Nickel in Foods: Data-Based Advice

 

Nickel is a common cause of allergic contact dermatitis, estimated to affect from 10% to 20% of the population. A subset of this group is sensitive enough to nickel that their skin reacts to the nickel in food. For some the reaction goes beyond dermatological, causing gastrointestinal and respiratory symptoms, headache, dizziness, fever, cystitis, and other symptoms consistent with fibromyalgia and chronic fatigue syndromes. This is known as Systemic Nickel Allergy Syndrome (SNAS).

 

A low nickel diet is a treatment option for SNAS, however advice on what constitutes a "low nickel food" is inconsistent, even within the scientific literature. One of the reasons for this is that the nickel content of a food can vary widely depending on many factors, including but not limited to:

  • The amount of nickel in the soil and water where the food was farmed, e.g. proximity to industrial pollution, fungicides, fertilizers or pesticides. Some regions of the world simply have higher ambient levels of nickel in the soil.
  • The stage of growth of the food.
  • How the food was prepared, e.g. the cooking method and equipment.

To gain a better understanding of the nickel content of foods, we've collected data from around the world into a single spreadsheet so that we can assess the nickel content of each food as an average over all samples. This also enables us to better see trends in preparation and storage methods. We express the nickel content in terms of a typical serving size to keep comparisons realistic. By doing this, we can give consistent advice based directly on scientific data, and enable sound recommendations for a low nickel diet.


The Data

The largest sources of nickel data are the food composition studies carried out by scientists in national health organizations. Nickel data is freely provided by Australia, Canada, Denmark, Estonia, Germany, Hong Kong, India, New Zealand, the United Kingdom, and the United States. Data for highly mixed foods were excluded because of the huge potential for variation in the ingredients and preparation methods. The scientific literature was also searched for data on the nickel content of foods. As of version 8.0 of the database, 243 sources have been included, giving us 20553 individual measurements for 827 unique foods. (Of these, however, only 478 have more han 3 data points; more breadth of data is needed.)


These sources were imported into a common spreadsheet, with each food placed into one of 26 categories: Dairy products and substitutes; Grain products and bakery; Whole grains, flours and starches; Fruits (berries, citrus, or other); Vegetables (root, leafy, other, or cooked); Meat, poultry and eggs (raw or cooked); Fish and seafood (raw or cooked); Beans and bean products; Nuts and seeds; Beverages (alcoholic, juice, hot, or other); Herbs and spices; Fats and oils; Snacks; Sugars and sweets; Sauces, dips, condiments and spreads; or Miscellaneous. Health Canada's serving sizes were used to scale the data to a typical serving size.


Explore the data in the Nickel Navigator app for Android

View summarized data tables in a PDF document

Download the latest Excel workbook


New data is added as it is discovered. Please be sure to tell us if you have some data to contribute. A complete list of the included data sources is supplied within the workbook.

Analysis by Food Group

Since the nickel content of a food varies, every food will have a range that its nickel content will most often lie within. To keep it simple, we assume that the nickel content for all foods obeys what's called a normal distribution (this is not exactly true but it's close enough for our purposes). In the summary data tables, where "Mean Ni" (<Ni>) is the mean (average) nickel content per serving, the standard deviation "Stddev" (σ) is a statistic that means that:

  • 68% of the time, a food will have a nickel content between <Ni> - σ and <Ni> + σ
  • 95% of the time, a food will have a nickel content between <Ni> - 2σ and <Ni> + 2σ
  • 99.7% of the time, a food will have a nickel content between <Ni> - 3σ and <Ni> + 3σ
The standard deviation (σ) gives you an idea of the range of nickel content most of the time. The last two columns show the minimum and maximum reported values, which is another indicator of how big the spread has been found to be. There are always a small number of outliers (samples where the nickel is very large or very small) whenever there are a significant number of measurements. In version 8.0 of the database, we removed entries that were more than 7σ from the average value to avoid the average being biased by outliers that are ridiculous, except in the case of cooked foods which depend on the cookware composition.


