lipoproteins at 231 mg/dL, my HDL at 85, and my triglycerides at 47.  Using the Friedewald equation they calculated the LDL at 138, but since I have very low triglycerides, using the Iranian formula calculator I calculate my LDL equals 104.  Since I have nearly twice as much HDL as triglycerides, and low fasting glucose, I have extremely low heart disease risk.  My liver enzyme levels and bilirubin all fell in low normal values, indicating no liver dysfunction.



Todd Hargrove said...


Thanks for another great post. I am really enjoying your blog.

Thomas said...

Don-this is a great "perspective" post-thanks. Fructose being "evil" in all forms is in vogue right now among many paleo eaters and thinkers-some even consider fruit candy bars from a tree (maybe a reference to the relative amount of fructose and fiber in today's fruits compared to paleo times). It's interesting how a simple idea like "overconsumption of HFCS is bad for you" can turn it into "fruit is bad for you." Posts like this one help to steady the ship.

Don said...


About the claim that wild fruits have less sugar, it is not even close to the truth. Brand-Miller discusses the carbohydrate contents of wild fruits consumed by Australian Aborigines and reported:

"The average nutrient composition of all the fruit samples analysed (n = 334) is shown in
Table 1 (macronutrients) and Table 2 (micronutrients). On first inspection they appear to be a
little higher in protein (2 v. 1 %) and fat (1 v. 0 %) compared with the average of 17 types of
cultivated western fruits. These small differences could be explained in large part by the lower
water content of the wild foods (72 v. 85 % in cultivated foods). Native fruits also appear to be
twice as high in both carbohydrate (21 v. 9 %) and fibre (8 v. 3 %). However, because the
methods used are not ideal (see above), the carbohydrate is probably an overestimate and the
fibre an underestimate."

So wild fruits have no less and possibly twice as much carbohydrate as cultivated!

Google "Australian Aboriginal plant foods: a consideration of their nutritional composition and health implications" to get the full text.

Dustin C said...


I have always been curious about studies linking fruit consumption and negative health outcomes. Even honey with similar fructose composition seems to be metabolically different from HFCS and table sugar.

Also, I like the new layout of the blog.

Melissa said...

When I was raw vegan I knew plenty of fruitarians. They always liked to bandy around how they were free of metabolic syndrome and had been to their doctors and declared free of insulin resistance. The problem with that diet is not the foods they are eating, but what they are NOT eating, which is foods that have minerals, DHA, etc. They might not have been diabetic, but their teeth were in scary condition!

Erik said...


Great post. What are your thoughts on the interaction between Vitamin D/sunlight exposure and fructose metabolism? It seems like fruit would have been widely available only in times of sunshine: year round in the tropics and seasonally in colder climates.

Vitamin D deficiency is associated with metabolic syndrome, insulin resistance, etc, all of which have also been linked to (excess amounts of) fructose. Might there be some connection?

Miki said...

This post is certainly an eye opener regarding fructose. I wonder if fructose in fruit has a different effect than fructose in sugar. The poor twisted faces of the children in NAPD by Weston Price continue to haunt me. Something (sugar? white flour? both?) must have caused it.

Anonymous said...

We can eat a boatload of fructose with a modern diet. Especially considering that HFCS is used as a fat substitute in just about everything with a "low fat" sticker. And we all know how healthier a low fat diet is, don't we.

Maybe we are still fully adapted to a high fructose diet. Or rather, we are still fully adapted to a high fruit diet. But I doubt it. I mean, we got rid of the very large abdomen needed to digest that much fruit. If we really wanted to eat a lot of fruit, we would have to grow back the larger abdomen too. Like that of a chimp or gorilla or most any other non-human primate actually. But then, if we grew a larger abdomen, we would have to trade tissue elsewhere.

Are you familiar with the expensive tissue hypothesis? It says that in order for our brain to grow bigger, other tissue must have grown smaller to compensate. It's all reasonable and very convincing. The tissue that grew smaller is the gut. So, a bigger brain means a smaller gut. Conversely, a bigger gut means a smaller brain.

There is physiological evidence for this tissue tradeoff. First, the brain requires a huge amount of fuel compared to any other organ. This much fuel can only come from fat, especially animal fat which contains a lot of saturated fat which is basically our preferred fuel substrate. Then, fat can be digested much more easily and cheaply than fiber ever could. And finally, the brain runs about 30% more efficiently on ketones, a fat by-produt, than on glucose. So, not only does fat provide enough fuel for the brain, but it's also much less expensive to digest. And now we have a much bigger brain and a much smaller gut.

