You don’t know your right from your left

Not knowing your right from your left in nutrition can get you into trouble.

In biological systems, there is an issue called “handedness,” or “chirality.” It means that there are right-handed (“Dextrarotatory”) and left-handed (“Levorotatory”) versions of compounds, or “D” and “L” versions, or isomers, much as we have right and left hands, mirror images of each other. But a right-handed glove does not fit on your left hand and vice versa. Likewise, enzymes only recognize one or the other isomer, not both. Mammals are largely L-isomer creatures, due to specificity of enzymes for L-versions of compounds. hands of hope

Most foods — and I mean real food, foods that are instinctively recognized as food by humans, such as shellfish, organ meats, berries, nuts, and roots–have proteins made of L-amino acid isomers, not D.

Things that don’t belong in the human diet, such as grasses from the family Poaceae, have plenty of D-isomer amino acids. Because enzymes are subject to the rules of chirality, human digestive enzymes, such as trypsin and chymotrypsin, that digest proteins receive a “stop” signal when they encounter an indigestible D-isomer in a protein, leaving that protein or peptide fragment undigested.

Add D-amino acids to the other generally indigestible components of wheat and grains. Beyond D-isomer amino acids, other indigestible components of the seeds of grasses include:

  • Gliadin–While some gliadin is degraded to small peptides that act as opiates on the human brain, a substantial proportion of gliadin remains undigested. The intact, undigested form is the form that initiates the zonulin mechanism that increases intestinal permeability, the first step in generating the diseases of autoimmunity.
  • Wheat germ agglutinin (WGA)–The complex, 4-part protein present in wheat, rye, barley, and rice is completely indigestible. WGA that enters the mouth comes out the back end–except for the small quantity that penetrates intestinal barriers, causing direct intestinal toxicity and entering the bloodstream to activate antibodies, mimic insulin, and block leptin (the hormone of satiety).
  • Trypsin inhibitors–Trypsin inhibitors block–no surprise–trypsin, a protein required for protein digestion. This further reduces the digestibility of grain proteins, a fact that organizations, such as the World Health Organization, grapples with when starving nations are fed grains but then struggle with malnutrition despite the calories.

There is a digestible component of wheat and the seeds of other grasses: the amylopectin A carbohydrate, highly susceptible to digestion by the amylase enzyme of saliva and stomach. This explains why two slices of whole wheat bread raise blood sugar higher than six teaspoons of table sugar. If you were starving, no real food in sight, and found yourself in a field of wheat, you could indeed harvest the seed, pulverize it, and eat it as porridge or ground into flour. It would serve as a source of carbohydrates and a minor source of proteins and oils. But you would soon suffer poor health and malnutrition, then die, as Homo sapiens cannot survive on the mix of components in the seeds of grasses.

If it often seems that there are SO many problems with wheat and grains, well, that’s because they never belonged in the human diet in the first place. Yes, we have committed a 10,000-year long mistake that began in desperation when we ran low on real foods, turning to the wild fields of grasses and harvesting their seeds. The food of desperation is now the food celebrated by all official agencies.

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Comments & Feedback...

  1. Bobbie Chapman

    This is just way beyond what I care about in being wheat free….too technical IMHO….just saying

    • > This is just way beyond what I care about in being wheat free …

      Alas, at this moment in human history, a sane diet is not just about avoiding modern gluten-bearing grains. A number of other problems hound us, including fructose, adverse fats, gut biome, various legume issues, and probably GMO and its entourage of unintended side effects.

      In each case, it’s nice that avoiding these things provides results that are convincing to the individual (esp. upon challenge – re-exposure), but exemplary health outcomes are mere “anecdote” to those wallowing in consensus dogma. For these prehensile folks, it’s nice to have some science for why a low carb, high fat, grain-free, low omega 6, soy free, GMO-free diet works.

      Take for example, adverse food contaminant #2 (after wheat): HFCS
      High fructose corn syrup, like wheat, is cheap, pervasive, and is found in almost as many packaged “foods” as wheat. It turns out that in addition to being a GI 100 carb, being higher in fructose than table sugar, and being largely free fructose …

      “… here’s the science bit – the isomer in HFCS is d-fructose and not l-fructose found in natural fruits. Therefore, the d-isomer which is artificial is not recognised in the Krebs’ (energy) cycle and is converted into the cardiovascular baddies triglycerides and body fat.”


      This left- vs. right-handedness is called “chirality” and may turn out to be more significant as time goes on, and as un-confounded nutritional trials are performed. A food compound that is safe as an L-isomer may be substantially less safe as a D-isomer.

      In the specific case of mono- and di-saccharides (simple sugars), there’s ample reason to avoid them the regardless of whether they pitch righty or southpaw. Avoid HFCS entirely. Restrict your fructose intake to actual fruit, and limit the net carbs thereof, and now you know why: fruit is L-fructose.

      • Let me put part of the above on hold, pending further investigation. The web is awash in conflicting information about whether HFCS fructose is “d-fructose” (“or “D-fructose”). It is pretty clearly free fructose, whether l- or d..

