Thursday, September 17, 2009

Brad Pilon on Losing Weight With Exercise

Brad Pilon of Eat Stop Eat has put up a nice video discussing why more exercise alone won't work to regulate weight.

Losing Weight With Exercise

Primal Potatoes, part 4

Red and white skinned sweet potatoes
Image source: Bon Appetit

As I mentioned in Paleo Potatoes, part 3, Bovell-Benjamin reports that “Early records have indicated that the sweet potato is a staple food source for many indigenous populations in Central and South Americas, Ryukyu Island, Africa, the Caribbean, the Maori people, Hawaiians, and Papua New Guineans” (1)

Sweet potato has also served as a staple for several other groups with high immunity to diseases of civilization, including Kitavans and Okinawans. It appears that this tuberous root has some unique components that may help explain why these groups sustain good health.

Note: I don't intend this as a promotion of a high carbohydrate, sweet potato based diet, just an exploration of the properties of this tuber.

Sweet potato component combats diabetes

Japanese researchers have isolated from the skin of the white-skinned sweet potato a component, known as Caiapo, that appears to have insulin-sensitizing antidiabetic and possibly antiatherogenic properties. Studies with diabetic patients have had positive results.

For example, Ludvik et al compared 12 weeks of Caiapo supplementation at 4 g/d with a placebo in a randomized, double blinded study with 61 clinically stable type 2 diabetes patients treated with diet alone (2). Thirty patients received Caiapo, and 31 received a placebo. After 3 months, The following results emerged:

• Average fasting blood glucose declined 15.2 mg/dl, from 143.7 mg/dl to 128.5, in the Caiapo group, but decreased only 6.1 mg/dl, from 144.3 to 138.2, in the placebo group. After 3 months of treatment, 48.3% of patients in the Caiapo group had fasting blood glucose levels below 126 mg/dl, the level diagnostic for diabetes.
• Average HbA1c declined from 7.21% to 6.68 in the Caiapo group, but increased from 7.04% to 7.10 in the placebo group. Caiapo performed better than either acarbose or nateglinide in controlling HbA1c.
• Average total lipoproteins (“cholesterol”) declined from 225.1 mg/dl to 214.6 in the Caiapo group, but increased from 240.9 to 248.7 in the placebo group.
• Average triglycerides declined from 211.6 mg/dl to 205.4 in the Caiapo group, but increased from 216.1 to 219.7 in the placebo group.
• Body mass declined in both groups, but to a greater degree in the Caiapo group (Caiapo, 3.7 kg; placebo, 1.0 kg).

Ludvik performed another study, this one lasting 5 months. “This study confirms the beneficial effects of Caiapo on glucose and HbA1c control in patients with T2DM after 5 months follow-up. Improvement of insulin sensitivity was accompanied by increased levels of adiponectin and a decrease in fibrinogen. Thus, Caiapo can be considered as natural insulin sensitizer with potential antiatherogenic properties” (3).

Of course, this Caiapo intervention did not perform anywhere near as well as a low carbohydrate diet, as discussed by Stephan here. Nevertheless, it did a pretty good job in the context of a high carbohydrate diet; perhaps it would have had a greater effect if the participants had also restricted their total carbohydrate intake. In any case, it appears that the sweet potato has unique properties perhaps not had by other starchy foods.

Miyazaki et al showed that the anti-diabetic components of the white skinned sweet potato “increased phagocytic activity and phagosome-lysosome fusion in neutrophils and monocytes in a dose-dependent manner” (4).

Caiapo found in orange sweet potato flesh as well as skin

Although Caiapo comes from the skin of the white sweet potato, a team from North Carolina State University College of Agriculture and Life Sciences “discovered that the Beauregard variety of sweet potatoes - which makes up about 85 percent of the production in North Carolina - has essentially the same protein patterns as a commercial dietary supplement known as Caiapo, marketed to control blood glucose in diabetics….. [and] that the protein content of the flesh of the Beauregard sweet potato was higher than that of the peel” (5).

How I Apply Sweet Potatoes In My Diet

As I have pointed out, you can eat sweet potatoes in moderation and still maintain a pretty low carbohydrate diet. Presently, I only eat one on each of the days that I spend glycogen in resistance training. Even on those days I don't go above a total of 150 grams of carbohydrate.

1. Bovel-Benjamin AC. Sweet potato: a review of its past, present, and future role in human nutrition. Adv Food Nutr Res. 2007;52:1-59.

2. Ludvik B, Neuffer B, Pacini G. Efficacy of Ipomoea batatas (Caiapo) on Diabetes Control in Type 2 Diabetic Subjects Treated With Diet. Diabetes Care 27:436–440, 2004.

3. Ludvik B, Hanefeld M, Pacini G. Improved metabolic control by Ipomoea batatas (Caiapo) is associated with increased adiponectin and decreased fibrinogen levels in type 2 diabetic
Diabetes Obes Metab. 2008 Jul;10(7):586-92. Epub 2007 Jul 21.

4. Miyazaki Y, Kusano S, Doi H, Aki O. Effects on immune response of antidiabetic ingredients from white-skinned sweet potato (Ipomoea batatas L.). Nutrition. 2005 Mar;21(3):358-62.

