Our bodies like to remind us that we aren’t as young as we used to be. The good news is that our digestive systems aren’t affected by aging as much as the other parts of us [1]. The bad news is that we can’t abuse our stomachs like we used to if we want to maintain the pleasure of eating. Does this mean that we have developed food intolerance? Not necessarily. To see why, let’s first look at the normal gastrointestinal signs of getting older, along with some age-related complications.
Age-related changes in digestion
Age brings with it certain changes in digestive function that some healthy people may notice more than others, including [2]:
Decreased lactase production. Older adults are more likely to be lactose intolerant and experience bloating, gas, or diarrhea after eating dairy products.
Decreased elasticity and slower emptying of the stomach. Some people cannot eat as much as they used to in one sitting without feeling fullness or bloating.
Overgrowth of certain bacteria in the small intestine. Our gut bacteria is mostly confined to the large intestine, and this is normal (although some bacteria are more desirable than others). As we age, the chance of bacterial overgrowth in the small intestine increases, producing pain, bloating, and weight loss.
Slowing or weakening of contractions in the large intestine. Constipation is more likely as we age.
If any of these points sound familiar, speak with your doctor to make sure that your symptoms are simply age-related and not part of a more serious problem. Be sure to discuss any signs of small intestinal bacterial overgrowth, because even though you can find plenty of Internet advice about “healing your gut” on your own, this condition may need medical treatment.
Other gastrointestinal symptoms are not caused by aging per se, but by things that go along with age [3], such as:
Medications. These can increase or decrease the time it takes for food to pass through us, resulting in either constipation or loose stools.
Age-related illnesses. Certain illnesses can also affect the proper functioning of the digestive system.
Obesity. Obesity makes heartburn more likely.
Continuing bad eating habits. Late-night fast food or too much coffee can cause heartburn and affect intestinal transit time.
In these cases, something as simple as a change in medication could provide much relief. As I said before, talk with your doctor about your concerns.
Relationship with food intolerance
If someone experiences a bad reaction after eating a certain food, it’s easy to understand why they might conclude that they have food intolerance – after all, it’s almost impossible to escape the association between food and digestion. But true food intolerance is a hypersensitivity reaction to food (emphasis on hyper-sensitivity) that most people will not encounter.
Continuing with our original question, are any age-related symptoms actually food intolerance? Well, there are three types of food intolerance [4,5]:
Enzymatic food intolerance – when the body does not make enough enzymes to digest or properly use a nutrient, as in lactose intolerance or phenylketonuria.
Toxic reactions – mainly histamine toxicity from spoiling fish (scombroid poisoning)
According to this classification, lactose intolerance is a type of food intolerance, but the other age-related digestive symptoms are not. This is an important distinction to make with regards to how we think about (and act on) our current state of health – in other words, do we continue to view ourselves as “normal” for our age, or do we start to feel like we have a “problem”?
What does this mean?
When food-related symptoms occur more frequently with age, this does not necessary mean that we have developed a medical problem – food intolerance – that needs to be treated by completely avoiding certain foods. It might just mean the we need to change our eating habits, like when we eat, how much we eat, and how much we can expect to indulge. For example, an adult with lactose intolerance may still be able to eat small amounts of dairy products (like yogurt) throughout the day, but they shouldn’t expect to go out after a soccer game and eat an ice cream sundae on an empty stomach like the rest of the kids. That said, if you are experiencing any of the symptoms mentioned in this article, see your doctor before attributing them to age.
1. Russell RM. Changes in gastrointestinal function attributed to aging. Am J Clin Nutr. 1992 Jun 1;55(6):1203S–1207S. PubMed
2. Effects of Aging on the Digestive System: Biology of the Digestive System: Merck Manual Home Edition [Internet]. [cited 2014 Apr 20]. Available from: http://www.merckmanuals.com/home/digestive_disorders/biology_of_the_digestive_system/effects_of_aging_on_the_digestive_system.html
3. Karen E. Hall, Wiley JW. Age-Associated Changes in Gastrointestinal Function. In: Hazzard W, et al. editors. Principles of Geriatric Medicine and Gerontology. 4th ed. New York: Mcgraw-Hill; 1998. p. 835–42.