The number of samples that we have for a food is important. Many foods have only one or a few samples in the data. Because of the wide variation in nickel content, a single sample could appear on the very low or very high end of the range (i.e., an outlier), which would be misleading. Only the foods with a large number of samples can really be trusted. Since only about 350 of the foods have more than 6 entries in the database, it is an important thing to watch for.


What does it mean to say that a food is low, moderate or high nickel? For treating nickel hypersensitivity, the recommended daily upper limit is 150 μg (micrograms) of nickel. If a person eats 3 – 4 different foods at each of 3 meals, plus 2 – 3 snacks of 1 or 2 different types of food, for them to stay under 150 μg each serving of food would on average have to have less than 10 μg of nickel. Therefore, we consider foods with less than 10 μg per serving to be low nickel, foods with between 10 and 20 μg to be moderate nickel, and anything greater to be high nickel.


Dairy products and substitutes

Dairy is consistently the lowest nickel food group. Cream, sour cream and cream cheese have less than 1 μg per serving. The vast majority of dairy foods are low in nickel.


Dairy substitutes are less straightforward. In general, those based on oat, cashew, and soy are high nickel. Coconut-based dairy substitutes are all over the place, running the gamut from low to high nickel unpredictably. Cheese and yogurt substitutes don't have very much data, but it does appear that cheese substitutes made from coconut oil are low nickel. For beverages, rice-based and almond-based appear to be the best options. Interestingly, the homemade almond milk is the only high nickel entry of the 6 entries. Non-dairy cream substitutes of all kinds appear to be low nickel, in part due to the very small serving size.


Grains, flours, grain products and bakery

The general rule is that whole grains, being essentially a seed, carry more nickel. The exception to the rule is rye. The foods with the least nickel per serving in this category are made with rye, corn, white rice, and white wheat flour. Foods with the highest nickel content are made with buckwheat, oats and millet. Whole wheat, brown rice and amaranth products fall somewhere in between these extremes. Uncooked quinoa ranges from very low to very high nickel.


For breads, the ingredients can vary greatly. In general, rye bread, white bread and baked goods made exclusively from white wheat flour have less nickel. Nuts, seeds and other whole grains have become popular additions, and oat or soy flour are sometimes added. Since these are high nickel ingredients, it is important to read the list of ingredients for pre-made bakery items.


Cooked pasta has less nickel than dry pasta, and cooked rice has less nickel than raw rice, which suggests that the cooking method is important. In fact, when rice is cooked at a ratio of 1 part rice to 6 parts water until softened and the residual water is discarded, its nickel content is reduced by about 45% and arsenic by 30%. (Unfortunately, some essential nutrients are also lost.) A similar effect can be seen for quinoa.


On a similar note, although we might expect all whole wheat products to have moderate to high nickel, we found that processed whole wheat cereals are mostly low nickel. We think that this may result from the grain being soaked and/or cooked in the inital processing stage, which releases some of the nickel into the cooking water to be discarded.


If you’re also on a gluten-free diet, it is particularly important to read the labels carefully, since many gluten-free alternatives are inherently high in nickel. A typical gluten-free flour blend is a mixture of several flours and starches. Bean flours (e.g. soy and chickpea) and nut flours (e.g. almond) are high nickel, as are buckwheat, millet, sorghum, coconut, and oat flours. White rice flour, like raw white rice, varies from low to high nickel, but combined with low nickel starches should balance out to something manageable. Corn, tapioca, potato and rice starches, though there are too few samples tested, all appear to be low in nickel. Corn and rice pasta, as well as starch-based noodles such as glass noodles, are a good gluten-free substitute.


Fruits

The lowest nickel fruits are cherries, apples, cranberries, blueberries and mangoes. Citrus fruits, bananas, grapes, kiwis, and strawberries have enough variability that they can get you in trouble, but for the most part they are low nickel. Pears, peaches, and melons can be low and moderate nickel; exercise caution.


Common fruits to avoid for their high variability include raspberries, blackberries, pineapples, dates, apricots, and plums. Interestingly, pineapple in the US is predominantly low nickel, while every other location in the world finds them to be moderate or high nickel. Depending on where you are, they might be okay.