5. Stanard S. Researchers reveal sweet potato as weapon against diabetes.

Thursday, September 10, 2009

Primal Potatoes, Part 2, Reply to Rambling Outside the Box

Well, my post Primal Potatoes, Part 2, appears to have struck some nerves. Drs Cynthia and David posted Primal Potatoes—a Contrary View at their blog, Rambling Outside the Box.

As I read their reply, I don’t see that they addressed the fundamental point of my post, which is that people eating low carbohydrate diets don’t have the same anaerobic capacity as people eating higher carbohydrate diets (although not necessarily “high” carbohydrate diets) that allow for greater glycogen storage. As I noted in my original post, even scientists who advocate ketogenic diets (e.g. Phinney, 1) accept this as an established fact and have demonstrated it themselves in controlled studies on keto-adapted athletes.

Cynthia and David report that one of my links to a reference did not work, so they started off their rebuttal by searching PubMed for the article. In such cases, I suggest asking me to correct it, or provide another avenue, rather than picking another article that has Fournier as an author, and assuming, perhaps wrongly, as in this case, that you have the right article in your hands.

In my post, the dead link referred to this article:

Fournier et al, Post-exercise muscle glycogen repletion in the extreme: effect of food absence and active recovery, International Society of Sports Nutrition Symposium, June 18-19, 2005, Las Vegas NV, USA

This paper includes this quote to which I referred:

“In fact, we store just enough glycogen to sustain our energy demands for only a few hours of intense aerobic exercise (Gollnick et al., 1973; Ivy, 1991), and so little glycogen is stored in our muscles that close to a third to half of these stores can be depleted within a few minutes of a maximal sprint effort (Gollnick et al, 1973; Fairchild et al., 2003). As a result, active individuals are at increased risks of experiencing a fall in their ability to engage not only in intense aerobic exercise (Ivy, 1991), but also in short sprint effort under situations eliciting fight or flight responses (Balsom et al., 1999; Fournier et al., 2002).”

Fournier et al here point out that even individuals on a mixed diet can experience declines in either intense aerobic or anaerobic (including fight or flight) performance due to glycogen depletion. It is reliably reproducible in experiment, so no one doubts it. I took this as the basis of my argument that human ancestors who did use tubers for starch intake would have had a selective advantage over those who did not, by having superior performance both in hunting related activities and in escape from predators.

Cynthia and David don't believe that glycogen depletes so quickly as claimed by Fournier et al. Let's take a look.

How rapidly does glycogen deplete?

Cynthia and David contend that the statement that close to a third to half of glycogen stores can deplete within a few minutes of a maximal sprint effort is “an exaggeration.” I disagree. Fournier et al make this statement based on research on glycogen depletion in man, some of which Lyle McDonald discusses in his book The Ketogenic Diet: A Complete Guide for the Dieter and Practitioner (Morris Publishing, 1998, pp. 120-123).

McDonald notes that researchers have collected data on glycogen levels under different conditions, including ketogenic diets, which I will now summarize:

• Supercompensated glycogen levels reach 175 mm/kg in trained athletes on high carbohydrate diets.

• Athletes on mixed diets have levels of 110-130 mmol/kg.

• Normal individuals on mixed diets have 80-100 mmol/kg.

• Normal individuals on ketogenic diets and doing no anaerobic training have 70 mmol/kg.

• Exercise performance will be impaired at 40 mmol/kg

• Exhaustion occurs at 15-25 mmol/kg.

• Protein gets converted to fuel during exercise when glycogen falls to 40 mmol/kg or below.

As McDonald points out, researchers in two studies (2, 4) have determined the rate at which glycogen gets consumed during such efforts. At 70% of maximum weight, both studies found a glycogen depletion rate of 0.35 mmol/kg/second of work performed. Translated to seconds:
• 30 second effort, 10 mmol/kg depleted
• 40 second effort, 14 mmol/kg depleted
• 50 second effort, 17 mmol/kg depleted
• 60 second effort, 21 mmol/kg depleted
• 70 second effort, 24 mmol/kg depleted
• 80 second effort, 28 mmol/kg depleted
• 90 second effort, 31 mmol/kg depleted

So, with this data you can see how an intense effort could deplete one-third to one-half of stored glycogen, depending on starting stores. If starting stores are 80 mmol/kg, and you engage in a 90 second lifting effort at 70% of maximum resistance, this will deplete 31 of 80 mmol, or 39% of glycogen, i.e. one-third to one-half.

Can recycled lactate replenish glycogen?

If an individual consumes no carbohydrate following glycogen-depleting exercise, a small amount of glycogen will get resynthesized from lactate. Now for some more numbers (McDonald cites Pascoe and Gladden, 2):

• Production of 1 mmol of glycogen consumes 2 mmol of lactate.

• Only about 20% of the lactate generated during anaerobic activity like weight training (bison lifting) can get converted back to glycogen.

• Lactate levels in muscle during intense anaerobic activity typically reach only 10-15 mmol, with a maximum of 21 mmol.

So, at 2 mmol of lactate per 1 mmol glycogen and an efficiency of only 20%, the lactate recycling would reconstitute only at most 2 mmol/kg of glycogen, an insignificant amount compared to original stores.