We might have retained some ability to metabolize fructose safely. But I doubt we retained the full adaptation to a high fruit diet, or even to a corresponding high fructose diet.

Gyan said...

Is it necessary for a trait to be actively selected against in order to be lost?

Cant a trait be lost just because of disuse?
I suppose it costs some metabolic energy to build fructose tolerance and continued disuse might lead to disappearance of fructose tolerance.

Ned Kock said...

Yes, those initial comments by Lustig are totally off mark. One of the staples of the Okinawan diet is pork:

But, more to the point of your excellent post, I have seen some research (I cannot find the reference now) arguing that liquid fructose consumption is the real problem.

That is, the ingestion of a large amount of fructose in liquid form (e.g., a non-diet soda) is problematic, but not consumption via fruits.

It seems to make sense from an evolutionary perspective, as our hunter-gatherer ancestors probably consumed only water in liquid form after weaning.

Greg said...

Lustig makes the case that fructose is metabolized like alcohol as something toxic to the liver. I think we still need to honestly answer the question: is fructose a liver toxin? Even if we are built to be able to handle a fair amount of fructose, not everyone has a healthy liver.

This goes with the question of is it *optimal* to consume fructose? I think the answer is no. However, you seem to be making the case that it is optimal to consume fruit, which happens to contain fructose, and the benefits of fruit far outweigh the minor negatives of fructose.

Anonymous said...

Honey...what are your feelinggs about 3 tsp per day too much?

Ryan Koch @ Health Matters to Me said...

Thanks, Don, for a being a voice of reason out there. A lot of people get caught up in thinking that all fructose is evil after listening to Lustig or reading a few papers. The thing that most folks miss if that HFCS is a very different beast than honey, fruit, maple syrup, or other natural forms of fructose. There are actually chemical differences!

D-fructose = natural fructose found in fruits, honey, etc.

L-fructose = synthesized through chemical means.

There are zero studies I know of showing that eating too much fruit or honey causes the same metabolic problems as isolated, artificial fructose.

In fact, there are some studies showing honey being protective to the liver in rats. All you fructose haters wrap your heads around that one!

Honey prevents hepatic damage induced by obstruction of the common bile duct

Substituting Honey for Refined Carbohydrates Protects Rats from Hypertriglyceridemic and Prooxidative Effects of Fructose

Stephan at Whole Health Source posted a paleo diet study a while back where the participants actually ate quite a bit of honey and still saw major health improvements.

Paleolithic Diet Clinical Trials Part III

Not all fructose is evil just as not all fats are evil. It's quality that counts!

Stephan said...

Hi Don,

I agree that there are examples of cultures such as the Kitavans and the Kuna that eat a fair bit of sugar and seem to tolerate it fine. The Kitavans in particular, but all their sugar is unrefined.

I still think sugar has a place in the diseases of civilization though. The first problem is that extracted sugar is totally devoid of micronutrients. Given that the average American gets 20-25% of his calories from sugar (~500 calories), that's a lot of missing micronutrients.

But the thing about fructose is it's one factor among others. Animal studies suggest that fructose and seed oils amplify one another's toxicity. Then there's the fact that plausible doses of fructose don't get properly absorbed in the small intestine in many people, causing bacterial growth.

I also think it's problematic to extrapolate the results of short-term feeding studies to long-term health outcomes. The effects that are seen with high doses in short-term trials may occur at lower doses over a longer timescale (or they may not). Also, it appears that the older and less fit a person is, the more susceptible they are to harmful effects of fructose.

I also know sugar makes me feel like crap, and it always has. Even fruit does it if I eat it on an empty stomach.

Helen said...

Thank you Don -- and Ryan, too! I've been suspecting the "fear of fruit" promoted on a lot of paleo blogs, some traditional foods blogs, and Dr. Davis' blog has been off the mark. My feeling is that we crave fructose because it is part of a package that has been beneficial to us - fruit.

I'm familiar with the argument that fruit uses fructose, an addictive substance, to trick us into eating it, but why would our bodies give fruit the upper hand, allowing it to poison us for its own nefarious purposes?

We evolved to exploit fruit at least as surely as fruit evolved to exploit us. My guess is that our bodies are telling us to eat fruit for good reason. We aren't "fooled by fruit," though we *can* be fooled by newfangled industrial foods containing refined/free fructose. The seasonality and rarity arguments about fruit have some merit, but have a northern European bias, as you've noted. (And, though it's almost all the product of cultivation, fruit is abundant here in seasonal New England from June through November.)

