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An Overview of Adverse Food Reactions

Information about food allergies, food intolerances, and food sensitivities can be confusing! In terms of scientific research findings, this area of food and health has become increasingly complicated over the years, and this growing complexity has definitely contributed to some confusion. But in addition, many people find it difficult to be certain whether they are having an unwanted reaction to a particular food or not. In short, adverse reactions to food can be doubly confusing, both in terms of our everyday experience and in terms of the research explanations.

Our goal in this article is to provide you with an overview of adverse food reactions from a research standpoint. We organized this research summary to include four basic types of reactions: (1) allergies; (2) intolerances; (3) environment-related cross reactions; and (4) other types of reactions. Each of these four sections will provide you with practical suggestions alongside of research findings in the area.


While sometimes complicated, allergies are the best understood of all unwanted food reactions because they always involve immune system reactions to very specific components in foods. If you have an allergic response to a food, certain proteins in your immune system identify and bind together with very specific components (called antigens) in foods. While food antigens are typically protein-like in nature, our immune system can mount an allergic response to some carbohydrates in foods, as well as some fat-plus-carbohydrate-containing molecules (called lipopolysaccharides). Still, in every one of these situations, our immune system gets involved in a food allergy, and, because it does, levels of immunoglobulins in our blood can be measured to document the allergenic response. (However, even though blood work can be used to help identify a food allergy, this blood work is not always conclusive, since food allergy tests can often show "false positive" results in which a food allergy is not actually present, and the immune system has reacted to some other non-food molecule.)

When should you consider the possibility that a whole, natural food that you enjoy is actually a bad fit in your meal plan due to food allergy? At WHFoods, we believe that it makes sense for everyone to consider the possible presence of a food allergy if they routinely eat foods commonly associated with food allergy. In the U.S., eight foods account for about 90% of all reported food allergies, and the Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) requires that the presence of these foods—or any food ingredient containing a protein derived from one of them—be identified on food packaging labels. These eight most commonly allergenic foods are as follows.

  • Milk
  • Eggs
  • Fish (e.g., bass, flounder, cod)
  • Crustacean shellfish (e.g. crab, lobster, shrimp)
  • Tree nuts (e.g., almonds, walnuts, pecans)
  • Peanuts
  • Wheat
  • Soybeans

To be sure, these eight foods are not the only foods that can trigger food allergy. However, they can be a good place to start in assessing food allergy risk. If you consume any of these foods on a regular basis, it's worth paying attention to see if you notice any pattern in the way you feel in the minutes and hours following food consumption. Most food allergies are both predictable and consistent in their occurrence. You typically don't experience an allergic reaction to the food on one day, and then no reaction whatsoever on the next. In addition, the timing and nature of the reaction are usually predictable. For example, if you feel cramps and pain in your abdomen two hours after eating a food, you would expect to experience the same problems in the same time frame whenever that food was eaten.

Given the very large number of factors that can cause symptoms resembling food allergy symptoms, it can be difficult to recognize this kind of pattern and link it up with food allergy on your own. Even if you are able to recognize a pattern on your own, food allergy many not end up being the culprit. That's because the same immune system proteins that can recognize and react to food antigens can recognize and react to molecules in bacteria, parasites, and pollens. It's possible to have an allergic reaction to any of these agents, and confuse the reaction with a food allergy. So as you can see, identifying a genuine food allergy can be complicated. However, it can be a step well worth taking for optimal nourishment and feeling your best. Many people find that reduction or elimination of verified allergenic foods from their meal plan results in very noticeable changes in their everyday sense of well-being. Often, the help of a healthcare provider is needed to identify a food allergy with certainty.

For persons interested in the more technical side of food allergy, we've created the following list of allergen types frequently found in animal and plant foods.