Low carbohydrate dieting does not make this process more efficient. One study looked at the rate of resynthesis of glycogen following resistance training absent carbohydrate intake, and found a rate of 1.9 mmol/kg/hr, with a total (maximum) regeneration of 4 mmol/kg (2).

I referred to the following carcass-carting episode as an example of anaerobic activity fueled by glycogen:

“In 1805, the Lewis and Clark expedition witnessed an Indian bison kill ….A small herd was stampeded over a cliff into a deep, broad ravine. As the bison fell one on top of the other, dazed and injured, hunters killed those on top with spears; the others were crushed and suffocated underneath. The ravine was twelve feet wide and eight feet deep; most of the bulls weighed over a ton, yet a team of five Indian hunters pulled nearly all the bison out of the ravine onto level ground for butchering.” (3)

About this Cynthia and David say:

“In the example given of hauling a buffalo carcass out of a ravine, this activity may involve some anaerobic activity, but it will necessarily stretch over an extended period of time and be completed primarily using aerobic metabolism. There may be brief bursts of high intensity effort as needed, and there may even be bursts of extreme effort for particular heavy lifting tasks, but on average the task will necessarily be completed with levels of effort that can be sustained over hours not minutes. We suggest that hauling out a buffalo carcass would not necessarily require a lot of glycogen, and even if it did, would not necessitate gorging on potatoes or other carb food to replenish glycogen stores.”

First, this was not “a” bison carcass, it was a small herd. Next, each bison weighs 1500 or more pounds, the bulls over a ton, and only five men completed the task. The carcasses were hauled out of the ravine intact, for butchering on level ground. If all members of the team participated in lifting each carcass, this means each man had to deadlift and carry up out of a hole at least 300 and at times 400 or more pounds.

Cynthia and David say that this would be completed “primarily using aerobic metabolism.” I see it differently. Let me use a more contemporary example. Although a strength training routine consisting of 15 hard sets of 30-60 seconds each may involve rests of 3-5 minutes between sets, and aerobic metabolism would dominate during the rest periods, I would not say—and I don’t believe any exercise physiologist would argue-- that a strength training routine is “primarily” fueled by aerobic metabolism just because "on average” the level of effort could be sustained “over hours” by the insertion of rest periods.

The activity of interest here consists of lifting bison, not of the rest periods between lifts, and the question is, does this lifting deplete glycogen or not? The answer is, yes it does, regardless of rest between efforts.

Cynthia and David “suggest” that this “would not necessarily require a lot of glycogen…” Let's take a look.

As an experienced lifter, I believe that I can reasonably assume that the men lifting those bison out of the ravine were lifting not more than 70% of their maximum capacity, because they most likely would not have been able to repeat 10 or more such lift-and-haul operations (10 sets of the same movement) in one session if the resistance had been higher than 80% of their maximum.

OK, now let us generously assume the herd consisted of only 10 animals, and moving each animal out of the hole required only 30 seconds of intense effort (doubtful given the task, but roughly equivalent to a 5 to 8 repetition set of deadlifting). The result would be a depletion of 100 mmol/kg of glycogen. That seems like a lot to me, given that normal glycogen stores on a mixed diet amount to not more than 100 mmol/kg, and stores on a ketogenic diet amout to only 70 mmol/kg.

Now above I noted that research has demonstrated that in the absence of post-effort carbohydrate ingestion, lactate recyling only replenishes a maximum of 4 mmol/kg. So you hunt on an empty stomach, fasted for more than 16 hours, which already depletes your glycogen by 50%. Then you help lift 10 bison—your portion amounting to at least 300 pounds--out of a ravine, which would deplete something like 100 mmol/kg of glycogen. You then rely on lactate recycling to “replenish” your stores, and you end up with 4 mmol/kg—way below the exhaustion and impaired performance level. You can see that you will definitely have need for some substrate other than recycled lactate for replenishing glycogen.

Even if I cut the depletion estimate in half, we still have a scenario in which 50 mmol/kg gets depleted, leaving a person with normal stores (due to a mixed diet) at a level of 50 mmol/kg, and a person on a ketogenic diet with only 20 mmol/kg—still below the level of exhaustion. And the lactate recycling still only producees 4 mmol/kg, nowhere near enough to replenish even a third of the original stores.

The need for a substrate

Absent dietary carbohydrate, the only way out of this would consist of converting either endogenous (lean tissue) or exogenous (dietary protein) amino acids into glycogen, at a rate of 1 g protein for each 0.7 g of resulting glycogen. This is where my calculations in Primal Potatoes, part 2, come in.

Cynthia and David state “Glycogen stores can thus be regularly replenished (at least partially- enough to call on in emergencies) as needed even during prolonged aerobic exercise, even when fasting, to support the needs of occasional anaerobic activity.” I did not see anywhere in their discussion any mention of the substrate needed for replenishing glycogen. It does not magically replenish itself out of thin air. Cells have to have glucose to make glycogen, and the glucose has to come from something else: dietary glucose, dietary protein, body protein, or lactate. I just showed that lactate can’t supply enough glycogen to replenish what would get spent in this type of effort. Therefore, the body will use dietary or body protein for the task, in the absence of dietary carbohydrate, because it will replenish glycogen at the expense of muscle mass, since it is definitely more important to be able to run from a predator than to have an abundance of muscle.