I do think that refined and especially isolated fructose molecules are awful stuff and we aren't meant to process those kinds.

But fruit has a lot in it besides fructose - soluble fiber, which is anti-inflammatory, bioflavonoids, vitamin C, and many other anti-inflammatory and/or anti-oxidant phytochemicals (protective against the dreaded AGEs, Dr. Davis), depending on the fruit.

I've wondered about the claims against honey, also, since it has been shown to be very anti-inflammatory.

My two-year-olds love fruit and even seemed to have a hunter-gatherer drive for picking the fruit and berries in our yard almost as soon as they could walk.

I really thank you for giving a well-reasoned counter-argument to the anti-fruit drumbeat that's been making the rounds. It makes me feel better as a parent. It's going to be hard enough to keep soda and candy out of their hot little hands - do I have to worry about apples, too? Thankfully, it seems not.

Dustin C said...

It seems honey offers more benefits than processed sugars when switched as the main sweetener. Although, is honey a health food or equivalent to fruit? That is of curiosity. Hunter gathers seems to have access to honey seasonally. Since honey has an indefinite shelf life, it could have become calories source annually. Also climate depends on honey productions which would either increase or decrease the availability.

Helen: Here is some more research on Honey:

Natural honey lowers plasma glucose, C-reactive protein, homocysteine, and blood lipids in healthy, diabetic, and hyperlipidemic subjects: comparison with dextrose and sucrose

Differential effects of honey, sucrose, and fructose on blood sugar levels.

Effects of natural honey consumption in diabetic patients: an 8-week randomized clinical trial.

Total antioxidant content of alternatives to refined sugar.

Honey with high levels of antioxidants can provide protection to healthy human subjects.

Natural honey and cardiovascular risk factors; effects on blood glucose, cholesterol, triacylglycerole, CRP, and body weight compared with sucrose

Effect of honey on serum cholesterol and lipid values

Anonymous said...

Very interesting subject today...and thanks all for your input on honey...I bet there is a lot more that can be said....

Dustin C said...

Opps, it seemed my hyper links didn’t work. Just Google/pubmed the titles, they should show up.

Don said...




Glad you like it.


I agree with you, effects of any food depend on quality, quantity, and context.


I would guess that people who drink a lot of sodas don't get much sun. Therefore, vitamin D deficiency coincides with high fructose consumption.


As Price emphasized over and over, those faces resulted from absence of vitamins and minerals, not just presence of starch and sugar.


You use terms without defining them. What counts as a "high fruit" diet?

You also ignore evidence. Kitavans run their brains quite well on a low (21%) fat diet, proving that humans don't require a high fat diet for normal brain development or function.

I am thoroughly familiar with the expensive tissue hypothesis, having read the original paper a few times. It does not state that humans require a high-fat to either produce or support the brain. Humans only require a foods with a higher caloric density and lower fiber content than other primates. Kitavans prove that a low fat diet consisting largely of tubers can provide adequate energy for the brain. Humans did not have to switch to exclusive fat burning to allow gut reduction and brain expansion, they only needed to get a diet with less fiber and more easily digested calories than available to chimps.

The fact that we have at least 3 times as many copies of the gene coding for salivary amylase, and produce 6-8 times as much salivary amylase production as chimps indicates that we adapted to starch ingestion long ago.

This is positive evidence that our ancestors ate carbohydrate-rich foods regularly.

The brain's ability to adapt to ketones does not prove that we evolved on a high fat diet either. Again, we required this ability to endure periods of fasting or low food availability, and it is not a unique feature of animals with carnivorous ancestry. The mouse brain also adapts to ketones.

The large guts of chimps and gorillas are not for digestion of fruit or fruit sugar, but for fermentation of fiber from raw leaves. In fact, it is their use of fruits as 75% of their diet that allows chimps to support a larger brain (relative to body size) and energy expenditure than animals like cattle.

The research clearly shows that humans easily tolerate and even benefit from the amounts of fructose in a diet containing several servings of fruit daily. You might call this a "high fruit diet" but I would disagree, it is a far cry from the chimpanzee diet in which fruit supplies up to 75% of total energy.

Don said...


We have no evidence that humans have lost tolerance or ability to metabolize fructose, so I don't see the relevance of the question. We still have metabolic pathways exclusively devoted to fructose metabolism.

Eskimos have eaten very low sugar diets for thousands of years, yet not more than 10% have lack of sucrase, the enzyme needed to digest sucrose, and it is not clear at all that these 10% are results of disuse atrophy of the system involved.


I agree to an extent. Even with sugar-sweetened beverages, the dose matters. I don't recommend that crap, but not just because it contains fructose.