These are some common allergens found in animal foods:

  • tropomyosins (contracting proteins found in muscle, and especially common allergens in shellfish, including crustaceans and molluscs)
  • parvalbumins (common allergens found in white muscle of fish, with cod, swordfish, and whiff being the best studied food examples)
  • ovomucoids and ovalbumins (predominant allergens in egg white)
  • caseins (common allergens in cow's milk)

These are some common allergens found in plant foods:

  • prolamins (a very large family of allergens that includes seed storage proteins in cereal grains, including gliadins and glutenins found in wheat; and also 2S albumins found in many tree nuts—including Brazil nuts, English walnuts—and also in seeds, including yellow mustard seeds)
  • profilins (an equally large family of allergens that have been best studies in melons)
  • cupins (another large family of allergens that includes beta-conglycinin, found in soybeans; conarachin and arachin, found in peanuts; and Jug r 2, found in lentils and walnuts)

We'd like to complete this first section on food allergies by providing you with an example of an allergen type that is not as common as the allergens listed above but which can still be the source of an adverse reaction. This allergen type involves sesame seeds. On a global basis, and especially in countries like Canada, Japan, and Israel, researchers have documented an increased prevalence of sesame seed allergy. Studies have identified three factors as potentially contributing to the rise in sesame seed reactions. First has been an increasingly widespread use of sesame oil and sesame seed components in both food and cosmetic products. Sesame oil has become an increasingly common component in skin and massage oils and can also be found in hair care products, cosmetics, perfumes, soaps, topical oils, and sunscreens. Within the food supply, sesame oil can often be found in cookies, crackers, pastries, dips and spreads, soy burgers, tempeh, granola bars, and other foods. Tahini is a butter made from sesame seed. Gomasio is a sesame-based salt. Halvah is a sweet dessert often made using sesame paste. On a product label, you should suspect the presence of sesame whenever you see any of the following descriptions: sesamol, sesamolina, tahini, tahina, gingelly oil, til oil, or benniseed.

A second factor involves cross-reactivity with other foods. Although we address environmental cross-reactivity below in section 3 of this overview article, most of the research on sesame seed reactions appears to involve cross-reactivity with other specific foods rather than non-food cross reactions that would fall into the category of "environmental" (like cross-reactions to pollens from trees or grasses). While not fully conclusive, research in this area suggests that individuals with food allergy to peanuts, walnuts, hazelnuts, or cashews may also experience allergic response to sesame seeds. This allergic response is likely to involve proteins like Ses i 6 or Ses i 7 that are found not only in sesame seeds but also in the other foods listed above. Alternatively, the allergic response to sesame seeds may be related to proteins like oleosins (which are storage proteins found in a wider variety of nuts and seeds).

The intermingling of sesame seeds with other nuts or seeds during processing is a third factor that has added confusion to analysis of sesame seeds as a potentially allergenic food. Foods not expected to contain any sesame seed components have sometimes ended up containing sesame seed components through shared equipment at food processing facilities or through accidental contact during storage and transit (for example, rotation of nut and seed products in bulk storage bins). This intermingling of sesame seed parts with parts of other nuts and seeds may have increased our exposure to isolated sesame seed components in a way that is still somewhat confusing from a research standpoint and will take more time to evaluate. Adverse reactions to sesame seeds provide a good example of food allergies and their challenges from a research perspective.


Food intolerances are less clear-cut than food allergies. But one thing is certain: food intolerance are not the same as food allergies, and they are not dependent on interactions between food antigens and our immune system. In fact, a food intolerance is not dependent on any single interaction, and for this reason, it tends to be less predictable than food allergy and also less consistent.

Perhaps the best known example of food intolerance is lactose intolerance. Since one entire category of food intolerances work in the same way as lactose intolerance, it is worth taking a close look at lactose intolerance and how this process occurs.