Gorging on potatoes?

Cynthia and David say that even if this bison lifting would deplete glycogen, this “would not necessitate gorging on potatoes or other carb food to replenish glycogen stores.” I would like to know where in any post I have advocated “gorging on potatoes or other carb food,” or stated that our ancestors did this?

In my original post, I based all my calculations on replenishing only one-third of maximum glycogen stores (i.e. about 133 g), not on filling glycogen stores to the maximum. I agree with them that keeping the stores somewhat empty has advantages—that is why I calculated for refilling only one-third. To replenish one hundred thirty-three grams of glycogen would require only 133 g of dietary starch, only 532 calories as starch, 26% of a 2000 calorie diet. If gotten entirely from sweet potatoes, you would consume 16 ounces of sweet potato. Since most people consume three to five pounds (48 to 80 ounces) of food daily anyways, I would not classify this as “gorging on potatoes.”

Advantages of dietary carbohydrate

Cynthia and David take issue with my suggested advantages of using tubers. I suggested that consumption of tubers would “Lower dietary protein/meat requirement, reducing the pressure for success in hunting large animals, and making it possible to feed more people (offspring) with each kill.” They seem to think I expressed a “misconception” that eating less carbohydrate means eating more protein, not more fat. Well, besides the fact that eating very little carbohydrate does most certainly increase protein requirements (see below), they missed my point, which is that if you eat tubers, your total requirement for meat (the reason I used “protein/meat”) will reduce because you will now be using a plant food to supply some of your calories and glucose and to dilute protein.

In connection with this, I suggest reading “Energy Source, Protein Metabolism, and Hunter-Gatherer Subsistence Strategies,” in which Speth and Spielman point out that observers recorded recent aboriginal hunters in temperate, subarctic, and arctic habitats having difficulty meeting caloric requirements in late winter and early spring due to the decline in fat stores on ungulants making only lean meat available (5). Very likely Paleolithic hunters had similar difficulties.

Native hunters would at those times abandon a kill consisting of lean meat, despite feeling hungry and having invested considerable energy in the hunt of it, because they knew protein poisoning could occur. If these hunters had a plant source of carbohydrate (or fat), they would not have had to abandon their lean kills, which would have improved the efficiency of their hunting (i.e. less waste). It seems clear to me that this would confer an adaptive advantage. After all, would it not be better not to have to waste hunting effort (energy) on useless meat (because too lean), and would not having enough food confer an advantage over starvation?

Hunter-gatherers certainly thought so—and they weren’t averse to eating carbohydrate instead of fat in lean times. As Speth and Spielman note, “Hunter-gatherer exchange of meat with horticultural populations in return for carbohydrates is documented for many areas of the world” (5).


I also offered that having carbohydrate in the diet would reduce the burden on the liver for ammonia detoxification. They say “this is nonsense.” Well, I happen to believe that the burden on the liver will in fact vary according to the amount of protein consumed. I find it difficult to understand why anyone would call this nonsense. If I make an organ do more work, doesn’t that increase the burden upon it? Let me put it another way: If I make you do more work, doesn’t that increase your burden?

Cynthia and David say “Protein poisoning is just not a serious risk” and state that “protein consumption tends to be self-limiting at levels well below anything that would present any significant burden to the liver.” How then do they explain this report from Randolph B. Marcy in the winter of 1857-1858 , quoted by Speth and Spielman:

“We tried the meat of horse, colt, and mules, all of which were in a starved condition, and of course not very tender, juicy, or nutritious. We consumed the enormous amount of from five to six pounds of this meat per man daily, but continued to grow weak and thin, until, at the expiration of twelve days, we were able to perform but little labor, and were continually craving for fat meat.”(5)

Five to six pounds of meat supplies 560 to 672 g of protein daily, an amount that provides more nitrogen than the liver can convert to urea in a day (6). Since Marcy and his team got weak and thin on it, this illustrates that man can consume protein at levels that can burden the liver. If not so, no one would have ever experienced “rabbit starvation” and protein poisoning as referred to by Stefansson (quoted in Speth and Spielman):

“If you are transferred suddenly from a diet normal in fat to one consisting wholly of rabbit you eat bigger and bigger meals for the first few days until at the end of about a week you are eating in pounds three or four times as much as you were at the beginning of the week. By that time you are showing both signs of starvation and of protein poisoning. You eat numerous meals; you feel hungry at the end of each; you are in discomfort through distention of the stomach with much food and you begin to feel a vague restlessness. Diarrhoea will start in from a week to 10 days and will not be relieved unless you secure fat. Death will result after several weeks” (5)

In short, protein poisoning presents a serious risk, well known to aboriginal hunters, who would abandon lean meat to avoid it, despite having spent an enormous amount of energy hunting it down while starving.


Cynthia and David also claim that my statement that eating tubers would make it easier for a hunter to maintain and increase lean mass in response to the stresses of high intensity activity, with a lower dietary protein requirement, is “False!”