Canning has no obvious effect on the nickel content of citrus fruits or apricots. However, since it is frequently advised to avoid canned foods, it is safer to choose fresh fruit whenever possible.


Vegetables

Solidly low nickel root vegetables include onions, carrots, celeriac, rutabaga, radishes, and turnips. Potatoes and beets are low nickel on average but they have a wide range from low to high. Sweet potato, yam and parsnips are moderate, although we'd like to see more data for them. Likewise, cassava, fennel and taro root seem to be on the high side, but there is little data available.


A UK study collected data on how much nickel accumulates in the peel of root vegetables, finding that there is significantly more nickel in the peel. However, if we analyze this data on a per-serving basis we find that the impact is usually small. Assuming that a serving with peel is 15% peel and 85% flesh and comparing it to a serving that is 100% flesh, most of the time the difference in nickel in a 100 g serving works out to less than 2 μg, although in a few cases it reached as high as 8 μg.


Of the leafy vegetables, cabbage and lettuces are reasonably low in nickel on average, but there is a lot of variation. Iceberg lettuce appears to be a slightly worse choice, leaning into the moderate range. Spinach appears to be the best choice for a dark leafy green, particularly when it's cooked by boiling. This cooking method also reduces the nickel content of collard greens substantially. All other leafy greens, including kale and seaweed, are moderate to high nickel.


For the crucifers, there isn't a lot of data for them in their raw form. Raw cauliflower appears to be low nickel, and raw broccoli and brussels sprouts moderate nickel. However, in their cooked forms we have more data, and they all average to low nickel but with a wide spread. Since boiling is the most common preparation method for these foods, we can assume that these foods are moderate nickel when raw, but when boiled lose enough of their nickel content to become low nickel.


Other common low nickel vegetables include tomatoes, olives, celery, cucumbers/pickles, corn, peppers, and mushrooms. Eggplant and zucchini have a low average value but more variability. Winter squash have a moderate average nickel and wide variability, as do green beans. Asparagus, peas and bean sprouts are high nickel.


The data confirms that the choice of cooking method is important for vegetables. In food studies, cooking is typically carried out by boiling, baking or frying, often using stainless steel pots and utensils. For some foods it increases the nickel content, but in some cases cooking decreases it significantly. Which cooking methods were used would probably explain the difference (e.g. boiling vs. frying), but we aren't always given that level of detail in the data. In all cases, the variability in nickel content is larger for cooked vegetables.


Canning only significantly raises the average nickel content for tomatoes. It isn't clear whether this increase comes from the can or from cooking prior to canning, since it has been proven that nickel-containing cookware releases nickel into tomatoes.


Meats, meat substitutes and eggs

Meats and eggs are generally low in nickel in their raw state. Organ meats can be higher in nickel, however; there appears to be a geographic dependency with the majority of moderate and high nickel samples coming from India's TDS.


Cooking has a significant effect on the nickel content of meats, most notably on the variability. The mean value increased the most with cooking for beef and pork, the difference being remarkable for ground meats. This may be due to the larger surface area being exposed to the cookware surface. The largest increases are consistently seen in the Canadian food studies; possibly nickel-containing cookware was used for these samples. Cooking had a much smaller effect on eggs and poultry regardless of the source. These may be safer choices for eating out.


The only reliably low nickel meat substitute is seitan, which is made from wheat gluten. All others are derived from soya or other beans. Soy-based sausages are sometimes low nickel, but this may be due to lower-nickel filler ingredients such as starches, or the use of "soy protein isolate", whose processing may remove some nickel (this has not been established by testing though). Read the labels carefully for all meat substitutes.


Fish and seafood

Around 85% of the raw and cooked fish samples are low nickel, and there does not appear to be a species that is better or worse. Not quite as many of the samples of raw crustaceans (e.g. shrimp, crab, lobster) are low nickel (68%), but when they are cooked this increases to 94%, probably because a common cooking method in food studies is boiling, during which nickel is extracted into the cooking water and discarded. In the case of cephalopods (e.g. squid and octopus), 92% of the samples are low nickel, whether raw or cooked.