4. Boyce JA, Assa’ad A, Burks AW, Jones SM, Sampson HA, Wood RA, et al. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary of the NIAID-Sponsored Expert Panel Report. J Allergy Clin Immunol. 2010 Dec;126(6):1105–18. http://dx.doi.org/10.1016/j.jaci.2010.10.008
Sometimes it is easy to figure out food sensitivities – especially when they only involve one food or one kind of symptom. For example, lactose intolerance (a type of enzymatic food intolerance where people are deficient in the enzyme needed to digest milk sugar) is related only to milk and milk products, so it’s easy to notice the gastrointestinal symptoms after a nice bowl of ice cream with the kids. But other sensitivities are not so obvious.
Take pharmacological food intolerance, or just ‘food intolerance.’ This type of food sensitivity has always been hard to pin down, on both an individual level and in clinical studies. Symptoms can arise hours or even days after you eat a trigger food, and their severity depends on how much you ate, whether you ate any other trigger foods in prior days, and if you have other health conditions or environmental sensitivities. Furthermore, your symptoms may be different from those of someone else who reacts to the same foods.
On top of this, food intolerance is a reaction to chemicals that are found in a wide variety of foods. For example, if you were sensitive to histamine, you would need to watch out for fruits, meats, cheeses, chocolate, etc. If you were sensitive to artificial colors and preservatives, you would need to read every food label. This is different than food allergies, where people are oversensitive to the proteins found in specific foods. With food intolerance, your food journal wouldn’t be tracking the foods as much as the chemicals inside them. And that’s when things start to fall into place, because, as we’ll see, your symptoms aren’t always caused by the last thing that you ate.
The term ‘pharmacological food intolerance’ underscores the idea that foods, no matter how natural, can contain chemical compounds that are foreign substances in our bodies (like benzoate in fruit or artificial colors in yogurt) or excess amounts of chemicals that our bodies normally produce (like tyramine or histamine in certain cheeses). These chemicals are referred to as xenobiotics, a term which also covers substances like medications, poisons, and environmental pollutants that enter our bodies. This means that pharmacological food reactions share characteristics that are already familiar to us from our experiences with other xenobiotics. In food intolerance:
The severity of your reaction depends on the dose. Below the threshold dose, no symptoms are observed.
Doses are additive across multiple meals. What you ate throughout the day, and even the previous day, counts towards your accumulated dose. Symptoms occur when the accumulated dose exceeds the threshold dose.
Multiple food chemicals can work together to exacerbate the effects of the others.
Withdrawal symptoms can occur.
You can become temporarily tolerant of a food chemical.
The most important of these ideas is the concept of a threshold dose. If you are very sensitive to a food chemical, you have a low threshold, and a small amount is all that is needed to produce symptoms. If you have a high threshold, eating small amounts of a substance will not produce any symptoms. And it’s not necessary to consume all of your food chemical in one meal in order to exceed the threshold dose – little bits can add up over a couple of days. If you were looking to see which food caused your symptoms, you might find that it was several foods over several meals that all contained the same trigger chemical.
In general, we can say that food intolerant people have lower dose thresholds than the rest of the population since most people do not react to food. This is partly due to differences in how well the body can rid itself of chemicals and partly due to how susceptible one is to experiencing adverse reactions – this is all part of the natural variations among people. However, it turns out that your personal threshold dose can also vary over time, depending on what else you have eaten, what medications you have taken, and other health-related factors.
An example of accumulated and threshold doses
The amount of chemical trigger in your body increases as successive meals are eaten.
Consider the chart on the right that tracks meals over four days – simplified, of course, for a hypothetical person. If you experienced symptoms on Day 4, would your first inclination be to blame the spaghetti dinner and perhaps the gluten-containing pasta in particular?
Our hypothetical person is actually sensitive to salicylate and amines, and she needs a mix of both to see symptoms – it turns out that honey, raspberries, guacamole, and tomato sauce all contain at least one of these chemicals. The chemicals accumulated in her body over the course of three days until her threshold dose (which, luckily for her, is rather high) was exceeded on the fourth day.
Our person had wondered about gluten sensitivity in the past, but didn’t seem to react reliably to wheat. Now that she is mindful of her trigger chemicals and her threshold dose, she can eat some of the foods she likes without adverse effects.
