This 2010 basic research study investigated differences between fructose and glucose metabolism in pancreatic cancer cells. Researchers found fructose upregulates pathways that significantly increase production of nucleic acids — the building blocks of DNA and RNA. While glucose generates more energy (ATP) per molecule than fructose in these pancreatic cancer cells, fructose increases activation of the pentose phosphate pathway and transketolase, both of which support nucleic acid production.
This observation is notable in the context of previous research suggesting cancer growth is primarily restrained not by a lack of energy but a lack of the “cellular building blocks” needed to build the DNA, RNA, and proteins in a new cell. These same fructose-favored pathways may also mitigate cellular oxidation, ameliorating a key cancer cell vulnerability. Researchers note fructose metabolism is not regulated as tightly by the body as glucose metabolism. Thus, fructose levels in the blood remain elevated longer after fructose ingestion than do glucose levels after glucose ingestion — in other words, consumption of fructose elevates cancer cells’ exposure to fructose over longer periods. Previous evidence has shown that pancreatic cancer patients have blood fructose levels 2.5-times higher than healthy controls (1), and sugar-sweetened beverage consumption is an independent risk factor for cancer (2). This study builds on this evidence by proposing the mechanism by which fructose may preferentially favor cancer cell growth and replication to a greater degree than glucose.
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Comments on Fructose Induces Transketolase Flux to Promote Pancreatic Cancer Growth
The fiber found in the naturally occurring fructose sources slows the fructose absorption such that, gram for gram, the physiologic response is somewhat different when eating highly processed foods containg fructose and naturally occurring foods containing fructose. Russ Greene made an important point, though, about the manipulation of fruit and the omnipresent plump, sweet, juicy berries that minimally resemble their wild cousins found in nature. It is for this reason, that I think "some fruit" in our CrossFit prescription is so salient. Eliminating the highly processed foods, including beverages, should be obvious. It is important to note, when we are considering what we are going to eat, that pancreatic cancer is on the rise. There is expected to be a 2% increase in pancreatic cancer daignoses from 2018 to 2019. Once again, we cannot control our genetics, so we must control our environment to the extent that we can.
Thank you very much, sirs! This is the context i wished for.
In articles about fructose, can you please specify the definition of fructose? In a previous posted study from Fribourg, Switzerland there was mentioned a difference between natural fructose in fruits and clinical/pure fructose. According Wikipedia fructose is natural and high in relation to glucose in apples and pears. So how and on wich foods could this be interpeted? Maybe its just me, sorry.
As far as the biochemical metabolism of fructose goes, there isn't any difference between refined fructose as found in table sugar or HFCS or pure fructose and the 'natural' fructose found in a pear or an apple. Fructose is fructose and it's handled the same way by the body's biochemical machinery. And it's handled more 'loosely' than glucose metabolically.
But there is a huge difference in the absolute amount consumed in a pear or an apple and the amount consumed from sugar- or HFCS- sweetened beverages (the main culprit in the markedly increased consumption of fructose seen nationwide and globally) and from commercially-processed foods.
There are about 12-15g of fructose in the average apple or pear. And about 20g in the average 12-ounce soda. That doesn't seem so different, but people generally will eat a pear or an apple, not four of them at a go. (Granted, there is the bizarre outlier of Steve Jobs, who apparently subsisted on some huge number of apples a day and not much else for weeks at a time. And perhaps it's worth noting in light of this study that pancreatic cancer was his fatal diagnosis, but that's just correlation in a 'n' of 1, not causation.)
Whereas in sodas, a single 12-ounce can is the outlier. It's not unusual at all for people (including kids, sadly) to go for the supersized soda, containing 32 ounces (with over 50g fructose) or more, and go back for a refill... or two. Then add the fructose load from packaged foods routinely consumed by the soda drinking crowd (toaster pastries, sugar sweetened cereals, sugar sweetened yogurt, pancake syrup, ice cream, and the endless list from there) and you could be staring a daily 200 to 300g fructose intake in the face before you blink.
As is so often the case with nutrition and disease, the deleterious effect of a food is a matter of degree. And fructose is likely no different. The culprit is more the perversion of the natural human diet from one of a wide variety of whole foods eaten ad lib to satiety (even those containing some fructose, which had evolutionary survival advantages of fattening us up for the winter) to one filled with Frankenfoods consisting chiefly of three components: concentrated, refined starch (wheat, corn, rice), sucrose and/or HFCS, and industrially processed 'vegetable' fats, processed into different forms, but basically all the same thing.
In addition to Dr. Eades' point on degree, which I agree with, I would also suggest that the context in which fructose appears differs in nature versus in industrial products ("processed food"). On the tree, fruit contains vitamin C, polyphenols, and fiber which affect how the fructose is metabolized and the health impact thereof. Drs. Robert Lustig and Barry Sears have both expounded on this point. So I would expect that even gram for gram, the fructose in an orange or grapefruit will not have the same effect as the fructose in soda pop.
That being said, man has manipulated nature to grow fruit larger and sweeter, and to make it available year-round, such that true "Paleolithic" eating likely requires less fruit consumption than one might prefer. A banana of 2019 is not the banana of 1419, AD or BC.
Fructose Induces Transketolase Flux to Promote Pancreatic Cancer Growth
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