Thursday, March 17

Ketomyths II

In the first post of these series I reviewed the evidence regarding mucin deficiency and glucose restriction. Its time to move on into a more complex topic: vitamin C and scurvy. The best article written on low carbohydrate diets and scurvy comes again from Dr. Jaminet. I will use some of his statements to explain my points of view on the subject. Before I start, I have to mention that ketogenic diets for epilepsy are not comparable to a paleoish ketogenic diet. It is too high in fat, too low in protein and the main source of fat are heart healthy vegetable oils high in n-6 PUFA. Most of the time patients are also water-restricted to increase blood ketone levels. Having said this, I will not discuss any example which uses an anti-epileptic ketogenic diet in the article (except the one on selenium deficiency, which is relevant for the post).

First, it is important to understand that ascorbate is asborbed in the small intestine modulated by glucose (1):

Na+ dependent glucose transport via SGLT1 receptors in enterocytes modulates the asborption of ascorbate, while transport of dehydroascorbic acid (DHA) is by facilitated difussion. As glucose content in the lumen and in the enterocyte increases, ascorbate transport is reduced. In layman's terms: ascorbate absorption is reduced by high glucose, so if you eat more glucose you will need to eat more ascorbate. This means, glucose increases your minimal requirement for vitamin C in your diet. 

But once ascorbate and DHA enter the bloodstream, they must be transported inside cells. 
"DHAA can be recycled back into vitamin C, but only inside cells. In order to enter cells, DHAA needs to be transported by glucose transporters. GLUT1, GLUT3, and GLUT4 are the three human DHAA transporters; GLUT1 does most of the work."
 Structurally, DHAA and ascorbic acid are similar to glucose:

Ascorbic acid, reduced form (left) and DHA, oxidized form (right)

This could be one of the reasons for the sharing of membrane transporters. The affinity of GLUT4 for DHA is low, so the main transporters are GLUT1 and GLUT3 (2), that is, glucose and DHA are both competitive substrates for some glucose receptors. High glycemia reduces the transport of DHA into cells. 

Jaminet states:
"Glucose transporters are activated by insulin. Thus, DHAA import into cells is increased by insulin, leading to more effective recycling of vitamin C [8]"
The reference takes us to a study done on osteoblastic cells (3). When these cells were incubated with insulin, the uptake of DHA and the intracellular concentration of ascorbate from DHA increased. But if you read look into the results, you will find: 
"Transport of [14C]DHAA was inhibited by D-glucose and 2-deoxyglucose, both of which are substrates of GLUT"
What? But isnt insulin, which is stimulated by glucose, supposed to increase DHA transport? Yes, but here is where interpretation problems arise. When we study cells in vitro we isolate the variable we want to study. This helps us understand the exact mechanism of action of certain molecule or pathway (because there is no other molecule/pathway influencing it) but this also creates a problem: our cells are not isolated. In fact, they are under many different convergent signals which might have sinergistic or antagonistic effects on one cellular process. If we focus only on the proximal cause (insulin increases DHA uptake) we miss the big picture for understanding metabolic processes (why insulin increases DHA uptake?). From my point of view, this is an evolutionary acquired mechanism. Vitamin C transport/recycling modulated by insulin/glucose can be illustrated using a different scenario: muscle protein balance. Insulin's role in different tissues is mainly inhibitory. In skeletal muscle, insulin inhibits muscle protein breakdown. But has a passive role on muscle protein synthesis, which is stimulated by plasma amino acid availability. On the other hand, the most powerful stimulus for insulin secretion, hyperglycemia, increases proteolysis (4). Hence, insulin counteracts the effect of hyperglycemia (until a threshold is reached) on muscle protein balance. This effect is also illustrated by glucose induced inflammation. Hyperglycemia is inflammatory (5, 6, 7) and contrary to popular beliefs, insulin is anti-inflammatory (8, 9). My guess is that glucose is the main stimulus for insulin secretion because it is inflammatory. Just like in skeletal muscle, insulin is released to prevent damage from glucose. 

Getting back to the topic, these examples help to understand why insulin might increase DHA transport and recycling. When there is a higher level of glucose competing with DHA, insulin's role is to increase the number of GLUT receptors for achieveing a normal intracelular DHA level for proper conversion to ascrobic acid (AA). 

