Recently, Chris Kresser published a series on dietary salt (sodium chloride) and health (1). One of the issues he covered is the effect of salt on blood pressure. Most studies have shown a relatively weak relationship between salt intake and blood pressure. My position overall is that we're currently eating a lot more salt than at almost any point in our evolutionary history as a species, so I tend to favor a moderately low salt intake. However, there may be more important factors than salt when it comes to blood pressure, at least in the short term.
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Showing posts with label hypertension. Show all posts
Showing posts with label hypertension. Show all posts
Monday, 21 May 2012
Wednesday, 22 February 2012
Is Sugar Fattening?
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Sunday, 13 February 2011
Polyphenols, Hormesis and Disease: Part I
What are Polyphenols?
Polyphenols are a diverse class of molecules containing multiple phenol rings. They are synthesized in large amounts by plants, certain fungi and a few animals, and serve many purposes, including defense against predators/infections, defense against sunlight damage and chemical oxidation, and coloration. The color of many fruits and vegetables, such as blueberries, eggplants, red potatoes and apples comes from polyphenols. Some familiar classes of polyphenols in the diet-health literature are flavonoids, isoflavonoids, anthocyanidins, and lignins.
The Case Against Polyphenols
Many diet-health authorities seem pretty well convinced that dietary polyphenols are an important part of good health, due to their supposed antioxidant properties. In the past, I've been critical of the hypothesis. There are several reasons for it:
A Reappraisal
After reading more about polyphenols, and coming to understand that the prevailing hypothesis of why they work makes no sense, I decided that the whole thing is probably bunk: at best, specific polyphenols are protective in rodents at unnaturally high doses due to some drug-like effect. But-- I kept my finger on the pulse of the field just in case, and I began to notice that more sophisticated studies were emerging almost weekly that seemed to confirm that realistic amounts of certain polyphenol-rich foods (not just massive quantities of polyphenol extract) have protective effects against a variety of health problems. There are many such studies, and I won't attempt to review them comprehensively, but here are a few I've come across:
In the face of this accumulating evidence, I've had to reconsider my position on polyphenols. In the process, and through conversations with knowledgeable researchers in the polyphenol field, I encountered a different hypothesis that puts the puzzle pieces together nicely. I'll discuss that in the next post.
* Serum levels of polyphenols briefly enter the mid nM to low uM range, depending on the food (2). Compare that with the main serum antioxidants: ~200 uM for uric acid, ~100 uM for vitamin C, ~30 uM for vitamin E.
Polyphenols are a diverse class of molecules containing multiple phenol rings. They are synthesized in large amounts by plants, certain fungi and a few animals, and serve many purposes, including defense against predators/infections, defense against sunlight damage and chemical oxidation, and coloration. The color of many fruits and vegetables, such as blueberries, eggplants, red potatoes and apples comes from polyphenols. Some familiar classes of polyphenols in the diet-health literature are flavonoids, isoflavonoids, anthocyanidins, and lignins.
The Case Against Polyphenols
Many diet-health authorities seem pretty well convinced that dietary polyphenols are an important part of good health, due to their supposed antioxidant properties. In the past, I've been critical of the hypothesis. There are several reasons for it:
- Polyphenols are often, but not always, defensive compounds that interfere with digestive processes, which is why they often taste bitter and/or astringent. Plant-eating animals including humans have evolved defensive strategies against polyphenol-rich foods, such as polyphenol-binding proteins in saliva (1).
- Ingested polyphenols are poorly absorbed (2). The concentration in blood is low, and the concentration inside cells is probably considerably lower*. In contrast, essential antioxidant nutrients such as vitamins E and C are efficiently absorbed and retained rather than excluded from the circulation.
- Polyphenols that manage to cross the gut barrier are rapidly degraded by the liver, just like a variety of other foreign molecules, again suggesting that the body doesn't want them hanging around (2).
- The most visible hypothesis of how polyphenols influence health is the idea that they are antioxidants, protecting against the ravages of reactive oxygen species. While many polyphenols are effective antioxidants at high concentrations in a test tube, I don't find it very plausible that the low and transient blood concentration of polyphenols achieved by eating polyphenol-rich foods makes a meaningful contribution to that person's overall antioxidant status, when compared to the relatively high concentrations of other antioxidants in blood* (uric acid; vitamins C, E; ubiquinone) and particularly inside cells (SOD1/2, catalase, glutathione reductase, thioredoxin reductase, paraoxonase 1, etc.).