        But what isomer is present in HFCS (and so-called agave nectar, high fructose agave root syrup) is an extremely minor issue. Consuming added common sugars (glucose, sucrose, fructose and several other ‘tols & ‘toses) above 15 grams/meal, is a mistake.

        One source, that of course I now cannot find, suggested that d-fructose is in fact very hard to make, is entirely indigestible (except as pre-biotic), and is the core ingredient in the alternative sweetener tagatose, which Dr. Bernstein (“The Diabetes Solution”) recommends for T1D diets. Dr. Davis has not to my recollection opined on tagatose. We have a T1D relative using it, but have not tried it ourselves.

  2. Judi

    To each his own – I find this fascinating even though I often need to read it through more than once for comprehension. Good stuff.

    • Culinary Adventurer

      I totally agree and I am so appreciative of everyone involved in conducting the scientific research so that we can have this information! Learning these details have helped me on many, many occasions!
      Keep ’em coming!

  3. rs711

    Hi Dr.Davis,

    Have you coma across this paper?
    “Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota, and may be the primary dietary cause of leptin resistance and obesity”

    Here are some extracts that might interest you:

    — Figure 1C shows a similar overlap of glycemic index between ancestral and modern foods for which data were available (5) with little correlation between carbohydrate density and glycemic index. Hence ancestral diets are strongly distinct from modern diets with regard to carbohydrate density, but not by either nutrient density or glycemic index. —

    — Although leptin levels have not been recorded for other people eating traditional diets, it has been widely reported that unless grains or refined foods had arrived, all bore remarkably low incidences of “Western diseases,” including obesity (3,4,6–9,16–29). Also notable is the apparent macronutrient-independence of the health associated with ancestral diets. The Kitavan case appears to argue against a primary causal role for carbohydrates or glycemic index in the genesis of obesity, at least when carbohydrates are in the form of root vegetables or fruit. —

    — This hypothesis may also explain (1) why obesity incidence scales with refined food intake, but has such confusing correlatory patterns with macronutrients; (2) why calorie-controlled diets of Westernized foods require a perpetual fight with homeostatic correction mechanisms; (3) the link between periodontal disease and systemic atherosclerotic disease and obesity; (4) why the benefits of a diet of fruit and vegetables have not been replicated by supplements of the constituent antioxidants, vitamins, minerals, and fiber alongside a Western diet; (5) why low-carbohydrate diets produce ad libitum weight loss, but low-fat diets do not; and (6) the relative resistance of European people to obesity and diabetes from Westernized diets. —

    Thoughts? Thanks!

  4. Richard Deitz

    It seems that part of the case being made is that because grass seeds are not easily edible in their natural form, they must not be good for people to eat. However, it seems there are foods that are similarly not edible in their natural form that can be good for us – flax seeds, for example. And there are many nutrients that we manufacture which can be good for us – like vitamins. So would it be better if we stayed away from the argument that foods may be bad for us because they are not edible in their natural form? I think people may get needlessly stuck on an idea of ‘natural’ rather than explore in an unbiased way which foods are good or bad based on what they do to us. And Dr. Davis has given a plethora of those reasons!

  5. I love the building blocks of knowledge you share with us. I appreciate how you have been parsing them out to us over the past few years–if you had written this 10 years ago the depth of my ignorance on this subject would have caused me to fell overwhelmed. Now we have a body of knowledge to build on and comprehension can be accomplished with a little help from Google! Plus, being able to pull some if this data out at a social function when people comment on our dietary choices is PRICELESS.
    Thank you Dr Davis!

  6. Uncle Roscoe

    I have read that the common allergic/autoimmune reaction to lutein is actually targeted at zeaxanthin. I believe the difference between lutein and zeaxanthin lies only in handedness. Most plants produce vegetables with both nutrients. However, different species and varieties produce veggies which weight far more heavily toward either zeaxanthin or lutein. So it’s possible for people with “lutein” intolerance (actually zeaxanthin intolerance) to eat small amounts of lutein-containing veggies if they can confirm they contain mostly lutein, with little zeaxanthin.

  7. Mark.

    Did a web search on D-amino acids and it turns out there can be a fair amount in some shellfish. Some food processing can make molecules of normal chirality go to the mirror isomer, and fermented foods can also have such flipped molecules: bacterial action tends to produce them. Just how big a problem this is for humans I don’t know: tends to make proteins less digestible at least.

  8. John

    The chemist in me needs to speak up. Capitol D and L- for amino acids, sugars, other molecules refers to the absolute configuration of the atoms in space around a central atom and have little to do with Dextrorotatory or Levorotary. Dextrorotation and Levorotation refer to the direction that the plane of polarized light is rotated when it is shined through a sample of a chiral molecule and is signified by either a small d or small l. Confusing, but these conventions have history.

    • Ray


      Are you saying there are D-configuration molecules that end up rotating polarized light in the Levorotary direction? (or vice versa)