Lactose is a sugar that is present primarily in milk of mammals, including cows. (For this reason, lactose is often referred to as "milk sugar.") Lactose is a compound sugar made up of glucose and galactose. (In technical terms, it is called a disaccharide.) Unless we can break lactose apart into glucose and galactose within our digestive tract, we cannot fully digest most milk or milk products. The way that lactose gets broken apart within our digestive tract is with the help of an enzyme called lactase. If enough lactase is present to break apart the amount of lactose present in the food, we do not become lactose intolerant. We are able to tolerate lactose because we have enough of the enzyme (lactase.) to break apart the amount of lactose that we consume. However, this "if" can be a big "if." Many people do not have enough lactase. enzyme in their digestive tract to break down the substantial amounts of lactose that they consume. (Over half of all adults experience this problem to varying degrees, and among Asian, African American, and Hispanic ethnic groups in the U.S., this percentage is substantially higher.) When there is insufficient lactase. enzyme to break apart the lactose in food, this lactose travels intact all the way down through our digestive tract until it reaches the large intestine, where it gets broken down by bacteria into water and carbon dioxide gas. As a result, we can get too much water in our bowel movements (diarrhea), as well as bloating and cramps from excessive gas.

Some people with lactose intolerance choose to avoid dairy foods altogether. This approach is effective, since dairy foods constitute our major source of exposure to lactose. (Other mammalian milks—like goat's milk—also contain lactose, even though the concentrations are typically lower than in cow's milk.) Many people find that fermented dairy products—especially hard cheeses and live culture yogurts—trigger fewer adverse reactions than fresh liquid milk. (This reduction in adverse reactions is due to the use of microorganisms in fermentation, which carry out either partial or thorough breakdown of lactose.)

Some people with lactose intolerance who enjoy cow's milk itself avoid problems through the purchase of lactose-free milk. Lactose-free milk has been pre-treated with the enzyme lactase to break the lactose apart into glucose and galactose. (We should note here that we are just beginning to see lactose-free versions of grass-fed cow's milk in stores. However, if this type of milk is not available in your area, you can still purchase regular grass-fed cow's milk and use the alternative method described below.)

An alternative method for enjoying milk yet reducing problems with lactose intolerance is to purchase lactase enzyme supplements in liquid form and add drops to the milk yourself. (About 10-15 drops per quart is often recommended.) You should let the milk sit overnight in the refrigerator if you use this method to allow time for the enzymes to take effect.

There is also an option with lactose intolerance involving the purchase of lactase enzyme supplements in chewable, caplet, or tablet form. Swallowing a supplement along with cow's milk (whenever it is consumed) is sometimes effective in lowering its lactose content. However, as you might guess, this approach tends to be less reliable than placing lactase enzymes directly in the milk because there are fewer complicating factors in the milk container than in your digestive tract. Inside of your digestive tract, it is more complicated for the lactase to pair up with lactose, and it is also more difficult for the chemical reaction to take place due to continuous changes in the digestive tract environment. Still, for some people, this approach to lactose intolerance is effective.

We want to remind you how different lactose intolerance is from cow's milk allergy (CMA). In CMA, the immune system is reacting to proteins contained in the cow's milk in a typically predictable and consistent way. (The most common cow's milk proteins involved in this process are called casein proteins, and they include alpha-s1-casein, alpha-s2-casein, and gamma-casein.) In the case of lactose intolerance, the process is not as predictable or consistent. The degree of problems that we experience is related to the amount of lactose we consume, the amount of lactase enzyme our body is making, and how favorable conditions are within our digestive tract for combining the lactose together with the lactase enzymes and breaking it apart into glucose and galactose. Before leaving the example of cow's milk, we would also like to note that it is possible for a person to experience both types of problems with milk, and to simultaneously experience milk allergy and lactose intolerance at the same time.

Lactose intolerance is just one example of an enzyme-related food intolerance. It is possible for a person to have an equal amount of difficulty breaking apart other sugars found in food. The general category of sugars involved in food intolerance is disaccharides. Each disaccharide is made up of two sugars. Below is a chemically simplified chart showing food disaccharides and the enzymes needed to break them apart.

