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What are anti-nutrients?

Minerals, Nutrition | November 11, 2020 | Author: Naturopath

general, Digestion

What are anti-nutrients?

Anti-nutrients are compounds in foods which can block the absorption of nutrients during digestion. Plants, although a natural food source, contain many components some of which are not easily digested. Whist a balanced diet of various food types can cause little health issues, for some people who are trying to build-up their nutrient level, such as with iron – deficient anaemia or calcium for the prevention of osteoporosis, what is eaten and when can be an issue. Others whose diet is based mainly on one food source, such as rice or legumes, can also suffer the consequence of nutrient deficiencies. And some anti-nutrients can actually offer beneficial effects.

In most cases the component of a food which negatively affects our health can be reduced or eliminated entirely by some simple pre digestive preparation, cooking, choosing a different part of a plant to consume, or by eating the food at a separate time away from important nutrients.

Common compounds which can act as antinutrients include phytates, lectins, glucosinolates, saponins, oxalates and tannins.

Phytates

PhytatesPhytates (phytic acid) is a compound found in many commonly eaten foods which can reduce the absorption of the minerals iron, zinc, magnesium and calcium. The good news about phytates is they offer health benefits in their own way – by helping lower cholesterol, balancing blood sugar levels and slowing the digestive process. Foods which contain phytates include:

  • whole grains
  • nuts
  • seeds
  • legumes

Lectins

Lectins can interfere with the absorption of calcium, iron, phosphorus and zinc. These are found in wholegrains and legumes such as:

  • peanuts
  • beans
  • soybeans

But you don’t have to give up your nuts, seeds, whole grains and legumes. Phytates and lectins can be removed from some sources by soaking, fermenting or sprouting.

Glucosinolates

Glucosinolates are a group of phytochemicals be found in cruciferous vegetables. Glucosinolates can block iodine from being absorbed which can affect the functioning of the thyroid gland and cause goitre development. This compound can mostly affect people with hypothyroidism (under-active thyroid) or iodine deficiency (common in Australia). 

GlucosinolatesData from 3 large prospective cohort studies have shown a modest association of dietary glucosinolates intake and the risk of the development of type 2 diabetes. Other studies have shown a glucosinolate intake was associated with a slightly higher risk of Coronary heart disease (CHD)  in adults. Further studies are required to confirm these findings.

The good news is glucosinolates are precursors isothiocyanates – known for their chemoprotective action and ability to reduce oxidative stress and inflammation.

The bottom line here is enjoy a balanced intake 

  • broccoli
  • brussel sprouts
  • cabbage

Microbiota in the colon are able to hydrolyse glucosinolates when they are cooked before consuming, but boiling will destroy the beneficial compounds (antioxidants). Don't over-cook.

Saponins

Saponins are bitter tasting plant chemicals which have a foaming action when mixed with water. Saponins can form insoluble complexes with minerals, such as zinc and iron, preventing absorption in the gut. On a positive, saponins may help in the reduction of cholesterol by preventing its absorption and increasing the excretion of bile salts. Saponins are found in:

  • legumes - such as chickpeas, soybeans, peas and beans
  • wholegrains
  • peanuts
  • asparagus
  • garlic
  • onion
  • spinach

Oxalates

Oxalates can bind calcium preventing its absorption. Calcium oxalate is the primary source of calcium in many foods - such as spinach, but unfortunately because the calcium component is bound to oxalate, it is poorly absorbed. Kidney stones are most commonly formed from calcium phosphate and calcium oxalate obtained through the diet.
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Good digestive gut flora plays an important role in the degrading of oxalate salts and can assist in preventing the formation of kidney stones. Human gut bacteria species Oxalobacter and Lactobacillus exist symbiotically and play this role.

Prolific tea drinkers with a tendency towards hyperoxaluria may need to be aware of over-consumption of dark or black tea. Green tea has the lowest oxalate content but over-consumption is still not recommended especially if dietary oxalate monitoring.

To limit calcium oxalate stone growth, it is recommended to drink water, limit oxalate-rich foods and consume adequate intake of calcium in the diet. Oxalates are found in:

  • leafy-green vegetables
  • beetroot
  • nuts
  • seeds
  • soy
  • tea

Reduce calcium oxalate by soaking or boiling

Tannins

Tannins are valuable polyphenols (proanthocyanidins) known for their health benefits and are responsible for some of the colour and flavour of foods. But tannins can perform as anti-nutrients as they may inhibit the absorption of iron. Not good for those with iron anaemia but can be beneficial for people with haemochromatosis. Tannins in tea can sometimes cause nausea if consumed on an empty stomach. Tannins are found in many foods such as nuts, seeds, legumes, spices and fruits. The bitter taste of foods is usually contributed by tannins amounts. The higher sources are found in:

  • tea
  • coffee
  • red grapes
  • red wine
  • chocolate

Reduce tanins by soaking and boiling

To Summarise

  • The good which is provided by foods containing anti-nutrients far out-weighs the negative
  • Foods which contain anti-nutrients also contain many other health-giving benefits such as antioxidant and cancer protection
  • Don’t let the fear of anti-nutrients prevent you from eating your broccoli and other foods
  • Eating anti-nutrient type foods away from mineral-dense foods can help reduce possible malabsorption issues 
  • Enjoy eating a variety of foods throughout the day

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References

https://www.hsph.harvard.edu/nutritionsource/anti-nutrients

Dietary glucosinolates and risk of type 2 diabetes in 3 prospective cohort studies https://academic.oup.com/ajcn/article/107/4/617/4964650

Intake of glucosinolates and risk of coronary heart disease in three large prospective cohorts of US men and women https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6029595/

Bioavailability of Glucosinolates and Their Breakdown Products: Impact of Processing /https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4985713/

Influence of Cooking Methods on Glucosinolates and Isothiocyanates Content in Novel Cruciferous Foods http://file:///C:/Users/lorna/Downloads/foods-08-00257-v2.pdf

Changes in levels of phytic acid, lectins and oxalates during soaking and cooking of Canadian pulses https://pubmed.ncbi.nlm.nih.gov/29580532/

https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/saponins

Role of gut microbiota against calcium oxalate https://pubmed.ncbi.nlm.nih.gov/28624518/

Oxalate, magnesium and calcium content in selected kinds of tea: impact on human health https://link.springer.com/article/10.1007/s00217-015-2548-1

Dietary oxalate and kidney stone formation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459305/

The Impact of Tannin Consumption on Iron Bioavailability and Status: A Narrative Review https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5998341/

Tannins: current knowledge of food sources, intake, bioavailability and biological effects https://pubmed.ncbi.nlm.nih.gov/19437486/

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