- There are a number of studies showing that the antioxidant capacity of the blood increases after eating polyphenol-rich foods. These are often confounded by the fact that fructose (in fruit and some vegetables) and caffeine (in tea and coffee) can increase the blood level of uric acid, the blood's main water-soluble antioxidant. Drinking sugar water has the same effect (2).
- Rodent studies showing that polyphenols improve health typically use massive doses that exceed what a person could consume eating food, and do not account for the possibility that the rodents may have been calorie restricted because their food tastes awful.
A Reappraisal
After reading more about polyphenols, and coming to understand that the prevailing hypothesis of why they work makes no sense, I decided that the whole thing is probably bunk: at best, specific polyphenols are protective in rodents at unnaturally high doses due to some drug-like effect. But-- I kept my finger on the pulse of the field just in case, and I began to notice that more sophisticated studies were emerging almost weekly that seemed to confirm that realistic amounts of certain polyphenol-rich foods (not just massive quantities of polyphenol extract) have protective effects against a variety of health problems. There are many such studies, and I won't attempt to review them comprehensively, but here are a few I've come across:
- Dr. David Grassi and colleagues showed that polyphenol-rich chocolate lowers blood pressure, improves insulin sensitivity and lowers LDL cholesterol in hypertensive and insulin resistant volunteers when compared with white chocolate (3). Although dark chocolate is also probably richer in magnesium, copper and other nutrients than white chocolate, the study is still intriguing.
- Dr. Christine Morand and colleagues showed that drinking orange juice every day lowers blood pressure and increases vascular reactivity in overweight volunteers, an effect that they were able to specifically attribute to the polyphenol hesperidin (4).
- Dr. F. Natella and colleagues showed that red wine prevents the increase in oxidized blood lipids (fats) that occurs after consuming a meal high in oxidized and potentially oxidizable fats (5).
- Several studies have shown that hibiscus tea lowers blood pressure in people with hypertension when consumed regularly (6, 7, 8). It also happens to be delicious.
- Dr. Arpita Basu and colleagues showed that blueberries lower blood pressure and oxidized LDL in men and women with metabolic syndrome (9).
- Animal studies have generally shown similar results. Dr. Xianli Wu and colleagues showed that whole blueberries potently inhibit atherosclerosis (hardening and thickening of the arteries that can lead to a heart attack) in a susceptible strain of mice (10). This effect was associated with a higher expression level of antioxidant enzymes in the vessel walls and other tissues.
In the face of this accumulating evidence, I've had to reconsider my position on polyphenols. In the process, and through conversations with knowledgeable researchers in the polyphenol field, I encountered a different hypothesis that puts the puzzle pieces together nicely. I'll discuss that in the next post.
* Serum levels of polyphenols briefly enter the mid nM to low uM range, depending on the food (2). Compare that with the main serum antioxidants: ~200 uM for uric acid, ~100 uM for vitamin C, ~30 uM for vitamin E.
Saturday, 3 July 2010
Tropical Plant Fats: Palm Oil
A Fatal Case of Nutritionism
The concept of 'nutritionism' was developed by Dr. Gyorgy Scrinis and popularized by the food writer Michael Pollan. It states that the health value of a food can be guessed by the sum of the nutrients it contains. Pollan argues, I think rightfully, that nutritionism is a reductionist philosophy that assumes we know more about food composition and the human body than we actually do. You can find varying degrees of this philosophy in most mainstream discussions of diet and health*.
One conspicuous way nutritionism manifests is in the idea that saturated fat is harmful. Any fat rich in saturated fatty acids is typically assumed to be unhealthy, regardless of its other constituents. There is also apparently no need to directly test that assumption, or even to look through the literature to see if the assumption has already been tested. In this manner, 'saturated' tropical plant fats such as palm oil and coconut oil have been labeled unhealthy, despite essentially no direct evidence that they're harmful. As we'll see, there is actually quite a bit of evidence, both indirect and direct, that their unrefined forms are not harmful and perhaps even beneficial.
