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Dynamic Evolution and The Gut

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  • Melissa McEwen Huntgatherlove.com has put the full transcript of her talk online here
    http://huntgatherlove.com/content/ancestral-health-symposium-talk
    So although the presentation is online at http://vimeo.com/27996223 those who don't understand English may want to cut and paste a transcript of the presentation into google translate or similar and follow the talk that way.
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  • When talking about the colon size it’s important to remember what happens in the colon 2. The colon is a bioreactor of sorts containing an entire ecosystem of microorganisms 3. To imagine the small of this population remember that humans have only 10 trillion human cells and 100 trillion bacterial cells in our bodies
  • 4. The bacteria in the colon don’t just process waste, they have numerous important functions, they process nutrients, produce nutrients, and fight off infections 5. Interestingly, scientists have discovered they play a role in nearly every disease, even in diseases you might not expect, such as a recent paper that showed that they play a role in heart disease by producing certain compounds in response to some nutrients that can harden the arteries 6. They may even play a role in behavior. Scientists changed the sexual orientation of fruit flies by changing their gut bacteria for example. 7. These bacteria are fed by “prebiotics” which are constituents of food that the bacteria eat 8. Fiber, for example, is a prebiotic
  • Host function Immune system Genetics Anatomy
  • Started researching this These papers recommend low-fat very high fiber diets Humans aren’t gorillas We don’t have the equipment Unique
  • 11. An example of the implications of gut bacteria are the fact they can produce short chain fatty acids, which the body can use as energy 12. Gorillas, for example, rely quite heavily on these short chain fatty acids, getting about 60% of their calories from them. So when you think gorillas are eating a low-fat diet remember their gut is converting all those leaves to fatty acids. 13. Maximum human estimates for energy from SCFA range from 7-9%, which is very low compared to gorillas 14. So humans are required to get more of their calories from the actual food itself, necessitating a higher quality diet Popovich The theoretical effect of different levels of fiber fermentation on the macronutrient profile of the gorilla diet. The points trace the theoretical reduction in energy contribution from protein, fat and carbohydrate as increasing amounts of energy are derived from fiber through the production of short-chain fatty acids (SCFA) (top panel). The bars in the bottom panel indicate the theoretical increase in energy value per gram of fiber, dependent on the degree to which fiber is fermented. At zero fermentation of fiber, the energy intake from fat, protein and carbohydrate (top panel) reflects the proportion of these nutrients in the gorilla diet (0.5 g fat, 11.8 g protein and 7.7 g available carbohydrate per 100 g dry weight). Values are then calculated for the macronutrient profile, assuming that an increasing proportion of the 74.0 g fiber per 100 g dry weight is fermented to SCFA with increasing energy available from SCFA (up to 100% fermented, i.e., 16.8 kJ/g fiber). The black bar (bottom panel) and solid symbols (top panel) represent our suggested level of fermentation and macronutrient profile, respectively, for the gorilla diet on the assumption that 6.3 kJ (1.5 kcal) per gram of fiber is a conservative figure for the energy value of fiber (1
  • 1. So it’s interesting to look at what is so special about the human gut, particularly in comparison with our nearest primate relatives 2. Using regressions based on data from other primates, we would expect our organ mass to be roughly like this 3. But look at what is actually the case for humans- a larger brain and a smaller gut
  • 6. So their hypothesis is that the higher quality diet drove the gut to shrink and the brain to expand. 7. One of the criticisms to the paper was by primatologist Katherine Milton and it was one of the drivers of my desire to write this 8. Her criticism is that perhaps modern humans don’t represent our species, as until quite recently we all ate a high-fiber diet and got much more of our energy from SCFA and such a diet also increased the size of our digestive system, an assertion I will explore later 9. She also asked whether humans with these larger guts had smaller brains....she said probably not. I say maybe....