Bivalves stand out as the highest nickel seafood (e.g. oysters, clams, mussels, and scallops); only 10% of the raw samples are low nickel. Cooking bivalves reduces their nickel content slightly, probably from releasing nickel into the boiling water, but even then they are still mostly moderate to high nickel.


Canning does not appear to affect the nickel content of fish or crusteaceans; over 98% of 136 samples are low nickel.


Beans

Beans are, in general, a high nickel food. Cooking reduces the nickel content, probably releasing nickel into the soaking/boiling water. Likewise, canned beans are cooked and left to soak in the can, so if the water is discareded there shoud be less nickel, and the data does appear to support this. There is variation among individual samples; 3% are low nickel, 18% are moderate nickel but the vast majority are high nickel even when cooked. The lowest-nickel beans appear to be chickpeas and white beans, but they are still at least moderate on average. Tofu, made from soybeans, is the highest.


Nuts and seeds

Nuts and seeds are, in general, a high nickel food. Peanuts, pistachios, and almonds are the lowest nickel nuts with between 20 and 30 μg per serving, while walnuts, cashews, pecans, and sunflower seeds have 100 μg or more per serving. The variability of nickel in nuts and seeds is large.


Nut butters can be slightly lower in nickel, but gram for gram the difference is only slight. A serving of nut butter is 15 grams (~1 tablespoon), while a serving of nuts is 30 grams, so pay close attention to the serving size when you make your decisions.


Beverages

Beverages are an important category, because we need to stay hydrated to support the body's detoxification systems, but even water contains nickel. Many municipalities produce annual reports on contaminant levels in their water supply and should be contacted for their testing results. The age and composition of the water pipes inside your home can also influence the nickel content. If you have misgivings about your water supply, bottled water may be the better option, however some bottled water samples have substantial nickel. Ask the manufacturer for test results. See Water for more information.


Juices follow the same trends as the fruits or vegetables they are made from, with the exception of tomato-based vegetable juices which are moderate nickel choices. Juices from concentrate may be higher in nickel. Canning does not appear to significantly affect nickel in juices, but since they are acidic (which can increase nickel release) choose bottles when available.


Liquors appear to be the best of the alcohols, with less than 1 μg per serving on average. Beer, wine and cider have around 5 μg or less per serving, but there are some high-nickel outliers. There does not appear to be a difference between red or white wines.


While tea leaves and coffee beans are moderate to high in nickel, the nickel in brewed tea and coffee is substantially lower. Coffee, at about 4 μg/cup, has less nickel than tea on average. The nickel in tea is much more variable and appears to be affected by several factors:

  • The data indicates that tea brewed from loose, whole-leaf tea has less nickel than tea brewed from a bag: 7 μg vs. 9 μg per cup. This may be because the tea in bags is crushed, making the nickel inside the leaf more accessible, or because tea bags also use older leaves, which have more nickel in them to begin with. It may also stem from the leaves having more contact with metal machinery during the crushing.
  • Like all plants, the amount of nickel in tea leaves increases with the amount of nickel in the soil where it was grown. Nilgiri tea, grown in the Nilgiri region of India, is lower in nickel because the soil is lower in nickel.
  • Although brewed green teas appear to have more nickel than brewed black teas, the data for the leaves themselves contradicts this trend with green tea leaves averaging 18 μg and black tea leaves avergaing a much higher 59 μg. There doesn't appear to be any reason for the difference in the production process. More data is needed for any conclusion to be drawn about green tea.

See Coffee and Tea for more information on brewing methods.


Herbal infusions of lemongrass, peppermint and chomomile appear to be low nickel choices. While there is no data for it directly, an infusion made from steeping fresh ginger in hot water should be low nickel because 1 tablespoon (about 6 grams) of fresh ginger has only 1 μg of nickel in it to give, as an upper bound.


Hot chocolate has high nickel levels. Other high-nickel drinks include coconut water and all chocolate beverages. Canned carbonated drinks have a much larger variability than non-canned.