Palm Oil and Heart Disease
Long-time readers may recall a post I wrote a while back titled Ischemic Heart Attacks: Disease of Civilization (1). I described a study from 1964 in which investigators looked for signs of heart attacks in thousands of consecutive autopsies in the US and Africa, among other places. They found virtually none in hearts from Nigeria and Uganda (3 non-fatal among more than 4,500 hearts), while Americans of the same age had very high rates (up to 1/3 of hearts).
What do they eat in Nigeria? Typical Nigerian food involves home-processed grains, starchy root vegetables, beans, fruit, vegetables, peanuts, red palm oil, and a bit of dairy, fish and meat**. The oil palm Elaeis guineensis originated in West Africa and remains one of the main dietary fats throughout the region.
To extract the oil, palm fruit are steamed, and the oily flesh is removed and pressed. It's similar to olive oil in that it is extracted gently from an oil-rich fruit, rather than harshly from an oil-poor seed (e.g., corn or soy oil). The oil that results is deep red and is perhaps the most nutrient-rich fat on the planet. The red color comes from carotenes, but red palm oil also contains a large amount of vitamin E (mostly tocotrienols), vitamin K1, coenzyme Q10 and assorted other fat-soluble constituents. This adds up to a very high concentration of fat-soluble antioxidants, which are needed to protect the fat from rancidity in hot and sunny West Africa. Some of these make it into the body when it's ingested, where they appear to protect the body's own fats from oxidation.
Mainstream nutrition authorities state that palm oil should be avoided due to the fact that it's approximately half saturated. This is actually one of the main reasons palm oil was replaced by hydrogenated seed oils in the processed food industry. Saturated fat raises blood cholesterol, which increases the risk of heart disease. Doesn't it? Let's see what the studies have to say.
Most of the studies were done using refined palm oil, unfortunately. Besides only being relevant to processed foods, this method also introduces a new variable because palm oil can be refined and oxidized to varying degrees. However, a few studies were done with red palm oil, and one even compared it to refined palm oil. Dr. Suzanna Scholtz and colleagues put 59 volunteers on diets predominating in sunflower oil, refined palm oil or red palm oil for 4 weeks. LDL cholesterol was not different between the sunflower oil and red palm oil groups, however the red palm oil group saw a significant increase in HDL. LDL and HDL both increased in the refined palm oil group relative to the sunflower oil group (2).
Although the evidence is conflicting, most studies have not been able to replicate the finding that refined palm oil increases LDL relative to less saturated oils (3, 4). This is consistent with studies in a variety of species showing that saturated fat generally doesn't raise LDL compared to monounsaturated fat in the long term, unless a large amount of purified cholesterol is added to the diet (5).
Investigators have also explored the ability of palm oil to promote atherosclerosis, or hardening and thickening of the arteries, in animals. Not only does palm oil not promote atherosclerosis relative to monounsaturated fats (e.g., olive oil), but in its unrefined state it actually protects against atherosclerosis (6, 7). A study in humans hinted at a possible explanation: compared to a monounsaturated oil***, palm oil greatly reduced oxidized LDL (8). As a matter of fact, I've never seen a dietary intervention reduce oxLDL to that degree (69%). oxLDL is a major risk factor for cardiovascular disease, and a much better predictor of risk than the typically measured LDL cholesterol (9). The paper didn't state whether or not the palm oil was refined. I suspect it was lightly refined, but still rich in vitamin E and CoQ10.
As I discussed in my recent interview with Jimmy Moore, atherosclerosis is only one factor in heart attack risk (10). Several other factors are also major determinants of risk: clotting tendency, plaque stability, and susceptibility to arrhythmia. Another factor that I haven't discussed is how resistant the heart muscle is to hypoxia, or loss of oxygen. If the coronary arteries are temporarily blocked-- a frequent occurrence in modern people-- the heart muscle can be damaged. Dietary factors determine the degree of damage that results. For example, in rodents, nitrites derived from green vegetables protect the heart from hypoxia damage (11). It turns out that red palm oil is also protective (12, 13). Red palm oil also protects against high blood pressure in rats, an effect attributed to its ability to reduce oxidative stress (14, 15).