  • 4. Within the gut you have even more differences, one part that is particularly small for humans is the colon, you can see here that the colon of the orangutan and chimp is much larger and more developed in general Katherine Milton plasticity
  • 5. Guts don’t fossilize very well, but in general, apes with big colons have pot bellies to accommodate them and that can be seen in the postcranial anatomy where you have rounded profile of the abs continuous with the lower portion of the rib cage , giving it a funnel shape and a wide pelvis with flared upper margins, which you can see in the chimp and a. afarensis here (AA from three million years ago) 6. in the human skeleton you have hallmarks of a flat belly and a defined waist
  • 7. If you strip the great apes down like this picture does, you can really see the differences in belly size, with orangs and gorillas having nice big potbellies for their large colons 8. Humans and gibbons both have waists and flatter bellies, consistent with higher quality diets that necessitate a much smaller colon
  • 11. An example of the implications of gut bacteria are the fact they can produce short chain fatty acids, which the body can use as energy 12. Gorillas, for example, rely quite heavily on these short chain fatty acids, getting about 60% of their calories from them. So when you think gorillas are eating a low-fat diet remember their gut is converting all those leaves to fatty acids. 13. Maximum human estimates for energy from SCFA range from 7-9%, which is very low compared to gorillas 14. So humans are required to get more of their calories from the actual food itself, necessitating a higher quality diet Popovich The theoretical effect of different levels of fiber fermentation on the macronutrient profile of the gorilla diet. The points trace the theoretical reduction in energy contribution from protein, fat and carbohydrate as increasing amounts of energy are derived from fiber through the production of short-chain fatty acids (SCFA) (top panel). The bars in the bottom panel indicate the theoretical increase in energy value per gram of fiber, dependent on the degree to which fiber is fermented. At zero fermentation of fiber, the energy intake from fat, protein and carbohydrate (top panel) reflects the proportion of these nutrients in the gorilla diet (0.5 g fat, 11.8 g protein and 7.7 g available carbohydrate per 100 g dry weight). Values are then calculated for the macronutrient profile, assuming that an increasing proportion of the 74.0 g fiber per 100 g dry weight is fermented to SCFA with increasing energy available from SCFA (up to 100% fermented, i.e., 16.8 kJ/g fiber). The black bar (bottom panel) and solid symbols (top panel) represent our suggested level of fermentation and macronutrient profile, respectively, for the gorilla diet on the assumption that 6.3 kJ (1.5 kcal) per gram of fiber is a conservative figure for the energy value of fiber (1
  • 8. Human gut variation is just starting to be studied 9. This paper is from 2010 in South Africa and found quite a bit of variation. The anatomists classified colons into three types shown here and then from autopsies figured out how many people of each race had each type of colon. 10. As you can see here, the long-narrow colon is more common in African populations and the smaller “classic” more common in Indians and Whites. 11. Can eating cause these differences? No, even found in children. 12. Interestingly a problem here is how genetically diverse Africans are, another study showing Baganda tribesman had larger colons than other nearby tribes in Uganda. 13. Does this correlate with brain size?????? I don’t know. Perhaps.
  • 10. And context is important, one of the best studied sets of coprolites are those from the Pecos basin in North America 11. They show evidence of a high-fiber diet, but in a paper extolling the healthiness of paleolithic hunter-gatherers they are bit misplaced since there are some of the few hunter-gatherer skulls with large amounts of dental cavities 12. Some anthropologists say it’s because mineral formations in their food wore down their teeth, but that doesn’t make any sense since lots of cultures have worn-down teeth and don’t have caries 13. here is an Ota tribesman with purposefully worn down teeth and that population has low levels of tooth decay 14. Here is another explanation: perhaps there is an upper limit on healthy fiber consumption for modern humans which is waaaay lower than apes 15. A clue to this comes from children eating macrobiotic diets, which are very “healthy” and very high in fiber 16. These children have abnormal levels of rickets since apparently high fiber levels lower vitamin D levels in the blood, as well as other mineral deficiencies 17. Furthermore intervention studies trying to tie high fiber diets with lower levels of diseases of civilization like heart disease haven’t been very effective
  • 6. How much fiber? Some paleolithic diet papers say 150 grams A DAY. Questionable methods based on cophrolites Another example is from food estimate of modern hunter-gatherers like the Hadza 7. Early studies just shipped their food to the lab where it was analyzed whole 8. But just like we don’t eat the peels of bananas or the knobby tops of bell peppers, it turns out that the Hadza for example spit out quite a bit of the fiber after chewing the food, so cultural context is important 9. I’d love to see ethnography brought back into the fold of physical anthropology since I think cultural cooking and consumption habits are quite important
  • Chimpanzee soaking leaf in a hollow in a tree
  • 9. There are other ways besides cooking humans have probably affected their food’s ability to produce this, such as grinding starch, which you can see this hunter-gatherer doing with sago palm starch. Chimps have been observed pounding and soaking.
