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Peanuts are Legumes (Beans) Not Nuts

Updated on March 17, 2017
Beth Eaglescliffe profile image

Science graduate and business advisor, health educator and author, Beth writes articles on a wide variety of subjects.

Golden peanut brittle is a tempting sweet dessert candy.
Golden peanut brittle is a tempting sweet dessert candy. | Source

About 3.5 million Americans are allergic to peanuts. Two-thirds of all nuts eaten by Americans are peanuts and peanut butter. In US the number of children affected by peanut allergy tripled between 1997 and 2009.

— US Center for Disease Control

Peanuts Are Not Tree Nuts

More than 1 in 100 people in US and Europe are thought to have a peanut allergy. If they eat even a small amount of peanut, the allergy can have fatal consequences. To prevent this from happening, sufferers need to avoid eating peanuts and peanut-related foods. Peanuts are part of the botanical family called "Leguminosae" or legumes. They are not a true nut like other nuts.

Legumes (commonly known as beans) are plants that have edible seeds enclosed in a pod. Some examples of the bean family are soya, peas and haricot. It is important that more people are made aware that peanuts (ground nuts) are legumes as correct food labelling information could save someone's life.

Peanut butter is a breakfast favorite in US and UK.
Peanut butter is a breakfast favorite in US and UK. | Source

Difference Between Beans (Legumes) and True Nuts

Legumes (beans)
Nuts (tree nuts)
Edible part of plant
Modified flower
Ovary wall
Seeds attached by thread
No attachment
Number of seeds or nuts
Multiple seeds in pod
Single nut in shell

Legumes are Seeds, Nuts are Flowers

In simple terms, legumes are a seed, whereas nuts are a kind of flower. Nuts are a type of fruit that is formed from the specialized flower of nut trees. Unlike other flowers, these have become modified so that the 'petals' harden but do not open. The maturing 'petals' create a shell structure which protects the nut as it grows.

A key botanical difference why peanuts are categorized as legumes and not nuts is to be found inside the pod. If you examine a true nut, you will see that it is not attached in any way to the ovary wall of the plant. Some examples of true nuts are almonds, walnuts, and pecan nuts. When you shell a nut, the edible part is loose inside the outer protective shell.

In contrast, a legume is attached by a thread to the inside of its pod. The seed remains attached to its pod until it reaches maturity. Examples of legume plants are peanuts, runner beans and butter beans. When you open up the pod, the attaching thread can be clearly seen in legumes such as peas and beans which are eaten soft. A peanut and its pod are harvested later, by which time the attaching thread has usually withered away, and so it is not so obvious.

Another characteristic of the peanut that shows it is a member of the legume family is that there are multiple peanuts inside each shell. A true nut will usually have only one nut inside each shell. A peanut’s shell is really a hardened pod and not a shell at all.

What Exactly is a Nut?

Anaphylactic Shock

Having a peanut allergy is a serious and life-threatening condition. For people who are susceptible, even tiny amounts of peanuts can send them into anaphylactic shock. Symptoms of anaphylactic shock include swelling of lips and tongue, generalized hives, loss of consciousness and eventually heart failure and death.

For more about the how's and why's of peanut allergy, a good reference book is "The Peanut Allergy Answer Book". The author, Michael C. Young, M.D., is Associate Clinical Professor of Pediatrics at Harvard Medical School.

People who know that they have this allergy usually carry an ephedrine automatic dispensing device so that they can self-administer adrenaline (ephedrine) as an antidote. A common name for one of these injecting devices is an EpiPen. Anyone affected should be taken immediately to the nearest hospital Emergency Room. The video below illustrates how quickly anaphylactic shock can occur after eating peanuts.

Allergic Reactions to Peanuts

Signs and Symtoms of Anaphylaxis

Signs and symptoms of anaphylaxis
Signs and symptoms of anaphylaxis | Source

Recent Research Into Peanut Related Allergies

Research by the Norwegian School of Veterinary Science in 2012 concluded that people who have a peanut allergy can also develop allergies to other legumes. A particular problem was found in relation to ingredients used in some ready meals. Lupin and fenugreek are “new” legumes that are not currently named separately on a ready meal’s ingredient list as the amounts used are too small. They fall under the broad term of spices or flour enhancers.

For someone with a peanut allergy, eating even small amounts of these legumes can cause them to produce an allergic reaction. The most serious of these allergic reactions is known as anaphylactic shock.

Peanut Allergy

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Why Are Peanut Allergies Becoming So Common?

Peanut Sensitivity Can Trigger Anaphylactic Shock

Some people are so sensitive to peanuts that they do not have to actually eat them in order to suffer anaphylactic shock. Merely being in the same room as peanuts or peanut dust can trigger a reaction.

Peanut-free foods must be produced in kitchens and factories where they cannot be accidentally contaminated with peanut particles. For this reason appropriate food labelling and warning signs play a crucial part of preventing allergic reactions.

The potential for a new trigger source for peanut allergy sufferers should not be underestimated. Many people regularly eat “take-away” and “ready meals” unaware that the “hidden” legumes of lupin and fenugreek that may be included under the umbrella name of thickeners or spices.

More Than 160 Foods Linked to Allergic Reactions

The US Food and Drug Administration (FDA) have identified more than 160 foods that cause allergies. Each year more than 8 million Americans suffer an allergic reaction to at least one of these foods. There is no cure for a food allergy, only avoidance.

Eight foods are known to cause 90% of all food allergic reactions. These must be listed on food labels under US law. These eight foods are milk, eggs, fish, shellfish, tree nuts (e.g., almonds, walnuts, pecans), peanuts, wheat and soybeans.

The UK Food Standards Agency (FSA) reports that ten people die each year in Britain from food induced anaphylaxis. European Union (EU) food regulations require 14 foods which are known to cause allergic reactions to be listed on food labels. These 14 foods are cereals containing gluten, crustaceans, eggs, fish, peanuts, soybeans, milk, nuts, celery (including celeriac), mustard, sesame seeds, sulfur dioxide, lupin and mollusk.

Difference between Food Intolerance and Food Allergy

There is a high level of incorrect self-diagnosis of food allergies. Someone may suffer from a food intolerance rather than an allergy and this is less severe. Such a person may restrict their diet unnecessarily and this can affect their intake of essential minerals and vitamins.

Allergies are caused by an incorrect response of your immune system to the food. Nut allergies can be diagnosed with a blood test. Food intolerances are more difficult to diagnose but they generally involve the digestive system. If you're not sure whether you have a food intolerance or food allergy, you should seek the opinion of a qualified medical practitioner. Up to 20% of the population self-reports that they have a food allergy, but the true figure is thought to be closer to 2%.

Peanuts can be eaten raw straight from the shell or roasted and salted.
Peanuts can be eaten raw straight from the shell or roasted and salted. | Source

Further Information

Allergy UK have produced a useful factsheet on Peanut and Tree Nut Allergies.

Food Allergy Research and Education (FARE) has information on food labelling requirements in the US relating to peanuts.

A summary of the research paper entitled "Cross-reactivity between peanuts and other legumes can lead to serious allergic reactions" can be read in the Science Daily newspaper.


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