As with all things nutritional, the dose makes the poison. We require vitamin A, but too much can have toxic effects. Same with protein, etc. As I pointed out, studies using "normal" intakes of fructose show no toxic effects.


I recommend not eating honey every day. However, I don't think I have a really solid rationale for that beyond that no hunter-gatherer did so. But I doubt 3 tsp daily has harmful effects, and may even have benefits as suggested by the studies cited by Ryan. I may have to do more research. It certainly did not appear to cause ill effects in the Frassetto paleo diet study that Ryan cites.


Thanks for those links. It seems they illustrate again my perspective that no naturally occuring food (like honey) can be reduced to any of its major constitutents, and that the natural whole has effects quite different from extracts or synthetic mimics. Honey is a valued medicine in TCM.


Of course I agree that replacing whole foods with refined, micronutrient free sugar has adverse effects, partly by route of creating nutrient deficiencies.

The study to which you link used crystalline fructose in doses of 25 and 50g, which corresponds to 50 and 100g of sucrose. Given the osmotic properties of a sugar solution I don't feel surprised that this caused diarrhea, etc.

I don't think we presently have any evidence that normal doses of fructose (<10% of total dietary energy) have any long-term adverse effects. I wasn't extrapolating from short term studies to long term effects, since the short term studies used absurd doses, I actually am pointing out that we can't extrapolate anything about low normal intakes from this kind of research. On the other hand, several of the studies cited by Aragon have looked for adverse effects of fructose in long-term consumers of normal amounts, with no evidence of adverse liver or lipidemic effects, despite the fact that the primary fructose source in these studies is HFCS. Again, I don't advocate eating that stuff, because it displaces nutrient-dense foods required for health (hard enough to get adequate nutrition without that interference).

BTW, as I recall, the classic Malhotra study comparing Northern Punjab Indians to Southern Madras Indians, which found lower heart disease in the north, also found that the Punjabis consumed more sugar, 50g/d compared to 12g/d in the southerners.


Thanks for those titles, I'll have a look at them.

Anonymous said...

How does any of this refute the idea that we eat a boatload of HFCS, and that eating lots of fructose in the form of HFCS, or even refined sugar, makes us sick?

Anonymous said...

Thanks Don, and greetings from Belize!...I just use a little honey for my tea. I'm strict Paleo otherwise...For that little amt. it might do no harm...I just "feel" it has benefit...just like for 30 years it felt right to eat "Paleo", and I didn't even know what that meant in terms of diet...I just did what felt right with my/for my body. Like your blog. Thanks again.

Stephan said...

Hi Don,

The study didn't just demonstrate digestive upset-- it showed that even 25g of fructose is not efficiently absorbed by a significant fraction of the population, just like lactose. It hangs around the small intestine and gets fermented by nasty bacteria, hence the breath hydrogen they measured. It's possible that it would behave differently in the context of sucrose or even HFCS, as glucose promotes fructose absorption. But I still found the result disturbing.

I also think the fact that sugar is one of the two key ingredients that destroys native health is telling. It could simply be a matter of micronutrient deficiency, but I'm not convinced that's the whole story...

gn said...

thanks for a post
...though i have some qualms regarding the statement "This is an unrealistic intake of fructose for a person eating a whole foods diet" - i wish i had the same good faith in humanity as you appear to!)))

the problem is that i personally (and i guess many other people as well) seem to be unable to limit myself to the safe amounts of fructose you refer to in the post: once i taste it, the craving rollercoaster loses its brakes, and i can pretty sure eat it in scary and metabolically-destructive amounts, being it fruit (dozens of bananas, bags of raisins) or honey

though, i'm ready to admit that it may be just my personal eating disorder, but when you think that even in moderate climate of african savanna really sweet stuff was available only seasonably, i wonder if it would have made sense for our ancestors to catch the moment, and in an eating-disorderish way gorge/feast/binge on it, thus storing energy for future, leaner times; however, modern people, genetically hard-wired for fructose binging, have all the fructose they want all the time - and that's where those with particularly weak willpower get broken

Don said...


You actually sit down and eat more than 18 pieces of fruit in a day?

I don't find that I have to exert "willpower" to avoid binging on fruits. I think most binging occurs as a result of undereating. I had a patient today who gave me a diet record. When I analyzed it, it provided only about 1400 kcal, 400 to 600 less than I estimated she requires. When I showed it to her, comment that she falls short of her energy requirements, she immediately understood why she eats a lot of candy and feels so tired much of the time. In my experience, undereating leads almost inevitably to overeating or sugar eating.