  • 13. Do populations eating these foods have even smaller guts? 14. Fermentation is an interesting bird because it has played such a huge role in so many cultures, I have a picture of fermented herring from sweden, which is very high in SCFA I suspect because it tastes like vomit, is that why people eat it?
  • 15. Fermented foods might play a complimentary or substitution role compared to fermentation in the colon, how has this affected human evolution?
  • 1. Butyric Acid and cultural mediators 1. Perhaps the emphasis on fiber is misplaced and we should be looking more at specific types of fiber and the compounds they produce in the gut 2. Here is where complex cultural behaviors are really important 3. I’m going to focus on on specific short chain fatty acid produced in the colon because of it’s cultural context and important role 4. Meet butyric acid, which plays a huge role in many important functions from modulating inflammation to providing cellular energy to colon cells 5. And example of potential importance comes from this mouse study that showed that mice fed a fattening diet didn’t gain weight if they were also given butyric acid 6. Of course we must remember mice have difference gut bacteria and might produce butyric acid differently
  • 7. That’s something that would be fascinating to explore, because given the importance of this fatty acid, it’s interesting that what humans use to produce it more effectively is a type of starch known as “resistant starch” which is only formed by cooking foods like potatoes and plaintains 8. Some of the fibers from common fiber supplements used in the aforementioned intervention studies aren’t so good at making it
  • 10. Another fascinating thing to explore would be exogenous butyric acid, that which humans get from their diet rather than their gut bacteria 11. It’s present in the fat of grazing animals, particularly in the milk, and most common in butter 12. It’s also in some fermented foods, mostly the very “off” tasting ones like ogi from Nigeria or skunked beer. Would love to test more of these.
  • similarity among bacterial communities based on phylogenetic distances. We also need more human samples. Reminds me of what my anthropology mentor, Dr. Ralph Holloway, once said “each great ape is the product of its own branch of the evolutionary tree, they are not analogues to our ancestors”
  • 40% of people have more efficient cellulose degrading bacteria, everyone has them (sample size caution), H2 -producing cellulolytic species in methane + people, Faecalibacterium prausnitzii 8 metabolite, xylan degredation shared with ruminants
  • 1. So human guts are more variation than what you might think 2. some potential sources of variation include cooking and food prep techniques 3. microbes in food, types of fiber, and total fiber consumption 4. Most of our gut bacteria is established when we are born through passing through our mother’s birth canal, and that has varied in modern times since some of us never take that trip 5. It’s also possible we may pass some gut bacteria to our sex partners, recent study showed that we can pass mouth bacteria that way and that actually can cause cavities 6. Antibiotic use can affect gut bacteria for many years afterwards 7. But ultimately I don’t agree with Katherine that the environment can affect the size of the gut, there is no evidence in animals for that certainly and none in humans
  • 14. Here is another recent study of variation, this time on the more plastic type, which is gut bacteria. 15. Here you can see gut bacteria of children in Burkina Faso Vs. children from Italy, which show quite significantly differences in microbe populations 16. These differences don’t show up in breastfed infants, only after eating solid foods.
  • 17. The authors of this paper thought it had to do with fiber consumption, but I would dare to posit it is more about other properties of the food 18. Agrarian African cultures practice tons of fermentation
  • 19. There was some controversy in the past whether or not bacteria from food really mattered because some scientists said it wasn’t possible for most of them to colonize a human gut 20. But that might not matter, a pretty interesting study came out last year showing that in Japanese individuals, gut bacteria had “stolen’ genes involved in the digestion of carbohydrates in seaweed from seaweed bacteria through horizontal transfer
  • Not too high or too low acid CAG+ and CAG-

Transcript

  • 1. Dynamic evolution and the gut Hypothesis hunting with Melissa McEwen Huntgatherlove.com
  • 2. What is so special about the human gut????