I guess they have never heard of the very well-established protein-sparing effects of dietary carbohydrate. Adding carbohydrate to a carbohydrate-free or very low carbohydrate diet reduces the amount of protein required for maintenance of lean mass, by supplying an alternative source of glucose. Absent dietary glucose, the liver generates glucose for maintaining normal blood glucose levels by gluconeogenesis, which is the conversion of amino acids into glucose. If you supply glucose directly, the liver will reduce gluconeogenesis, which reduces the use and need for dietary protein as a glucose source. This in turn means that the individual can maintain lean mass on less dietary protein. Simply put, the less dietary carbohydrate you ingest, the more protein you must ingest (enough for maintenance of lean mass plus some for generating variable amounts of glucose).

Low carb doesn't work magic

Let me repeat, low carb diets do not work magic. They do not enable the body to create blood glucose or glycogen out of thin air. They do not entirely eliminate the need for glucose, they just shift the individual from use of dietary glucose to endogenously produced glucose generated by gluconeogenesis (the reason for the high blood glucose they find after runs). They do not magically increase the efficiency of recycling of lactate into glycogen. They do not make it possible to consume unlimited calories without gain of body mass. They do not cause body fat to evaporate independent of energy expenditure. They do not eliminate the need to ingest essential micronutrients. They operate under all the same physical and biochemical laws as high carbohydrate diets.

Insulin spikes

On another topic, Cynthia and David state: “And carbohydrate consumption always causes blood insulin levels to spike, which has a whole series of negative consequences.” I don’t know if they have read “An insulin index of foods: The insulin demand generated by 1000 kJ portions of common foods” (7). This project demonstrated that protein-rich foods also cause insulin levels to rise, due to insulin also having a function of clearing amino acids from the blood stream. The insulin scores for beef and fish exceed those for several high carbohydrate foods (white pasta, brown pasta, porridge) and are comparable to others (brown rice, whole grain bread). While in general it is true that limiting carbohydrate reduces insulin responses, I would caution anyone against stating broadly that “carbohydrate consumption always causes blood insulin levels to spike,” without specifying what type of carbohydrate. Since dietary protein also causes release of insulin in amounts comparable to some carbohydrate sources, I suggest taking care not to assert that only carbohydrate causes insulin "spikes."

As another relevant aside, short-term, high intensity exercise also causes a “spike” in blood glucose levels along with an increase of insulin levels to 60 microU/ml, a 2-fold increase over resting values (2). Does this spike have “a whole series of negative consequences”? No. This spike has the function of promoting conversion of blood glucose into glycogen, an essential function for preserving fight or flight capacity. Not all spikes of insulin cause the sky to fall.

Finally, I suggest distinguishing between temporary spikes in insulin, and chronic hyperinsulinemia. The undesired effects of insulin arise from chronic hyperinsulinemia, not temporary rises in insulin levels, so long as those rises quickly subside.

To end, I will quote Speth and Spielman:

“The greater protein-sparing capacity of carbohydrate under conditions of marginal calorie or protein intake may also help to explain why hunter-gatherers in the early Holocene began to invest time and energy cultivating plants, despite the meager returns many of these cultigens
would have provided in their early stages of domestication.”

Not to belabor the obvious, but the Paleolithic lifestyle of hunting big game and tossing any animals with low body fat met up against ecological constraints that made it unsustainable. In response, I suggest that it appears that our ancestors looked for an option, and they discovered that carbohydrate could replace fat as a method of diluting protein, with superior results.


1. Phinney SD. Ketogenic diets and physical performance. Nutrition & Metabolism 2004, 1:2.
2. Pascoe DD and Gladden LB. Muscle glycogen resynthesis after short term, high intensity exercise and resistance exercise. Sports Med (1996) 21:98-118.
3. Eaton SB, Konner M, Shostak M. The Paleolithic Prescription. New York: Harper& Row, 1988.
4. Robergs RA et al. Muscle glycogenolysis during different intensities of weight-resistance exercise. J Appl Physiology (1991) 70:1700-1706.
5. Speth JD and Spielman KA. Energy Source, Protein Metabolism, and Hunter-Gatherer Subsistence Strategies. J Anthro Archaeo 2, 1-31 (1983).
6. Rudman et al, Maximal Rates of Excretion and Synthesis of Urea in Normal and Cirrhotic Subjects, J Clin Invest. 1973 September; 52(9): 2241–2249.
7. Holt SHA, Brand-Miller J, Petocz P. An insulin index of foods: The insulin demand generated by 1000 kJ portions of common foods. Am J Clin Nutr 1997:66:1264-76.

Tuesday, September 8, 2009

Primal Potatoes, part 3

While thinking about the role of tubers in human evolution, I decided to revisit some of the data on tooth decay collected by Weston Price, and rediscovered something that may surprise some people.

Starch and Caries

When Price visited Alaska, he found that isolated Alaskan Indians living on native foods had 0.3% of teeth attacked by decay; isolated Kokamute Eskimos living only on native foods had 0.1% of teeth attacked by decay; and lower Kuskokwim Eskimos living only on native foods had 0.09% attacked by decay (1).

