Exploring why it’s so important for vegetarians – and especially vegans – to know about antinutrients such as phytates.
What are antinutrients?
They are compounds that interfere with the absorption of nutrients. In this article we shall look at antinutrients that naturally occur in plants. Their purpose is to protect the plant from herbivores, insects, fungal and bacterial infection and adverse growing conditions. The highest concentration is in the seeds, the most important part of the plant to protect. As an example, flax seeds, if not ground, are able to pass through the whole digestive system without being affected.
Are they all bad?
Not necessarily. Research has been and is still being carried out on the beneficial effects of certain substances with particular emphasis on phytates and cancer.
The question is one of scale. In omnivores the consumption of antinutrients is unlikely to pose serious problems but in a vegetarian or, even more so, a vegan diet with a high proportion of nuts, seeds, grains and legumes some of these substances can start to cause problems.
How many antinutrients are there?
A lot. Here are some examples:
- Protease inhibitors
These inhibit the the actions of substances like pepsin, which breaks down proteins in the stomach, and trypsin, which breaks down proteins in the small intestine. They can be deactivated by cooking.
- Lipase inhibitors
These interfere with enzymes that help with the digestion of fat. These are actually used in anti-obesity drugs, causing a percentage of fat to pass through the system undigested. They can be deactivated by cooking.
- Amylase inhibitors
Amylase is involved in the breakdown of carbohydrates, allowing sugars to be absorbed. Amylase inhibitors are also used in weight loss drugs. They are found in many kinds of beans. They can be deactivated by cooking.
- Phytic acid
This binds strongly to minerals like calcium, magnesium, iron, copper and zinc making them unavailable for absorption in the intestines.
- Oxalic acid / oxalates
Present in many plants, particularly the spinach family. Oxalates bind to calcium and iron, preventing absorption.
These prevent the uptake of iodine, affecting thyroid function. They are found in broccoli, brussels sprouts, cabbage and cauliflower.
- Lectins (1)
Otherwise known as haemmagglutinins. Lectins have the ability to bind to the cells lining the intestine, impairing nutrient absorption and damaging the gut wall, allowing bacteria to enter the bloodstream. This is commonly known as leaky gut syndrome and could lead to immune disorders. Lectins can cause malabsorption of vitamin B12 and sugars. They can be deactivated by cooking.
This group includes tannins. These compounds bind with metals like iron and zinc, reducing their absorption. They also inhibit digestive enzymes and protein digestion.
These are responsible for the foaming when you cook chickpeas, for example. The name is derived from the soapwort plant (saponaria) the root of which was used to make soap. Saponins are often bitter to the taste, a good plant defence mechanism. They are not thought to be particularly dangerous in moderate amounts.
How serious is this?
You can see that a diet high in nuts, seeds, grains and legumes – that is a vegetarian or, even more so, a vegan diet – can result in various deficiencies, even though on paper it looks highly nutritious.
Because we are all different we all respond to this challenge in different ways. A lot of the potential dangers are down to gut flora. We shall talk about this in more detail in a future post. A strong community of good bacteria in the gut will deal quite well with these antinutrients but if this is not the case there is a high risk of a number of different deficiencies.
The quantities of these antinutreints can be significantly reduced by careful preparation of food. As shown above, many will be deactivated by cooking, but one in particular, phytic acid, is not so easily dealt with.
A closer look at phytic acid
Phytic acid is a plant’s phosphorus store. Phosphorus is a vital compound for seed development and successful seedling growth. Any gardener will be aware of the need for phosphorus to produce healthy plants. High phosphate fertilisers will tend to increase the amount of phytic acid in a plant. These are commonly used in commercially grown food, but not in the production of organic food.
The molecules of phytic acid are very stable and humans and animals with only one stomach are not able to break the molecules down, so the phosphorus is not available to us. Furthermore, these molecules also have the ability to bond with other minerals such as calcium, magnesium, iron, zinc and copper making them unavailable also. In this form the compound is referred to as a phytate.
