Like many other plant foods, nuts contain anti-nutritional compounds (or ‘anti-nutrients’).

Studies show that these natural plant compounds can make it harder for our bodies to absorb certain nutrients (1,2). But research suggests the health benefits of eating plant foods, like nuts, outweigh any negative nutritional effects from the anti-nutrients they contain (2).

The most common anti-nutrients in nuts are phytates, tannins, lectins, and oxalates.

What are anti-nutrients?

Anti-nutrients are natural bioactive compounds produced by plants, mainly as a ‘defense mechanism’ – to protect the plant against factors like bacterial infections or insects (1). 

Anti-nutrient compounds cause various metabolic effects in our bodies when we eat them – which may be beneficial, detrimental, or a combination of both

Plant foods, like legumes, cereal grains (such as wheat and rice), pseudocereals (such as quinoa and buckwheat), fruits, vegetables, nuts and seeds, all contain anti-nutrients – in varying amounts and of different types.  

The levels of anti-nutrients in plants is influenced by factors such as genotype, environmental conditions, and where they are grown (1).

Plant foods provide many beneficial nutrients, such as fibre, vitamins, minerals, and antioxidants, and well as anti-nutrients. And evidence now suggests that ‘anti-nutrients’ can also have health-promoting effects (1,2).

What are the common anti-nutrients in plant foods?

Protein anti-nutritional compounds:

Enzyme inhibitors:

• Protease inhibitors: Can reduce protein digestibility and the bioavailability of amino acids. They are mostly found in raw cereals and legumes (particularly soy beans).
• Amylase inhibitors: Can reduce carbohydrate metabolism, and have been found in numerous grains, legumes (such as common beans and soy beans), tubers and fruits.  

→ Nuts are not considered a major source of enzyme inhibitors.

Did you know? Amylase inhibitors slow carbohydrate digestion and absorption time. In doing so, they help prevent rapid spikes in blood glucose levels, which is important in diabetes management. 

Lectins:

Lectins are a diverse family of proteins that bind to carbohydrates. They are found in nearly all plant foods, particularly legumes (such as soy beans and kidney beans) and grains, but also fruits, vegetables, nuts and seeds.

Lectins can be harmful in high amounts or when high-lectin foods, such as pulses (like beans and lentils), are eaten raw or are under-cooked. But processes, such as soaking, roasting, and boiling, significantly reduce the lectin levels of foods.

→ Nuts contain lectins.

Non-protein anti-nutritional compounds:

Oxalate:

Oxalates can bind to certain minerals, such as calcium, magnesium, and iron, in the gut, affecting their absorption. Some evidence suggests that oxalates may increase calcium kidney stone formation.

If you’re prone to kidney stones or have a history of kidney disease, reducing oxalate intake may be recommended.

The plant foods with the highest oxalate content include green leafy vegetables (like spinach, Swiss chard, and sorrel), and root vegetables (such as sweet potato, taro, and beetroot).

Legumes (such as chick peas and faba beans), whole grains (like quinoa and buckwheat), nuts, cocoa, and tea also contain oxalate, though in smaller amounts.

A varied, balanced diet typically contains only small amounts of oxalates (2).

Table: The total oxalate content of nuts and select other foods (1,3):

→ Nuts contain oxalates, though in relatively small amounts, compared with certain vegetables.

Phytate (or phytic acid):

Phytate forms ‘complexes’ with other components, such as iron, zinc, calcium, magnesium, manganese, and copper, so can affect the body’s absorption of these nutrients.

Tip: Pair foods containing iron with foods rich in vitamin C, to help improve the absorption of the iron in foods containing phytates.

But studies also suggest that phytate has health-promoting effects, thanks to its potent antioxidant properties. In fact, some research has linked phytic acid with protection against various cancers and cardiovascular disease (1).

Phytate is found in legumes, cereal grains, pseudocereals (such as amaranth, quinoa, millet), nuts, and seeds. While roots, tubers and vegetables have lower concentrations (1).

→ Nuts naturally contain a reasonable amount of phytate.

Did you know? Soaking has been shown to reduce phytate levels in grains and legumes. But soaking nuts in water (or ‘activating’ them) does not result in meaningful reductions in phytate concentrations (6).   

Overall, by consuming a colourful, plant-based diet, the benefits of phytate-containing foods to human health exceed the impacts on mineral absorption (2).

Goitrogens:

The term ‘goitrogen’ broadly refers to ‘agents’ that interfere with thyroid function, thereby increasing the risk of goiter (enlargement of the thyroid gland) and other thyroid diseases – especially if iodine intake is low.