DisaccharideSugar ComponentsEnzyme Needed for Digestion
LactoseGlucose and GalactoseLactase
MaltoseGlucose and GlucoseMaltase
SucroseGlucose and FructoseSucrase
TreheloseGlucose and GlucoseTrehelase

Enzyme-related food intolerances also commonly occur in relationship to beans and legumes. The most common symptom experienced with this type of food intolerance is excessive formation of intestinal gas. In some cases, dietary supplements that provide alpha-galactosidase enzymes (often commercially obtained from the yeast aspergillus niger) can be used to help reduce gas formation. Instead of breaking apart disaccharide sugars, these alpha-galactosidase enzymes break apart sugar-related components of more complicated food molecules involving sugar-fat combinations (glycopilids) and sugar-protein combinations (glycoproteins).

Like food allergies, food intolerances are well worth investigating if suspected as a potential health problem. And like food allergies, they may require the help of a healthcare provider to identify with certainty.

Environment-related cross reactions

Environment-related cross reactions are very closely related to allergies since they always involve the activity of our immune system. At its most basic level, cross reactivity involves the ability of our immune system to recognize similarities between all types of allergens regardless of their source. Earlier in this article, we focused specifically on food allergens that our immune system gets exposed to through the process of eating. But things we do not eat can also contain allergens, and if these allergens closely resemble certain protein structures in our food, cross reactions can occur. When cross reactions occur, our immune system ends up responding to a second protein structure in the same way that it responded to the initial allergen. For example, we might breathe in pollen from a birch tree during the season in which birch trees release their pollen. (The specific season depends on geography and climate, but in most cases, birch tree pollen is most abundantly present in late winter and early spring.) Inside of birch pollen is a potential allergen called Bet v 1. Our immune system can react to this birch pollen allergen, and as a result, we can end up with a seasonal allergy to this tree pollen allergy.

Now let's consider the food side of this cross reaction. Inside the protein structure of an apple, there is a protein molecule called Mal d 1. This molecule is similar to the Bet v 1 molecule found in birch pollen, and it can also act as an allergen. Because our immune system can recognize the similarity between the Mal d 1 molecule in apples and the Bet v 1 molecule in birch pollen, we can end up not only with a seasonal tree pollen allergy, but with a year-round allergy to apples as well. This phenomenon is referred to as a cross reaction, and in this case, it involves a cross reaction between an inhaled molecule in the environment (birch tree pollen), and a molecule in food (apple allergen).

While there are a virtually limitless number of possible allergenic cross reactions, five categories seem especially important when considering environment-related allergens and food. The five basic categories involve: (1) alder tree pollen, (2) grass pollen, (3) mugwort weed pollen, (4) ragweed pollen, and (5) birch tree pollen. A particularly large number of foods appear to be involved in cross reaction with birch tree pollen.

Below is a chart listing these five categories of cross reaction and some of the key foods involved. This chart is not intended to represent all possible environmental allergens, or all possible cross-reacting foods. Instead, it is meant to provide you with examples of common pollen allergens and commonly cross-reacting foods.

Environmental AllergenCross-Reacting Foods
alder tree pollenalmonds, apples, celery, cherries, hazelnuts, peaches, pears, parsley
grass pollenmelons, tomatoes, oranges
mugwort weed pollencarrots, celery, coriander, fennel, parsley, bell peppers, hot peppers, sunflower seeds
ragweed pollenbananas, cantaloupe, cucumbers, zucchini, honeydew, watermelon, chamomile
birch tree pollenalmonds, apples, apricots, carrots, celery, cherries, coriander/cilantro, fennel, hazelnuts, kiwifruit, lychee fruit, nectarines, oranges, parsley, parsnips, peaches, pears, bell peppers, hot peppers, persimmons, plums/prunes, potaotes, soybeans, wheat
Latex-Fruit Syndrome

While widely publicized and extensively researched, latex-fruit syndrome is well-documented food sensitivity that has been shown to occur worldwide but has yet to be fully understood. Researchers are not sure about the exact nature of latex-fruit syndrome, even though they know it is a real phenomenon experienced by many people.