    • Why not just eat like this nice ape, shown in the picture on the left?
    • She eats a healthy high fiber diet! Low in fat! High in leaves! Leaves are good for you!!! Your doctor says so!
  • 3. Different Viewpoints
  • 4. Statics
  • 5. Whither The Cambrian Diet??? 52 vs. ~2.5 There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain --Stephen J. Gould, 2000.
  • 6. Dynamic
  • 7. Dynamism Relatively unexplored Shift towards exogenous food processing
  • 8. Cells in the Human Body 10 trillion
  • 9. How important?????
    • Process nutrients
    • Produce nutrients
    • Fight off infections
    • Role in nearly every disease, even diseases you might not expect
      • Metabolites in heart disease
    • Behavior????
      • Sexy fruit flies
  • 10. Seven Factors
  • 11. Do other primate diets have relevance to human health?
    • Nutritional characteristics of wild primate foods: do the diets of our closest living relatives have lessons for us? By Katherine Milton
    • The Western Lowland Gorilla Diet Has Implications for the Health of Humans and Other Hominoids by Popovich et al.
  • 12. Primate Diet for Humans Revisited
    • “ The western lowland gorilla , whose diet may approximate a paleolithic human diet, has been estimated to take nearly 60% of its calories through the colon ” from Case Closed?: Diverticulitis: Epidemiology and Fiber in Journal of Clinical Gastroenterology
  • 13.  
  • 14.  
  • 15. Food Quality as Driver
  • 16. Gut brain tradeoff
  • 17.  
  • 18.  
  • 19. Funnel Shape Wide Pelvis
  • 20.  
  • 21.  
  • 22.  
  • 23. Evidence for paleolithic humans eating a high-fiber diet
    • Pecos basin paleolithic hunter-gatherers
    • Caries caused by tooth wear?
    • Impairment of calcium and Vitamin D
    • Infants on macrobiotic diets
    • Upper limit to fiber consumption?
    • Cultural context!
  • 24.  
  • 25. Don’t Forget Culture
  • 26. Uniquely Human Methods of Improving Food Quality Shift to exogenous
  • 27. A Different Type of Culture
    • Bioavailability of protein and several micronutrients
    • Preservation
    • SCFA??????????
    • Source of symbiotic bacteria????
    • Some fermented foods in danger of dying out
  • 28.  
  • 29. Butyric Acid Fiber vs. fiber byproducts???
  • 30. The African Conundrum and Endogenous Sources of Butyric Acid
  • 31. Exogenous Butyric Acid
    • Fat of grazing animals
    • Ogi
    • Spoiled beer and other fermented foods
    • Crappy traditional foods from around the world??????
  • 32. Differences between primates in the microbiome???
    • Relatively unstudied
  • 33. Spatial Heterogeneity
    • Methane and non methane excretors- different byproducts and transit times
    • Biodiversity interspecies and intraspecies
  • 34. Potential Sources of Human Variation
    • Cooking and food prep techniques
    • Microbes in food
    • Types of fiber in food
    • Total fiber consumption
    • Maternal colonization
    • Sexual colonization????
    • Antibiotic use
    • Genes??????
  • 35.  
  • 36.  
  • 37. The Seaweed Revelation Co-evolution with plants? What about the future? GMOs?
  • 38. Using Bacteria to Track Human History
  • 39. What is Normal??? “ Pig bel”=Clostridial necrotizing enteritis Vegetarian case
  • 40. Human Diversity and Dynamism
    • We humans are truly unique
    • And we still aren’t sure how we got this way
    • Within our population lies a biodiversity waiting to be discovered
    • Loss of biodiversity and cultural adaptations is a real issue
  • 41. The Key is Balance
  • 42. Thank you Dr. Ralph Holloway Chris Masterjohn Dr. Stephan Guyenet Dr. John Speth