There are other vitamin C transport systems used by cells, namely SVCT1 and SVCT2, two sodium dependent transporters for AA, which are regulated among others, by AA plasma concentrations. This transport is not regulated by insulin. So we have two ways by which vitamin C is transported into cells (10):

AA is transported inside cells by Na+ dependent transporters coupled to a Na+/K+ATPase, while DHA is transported through GLUT proteins. DHA is rapidly reduced to AA, which can excit the cell by different uncharacterized mechanisms (beyond the scope of this post).
Remember that DHA is the oxidized form of AA, which explains its antioxidant nature. AA is oxidized to the ascorbyl free radical (transfering of one electron to a metabolic oxidant) which is further oxidized, losing a second electron, producing finally DHA (this is illustrated in the second figure in the post, although simplified and the ascorbyl free radical is not shown). If there are more oxidants, higher levels of AA are needed to reduce them so there is an increase in the DHA/AA plasma ratio, as observed in diabetics. Regarding this issue, Jaminet says:
"Confirming the role of insulin in promoting vitamin C recycling, Type I diabetics (who lack insulin) have lower blood levels of vitamin C, higher blood levels of DHAA, increased urinary loss of vitamin C metabolites, and greater need for dietary vitamin C. [9, 10]"
The first mistake is comparing no insulin (such as in type I diabetics) with low insulin. But why do type I diabetics have lower levels of AA and higher levels of DHA? Is it because a defective recycling via lower DHA cell uptake? Maybe. But I dont think it is the only cause. Hyperglycemia, as mentioned earlier, produces oxidative stress, increasing the formation of reactive oxygen species which react with AA, oxidizing it to form ultimately DHA. Because there is a defective transport of DHA into cells (because of competitive inhibition by glucose and abscence of insulin), the balance is shifted towards DHA. The main source of mitochondrial ROS seems to be complex III during the oxidation of complex I substrates (NADH dehydrogenase) (11). Without going into details (maybe on a different post), complete (aerobic) glucose oxidation produces a ratio of NADH to FADH of 5:1. This means that mitochondrial energy metabolism relies more on complex I than complex II, increasing the production of ROS. This scenario is also observed in type II diabetics (12, 13), who in fact have the opposite (chronic hyperinsulinemia), but glucoregulatory alterations. Despite having high insulin levels, they have low plasma vitamin C. Increased ROS production both by systemic inflammation, hyperglycemia, carbohydrate-based mitochondrial energy production and defective cellular transport are the likely causes of vitamin C alterations observed in these patients. In uncontrolled TIDM, abscence of insulin makes things worse. This is by no means applicable to ketogenic diets.
"Dehydroascorbate, the fully oxidized form of vitamin C, is reduced spontaneously by glutathione, as well as enzymatically in reactions using glutathione or NADPH. [11]"
Then, Jaminet states: 
"Glutathione is recycled by the enzyme glutathione peroxidase, a selenium-containing enzyme whose abundance is sensitive to selenium status. One difficulty with zero-carb diets is that they seem to deplete selenium levels."
For this assupmtion, he references a study on a sudden cardiac death on a ketogenic diet for seizure control (14). From the cited study:
"Selenium is an essential nutrient in the human diet. Sources of selenium include cereals, meats, and fish [8]. However, depending on the intake of those foods and the source of cereals (e.g., soil rich or poor in selenium), selenium levels in humans are variable. Patients on the ketogenic diet have little cereal intake, and only moderate fish and meat intake, and thus are predisposed to low selenium levels."
Even I said I wasn't going to refer to seizure-control ketogenic diets, its worth mentioning that according to the last recommendations of the International Ketogenic Diet Study Group (15), the "normal" diet used in this cases is 90% fat and 10% of carbohydrates and protein combined. They state that "Calories are typically restricted to 80%–90% of the daily recommendations for age". Not very similar to popular paleo-keto diets. To achieve this incredibly low level of protein, they have to restrict important sources of Se, specially those eaten in abundance by low carbers like meat and fish, being the former one of the foods with best Se bioavailability (16). The recommended Se intake seems to be around 40ug/day (17) and muscle meats, on average, have 0.3-0.4mg Se/kg (organ meats such as liver and kidney concentrate more Se, from 4 to 16 fold the amount on muscle). Remember that 1000ug = 1mg, so 0.4mg = 400ug. If you eat 100g of meat a day (excluding other animal sources) you are eating 40ug of Se, the recommended intake (for reference, 100g equals to 3.5oz/0.22lb).  

Jaminet concludes:
"So here we have a second mechanism contributing to the development of scurvy on a zero-carb diet. The diet produces a selenium deficiency, which produces a glutathione deficiency, which prevents DHAA from being recycled into vitamin C, which leads to DHAA degradation and permanent loss of vitamin C."
As we have seen, using a clinical case based on a ketogenic diet for seizure control leads to a flawed conclusion. 