The environmental allergens in latex-fruit syndrome come from the rubber tree (Hevea brasiliensis). When latex is produced from natural sources (versus synthetically manufactured), this rubber tree is the most widely used source for obtaining the thick sap that can be processed into latex. Early studies on latex-fruit syndrome focused on hevein-related proteins in natural rubber latex, including Hev b 1, Hev b 2, Hev b3 (and so forth) all the way up to Hev b 12. However, scientists now know that these hevein-related allergens are not the only allergens found in latex. (For example, other allergens include heat shock proteins, proteasome subunits, protease inhibitors, and hevamines.)

In addition to this diversity of allergens contained in natural rubber latex, there is an equal diversity of similarly shaped protein molecules in numerous foods. On this food side of the equation, researchers originally focused on food proteins belonging to the enzyme family called class I chitinases, including Pers a 1 from avocado and Cas s 5 from chestnut. At present, however, scientists know that more types of food proteins may be involved in latex-fruit syndrome, outside of this class I chitinase family.

The best-researched foods known to be involved in latex-fruit syndrome are banana, avocado, and chestnut. Although the research on kiwifruit is somewhat controversial, many observers would put kiwifruit in this same uppermost list. After the foods listed above, foods most commonly associated with latex-fruit syndrome include papaya, potato, tomato, apple, carrot, and melons. However, even within this relatively short list of foods, there is considerable controversy and lack of consensus. In bananas, for example, food scientists have identified at least 16 different allergens, with only 2 belonging to the class I chitinase family possessing hevein-like proteins. Researchers do not know for certain what role these different banana allergens might or might not play in latex-food syndrome.

Over two dozen additional foods have been proposed as being involved in latex-fruit syndrome, and these foods include: apricot, cherries, mango, peach, grapes, figs, citrus fruits, lychee, nectarines, passion fruit, pears, persimmons, pineapple, strawberries, almonds, hazelnuts, walnuts, pistachios, sunflower seeds, peanuts, peas, beans, lentils, soybeans, chickpeas, eggplant, capers, lettuce, zucchini, shellfish, wheat, buckwheat, rye, bell and hot peppers, dill, oregano, sage, and coconut. As you can see, this list is a long and confusing one, and unlikely to be helpful in helping you identify possible food sensitivities. The shorter list of foods above (as noted in the previous paragraph), however, might be helpful for you to consider as possible mismatched foods in your meal plan if you have already identified latex allergy as a personal health issue. In this particular area of cross reaction between environmental allergens and food allergens, the jury is still partially out. But there is still a solid core list of about 10 foods—banana, avocado, cherries, kiwifruit, papaya, potato, tomato, apple, carrot, and melons—that deserve to be considered as potentially problematic in the wake of latex allergy.

Cross Reactions Summary

Environment-food cross reactions can be as complicated or even more complicated to recognize as food allergies and food intolerances. On the environment side, they might be seasonal and only a problem during certain times of year. On the food side, they are likely to be year round, and may involve a half dozen or more foods. Due to all of these complicating factors, cross reactions may often require the help of a healthcare provider to correctly identify.

Other Reactions

Our last category is a catch-all category: it involves any food or food component that can either directly or indirectly disrupt a body process. This last category is admittedly a very large one, and may potentially involve all of our body systems, and not simply our digestive or immune system. As regulation of our cellular metabolism becomes better and better understood, so does our understanding of food components and their ability to influence cellular activity. Added to this evolving understanding of our body systems and our cellular metabolism has been the evolving understanding of our gut bacteria. Interactions of our gut bacteria with food can result in the sending of signals from our digestive tract to tissue throughout our body, including pro-inflammatory signals that can increase risk of chronic inflammation and chronic inflammatory disease. In short, what we are looking at in this last category of potential food avoidances are foods or food substances that may need to be avoided not because of a reaction exclusive to our immune or our digestive systems but because of interactions between multiple body systems mediated at the level of cellular metabolism. In addition, our gut bacteria may play a role in each of these interactions.