Together, the evidence suggests that red palm oil does not contribute to heart disease risk, and in fact is likely to be protective. The benefits of red palm oil probably come mostly from its minor constituents, i.e. the substances besides its fatty acids. Several studies have shown that a red palm oil extract called palmvitee lowers serum lipids in humans (16, 17). The minor constituents are precisely what are removed during the refining process.
Palm Oil and the Immune System
Red palm oil also has beneficial effects on the immune system in rodents. It protects against bacterial infection when compared with soybean oil (18). It also protects against certain cancers, compared to other oils (19, 20). This may be in part due to its lower content of omega-6 linoleic acid (roughly 10%), and minor constituents.
The Verdict
Yet again, nutritionism has gotten itself into trouble by underestimating the biological complexity of a whole food. Rather than being harmful to human health, red palm oil, an ancient and delicious food, is likely to be protective. It's also one of the cheapest oils available worldwide, due to the oil palm's high productivity. It has a good shelf life and does not require refrigeration. Its strong, savory flavor goes well in stews, particularly meat stews. It isn't available in most grocery stores, but you can find it on the internet. Make sure not to confuse it with refined palm oil or palm kernel oil.
* The approach that Pollan and I favor is a simpler, more empirical one: eat foods that have successfully sustained healthy cultures.
** Some Nigerians are also pastoralists that subsist primarily on dairy.
*** High oleic sunflower oil, from a type of sunflower bred to be high in monounsaturated fat and low in linoleic acid. I think it's probably among the least harmful refined oils. I use it sometimes to make mayonnaise. It's often available in grocery stores, just check the label.
The concept of 'nutritionism' was developed by Dr. Gyorgy Scrinis and popularized by the food writer Michael Pollan. It states that the health value of a food can be guessed by the sum of the nutrients it contains. Pollan argues, I think rightfully, that nutritionism is a reductionist philosophy that assumes we know more about food composition and the human body than we actually do. You can find varying degrees of this philosophy in most mainstream discussions of diet and health*.
One conspicuous way nutritionism manifests is in the idea that saturated fat is harmful. Any fat rich in saturated fatty acids is typically assumed to be unhealthy, regardless of its other constituents. There is also apparently no need to directly test that assumption, or even to look through the literature to see if the assumption has already been tested. In this manner, 'saturated' tropical plant fats such as palm oil and coconut oil have been labeled unhealthy, despite essentially no direct evidence that they're harmful. As we'll see, there is actually quite a bit of evidence, both indirect and direct, that their unrefined forms are not harmful and perhaps even beneficial.
Palm Oil and Heart Disease
Long-time readers may recall a post I wrote a while back titled Ischemic Heart Attacks: Disease of Civilization (1). I described a study from 1964 in which investigators looked for signs of heart attacks in thousands of consecutive autopsies in the US and Africa, among other places. They found virtually none in hearts from Nigeria and Uganda (3 non-fatal among more than 4,500 hearts), while Americans of the same age had very high rates (up to 1/3 of hearts).
What do they eat in Nigeria? Typical Nigerian food involves home-processed grains, starchy root vegetables, beans, fruit, vegetables, peanuts, red palm oil, and a bit of dairy, fish and meat**. The oil palm Elaeis guineensis originated in West Africa and remains one of the main dietary fats throughout the region.
To extract the oil, palm fruit are steamed, and the oily flesh is removed and pressed. It's similar to olive oil in that it is extracted gently from an oil-rich fruit, rather than harshly from an oil-poor seed (e.g., corn or soy oil). The oil that results is deep red and is perhaps the most nutrient-rich fat on the planet. The red color comes from carotenes, but red palm oil also contains a large amount of vitamin E (mostly tocotrienols), vitamin K1, coenzyme Q10 and assorted other fat-soluble constituents. This adds up to a very high concentration of fat-soluble antioxidants, which are needed to protect the fat from rancidity in hot and sunny West Africa. Some of these make it into the body when it's ingested, where they appear to protect the body's own fats from oxidation.
