There seems to be a lot written about “antinutrients” in the diet-blogosphere these days, especially by those who have aligned themselves with ancestral or low carb diets. Usually antinutrients are discussed in terms of why they should be avoided. I mean, really, they're called antinutrients, aren’t they? If nutrients are good, then it’s obvious that antinutrients are bad, right?
Or...maybe, it’s more complicated than that.
The confusing thing, from a nutritional standpoint, is that these antinutrients are found in foods that are generally considered healthful, such as whole grains, legumes, nuts, seeds and even some fruits and vegetables. The same foods that dietitians and nutrition experts have been encouraging us to eat for years.
So, what gives? What are antinutrients and should we be avoiding them? Let’s take a closer look…
What are Antinutrients?
First of all, it should be noted that antinutrients are natural components of food, particularly that of plant foods. They are not man made, nor the product of genetic engineering. They are a normal part of the foods we eat.
Some of the more commonly discussed antinutrients are phytates (found in whole grains, nuts and legumes), lectins (in whole grains and legumes), tannins (in tea, wine, grapes, chocolate, nuts...), protease inhibitors (in legumes and grains) and saponins (in legumes, oats, quinoa, amaranth, soy…).
As you can see, the foods in which these antinutritional factors are found are those that we do consider healthy...high fiber legumes and whole grains, nuts that contain heart-healthy fats, and nutrient-packed fruits and veggies. If these antinutrients were only components of unhealthy foods, it would make the decision to cut them from our diet a no-brainer...but they're not. And that is what complicates the issue when "experts" try to persuade us to avoid them.
What Do Antinutrients Actually Do?
If these antinutrients are normal components of food, what is so bad about them? What does the term antinutrient actually mean?
In general terms, if you think of nutrients as food components that provide us with something, then antinutrients are components which either take something away from us or inhibit nutrients from being absorbed. In essence, antinutrients decrease the nutritive value of food in some way.
When you think of antinutrients like this, then yes, they sound pretty bad. Why wouldn’t anyone with a bit of nutritional savvy want to avoid them? Well, the truth is that the whole situation around antinutrients isn’t a clear cut black and white one.
- Phytate has a very good ability to bind to nutrients, particularly calcium, iron, zinc, magnesium, copper and some proteins. This means that once these nutrients bind to phytate our body cannot use them.
- While there have been cases of phytate-related nutritional deficiencies, they seem to be isolated (for the most part) to those in developing countries eating an unvaried, high cereal grain diets.
- While the presence of dietary phytates can influence nutrient absorption, it is unlikely to impact overall nutritional status of those eating balanced and varied diets. That means a diet rich in fruits and vegetable, whole grains, unprocessed meats and/or legumes.
- Phytates only impact the nutrients with which they are consumed. They do not impact subsequent meals or snacks.
- The phytate content of foods is reduced by soaking, fermentation and boiling (which reduces phytates by 20%).
- Even for those most at risk for developing phytate-related nutritional deficiencies, vegans and vegetarians, the chance of their body not absorbing enough of the nutrients they need is low...if they are eating a balanced and varied diet and meeting their recommended daily intake of nutrients.
- If you consume meat regularly, then you don’t have to worry about the negative effects of phytate on iron, or even zinc.
- One study found that despite the higher phytate content of whole wheat bread, compared to white bread, more zinc was absorbed from consuming the whole wheat bread. This is because there is an overall higher level of zinc in whole wheat bread and it more than makes up for the higher phytate content. Sometimes you have to look at the bigger picture, don’t you?
- There is evidence that phytate improves glucose response (beneficial for those with diabetes), reduces kidney stones, has anti-cancer properties, and acts as an antioxidant.
If you are cooking most of your high phytate foods and eating a balanced and varied diet, you probably don’t have to worry about the phytate content of your foods. So, if you are eating well, the “good” aspects of phytates should outweigh the “bad”.
Lectins, found in legumes, whole grains and to a lesser degree in dairy, seafood, the nightshade family of vegetables (i.e. tomatoes, peppers, eggplant, potatoes) are often cited as a nutrient that needs to be avoided due to their ability to selectively bind to carbohydrates (or the carbohydrate portion of certain proteins).
- Lectins have the ability to bind directly to the lining of the small intestine, inhibiting absorption of nutrients and potentially causing lesions on the intestine and leaky gut syndrome (yikes!).
- Lectins may increase risk of autoimmune disease in susceptible individuals.
- The positive news is that lectins can be destroyed by wet heat such as boiling or steaming, and by soaking and fermentation. Boiling is a pretty common method used to cook whole grains and legumes. So, these “nasty” lectins are destroyed by the cooking methods we commonly use.
- Boiling beans or legumes for 10 minutes has been shown to reduce lectin content by 200 times.
- The canning process also reduces lectin content. In one study involving canned navy beans, lectin was reduced to less than 0.1% of its original level. So, there is a good chance those canned beans you buy are fairly low in lectin.
- There are a number of different types of dietary lectins, some of which have been found to provide us with health benefits, such as inhibiting tumour growth.
You probably don’t have to worry too much about those high lectin foods as they are typically cooked or processed in some way before consuming.
The evidence seems a bit unclear if lectins are indeed a contributing factor in autoimmune diseases. Good quality randomized controlled trials (RCTs) are needed for an across the board recommendation for avoidance of lectins by susceptible individuals. However, if you have, or have a significant family history of an autoimmune disease, there may be some benefit in avoiding dietary lectins or at least, large quantities of lectin containing foods. It’s always best to discuss any dietary changes, like lectin avoidance, with an experienced Registered Dietitian to figure out if this change would benefit you.