Examples of potential food avoidances in this "other" category include the following.


Many people are familiar with sulfites from one or two types of food purchases: red wine and/or dried fruit. However, these two foods do not really tell the story of sulfites, which can be found in a much greater variety of foods.

Sulfites are naturally occurring forms of sulfur, both in the environment and in living things. Their balance with other sulfur forms is important, and most healthy people are able to convert sulfites into other forms of sulfur as needed.

Sulfites occur naturally during fermentation of wine, and they are also often added during fermentation to help regulate the process and preserve the wine. Sulfite levels in wine can vary significantly, from levels as low as 10 parts per million (ppm) to levels as high as 350 ppm. (When levels are 10 ppm or greater, the presence of sulfites much be indicated on the label.) In other foods—including some dried fruits, some bottled and frozen juices, some pickled foods, and some potato-containing products (including dried potato products that get reconstituted at the time of preparation) —sulfite content can also vary significantly. Once again, all packaged foods containing 10 ppm of sulfites or greater are required to identify the presence of sulfites on the label. Since 1986, the use of sulfites on fresh vegetables (including lettuce) or fresh fruits at restaurant salad bars has been prohibited.

As food additives, sulfites are included on food ingredient lists. Below is a list of terms that can all be found on food packaging labels containing this preservative.

  • sulfite
  • bisulfite
  • sodium sulfite
  • sodium bisulfite
  • sodium metabisulfite
  • potassium sulfite
  • potassium bisulfite
  • potassium metabisulfite

Not everyone reacts in the same way to food sulfites, and among people who do experience unwanted reactions to this preservative, there is no clear threshold where reactions start in terms of sulfite amount. However, researchers have shown that a relatively small percentage of persons diagnosed with asthma are likely to have their asthma symptoms worsened by exposure to sulfites, as are some individuals diagnosed with other types of health problems.

At least one team of researchers has proposed an actual mechanism of action for sulfite-triggered problems in nervous system function. This mechanism involves blocking of an enzyme called glutamate dehydrogenase (GDH). However, this research is in the early stages, and to date, it only involves animal studies.

As food components that can potentially interfere with normal metabolism, we believe that sulfites can correctly be considered as potential contributors to food sensitivity. For some people, they can be a "wrong fit" food component worth considering in development of an optimal meal plan.

Oxalates are naturally occurring organic acids that are found throughout nature and in our body. About 20-40% of the oxalates in our bloodstream come from preformed oxalates in our food. Among the foods that we profile on our website, the most concentrated oxalate sources (all listed in terms of milligrams per 3-1/2 ounces) include spinach (750-800mg), beet greens (600-950mg), almonds (380-470mg), Swiss chard (200-640mg), cashews (230-260mg, and peanuts (140-184mg). Oxalates can be obtained not only from food but also from non-food sources, and they typically become problematic only if they overaccumulate inside our body. You can find in-depth information on oxalates in our article, Can you tell me about oxalates, including the foods that contain them and how are they related to nutrition and health?
Two or three decades ago, purines were recognized for primary two reasons: (1) as building blocks for DNA (the primary genetic material in our cells) and (2) as substances that could be broken down to form uric acid and potentially increase our risk of gout. Thanks to extensive research on the role of purines in the health of our cardiovascular system and digestive system (including our mouth, stomach, and intestines), we now know that purines have their own special receptor system on our cells that allow them to connect up with the cell membranes and have far-reaching effects. These effects include changes in our blood flow, heart function, inflammatory response, digestion of nutrients, absorption of nutrients, and experience of pain. More extensive information about purines can be found in our article, What are purines and how are they related to food and health?