In this day and age, it’s hard to imagine medical tests that don’t draw blood or that don’t involve expensive, room-filling equipment; however, for food intolerance and some immune-mediated reactions, the tried and true diagnostic requires only a pencil, paper, and food. Doctors, dietitians, and medical researchers rely on elimination diets and food challenges to identify food sensitivities, which can be used regardless of the underlying mechanism – this is important because right now we have only rough ideas of how these some of these reactions might work.
Diet investigations are deceptively simple – start from scratch and add only one potential trigger at a time until the culprit is found – but they also require a detailed knowledge of food chemicals. For this and for safety reasons – after all, you need to rule out if you actually have an allergy or another condition – you should always undergo a diet investigation with the help of a doctor or a registered dietitian. To help you prepare, let’s look at the three phases of the process: the elimination diet, the food challenges, and the modified diet. Before you start, your dietitian may also ask you to briefly keep a food and symptom journal to provide a baseline on the severity and frequency of your symptoms.
The information here is provided to give you an idea of the diet investigation process; it is not a set of instructions to carry out the procedure yourself. Always check with a doctor or a registered dietitian before modifying your diet. The elimination diet/food challenge process is not appropriate for pregnant women. People with asthma or laryngeal edema (swelling in the throat/upper airways) should only undergo food challenges in a clinic where resuscitation facilities are available. People with Crohn’s disease should not try an elimination diet without medical supervision.
Phase 1: Elimination diet
The elimination diet consists of only a few foods that are unlikely to cause symptoms in most people; depending on your history, it might be less restrictive. You must adhere to the diet even if you think that you know which food chemical makes you ill because you might be sensitive to more than one chemical. In most people, symptoms improve after two to four weeks on the elimination diet. You may experience a withdrawal reaction (a flare-up of symptoms) after the first or second week.
The elimination diet is necessary for several reasons. First, it indicates whether you are on the right track: if there is no change in symptoms after four weeks of strict adherence to the diet, then food intolerance is unlikely. Second, it removes the variability (the ‘noise’) in your symptoms so that changes can be detected during the food challenge phase. Finally, it lowers the amount of trigger chemical that you need to eat in order to see symptoms.
The food challenges determine which food chemicals are triggering symptoms. After at least two weeks on the elimination diet, specific foods are reintroduced into your diet one at a time – these are the ‘challenges.’ If a reaction occurs after a challenge, then you must wait until the symptoms subside, plus a few days, before moving on to the next food. Such challenges are referred to as ‘open’ challenges because you are aware of what you are eating. In research studies, participants are given food chemicals in capsules so they do not know which chemical is being tested or whether they are getting a placebo – these ‘blind’ challenges provide the most reliable diagnosis.
Wheat and milk are often tested first because reactions to these foods are just as common as pharmacological food intolerance reactions; then salicylate, benzoate, amines, MSG, artificial colors, etc. are tested on the advice of your dietitian. Ideally, challenge foods would only contain one trigger chemical, but this is not always possible. When challenge foods contain more than one trigger, the ordering of the challenges is important to systematically rule out all possibilities.
Your dietitian will design a modified diet for you based on your challenge results. You will be reevaluated in 1 or 2 months to see how well the restricted diet is working and to decide whether it is safe to liberalize what you eat. In this part of the process, you will be checking to see whether you have a high or low dose threshold for symptoms; you may also be able to gradually increase the amount of triggers that you eat, but, for your safety, you should always work on this with a dietitian or doctor. Since threshold doses can decrease after avoiding a food chemical, sensitive people could experience dangerous reactions when reintroducing foods to their diet, even in amounts that previously did not cause symptoms.
More information
Consult these books if you are interested in learning more about diet investigations:
Brostoff J, Gamlin L. Food Allergies and Food Intolerance: The Complete Guide to Their Identification and Treatment. Inner Traditions/Bear; 2000. 486 p.
Clarke L, McQueen J, Samild A, Swain A. The dietary management of food allergy and food intolerance in children and adults. Australian Journal of Nutrition and Dietetics. 1996;53(3):89–98.
Food intolerance is a broad label that describes adverse reactions to food that do not involve the immune system. This site uses the term food intolerance as it has been defined by the Allergy Unit at the Royal Prince Albert Hospital in Australia, which corresponds to what some call pharmacological food intolerance.
What is food intolerance?
Food intolerance occurs when chemicals in food produce side effects, similar to the way that drugs produce side effects. Some people are more sensitive to these effects than others.
