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.
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.
"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.