"Goitrogen" is a medical term that is used to describe any substance that interferes with function of the thyroid gland. The word itself comes from "goiter," which means enlargement of the thyroid. If its ability to produce thyroid hormones becomes impaired, the thyroid gland can grow in size in an effort to keep up with the body's need for thyroid hormones.

Most of the in-depth research available to us about food components and thyroid function comes from animal studies. In these studies, the focus has been on cruciferous vegetables. These vegetables—all members of the Brassica family of plants—include broccoli, Brussels sprouts, cabbage, cauliflower, and mustard greens. Glucosinolates are sulfur-containing phytonutrients originally synthesized in plants from sugars and amino acids. While not exclusively found in cruciferous vegetables, glucosinolates are especially concentrated in this food family. Over 125 different glucosinolates have been identified in cruciferous vegetables, and studies on these glucosinolates have shown them to have anti-cancer properties, primarily when converted into their isothiocyanate derivatives. However, in very concentrated, high-dose amounts—not usually available from everyday foods—these isothiocyanates have been shown to potentially compromise thyroid function. More information on goitrogens can be found in our article, What is meant by the term "goitrogen" and what is the connection between goitrogens, food, and health?


Of special interest—and considerable controversy—in the area of food and metabolism are lectins. Lectins are proteins that share the common physiological characteristic of preferentially binding to carbohydrates (and more technically, monosaccharides, oligosaccharides, and glycoproteins). A good bit of the scientific research on these carbohydrate-binding proteins has focused on their role as hemagglutinins. ("Hemagglutinins" are substances that help promote the clumping together of red blood cells.) However, lectins are also known to serve a wide variety of physiological functions including cellular communication (especially through protein-carbohydrate recognition), inflammatory response, cell development, host defense, and other functions. The ability of lectins to bind selectively to carbohydrates on cell membranes serves as the basis for their key role in cell signaling, cell-cell recognition, and host-pathogen interactions (that are required for host defense).

Virtually all foods—including both plant and animal foods—contain lectins. Among plant foods, the best-studied sources of lectins are legumes. Among animal foods, the best-studied sources of lectins are seafoods. We have not seen any large-scale human studies that link lectin intake to food groups, including legumes, seafoods, or other food groups like grains. Similarly, we have seen research that ties lectin intake to either protein or carbohydrate intake. In the absence of this research, we do not believe that there is any current basis for linking lectin intake to any particular diet type —for example, high-protein, high-carbohydrate, high-grain, low-grain, etc.

Some of the research on lectins and their function has served as the theoretical basis for certain "blood type" diets. These diets link the desirability of our food choices to the differing lectin content of foods and their metabolic consequences. "Blood type" diets generally take the approach of analyzing the diverse lectin content of foods and determining the best metabolic match for each individual. Once again, we have yet to see large-scale human studies that confirm the validity of this diet approach.

Of great debate in hypotheses about lectins and their role in health is their relationship to a hormone called leptin. Leptin is a small (peptide) hormone and messaging molecule that is synthesized and released from our fat cells. Its release is associated with an increased feeling of satiety and fullness. As a very general rule, leptin release tends to decline during the day (from 8am to 4pm) and to increase from 4pm onward. Both of these patterns are consistent with a need for greater food intake during the day and less food intake in the evening since an increase in leptin means an increase in our sense of fullness and a decreased desire to eat. Some researchers have hypothesized that certain lectins—especially those associated with carbohydrates found in certain categories of plant food, particularly grains—could either directly or indirectly trigger leptin resistance. In other words, these researchers have wondered whether our feelings of satiety due to leptin release may be altered by lectin presence and activity. In addition, researchers have wondered whether other unwanted metabolic events may take place due to dietary lectin exposure.

It's important to underscore the current theoretical nature of this research. As described earlier in this section, studies have yet to establish practical everyday connections that link any specific diet type or intake of any specific food group with lectin-based events, or with potential downstream consequences like leptin resistance.


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