Food intolerance is not an allergy. A food allergy is an oversensitivity to a protein in a specific food, while food intolerance is a sensitivity to chemicals found in a wide variety of foods.
Organic, fresh, or processed foods can all cause adverse reactions – not all trigger chemicals are man-made.
Symptoms can be physical or behavioral, especially in children. Some people suffer from more than one symptom, and symptoms can change over time.
Food intolerance may affect up to 10% of the population when all food chemicals are considered, which is at least 2 times the prevalence of food allergy. Still, this means that food intolerance is relatively rare: for each food chemical, perhaps 99% of the population will experience no adverse effects.
Food intolerance is more common in adults than in children. Lifestyle factors may play a part in this. In comparison, more children suffer from food allergies than adults.
Children with food intolerance are more likely to be sensitive to food additives (artificial colors, flavors, and preservatives) than adults.
Food intolerance seems to run in families, although each family member may be sensitive to a different food chemical. More women experience food intolerance than men.
Food intolerant people are also likely to suffer from allergies. Food intolerance can make existing flare-ups of eczema and asthma worse, but cannot bring about these conditions on its own.
When do people experience food intolerance symptoms?
Symptoms can take hours to days to appear.
The severity of symptoms depends on how much of a food chemical was eaten, even over the course of several days.
Since symptoms are dose-dependent, they may seem unpredictable – sometimes they happen, sometimes they don’t. But if you think of food in terms of its chemical constituents, it all starts to make sense.
Some people are sensitive to more than one chemical and need to eat them in combination in order to see symptoms. Others only experience symptoms when they are under stress, sick, or have been exposed to chemicals in their environment.
Food intolerance should be considered only after your doctor has ruled out food allergies and other conditions and has given you the go ahead.
An elimination diet followed by food challenges is the only way to diagnose food intolerance.
Foods can contain more than one trigger chemical, making the order of the food challenges very important for ruling out all possible triggers. A registered dietitian can help.
Imagine that you are in a Chinese restaurant with your family. You’ll probably get a migraine later tonight (maybe from the amines in the soy sauce), but you’ve been craving Chinese food all week and you haven’t made the connection yet. Your daughter is drinking cup after cup of jasmine tea with her five spice stir fry, and this, combined with the other things she ate during the day, will give her hives again this evening. Your son asks you to read the fortune in his fortune cookie – “Knowledge is power,” it says, but it doesn’t warn you about the tartrazine in the cookie. He’ll be cranky tonight and distracted tomorrow morning. This is what you might experience if you suffer from food intolerance.
Lesson 1: What is food intolerance?
Is food intolerance real?
Yes. The existence of pharmacological food intolerance has been established by double blind placebo-controlled food challenges. The bulk of the research on food intolerance has been conducted in Australia, the UK, and Germany, and there is an increased awareness of food intolerance in these countries.
That said, two points should be kept in mind. First, even though food intolerance is real, it is relatively rare. These reactions are aptly categorized as ‘hypersensitivity‘ reactions, meaning that most people – perhaps 99% depending on the substance – will not experience any problems from food chemicals at normal amounts. Second, not all evidence carries equal weight when it comes to the different trigger chemicals, and many questions still need to be answered.
Food intolerance, as defined by the Allergy Unit at the Royal Prince Albert Hospital in Australia, is a sensitivity to chemicals found in a wide variety of foods. It is also known as pharmacological food intolerance, a type of non-allergic food hypersensitivity. Food intolerance does not involve the immune system.
The term ‘pharmacological’ is related of the nature of the substances that elicit food intolerance reactions. In addition to nutrients, foods contain chemicals that are foreign to our bodies (like benzoate in fruit or artificial colors in yogurt) or excess amounts of chemicals that our bodies normally produce (like tyramine or histamine in certain cheeses). This is obvious in the case of processed foods, but it is true for fresh or organic foods as well. The foreign or excess chemicals are processed in the body along the same lines as drugs, and in food intolerant people, they also produce drug-like effects. But why would such chemicals be present naturally in food? Because they are important to plants or because they are part of the normal ripening and aging processes.