Although impressive, the Maori, an omnivorous population, had an even lower incidence of dental decay. Dr. Price quotes Pickerill, who studied both skulls and “relatively primitive” living Maori:
“In an examination of 250 Maori skulls—all from an uncivilized age—I found carious teeth present in only two skulls or 0.76 per cent. By taking the average of Mummery’s and my own investigations, the incidence of caries in the Maori is found to be 1.2 per cent in a total of 326 skulls. This is lower even than the Esquimaux, and shows the Maori to have been the most immune race to caries, for which statistics are available.” (2)

Dr. Price comments that Pickerill’s numbers report the percentages of individuals with caries; expressed in percentage of teeth attacked by dental caries, the Maori had an incidence of 0.05% or 1 in 2000 teeth. Thus, the Esquimaux—now spelled “Eskimo”—had a decay incidence at least double that of the Maori, who were living “relatively primitive” lives.

What did the Maori eat? Price reports that they ate mutton birds, seafoods, vegetables and fruits, and “Large quantities of fern root were used” (3). Bovell-Benjamin reports that “Early records have indicated that the sweet potato is a staple food source for many indigenous populations in Central and South Americas, Ryukyu Island, Africa, the Caribbean, the Maori people, Hawaiians, and Papua New Guineans” (4).

According to Cambie and Ferguson, the Maori also used taro corms (Colocasia esculenta), which they introduced to New Zealand (the Maori migrated to N.Z. from Polynesia) (5). Thus, the Maori apparently had less tooth decay than Eskimos, although eating sweet potatoes and taro corms.

When Price visited the Amazon Jungle Indians, he found an even more impressive immunity to dental decay; he did not find a single decayed tooth in the group he studied, an incidence of 0.0%. What did they eat? Price reported:
“The native foods of these Amazon Jungle Indians included the liberal use of fish which are very abundant in both the Amazon and its branches….; animal life from the forest and thickets; bird life, including many water fowl and their eggs; plants and fruits. They use very large quantities of yucca which is a starchy root quite similar to our potato in chemical content.” [Emphasis added](6)

Again, the Amazon Indians had less tooth decay than the Eskimos, while eating a diet containing large amounts of starchy roots.

Among the Australian Aborigines, Price found “dental caries or tooth decay was exceedingly rare among the isolated groups” (7). Cordain et al estimated that about 24 percent of plant foods in the Aborigine diet consisted of underground storage structures––tubers, roots, and bulbs (8). Brand-Miller and Holt report that Aborigines ate Dioscorea species (yams), Ipomoea costata (wild potato, related to Ipomoea batatas, i.e. sweet potato), and Cyperus species (native onion) (9). Tubers of I. costata range up to the size of a human head. We can eat them raw or cooked and have a slightly sweet taste.

Considering all roots and tubers eaten by aborigines, Brand-Miller and Holt report that “Some have a composition which is similar to a potato with about 15-20% carbohydrate, but others are more like a carrot with much less carbohydrate and less energy, but lots of fibre”(9). In the aborigine diet, “If plants provided 20 to 40 % of the energy in the diet (the most likely range), then plants would have contributed 22-44 g protein, 18-36 g fat, 101-202 g carbohydrate, 40-80 g fibre and 90-180 mg vitamin C in a 12500kJ (3000kcal) diet” (9) Two hundred grams of carbohydrate supplies 800 calories, only 26% of 3000 calories, so even at the high end, this does not constitute a high carbohydrate diet (compared to the 60% recommended by some), yet this intake does go higher (nearly 3 times higher) than the 75 g per day maximum suggested as a “low” carbohydrate diet by advocates of the same, such as Lutz. Nevertheless, it provides significant protein-sparing action.

For comparison, Price found 1.2 percent of teeth decayed among the Gaelics who consumed oats as a staple food, 4.6 percent among Swiss living on rye bread and dairy products, and 5.5 percent among Kikuyu living on largely vegetarian diets based on millet. Thus, the Gaelics had a tooth decay incidence twenty-four times that of the Maori. Price’s findings suggest that a primitive diet containing substantial amounts of tubers has little or no cariogenic activity compared to a diet containing substantial amounts of cereal grains.

Thus, it appears that some populations eating diets containing both animal meat and non-cereal vegetal starch have displayed a higher resistance to tooth decay than populations eating diets composed almost exclusively of animal-derived food, despite the fact that starch in the diet can increase the growth of caries-causing acidogenic bacteria in the mouth.

How To Explain These Findings?

I can presently suggest these possible explanations for these observations:
1) vegetal foods—including some starchy but non-cereal vegetal foods--provide some micronutrients that improve immunity to tooth decay, in greater quantities than provided by meat.
2) the cereal grains contain compounds that block vitamin D action and probably otherwise interfere with calcium metabolism and hence bone and tooth health, and these substances may not occur in tubers.
3) the intake of starch among the Maori and Amazon natives did not reach a threshold for increasing tooth decay
4) Eskimos' use of teeth for various tasks increased their susceptibility to caries

Regarding number 1, I have no difficulty coming up with nutrients more easily supplied in a omnivorous as opposed to a strictly carnivorous diet. Some of the essential micronutrients that play a role in maintenance of bone and tooth integrity include vitamin K1, calcium, copper, and magnesium. A strictly carnivorous, dairy-free diet tends to supply lower amounts of vitamin K1, calcium, copper, and magnesium compared to a cereal-free omnivorous diet.