Herbs and spices

Salt is the best-tested in this category with 29 studies, and it has the lowest nickel of all with an average below 0.05 μg per gram (1/6 teaspoon). Other well-tested spices that are low enough nickel so as not to contribute too much to your daily limit include ginger, garlic and paprika. Although not as well tested, wasabi, dill, cloves, nutmeg, allspice, turmeric, coriander, chives, cilantro, and cinnamon have less than 1 μg in a 0.5 gram serving.


With the data we have, it looks like herbs tend to be higher nickel. The data for herbs is a little contradictory with fresh basil, rosemary, and parsley having 2 or more μg on average while their dry counterparts average less than 1 μg. Dry sage and thyme may contribute a significant amount with around 3 μg in 0.5 grams. Oregano has around 5 μg whether fresh or dry.


It appears that hot spices are higher in nickel; cayenne pepper and hot peppers have over 5 μg in a typical serving, and black pepper averages 2.4 μg. Use with care.


Think carefully about which spices a recipe really needs, because they may add up to a significant amount per serving. Consider using a scale and Nickel Navigator to measure it out. However, a dash here and there (around 0.2 g) can bring a lot of joy for only a little nickel.


Fats and oils

Cooking oils are all fairly low in nickel on average. The relative average nickel content of some commonly-used oils is, per 2 teaspoon serving:

  • olive (0.3 μg) ≈ corn (0.3 μg) < sunflower (0.5 μg) < avocado (0.6 μg) < peanut (0.8 μg) < soybean (0.9 μg) ≈ coconut (0.9 μg) < canola (1.2 μg)

All of them are low enough to use in cooking without a significant impact on your total nickel intake, but olive oil is well known to confer other health benefits and is the lowest nickel. Anecdotally, soybean oil and coconut oil have been problematic for some people with a systemic nickel allergy despite their low nickel content.


Butter and lard have about 0.4 μg of nickel in 2 teaspoons. Margarine comes in slightly higher at 1.2 μg, probably because of the tendency for margarines to contain soy or canola oils, but with a possible contribution from the nickel catalyst used in the hydrogenation process and the nickel in the equipment used in its manufacture. Ghee and shortening were found to be quite high in nickel in research from Pakistan; home-made ghee made from butter using low nickel equipment would be more reliably low nickel. There are many methods for making ghee but my favourite is this very simple method. Vegetable shortening in pastries can be replaced with lard and/or butter.


Snacks

With a few exceptions, snacks are processed foods that don't provide a lot of nutrition for the nickel. Enjoy them in moderation. Always read the ingredient list on processed foods.


Low nickel options for a sweet treat include flavoured gelatin (e.g., Jello), applesauce, popsicles, sherbert/sorbet, vanilla ice cream and frozen yogurt, graham crackers, raisins, rice cereal bars, and cookies that don’t contain chocolate or nuts (e.g., shortbread). The lowest-nickel savory food is pretzels. Potato chips are also acceptable but can be moderate nickel, so exercise moderation. Corn chips and popcorn are moderate nickel with a wide spread, so may not be the best choice for snacks. The snacks that are highest in nickel are those that contain high nickel ingredients such as beans, chocolate, nuts, or oats.


Gelatin is not permitted in some low nickel diets despite it testing as having low nickel. There is little doubt that it causes symptom flare-ups in some people, however it is not evident that nickel is at the root of it.


Sugars and sweets

The highest nickel sweets are those which contain chocolate and/or nuts, and the darker the chocolate, the higher the nickel content. White chocolate, on the other hand, may be lower in nickel (based on just 2 samples) which makes sense because it is made from cocoa butter, which is low nickel. Candies that are not chocolate-based are low in nickel.


White sugar is very low nickel; a teaspoon has less than 0.1 μg nickel. Brown sugar has slightly more nickel, but is still less than 0.5 μg in a teaspoon. Honey is well-tested and has only 2.6 μg in a tablespoon on average, although some samples are higher nickel. Syrups that aren't chocolate-based are mostly low nickel, having 2.2 μg nickel in a 60 gram (4 tablespoon) serving, except for maple syrup which averages 17 μg for the same amount. However, if you use maple syrup in the same way as you use honey, the nickel content is comparable at around 4 μg. The devil is in the dose.