Mainstream nutrition authorities state that palm oil should be avoided due to the fact that it's approximately half saturated. This is actually one of the main reasons palm oil was replaced by hydrogenated seed oils in the processed food industry. Saturated fat raises blood cholesterol, which increases the risk of heart disease. Doesn't it? Let's see what the studies have to say.
Most of the studies were done using refined palm oil, unfortunately. Besides only being relevant to processed foods, this method also introduces a new variable because palm oil can be refined and oxidized to varying degrees. However, a few studies were done with red palm oil, and one even compared it to refined palm oil. Dr. Suzanna Scholtz and colleagues put 59 volunteers on diets predominating in sunflower oil, refined palm oil or red palm oil for 4 weeks. LDL cholesterol was not different between the sunflower oil and red palm oil groups, however the red palm oil group saw a significant increase in HDL. LDL and HDL both increased in the refined palm oil group relative to the sunflower oil group (2).
Although the evidence is conflicting, most studies have not been able to replicate the finding that refined palm oil increases LDL relative to less saturated oils (3, 4). This is consistent with studies in a variety of species showing that saturated fat generally doesn't raise LDL compared to monounsaturated fat in the long term, unless a large amount of purified cholesterol is added to the diet (5).
Investigators have also explored the ability of palm oil to promote atherosclerosis, or hardening and thickening of the arteries, in animals. Not only does palm oil not promote atherosclerosis relative to monounsaturated fats (e.g., olive oil), but in its unrefined state it actually protects against atherosclerosis (6, 7). A study in humans hinted at a possible explanation: compared to a monounsaturated oil***, palm oil greatly reduced oxidized LDL (8). As a matter of fact, I've never seen a dietary intervention reduce oxLDL to that degree (69%). oxLDL is a major risk factor for cardiovascular disease, and a much better predictor of risk than the typically measured LDL cholesterol (9). The paper didn't state whether or not the palm oil was refined. I suspect it was lightly refined, but still rich in vitamin E and CoQ10.
As I discussed in my recent interview with Jimmy Moore, atherosclerosis is only one factor in heart attack risk (10). Several other factors are also major determinants of risk: clotting tendency, plaque stability, and susceptibility to arrhythmia. Another factor that I haven't discussed is how resistant the heart muscle is to hypoxia, or loss of oxygen. If the coronary arteries are temporarily blocked-- a frequent occurrence in modern people-- the heart muscle can be damaged. Dietary factors determine the degree of damage that results. For example, in rodents, nitrites derived from green vegetables protect the heart from hypoxia damage (11). It turns out that red palm oil is also protective (12, 13). Red palm oil also protects against high blood pressure in rats, an effect attributed to its ability to reduce oxidative stress (14, 15).
Together, the evidence suggests that red palm oil does not contribute to heart disease risk, and in fact is likely to be protective. The benefits of red palm oil probably come mostly from its minor constituents, i.e. the substances besides its fatty acids. Several studies have shown that a red palm oil extract called palmvitee lowers serum lipids in humans (16, 17). The minor constituents are precisely what are removed during the refining process.
Palm Oil and the Immune System
Red palm oil also has beneficial effects on the immune system in rodents. It protects against bacterial infection when compared with soybean oil (18). It also protects against certain cancers, compared to other oils (19, 20). This may be in part due to its lower content of omega-6 linoleic acid (roughly 10%), and minor constituents.
The Verdict
Yet again, nutritionism has gotten itself into trouble by underestimating the biological complexity of a whole food. Rather than being harmful to human health, red palm oil, an ancient and delicious food, is likely to be protective. It's also one of the cheapest oils available worldwide, due to the oil palm's high productivity. It has a good shelf life and does not require refrigeration. Its strong, savory flavor goes well in stews, particularly meat stews. It isn't available in most grocery stores, but you can find it on the internet. Make sure not to confuse it with refined palm oil or palm kernel oil.
* The approach that Pollan and I favor is a simpler, more empirical one: eat foods that have successfully sustained healthy cultures.
** Some Nigerians are also pastoralists that subsist primarily on dairy.
*** High oleic sunflower oil, from a type of sunflower bred to be high in monounsaturated fat and low in linoleic acid. I think it's probably among the least harmful refined oils. I use it sometimes to make mayonnaise. It's often available in grocery stores, just check the label.
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