Who is eating a "boatload" of HFCS? Or of sugar? What size of boat?

I did not post to exonerate HFCS or sugar, only to show how the data collected on fructose can't be applied to eating normal amounts of fruit.


I don't think studies on isolated crystalline fructose tell us anything about how sucrose or HFCS or fruit or honey behaves, just like Campbell's studies of isolated casein promoting cancer don't tell us anything about how whole milk, meat, or eggs behave.

Again, although I don't endorse eating sugar, the Malhotra study I cited showed that the southern Indians eating a rice-based diet containing only 12g sugar daily had 15 times higher ischemic heart disease mortality than the northern Indians consuming 50g of sugar daily in the context of a dairy-rich, wheat-based diet. In addition, the northern group consumed nearly 3 times as much seed oil (south=7g peanut oil, north=20g/d mustard or sesame oil). But they had 10x as much fermented milk, and ate more greens. In short, they had a more nutrient dense diet despite consuming more sugar.

Teddy said...

"I can't imagine a scenario in which the environment would select against fructose tolerance, i.e. in which maintenance of fructose tolerance despite a fructose-poor environment, would cause a person to lose fertility or die before having a chance to reproduce. I also can't imagine a scenario in which the environment (seasonal variations in supply of fructose) would select for fructose-intolerance, i.e. favor the reproduction of fructose-intolerant individuals."

Great blog, just thought I'd chime in to help you imagine a scenario where fructose intolerance is selected for. My argument comes along the lines of the expensive tissue hypothesis. If fructose tolerance is selected against, it would seem that another trait would be selected for, perhaps a trait providing for more amylase for starch digestion as an example. The body cannot be tolerant to everything and must work with a tight set of parameters. Its all give and take, there is no free lunch. There are plenty of examples you can make here. Like trading in fructose tolerance for a more manageable way to deal with nitrogen waste products for those areas where fruit isn't as abundant.

Paul Bergner said...

I believe the issue historically has not been fruit but the introduction of free fructose in syrup form in the 1970s, the issue covered in great detail in:

George A Bray, Samara Joy Nielsen, and Barry M Popkin. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. Am J Clin Nutr 2004;79:537–43.

Metabolically, there is a brake on the glycolysis pathway at the PFK enzyme, where high ATP slows the entry of glucose metabolism into the energy burn/store pathways. Fructose bypasses the control mechanism and floods the fat storage pathways. A slow dribble of a moderate amount of fructose from fruit may be normal, but even the same dose of fructose as free fructose would have a "flooding" effect on the pathways, and trials show that it upregulates storage enzymes and downregulates ATP production. Historically even this might not be a problem in a individual who is walking around 6-9 miles a day. The full horror is the individual who is insulin resistant with persistent hyperinsulinemia, the insulin also promoting storage pathways, flooding the same pathways with free fructose.

That said I have seen ad libitum fruit consumption wreck the recovery of former diabetics or insulin resistant obese patients even after 5-7 years of good control. Two recent cases, their blueberry consumption started to rise up to 8-16 ounces per day on average, after some years of near perfect control, and the TG went up, the HDL down, the waist grew, and HBAiC began to creep up. Both had a rapid reversal in blood parameters and some wt loss after limiting fruit to 1 cup of berries or one piece of fruit per day and increasing greens. Both highly genetically insulin resistant.

jandro said...

You might also be interested in reading this paper. Supports the idea that fructose is not dangerous as long as it no in excess.

Stewart Griffin said...

I watched that Lustig video last night and (as I remember it) he does oppose fructose, but not in fruit. He claims in the video that fibre helps prevent the problems of fructose and in fruits the fibre comes in a high enough proportion to the fructose for everything to work out well. Does anyone know if this is true?

For him the major enemy seemed to be sugared drinks followed by sweets and candy.

Don said...


Fruit does not provide enough fructose to cause the harm people seem to fear. It isn't that the fiber prevents evil effects of fructose, its that the concentration of fructose in fruit is too low to cause harm. Just the same, you could eat a teaspoon of pure white sugar every day of your life, and if you never exceeded that dose, you would never get harmed by the fructose in that teaspoon of sugar, it is just too small a dose to cause harm.

Neonomide said...


About that Princeton rat study which showed skewed metabolic response to HFCS, here's researchers' public rebuttal in case that is worth commenting:

I find it interesting to think that the fructose in HFCS is metabolized much faster than when digested in a form of sugar molecule.

Lustig clearly states that this is not the case. We are left to wonder, if human fructose metabolism is different enough from these rats ?

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