Micronutrients not yet considered essential, but known to benefit bone integrity, include boron and silicon. Fruits and vegetables supply boron and silicon more abundantly than meat. In fact, sweet potatoes consumed by Maori have an extraordinary need for boron during growth, so they generously supply boron.

Regarding number 2, at least one study has shown that a diet high in cereal fiber reduces the serum plasma half life of vitamin D by nearly 30%, perhaps by fiber binding the vitamin D and reducing its reuptake and increasing its excretion (10).

1. Price W. Nutrition and Physical Degeneration. La Mesa, CA. PPNF. Pp. 61-62.
2. Ibid. P. 201.
3. Ibid. P. 262.
4. Bovel-Benjamin AC. Sweet potato: a review of its past, present, and future role in human nutrition. Adv Food Nutr Res. 2007;52:1-59.
5. Cambie RC and Ferguson LR. Potential functional foods in the traditional Maori diet. Mutat Res. 2003 Feb-Mar;523-524:109-17.
6. Price, op cit, p. 255.
7. Ibid, p. 174.
8. Cordain L, Brand Miller J, Eaton SB, Mann N, Holt SHA, Speth JD. Plant-animal subsistence ratios and macronutrient energy estimations in worldwide hunter-gatherer diets. Am J Clin Nutr 2000; 71:682–92.
9. Brand-Miller JC, Holt SHA. Australian Aboriginal plant foods: a consideration of
their nutritional composition and health implications. Nutrition Research Reviews (1998), 11, 5-23.
10. Batchelor AJ, Compston JE. Reduced plasma half-life of radio-labelled 25-hydroxyvitamin D3 in subjects receiving a high-fibre diet. Br J Nutr. 1983 Mar;49(2):213-6.

Thursday, September 3, 2009

Primal Potatoes, part 2

In addition to our high level of amylase production, we also have another feature that raises questions about idea that Paleolithic people ate a strictly carnivorous or starch-free diet: we store glycogen, a starch, in our liver and muscles. The typical human can store 100 g of starch in the liver, and 300 g in muscle tissue. This implies that natural selection favored the survival of people who could store starch in amounts up to 400 g at a time¬––an amount impossible to get from non-starchy vegetables. What purpose could this serve?

Supporting this feature, we have the insulin system. Although many paleodiet thinkers focus on the lipogenic effects of our insulin response to carbohydrate, lipogenesis via insulin only occurs if we have no immediate use for the glucose and we have full glycogen stores. If we don’t have full glycogen stores, insulin will convert glucose to glycogen first. This interaction between insulin, dietary glucose, and glycogen indicates that human physiology evolved in an environment in which conversion of dietary glucose into glycogen stores conferred a survival advantage.

Starch, Glycogen, and Hunting Success

Glycogen storage appears to have a significant effect on physical performance. Phinney investigated the effect of a ketogenic diet on physical performance, and found that, given adequate adaptation time and mineral nutriture, a ketogenic diet can support endurance performance equivalent to a high-starch diet. However, he also noted that athletes on ketogenic diets show decrements in anaerobic performance—e.g. weight training, weight lifting, or sprint performance, particularly at the end of an endurance event. This occurs because sprinting or lifting requires the production of ATP in the absence of oxygen, and human mitochondria cannot derive ATP from fat in the absence of oxygen. Thus, we require intramuscular storage of glycogen to retain and develop maximum strength or sprint performance, as needed in the “fight or flight” response.

Aerobic or steady state endurance activity has very little impact on glycogen stores unless carried out for one hour or more. In contrast, high intensity activity--like sprinting or resistance training--rapidly depletes muscle glycogen. Whereas typical glycogen stores will support an intense aerobic exercise for a few hours, a single maximal sprint effort will deplete one-third to one-half of glycogen stores (Fournier et al, 2004).

Humans can replenish glycogen stores without dietary carbohydrate, and even while fasting (Fournier et al, 2004), which emphasizes the importance of glycogen stores for survival (specifically, in fight or flight situations). In the absence of food, lactate and endogenous amino acids provide the substrate for glycogen replenishment--you sacrifice lean mass for glycogen. In the absence of dietary carbohydrate, dietary amino acids would supply the substrate for glycogen replenishment.

Since we can store approximately 400 g of glycogen, and it takes one gram of protein to produce one gram of glucose/glycogen, in the absence of dietary carbohydrate, replenishment of just one-third of muscle glycogen (100 g) depleted by one maximal effort each day would require intake of 100 g of protein above dietary requirements, or the breakdown of up to 100 g of lean mass––nearly one-quarter of a pound of muscle.