Phytic acid also inhibits certain enzymes that we use to digest our food, for example pepsin, which breaks down proteins in the stomach; trypsin, which breaks down proteins in the small intestine and amylase, needed for breaking starch down into sugar. So already we can see that our digestive system is not being permitted to absorb all the good things on our dinner plate.
How can we deal with this problem?
In the case of phytic acid, this can be done in two ways – by reducing phytate intake and increasing phytase intake. It is possible to reduce phytate levels by various methods of food preparation, namely soaking, germination, fermentation and cooking. These methods can also help with other antinutrients.
1. Increasing phytase
Phytase is the enzyme that neutralises phytic acid and releases the phosphorus. Phytase and phytic acid co-exist in plants. The rumen, which is the first stomach in ruminant animals, produces phytase, breaking down the phytic acid. Humans do not produce enough phytase to deal with a high phytate diet.
The good news is that ‘good’ bacteria like lactobacilli, can produce phytase. So an increase in the consumption of good bacteria will help to make digestion more effective and enable us to absorb the nutrients we need. Those blessed with a good balance of gut bacteria will find it easier to cope. It has been suggested that introducing probiotic lactobacilli to the diet can help in this regard (2).
When seeds sprout, phytase is produced, thus reducing phytic acid. Soaking in a warm acid medium also activates phytase. Soaking and sprouting are therefore good ways of preparing food. Soaking in a solution containing lactobacilli will also help.
It has been shown (3) that by soaking at temperatures between 45 and 60ºC and at ph of between 5 and 6, a good level of phytate reduction can be achieved.
As shown below, the addition of citric, lactic or acetic acid increases phytate reduction. The acid solutions can improve the way water is absorbed into the food being soaked, making it easier for the phytates to leach out into the soaking water. Hence the advantage of a long soak with changes of water. Soaking with the addition of lactobacilli will help with the activation of phytase and also helps prevent unwanted bacterial growth.
During the germination process the phytase level increases, thus bringing down the phytic acid level. This is the point at which the phosphorus bound up in the phytic acid is released to get the plant growing. Studies have shown a significant increase (over 60%) in the bioavailabilty of, for example, iron and calcium (4) after germination.
Fermentation is the most reliable way to deal with anti-nutrients. Not only does it make the food more digestible and the nutrients more bioavailable, the ‘good’ bacteria will keep the gut healthy.
Lectins and trypsin inhibitors are especially found in legumes. They are inactivated by heat, so proper cooking will solve the problem. They will leach out into the cooking water so if foods like beans and chickpeas are soaked prior to cooking, with the soaking water and subsequently the cooking water discarded, lectins and trypsin inhibitors should be eliminated. (5). Phytates, on the other hand, are not easily removed by cooking.
Another line of attack is to take note of ways of helping our systems make better use of minerals, thus countering the harmful effects of antinutrients. For example vitamin D will help in the absorption of calcium, vitamin C will help in the absorption of iron and so will vitamin A and beta-carotene.
What about some figures?
This is where it gets really tricky. For example, phytate levels in almonds can be quoted as anything from 350 to 9420mg per 100g.
“These enormous ranges of phytic acid or phytate concentrations published do not only reflect the great number of botanical varieties of seeds, various environmental or climatic conditions of growing but also the different stages of seed maturation. All these factors influence the phytic acid contents presented, along with differences resulting from various unspecific and specific methods for the determination of phytic acid or phytate in food. To avoid confusion and to compare results on a common basis, international standardisation of specific methods for the determination of phytic acid/phytate and other inositol phosphates in foods and of listing either the phytic acid or the phytate content in food tables is absolutely essential.” (6)
What we can do is quote some examples of measured antinutrient reductions using different techniques:
An example of phytate reduction in quinoa (7)
|Cook for 25 minutes at 100ºC||15-20|
|Soak for 12-14 hours then cook||60-77|
|Ferment with whey for 16-18 hours @ 30ºC then cook||82-88|
|Soak 12-14 hours, germinate 30 hours, lacto ferment
16-18 hours then cook at 100ºC for 25 minutes
An example of phytate reduction in barley (8)
|Soak in water at 55ºC for 12 hours 41||41|
|Soak in acetic acid solution pH 4.8 at 55ºC for 12 hours||61|
|Soak in citric acid solution at 55ºC for 12 hours||54|
|Soak in lactic acid solution at 55ºC for 12 hours||69|
An example of antinutrient reduction by roasting (9)
|Roasting peanuts for 20 minutes @ 180ºC||phytic acid 15.6, tannins 18, lectins 99, trypsin inhibitors 37.5|
|Roasting sesame seeds for 10 minutes @ 180ºC||phytic acid 23, tannins 16.6, lectins 50, trypsin inhibitors 61.2|
So what should we do?
