I did a short interview with Dr. Ian Spreadbury, as part 3 of the Gut Health series, to focus on the effects of modern carbohydrates on the gut and where in the gut different types of carbohydrates are digested.
Dr. Ian Spreadbury, Phd is a former scientist at the Gastrointestinal Diseases Research Unit, Queen's University, Kingston, Ontario, Canada, and now is on Medical school in Quebec. In 2012 he published a groundbreaking article in PubMed regarding the cellular and acellular qualities of carbohydrates and its impact on gut health and the obesity epidemic.
In his paper Dr. Spreadbury did a spectacular job in bringing to light important scientific work done since the 1970’s on digestion of modern carbohydrates, and brilliantly made sense of it all by creating a hypothesis that helps to explain the current rising of chronic inflammation and obesity.
After Dr. Spreadbury published the paper, questions arose in the paleo/ancestral communities regarding the best carbohydrate choices for a healthy diet. This short interview clarifies some basic questions and offers takeaways at the end to put into practice.
Summary of Dr. Spreadbury’s paper:
Dr. Spreadbury divided carbs in two main categories cellular and acellular. Cellular carbs contain a cell wall within and take longer to be absorbed. Cellular carbs was predominantly consumed by ancestral hunter gatherers populations and is the healthier of the two. Some examples are whole roots, plants and vegetables.
Carbs that do not contain a cell structure are acellular. Examples are dried up grains and seeds, flours, pulverized and liquid forms of starches and sugar, which are more present in the modern world diets. Acellular carbs cause two main problems:
1- They are susceptible to break down sooner than when it is beneficial. Instead of breaking down in the colon, they are processed in the small intestines, creating bacteria and fermentation. The small intestine environment is designed to be more neutral with minimal bacteria and fermentation when compared to the large intestine, as I described in detail in the Gut Health Fundamentals article.
2- Because acellular carbs have been processed into powder or liquid, they are concentrated and it is easy to consume too much of it. Therefore, in the modern world, diets based on acellular carbs, are much higher in carbohydrate density than that of our ancestors.
In the last one hundred years humans have consumed more acellular carbs and have had higher incidence of gut issues like SIBO (Small Intestine Bacterial Overgrowth), which is increased bacterial presence in the small intestine. We also see high incidence of leptin resistance. Leptin being the protein like hormone that regulates appetite control and fat storages. In sum, leptin resistance is when the brain does not effectively receive messages of satiety, and there is a continuous feeling of hunger. Leptin resistance correlates with gut inflammation as well as with long-term consumption of high density acellular carbs.
Carb densities in ancestral and modern diets. Chart from Spreadbury’s paper:
Interview with Dr. Ian Spreadbury
Laura: I noticed in your carb density and glycemic index graph (above) that the “Western foods” represented were highly processed in their majority. I will ask some questions to clarify for our readers where whole grains, legumes and root flours/starches would stand regarding healthy eating.
Dr. Spreadbury: The concept is pretty easy when it comes to sorting Twinkies from fruit, but of course in between there is a lot of grey area for certain foods. I'll give it my best shot.
Laura: Are whole grains structurally cellular?
Dr. Spreadbury: Not as I understand them. Grains, especially the cereal ones, have deposited those stores of energy in their endosperm by having the cells storing the starches / proteins finally apoptose (undergo programmed cell death) as the store became more dense. There are some fragments of cell wall in there indicating there were cells there once, but it's practically a big energy store in there without much water in the mature grain. If this gets milled in any way, you've got something with a high energy density that didn't evolve to exist in that form in the presence of microbes. "Whole grains" as they're currently marketed are grain products that had more of the outer structures left - I believe some of these accessory bits were cellular (the aleurone - here's a Wikipedia link https://en.wikipedia.org/wiki/Aleurone), and other bits that are more fibrous, the structure depending on the species of grain. I wouldn't expect the presence of any of these to make much difference in a milled flour except by displacing by volume some of the problematic flour, and indeed the balance of the literature indicates whole grains don't enjoy marked benefits over refined ones. The effects that are reported are small, which when you consider publication bias likely means there's no practical improvement by whole grains. I can imagine that swallowing grains whole with little chewing might be a better option, but who would do that? :)
I should add that I've no idea whether cellularity is the property that counts. It may just be that to refine a starch / sugar store to a density where it becomes a nutrient broth for bacteria almost inevitably involves breaking down the cells and finer structure of the foods. Perhaps dried fruit would be a good test there. They probably retain a lot of cellular structure, although shriveled, but may prove to be foods the recovering obese can't eat regularly without weight gain. Someone with funding is going to have to test this one day (if the concept becomes of more interest to funded scientists!).
Laura: How about sprouting grains?
Dr. Spreadbury: They'd have a small stem, and the endosperm would presumably be half-digested by enzymes, and part used by the baby plant. So, yes they'd have some more living (low density) cells, and slightly less (proportionately) flour. Personally I'd suspect products based on sprouted grains would be a smidge less obesogenic, but only a smidge. Once someone is recovering from obesity or metabolic issues / fatty liver etc, my advice would be to steer clear of all grains, just in case. Again, it would have to be tested to be sure though.
Laura: Are legumes cellular?