People with physical activity levels similar to hunters doing persistence hunting require 1.0 to 1.6 g of protein per kilogram of body mass to maintain nitrogen balance if eating a mixed diet containing adequate glucose (Tarnopolsky, 2004). A 150 pound (68 kg) individual would thus require 68 to 108 g of protein to maintain lean mass assuming a mixed diet containing carbohydrate. If his diet had no carbohydrate, he would require 133 g additional protein each day on which he made efforts requiring him to replenish just one-third of his total (muscle and liver) glycogen. So, his total requirement would be at least 201 up to 241 g of protein daily to prevent loss of lean mass. This would require the consumption of about 28 to 34 ounces of lean meat – 1.75 to 2 pounds. If he depleted one-half of his glycogen daily, he would require 268 to 308 g of dietary protein, or 38 to 44 ounces of lean meat (2.4 to 2.75 pounds) every day.

Such an individual would expend about 3000 calories daily. An intake of 201 grams of protein provides 1064 calories, 27% of the total caloric intake. An intake of 241 g of protein would provide 32% of calories. This gets near the maximum intake of protein possible without exceeding the liver’s ability to detoxify the ammonia that results from deaminating the amino acids in the process of converting them to glucose. An intake of 308 g of dietary protein would provide 1232 calories, 41% of total caloric intake, an amount that would likely cause protein poisoning.

These apparent facts raise the intriguing possibility that the use of tubers fueled human success in hunting. Simply put, people who had fuller intramuscular glycogen stores would have superior sprinting, wrestling, and lifting ability compared to people without them. Such ability certainly would not improve human ability to harvest tubers, since they don’t run away or resist capture. But I imagine that when humans hunted on foot, with spears and such, using some type of persistence hunting, those who had the best “kick” into a sprint would frequently have had greater hunting and reproductive success than those who did not.

Consider this feat of strength recounted in The Paleolithic Prescription:
“In 1805, the Lewis and Clark expedition witnessed an Indian bison kill ….A small herd was stampeded over a cliff into a deep, broad ravine. As the bison fell one on top of the other, dazed and injured, hunters killed those on top with spears; the others were crushed and suffocated underneath. The ravine was twelve feet wide and eight feet deep; most of the bulls weighed over a ton, yet a team of five Indian hunters pulled nearly all the bison out of the ravine onto level ground for butchering.”

This is all anaerobic activity. Our current knowledge indicates that men who had more stored glycogen would have had greater success in feats like this, compared to men who did not.

In addition, if attacked by a predator, natural selection would have favored the survival of those who had a strong “kick” fueled by glycogen over those who had less stored glycogen and limited sprint ability.

I can think of several other advantages people using starch from tubers instead of protein from meat to supply glucose for replenishing glycogen would have realized:
1. Lower dietary protein/meat requirement, reducing the pressure for success in hunting large animals, and making it possible to feed more people (offspring) with each kill.
2. Less burden on the liver for ammonia detoxification.
3. Easier to avoid protein poisoning while at the same time maintaining greater glycogen stores.
4. Easier to maintain and increase lean mass in response to the stresses of high intensity activity, with a lower dietary protein requirement.
5. Reduced pressure to hunt only the fattest animals by use of carbohydrate instead of fat to dilute the protein content of the diet; which greatly enlarges the pool of potential prey, increasing dramatically the amount of energy available for harvest.

Thus it seems likely that people who ate both meat and tubers regularly and had increased amylase and had the ability to store glucose as intramuscular glycogen, rather than as fat, would have scored more often in hunting, more often avoided predators, had access to more prey, and had ability to support more offspring, compared to those who did not eat tubers, or did not have enough amylase, or did not store glucose from tubers as glycogen.

Glucose, glycogen, insulin resistance, and intermittent feeding

Modern people easily consume 300 to 400 grams of glucose daily, which means that they will always have full glycogen stores unless they do something to deplete them on a daily basis. When muscle have full glycogen stores, they exhibit insulin resistance, but if you deplete the muscles of glycogen, they become insulin sensitive.

I have already noted that hunters engaged in the type of high intensity activity required to deplete glycogen stores and maintain insulin sensitivity. In addition, hunter-gatherers typically ate only once or twice daily. When you fast, the liver store of glycogen gets used up in 8 to 10 hours, and muscle glycogen reduces by about 50 percent in 24 hours. Thus, the primal combination of high intensity exercise and intermittent feeding would likely have maintained insulin sensitivity even with regular intake of glucose-rich starches.

Also consider that Holt et al (see Mendosa’s report) performed a study to determine the satiety value of various foods. White potatoes turned out to have the highest satiety index of any food tested, twice as satisfying as cheese or eggs, nearly twice as satisfying as beef, and about 50% more satisfying than ling fish, measured two hours after feeding. If that to which we have adapted gives us the greatest satisfaction, then this supports the idea that foods like the potato played a very important role in satisfying our ancestors. Since meat also had a high satiety value (nearly 75% greater than that of white bread), roasted meat and potatoes would have provided our ancestors with very satisfying fare.

Thus, I have come to accept that tubers probably played important roles in human evolution, and propose that the use of tubers actually increased success in hunting by improving physical performance. This seems to me the best explanation of all the unique features of human physiology. I think it may explain why many people find meals of meat and potatoes deeply satisfying “comfort” food.

The next question is, will a diet high in tubers adversely affect dental and therefore general health? I will address that question in Primal Potatoes, part 3.