Tannins are a polyphenolic compound found naturally in tea, chocolate, grapes, wine, legumes, berries, barley, nuts, along with an number of other foods. They are typically described as giving food a bitter or astringent taste.
- Some types of tannins form bonds with proteins which decreases the protein quality of food.
- Tannins can also form a strong bond with iron.
- In animal experiments, tannins have caused decreased growth rate.
- Tannins are not destroyed or deactivated by cooking.
- Although tannins will decrease protein digestibility, there is not a lot of evidence that they bind with digestive enzymes (which are also proteins) within our digestive tracts. So, although some of the proteins we eat with tannin-rich foods will not be available to us, our digestive enzymes can still break down the non-tannin bound proteins.
- Tannins are known antioxidants. That is, they can neutralize chemicals within the body that cause cell damage.
- In a 2003 literature review, it was concluded that tannins have a high potential to be protective against cancer. This anti-cancer property is likely related to their status as an antioxidant.
- Tannins have antimicrobial properties.
- Tannins may increase glucose uptake and improve blood sugar levels.
- The tannins in green tea (also known as polyphenols) are thought to have positive effects on the cardiovascular system and reduce cancer risk.
The tannins in our food will affect some protein digestibility, however, it’s probably not something that is going to make a huge impact on your overall protein absorption. Most people (in the developed world, at least) are not protein deficient. In fact, most people consume above and beyond the current protein recommendations.
As for iron absorption, if you have or are at risk for iron deficiency, it may be wise to consume tannin-rich tea, coffee, and wine between meals to maximize iron absorption.
Protease inhibitors are another type of antinutrient found in legumes and grains. Soybeans are particularly well known for being a source of this antinutrient.
- Protease inhibitors block the digestive enzymes that break down proteins in our digestive tract.
- Cooking (heat) deactivates protease inhibitors. So, as long as heat has been applied to your legumes and grains, you’ll probably be okay.
- The protease inhibitors from soybeans are associated with a decrease in the development of chemically induced cancers.
Protease inhibitors are not something to be too worried about. They are easily deactivated by heat. So, it’s simple, just cook your legumes and grains to rid your food of this antinutrient.
Saponins are compounds that can form a foam, or soap-like, substance when shaken in a watery solution. Like most other antinutrients mentioned here, saponins are found in a number of legumes and grains and in high enough concentrations, they cause a bitter or astringent taste.
- Saponins bind to various nutrients inhibiting our ability to use them.
- Digestive enzymes have been shown to be inhibited by saponins causing a decrease in protein digestibility and absorption.
- Saponins were once considered toxic because of their effects on fish and cold-blooded animals.
- Some types of saponins have hemolytic activity (ie. ability to breakdown red blood cells).
- The saponin content of foods is easily reduced. They are sensitive to heat, as well as, washing, soaking and blanching.
- Saponins are poorly absorbed from the digestive tract in humans and animals.
- There is some evidence that saponins can help lower cholesterol, and may reduce incidence of cancer.
- Saponins have also been credited with lowering post-meal blood glucose response.
- A diet rich in saponins has been shown to inhibit dental caries (cavities) and renal stones.
The normal preparation and cooking processes used with legumes and whole grains can reduce the saponin content quite a bit. And contrary to what was previously believed, saponins don’t seem to be absorbed well in humans. The presence of saponins in food isn't a good enough reason to avoid the foods that contain them.
The next time someone cautions you about antinutrients, remember that the benefits of these antinutrient containing foods, as well as the antinutrients themselves, seem to far outweigh any of their negative aspects.
If you are eating a balanced and varied diet, even if your diet is rich in antinutrients, you will likely not suffer any ill effects. That being said, if you are iron deficient (or at risk of another nutrient deficiency), it may be wise to plan your meals in such a way that you can optimize absorption. But...and this is a huge BUT, you do not have to avoid antinutrient-rich foods such as whole grains, legumes, nuts or seeds. Anyone struggling with a nutrient deficiency or malnutrition should be working with a registered dietitian (RD) to maximize their nutrition.
For antinutrients, it seems we only focus on their negative (or perceived) negative attributes. This is short sighted. Certainly, these “antinutrients” do inhibit some of the nutrients that we need but when you look at the bigger picture, they have the potential to offer so much more.
We need to remember that digestion involves a number of chemical reactions. And yes, some of these reactions will cause nutrients to bind to each other, while other reactions make it so nutrients ARE available to us. Some of these reactions are beneficial to our health - to our digestive system, our heart, or our blood sugars. It’s the overall product that we need to focus on.
For me, as a Registered Dietitian, the bigger picture is this - diets rich in antinutrient containing foods including legumes, whole grains, nuts, seeds, fruits and veggies are those that are associated with lower rates of diseases including cancer, diabetes, and cardiovascular disease. Consumption of antinutrient-rich diets also appear to be associated with healthier weights, decreased inflammation and healthier gut microbiomes (ie. those friendly little bacteria in the colon). It’s really hard to argue with this information.
It seems myopic to just focus on a single attribute or component of a food. We need to start looking at the overall picture when it comes to food and nourishment. Do the pros of eating a food that contain these antinutrients outweigh the cons? In most cases and for most individuals, the answer is a resounding YES.
Until the evidence against antinutrients, and the foods which contain them, gets stronger, this Dietitian will continue to recommend them. The presence of antinutrients is not a good enough reason to avoid legumes, grains, nuts and seeds. It just isn’t. It doesn’t make sense at this time. So, for now, I’ll wait with an open mind until more convincing evidence comes across my desk.