Dr. Spreadbury: I think they may be - they probably retain a lot more structure than grains. Although as I mentioned above, the cellularity may be less important than the density and or the molecular complexity. Retaining all the evolved bits, even if mixed up, might be the key. I'm sorry, we've just no way of knowing without doing the experiments (and I've no funding nor a position as an independent researcher, so I can't do these myself either). I've not looked into peanuts to be honest, but beans (once cooked) seem to have a low carbohydrate density on a par with most other plant foods, and I wouldn't expect to be part of the obesity / metabolic problem. They do however bear a lectin load which may have an adjuvant effect on the immune cells in or near the gut. For some this may promote some inflammatory issues - peanuts especially. In my own case, I can't eat peanuts for what they do to my joints(!), but many other beans I do currently eat.
Laura: Are root flours and starches, such as plantain flour, tapioca starch acellular?
Dr. Spreadbury: Yes, and dense too. I'd expect these to be part of the problem. Perhaps slightly less systemically inflammatory for many, due to the absence of lectins and other cereal proteins, but still not a good idea for optimal health.
Laura: In that case, yucca, or cassava would be considered high density?
Dr. Spreadbury: It's higher than most roots for sure, but maybe yucca and cassava get away with it by having some interesting chemical anti-microbial defenses. Or maybe the preprocessing that cassava seems to need is what elevates the density. Again, I'm sorry, I really don't know. Someone would have to do some experiments. I included cassava in the chart because I didn't want to cherry-pick the data, even though I knew it would raise questions I couldn't answer.
CARB DENSITY IN ANCESTRAL POPULATIONS DIETS
Laura: Do you confirm if a carb density (carbs minus fiber divided by the weight) of lower than 23 is considered low density, and similar to what was consumed in ancestral populations?
Dr. Spreadbury: 23% was a number I pulled out of the air, looking at the array of foods in the table. I've no idea if it's a magic cut off number for living plants, or if anything above that starts to fall prey to increased microbial susceptibility. It's a very interesting question, as it taps into the nature of the evolutionary pressures facing tubers, and why they are the way they are. There are other practical considerations, like the need for living cells to be runny enough to ferry around all their crucial enzymes and other soluble parts needed for life. That may also put a cap on the highest carb density a living cell can maintain.
I think the key to the whole "is it good to eat" idea is going to be: "Does this food retain structures or other features than prevented the rapid bacterial breakdown of it when it was a living thing?" The carb density has to play a role in this, but there may also be other factors. Chemicals that mess with microbial functions, or cause microbes to busy themselves producing their own evolved responses to mammalian defenses. Layers that take time to get through (perhaps cell walls, or the membranes around organelles storing starches). Enzymes that produce anti-microbial defenses perhaps. Peter Cleave, the visionary medic who first realised dead-dumb diet and bacteria might be behind differences in colonic health in the Western world, he cleverly ducked the whole issue by saying something along the lines of "we don't know what these evolved processes are, but suffice to say they work". We're little better informed about these mechanisms now, as no-one is (yet) looking.
HONEY ANTIMICROBIAL PROPERTIES
Honey's a great case in point, as it appears at first to break the rules (high density and acellularity), but is nicely evolved to not 'go off', and is eaten by many hunter gatherers. It's SO dense that microbes can't live in it (by osmotic strength, like salt on slugs). It also has an array of antimicrobial defenses that are slowly being studied, and seem to involve peroxidase enzymes. You can dilute honey down below the levels a simulated runny sugar solution can be, and it retains its anti-microbial properties for longer (it kills microbes rather well, some propose it be use it for wound dressings, especially for MRSA etc). That indicates it's got some active ingredients against microbes beyond just the high osmolarity.
Of course that only works to a certain dilution. My hunch is honey might be fine when spooned straight into the mouth or eaten off the comb, but when you use it well-diluted as a sweetener / ingredient, it's just more sugar and would act like any other sugar.
Whole grains are acellular dense energy stores, rich in inflammatory lectins and prone to be absorbed too soon in the digestive track (small intestines) creating misplaced and harmful bacterial growth and fermentation, commonly seen as abdominal distention and SIBO. The fact that it is is “whole” does not mean healthier.
Legumes have some cellularity. This tells us that when tolerated, legumes may be a beneficial addition as long as consumed within ancestral nutrition amounts. This means not consuming legume flours and not having it as an everyday staple. They can be a good source of prebiotic fiber for the gut microbiome. Sprouting legumes decreases some of the inflammatory lectins.
Root starches (e.g. tapioca flour) are still a better choice than grain based carbs when transitioning to an ancestral diet since they do not have lectins. They are also dense, so regular consumption is a “big no no” if the goal is weight loss. A better choice for the gut microbiome and blood sugar regulation is to have whole roots rather than isolated starches and root flours.
Having clarity on the fact that highly processed starchy carbs tend to be fermented in the small intestine, therefore too soon in the digestive track, may bring new insight if you suffer from bloating, indigestion and chronic inflammation.
The data that Dr. Spreadbury compiled helps to understand some of the mechanisms behind why we feel better when we consume carbohydrates that are whole plants, e.g. roots and fruits, rather than twinkies!
REFERENCES AND RECOMMENDED READING
Spreadbury, Ian PubMed 2012 Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota, and may be the primary dietary cause of leptin resistance and obesity
Have you noticed any differences in digesting cellular or acellular carbs? Did this article give you any further insight into your diet? Share your comments or questions below.