There are no hard and fast rules. The important thing is to do something. If your health is not good the prospect of taking on more work will be daunting. However, we are convinced that the right food prepared in the right way can lead to better health. Here are some tips:
- Plan ahead
Plan your meals. Preparation of ingredients takes time. At the very least nuts, seeds, beans and pulses need soaking overnight and possibly subsequent boiling, dehydrating or roasting. The combination of foods, as discussed above, is important so planning before shopping is crucial.
Overnight soaking in plain water at room temperature is a start. Adding salt, lemon juice or raw cider vinegar to the water helps to get the water into the food. Adding lactobacilli to the water will help to activate the phytase. Increasing the temperature of the water will also help – we use 42°. Think about using a yoghurt maker to enable you to do this easily. Soak grains, beans and legumes for 24 hours if you can, changing the water after 12 hours. Hygiene is especially important when soaking, especially at this temperature, as microbes love it. Ideally soak in a glass jar with a good seal, and make sure it’s carefully washed before use – either in a dishwasher or in very hot water (not boiling, or it might crack). More about soaking nuts here »
This process really helps to reduce the levels of anti-nutrients and increase the levels of phytase. It is, however, rather daunting and time consuming and hygiene is crucial.
Use fermented food or make your own as much as you can. Think about making kombucha tea, fermented vegetables to add to your salads, yoghurt and yoghurt milk made with coconut milk. Smoothies made with yoghurt milk and good mixtures of fruit and vegetables.
While raw food undoubtedly contains the most nutrients, in some cases the antinutrients will make them difficult to absorb. As well as cooking beans and legumes, consider toasting some of your nut and seed intake, for example.
- Look at the whole picture
Consider not only getting rid of antinutrients, but also getting plenty of nutrients into your diet to counter their effect. More on bioavailability at a later date.
Find out what works for you
We are all different. The important thing is to be aware of the potential dangers in our food and think about how to minimise them. The prospect of spending a lot of time preparing food in the ways we have discussed is initially daunting but once you get into a routine it does get easier and you should start to feel the benefits.
- Plan ahead
1. Plant Lectins: Properties, Nutritional Significance and Function, Irvin E Liener
2. Probiotic Lactobacilli: An innovative tool to correct the malabsorption syndrome of vegetarians? Giusseppe Famularo, Claudio De Simone, Vandona Pandey, Adita Ranjan Sahu and Giovanni Minisola
3. Reduction of phytic acid and enhancement of bioavailable micronutrients in food grains, Raj Kishur Gupta, Shivraj Singh Gangoliya, Nand Kumar Singh
4. The impact of germination and dehulling on nutrients, antinutrients, in vitro iron and calcium bioavailability and in vitro starch and protein digestibility of some legume seeds, Reihaneh Ahmadzadeh Ghavidel, Jamuna Prakash
5. Anti-Nutritional Factors in Foods and their Effects, Parul Bora
6. Phytates in foods and significance for humans, Ulrich Schlemmer, Wenche Frolich, Rafael Prieto, Felix Grases
7. Influence of Processing Technologies on Phytate and its Removal, Shridar K Sathe, Mahesh Venkatachalam
8. Phytate Reduction in Whole Grains of Wheat, Rye, Barley and Oats after Hydrothermal Treatment, K Fredlund, N -G Asp, M Larsson, I Marklinder and A -S Sandberg
9. Effect of Heat Treatment on Certain Antinutrients and in vitro Protein Digestibility of Peanut and Sesame seeds, Hassad El-Sayed Embaby
Got any tips or questions of your own about antinutrients? Leave us a comment below, we’d love to hear from you.