Finally, as said by one of the PHD readers in the comment section, ketogenic diets have shown to increase GSH levels (18).

The hypothesis proposed by Jaminet is not supported by facts, only by assumptions based on misinterpretation of the existing data. Proper ketogenic diets dont produce vitamin C, glutathione or selenium deficiency. Loss of glucoregulation does.


  1. malpaz

    so, are you saying in the presence of a diet with more carbs ones body increases the need for C, glutathione and selenium?

    or, are you saying the ketogenic diet done correctly provides adequate selenium, C and glutathione?

    this is interesting: "Is it because a defective recycling via lower DHA cell uptake? Maybe. But I dont think it is the only cause. Hyperglycemia, as mentioned earlier, produces oxidative stress, increasing the formation of reactive oxygen species which react with AA, oxidizing it to form ultimately DHA. Because there is a defective transport of DHA into cells (because of competitive inhibition by glucose and abscence of insulin), the balance is shifted towards DHA."

    have any other info on it? or some dumbdumb explanation for a layperson!?

  2. Hi malpaz,

    In short, yes and yes. In layman's terms (I hope):

    You have vitamin C in its oxidized form DHA, and reduced form AA. "Oxidants" oxidize AA, forming DHA. So the free radical scavenging (active)form of vit C is its reduced form, ie. AA. You want AA to reduce this oxidants so they cant oxidize lipids and DNA.

    You can have more plasma DHA either by decreasing transport into cells (DHA can be recycled back to AA but mostly inside cells) as in T1DM or by producing more ROS, which oxidize AA into DHA. In uncontrolled T1DM, both the increase in oxidative stress and lack of efficient transport into cells shift the balance towards DHA, which in turns lowers AA, reducing its antioxidant potential. Accumulation of DHA in plasma has deleterious effects.

    Glucose metabolism per se increases ROS formation, increasing the need for active AA. I guess you can couple the deficit for some time (specially if your vit C intake is high), until glucotoxicity occurs.

    Bottomline, glucose competes with AA absorption at the intestinal level and at the cellular level, reducing DHA transport to be recycled. More oxidative stress, more AA needed.

  3. Dear Lucas Tafur:

    Thank you very much for this article. I posted a comment on Dr. Jaminet's site referring to this article of yours:


    Zooko Wilcox-O'Hearn

  4. I thought the Vilhjalmur Stefansson all-meat trial at Belleview Hospital should have laid this vitamin C issue to rest. Great post of the biochemistry behind it.

  5. @Zooko and Poisonguy,

    Thank you for your words.

  6. Great article Lucas. I espeically like the part about mucin production as this is the one that I posted extensively on Pauls forum

    When there is a higher level of glucose competing with DHA, insulin's role is to increase the number of GLUT receptors for achieveing a normal intracelular DHA level for proper conversion to ascrobic acid (AA).
    Insulin will also reduce liver production of glucose which might be more important. Furthermore, at least RBCs GLUT1 transpoerters may not entirely be dominated by glucose antagonism since they have stomatin switch which shifts preference of GLUT1 to DHAA over glucose.

    Accumulation of DHA in plasma has deleterious effects.
    DHA doesn't typically accumulate in plasma. It could be result of severe infection. Redox potential DHAA/AA is marker of disease state. It can be rapidly cleared by IV vitamin-c for people not genetically susceptible to hemolisis (G6PD def etc..).
    Furthermore, brain can only use DHA as it is the only one to cross BBB. In animals, brain starts to xpress SVCT transporters only after injury.

    Ketogenic diet may cause vitamin C deficicency. Those are high fat diets which promote endotoxemia, and intestinal vitamin C is used by the body to prevent negative effects of LPS. Combined with any existing infection and wrong diet you can seariously become malnourished. By wrong diet I mean that when protein sources are in question, people typically do not eat organs which contain substantial amounts of C unlike muscle. Furthermore, ketogenic diets are usually not raw, and cooking and industrial procedures all diminish C content. High protein diets promote uric acid which is inversly correlated with C level. People on paleo diets often do IF and natriuresis of fasting could reduce circulating blood volume and cause secondary renal potassium wasting. This will affect SVCT as it needs sodium.

    On the positive side we have GSH upregulation which is protective and probably less fasting glucose (I say probably, because in some people fasting glucose is higher on ketogenic diets, probably result of malnutrition). Fructose omition is definitelly positive regarding to C status.

    So, there are situation, especially when combined with potential SNPs in SVCT1 and age which diminishes its level, which could spell vitamin C deficiency.

    Its actually highly probable to go C insuficient on any diet.