Food intolerance is different in each person. Some people will be sensitive to certain trigger chemicals for their entire life, and these people will need to avoid foods that contain these chemicals in order to remain symptom-free. Others will only need to avoid their culprit foods for a time until they can resume eating them – perhaps in limited quantities – without seeing symptoms. Still others might only see problems when they eat large amounts of their offending foods or eat certain combinations of foods. But for everyone, the key to living life to the fullest is an accurate determination of which food chemicals are causing the problem. A registered dietitian or doctor can help you find your triggers through an elimination diet and food challenges.
Lesson 2: Food triggers linked to food intolerance
Table 1 contains the most commonly discussed food triggers linked to food intolerance. More than one trigger can be present in a given food, making it difficult to determine which foods contributed to your symptoms. Please be aware, though, that not all of the chemicals listed below are implicated in food intolerance by the same degree of evidence — for all the details, I recommend this recent open-access review:
Alcohol can modulate, for better or for worse, the effects of some food chemicals by increasing their absorption or altering their breakdown.
Lesson 3: Food intolerance symptoms
Food intolerance symptoms can arise hours or even days after eating a trigger food, and their severity depends on how much you ate, what you ate during the previous few days, and whether you have other health conditions. On top of this, symptoms can be aggravated by illness, environmental chemicals (like fragrances), medications, hormonal changes, or stress. The most common symptoms of food intolerance are given below.
System
Symptom
Skin
Hives (urticaria), swelling (angioedema), itching, aggravation of eczema
Migraine, vertigo, fatigue, muscle pain (myalgia), growing pains, behavioral changes in children
Generalized
Non-immune anaphylaxis
Lesson 4: Food intolerance as a food hypersensitivity
Adverse reactions like food intolerance and food allergy are classified as hypersensitivity reactions, where the concept of hypersensitivity has real meaning. Food hypersensitivities are reproducible reactions brought about by quantities of foods that most people can tolerate. In other words, to classify an adverse reaction as a food hypersensitivity, you must first think about the effect that a normal amount of that food would have on the average person.
Food hypersensitivities are divided into two main groups: those that are caused by the immune system (immune-mediated hypersensitivities) and those that aren’t (non-immune mediated hypersensitivities). If we consider food allergy – the poster child for immune-mediated food hypersensitivities – it is easy to see why hypersensitivity is an appropriate description. Allergies occur when the immune system overreacts to harmless proteins in foods, like milk, eggs, wheat, and soy, that lie at the heart of the Western diet. Only about 5% of the overall population is suffering from some type of food allergy, and the amount of food needed to trigger an allergic reaction can be much less than a typical portion.
There are more immune-mediated food hypersensitivities than just food allergies. These reactions involve other aspects of the immune system and may take a longer time to develop than a classic allergic reaction. Here I’m talking about problems like cow’s milk protein intolerance, soy protein intolerance and food protein induced entercolitis in children, celiac disease, and eosinophilic esophagitis — in some cases, asthma and eczema are also related to food. Notice that these conditions are occasionally lumped under food intolerance (and ‘intolerance’ even appears in a few of the labels), but strictly speaking, these are immune reactions.
The term food intolerance is used as the common name for non-immune mediated food hypersensitivities. The best-known type of food intolerance is lactose intolerance, the gastrointestinal discomfort that results from undigested lactose (milk sugar) in the colon. Roughly 75% of the world’s adults — 25% in the US and even fewer in northern Europe — do not produce enough lactase to digest all of the lactose they consume, but not all of these people will experience symptoms and, thus, lactose intolerance. In lactose intolerance, symptoms depend on a person’s gut bacteria and eating habits.
Pharmacological food intolerance, the focus of this primer, is also a non-immune mediated food hypersensitivity. For example, consider a person who has worked with their doctor to determine that their headaches and diarrhea are symptoms of histamine intolerance. In histamine intolerance, a person’s ability to break down histamine is impaired, so foods that are rich in histamine or that cause histamine to be released in the body can lead to symptoms. Histamine intolerance is a food hypersensitivity, because most people can tolerate normal quantities of histamine-rich or histamine-releasing foods.
That said, how do we gauge what “most people” can tolerate? As with food allergy and other immune-mediated food hypersensitivities, the non-immune hypersensitivities generally affect less than 10 or even less than 5% of the population. For example, less than 1% of adults are sensitive to food additives, at least 1% have histamine sensitivity, and around 6% suffer from food-induced migraines. This means that for any food hypersensitivity, perhaps 99% of people will experience no adverse reactions to those foods or food chemicals.
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