Sauces, dips, condiments and spreads

Condiments are usually low nickel in their typically small amounts. Mayonnaise, mustard and fruit jelly are particularly low nickel. However, some condiments need special attention even though they are on average low in nickel: soy sauce has quite a bit of variation; ketchup and salsa are tomato products that may pick up nickel from the processing equipment; and guacamole is made with avocado, a high nickel fruit. Tartar sauce averages unexpectedly high in nickel, but this is likely biased by a large outlier since its fundamental ingredients are low nickel. Making your own with low nickel ingredients would ensure a low nickel result. Not surprisingly, hummus, pesto made with nuts, seeds or peas, and hazelnut chocolate spread are moderate to high nickel.


Miscellaneous Foods

This category contains items often used in cooking and baking. The serving sizes used here represent the amount that would typically be found in a serving of food that contains it. For example, the serving size for baking powder or baking soda is 0.6 grams or 1/8 of a teaspoon, representing what may be present in 2 pancakes, 1-2 muffins, or several cookies. On that basis, baking soda and baking powder are low in nickel.


A cup of ready-made broth has about 11 μg of nickel on average, however the concentrated powders seem to have less. It would be useful to know whether home-made broth would contain less nickel if appropriate equipment was used, but unfortunately that information isn't available to us.


Tomato paste and sauce are higher nickel than fresh tomatoes, because they are concentrated and they pick up nickel during cooking depending on the equipment used to prepare them. Cocoa and dried coconut are high in nickel, as expected.

A Few Notes on the Data

The amount of nickel in food is measured using a spectrometer, such as a graphite furnace atomic absorption spectrometer (GFAAS), inductively coupled plasma mass spectrometer (ICP-MS), or inductively coupled plasma optical emission spectrometer (ICP-OES). These devices have a limit of detection (LOD) that specifies the smallest level of nickel it can reliably detect. Some decisions had to be made on how to handle data with respect to the LOD.

  • If a value wasn't given but a measurement was marked as being lower than the LOD, we used 1/2 of the LOD as the sample's value.
  • Values that were reported as zero without giving an LOD were left out because they can give a false bias to the average.
  • If the LOD was large relative to the average of the other available data for a food, the measurement was omitted if it made the average value artifically high.

Values that were extraordinarily high (extreme outliers) were also left out. For example, in some research articles the values differed from the food composition studies by as much as two orders of magnitude. Other outliers that were more than 7 standard deviations from the average were left out if there were sufficient data to make a decision, which is admittedly a judgement call. The outliers for cooked and processed foods were not excluded, however, because those could conceivably be real depending on the cookware and method used.

 

We're not complaining, but in some cases a single country contributed more than one measurement of a food. For example, one study from Romania dominates the herbs and contributes 4 measurements for each. The United States and Canada have contributed the most data overall, so North American data does tend to dominate. As well, the Estonian and Danish databases have the same values for several foods; the labels differ but they may be from the same source. These cases both affect the final result by biasing the average. You can, and should, use Nickel Navigator to look deeper into the data.

Discussion

The foods with the most nickel are botanically classified as seeds: nuts, seeds, beans, whole grains, and the foods made from them, such as chocolate and tofu. While the "heavy hitters" for nickel content are obvious, trends in the other foods aren't so clear and this has created confusion due to the conflicting information in the various "low nickel diet" lists. We hope that this data provides you with another tool in your decision-making toolbox. Please see the Low Nickel Diet page for quick reference sheets on the nickel in food and other advice on living with a systemic nickel allergy.

 

For the majority, a healthy diet includes nuts, seeds, whole grains, and a wide variety of fruits and vegetables. But for a portion of the population these guidelines have the opposite effect, one that actually decreases health and well-being. If you have a systemic nickel allergy, re-think the rules. Individualized advice from a nutritionist or doctor can help you achieve a truly healthy diet.