Sources of these compounds include medications, environmental toxins, and a surprisingly wide variety of foods.

Brassica vegetables (like kale, Brussels sprouts, cabbage, cauliflower, and broccoli) are the most well-known goitrogen-containing foods. Some fruits and starchy plants (such as sweet potatoes and corn), soy-based foods, and nuts (such as peanuts, pine nuts, and walnuts) also contain these compounds.

→ Nuts are not considered a major source of goitrogens.

Did you know? Foods exist as a complex matrix of compounds, which often have synergistic effects. For instance, foods considered to be ‘goitrogenic’ also contain thousands of other bioactive compounds that may help protect against thyroid cancer (2).

Phytoestrogens:

These polyphenolic dietary compounds are structurally like oestrogen, the primary sex hormone in females. As a result, they have many health benefits – but may also act as ‘endocrine disruptors’ that interfere with hormones.

Phytoestrogens are found in various plant foods, particularly soy and soy products, and flaxseeds, with very small amounts in fruits, vegetables, and nuts.  

→ Nuts contain negligible amounts of phytoestrogens.

Tannins (or tannic acid):

Tannins are a broad class of polyphenol compounds, which act as antioxidants by scavenging harmful free radicals in the body.

On the flip side, they can also hinder the activity of the body’s digestive enzymes, which can reduce the absorption of certain minerals, such as iron. They can also form ‘complexes’ with proteins, which impacts protein digestibility.

Tannins are found in a wide range of plant foods, including tea, cocoa, fruit (such as grapes, berries, apples, stone fruits), vegetables (like green, leafy vegetables) nuts, legumes, and whole grains.

Overall, evidence suggests that the many health benefits of a diverse, plant-based diet, rich in polyphenol and bioactive containing foods and drinks, far outweighs the potential impact of tannins on iron status (2).

Table: The tannin (proanthocyanidin) content of nuts and select other foods (4):

→ Nuts, along with most other nutrient-rich plant foods, contain notable amounts of tannins.

Saponins

Saponins are a diverse group of natural compounds, which are widely distributed in the plant kingdom. They form ‘complexes’ with other food components, such as proteins, lipids, and minerals (such as iron, zinc, and calcium).

Saponins have also been shown to have potential health benefits, including cholesterol-lowering and anti-cancer effects (1).

Legumes, such as soy beans, broad beans, kidney beans, lentils, chickpeas, mung beans, and peanuts, are key dietary sources of saponins (1). Other sources include oats, spinach, tea and quinoa.

→ Nuts are not considered a major source of saponins.

Cyanogenic glycosides

Cyanogenic glycosides are a group of chemical compounds known as phytotoxins (toxic chemicals produced by plants), because when they are broken down, they release hydrocyanide (or hydrocyanic acid).

At least 2,650 plant species are known to produce cyanogenic glycosides, as a defense mechanism (1).  

Lima beans, stone fruits (like apricots and peaches), sorghum, cassava, and the ‘bitter’ class of almonds (which are not commonly consumed, or available) are some foods known to contain cyanogenic glycosides.

Roasting and soaking are among the processing methods used to reduce hydrocyanide, with studies suggesting >80% reduction in levels with these methods (1).

→ Nuts are not considered a major source of cyanogenic glycosides.

A note on cyanogenic glycosides in almonds:

Almonds can be broadly classed as ‘sweet’ or ‘bitter’. Sweet almonds contain negligible amounts of cyanogenic glycosides (25.2mg/kg), compared with bitter almonds which contain 1,062mg/kg (5).

We eat the ‘sweet’ class of almonds (which are the ‘regular’ type found in grocery stores) and these are safe to eat. We don’t eat ‘bitter’ almonds, as they’re not commercially available. Bitter almonds are sometimes used in making non-edible products, like soaps and perfumes.

The bottom line? Regular (sweet) almonds are safe to consume.

Did you know? The effects, whether harmful or beneficial, of an isolated food compound are often quite different when that same compound is within the complex food matrix (2).

Bottom line:

• While more research is needed into how anti-nutrients impact the bioactivity of nutrients, particularly within the food matrix, the effects of anti-nutrients are not considered of major concern for most people, eating a balanced diet.

• Many anti-nutrients, such as phytates and lectins, can be reduced or removed by processing and cooking.

• Recent research reviews have concluded that the health benefits of eating a wide variety of plant-based foods (aim for 30 different plant foods a week!) outweigh any potential negative nutritional effects from anti-nutrients.

• Studies have shown that anti-nutrients exert health benefits of their own!