Tough nuts: why peanuts trigger such powerful allergic reactions



The humble peanut. Tasty for most, treacherous for some.
Dr Dwan Price, Author provided

Dwan Price, Deakin University

Food allergens are the scourge of the modern school lunchbox. Many foods contain proteins that can set off an oversized immune reaction and one of the fiercest is the humble peanut.

Around 3% of children in Australia have a peanut allergy, and only 1 in 5 of them can expect to outgrow it. For these unlucky people, even trace amounts of peanut can trigger a fatal allergic reaction.

But what sets the peanut apart from other nuts? Why is it so good at being an allergen?

To answer this, we have to explore the pathway from allergen to allergy, and just what it is about an allergen that triggers a response from the immune system.




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How food gets to the immune system

Before coming into contact with the immune system, an allergen in food needs to overcome a series of obstacles. First it needs to pass through the food manufacturing process, and then survive the chemicals and enzymes of the human gut, as well as cross the physical barrier of the intestinal lining.

After achieving all of this, the allergen must still have the identifying features that trigger the immune system to respond.

Many food allergens successfully achieve this, some better than others. This helps us to understand why some food allergies are worse than others.

The most potent allergens – like peanuts – have many characteristics that successfully allow them to overcome these challenges, while other nuts display these traits to a lesser extent.

Strength in numbers

The first characteristic many allergenic foods have, especially peanuts, is strength in numbers. Both tree nuts and peanuts contain multiple different allergens. At last count, cashews contain three allergens, almonds have five, walnuts and hazelnuts have 11 each and peanuts are loaded with no less than 17.

Each allergen has a unique shape, so the immune system recognises each one differently. The more allergens contained in a single food, the higher the potency.
Additionally, many of these allergens also have numerous binding sites for both antibodies and specialised immune cells, further increasing their potency.

Stronger through scorching

The first hurdle for a food allergen is the food manufacturing process. Many nuts are roasted prior to consumption. For most foods, heating changes the structure of proteins in a way that destroys the parts that trigger an immune response. This makes them far less potent as allergens.

This is not the case for many tree nuts: allergens in almonds, cashews and hazelnuts survived roasting with no loss of potency.

And for the major peanut allergens, it’s even worse. Roasting actually makes them more potent.




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The gauntlet of the gut

From here, the allergen will have to survive destruction by both stomach acid and digestive enzymes within the human gut. Many nut allergens have the ability to evade digestion to some degree.

Some simply have a robust structure, but peanut allergens actively inhibit some of the digestive enzymes of the gut. This helps them safely reach the small intestine, where the allergens then need to cross the gut lining to have contact with the immune system.

This is where peanut allergens really stand apart from most other allergens. They have the ability to cross the intestinal cells that make up the gut lining. Given their relative sizes, this is like a bus squeezing itself through a cat flap.

Peanut allergens accomplish this remarkable feat by altering the bonds that hold the gut cells together. They can also cross the lining by hijacking the gut’s own ability to move substances. Once across, the allergens will gain access to the immune system, and from there an allergic response is triggered.

Peanut allergens attack the bonds that hold intestinal cells together.
Dr Dwan Price, Author provided

The combination of multiple allergens, numerous immune binding sites, heat stability, digestion stability, enzyme blocking, and the effect on the gut lining makes peanut a truly nasty nut.

Where to from here?

This leaves us with a nagging question: if peanuts are so potent, why doesn’t everyone develop a peanut allergy? We still don’t know.

Recently, a potential vaccine developed by researchers from the University of South Australia has shown promise in reprogramming the immune system of mice and blood taken from people with peanut allergy. Will this translate to a potential treatment for peanut allergy? We will have to wait and see.

For now, the more we learn about the action of allergens, and the more we understand their effects on our body, the more we can develop new ways to stop them. And eventually, we might outsmart these clever nuts for good.The Conversation

Dwan Price, Molecular Biologist and Postdoc @ Deakin AIRwatch pollen monitoring system., Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Health check: will eating nuts make you gain weight?



File 20190214 1726 10qcw1z.jpg?ixlib=rb 1.1
Nuts contain “good” fats.
From shutterstock.com

Elizabeth Neale, University of Wollongong; Sze-Yen Tan, Deakin University, and Yasmine Probst, University of Wollongong

The Australian Dietary Guidelines recommend we eat 30g of nuts – a small handful – each day. But many of us know nuts are high in calories and fat.

So should we be eating nuts or will they make us gain weight?

In short, the answer is yes, we should eat them, and no, they won’t make us gain weight if eaten in moderate amounts. The fats in nuts are mostly the “good” fats. And aside from that, our bodies don’t actually absorb all the fat found in nuts. But we do absorb the nutrients they provide.




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Dietary fat: friend or foe?

Nuts do contain fat, and the amount of fat varies between nut types. For example, a 30g serving of raw cashews or pistachios contains around 15g of fat, whereas the same amount of raw macadamias contains around 22g of fat.

There are different kinds of fats in our diet and some are better for us than others. Nuts contain mainly monounsaturated and polyunsaturated fats. These types of fats are known as “good fats”. They can help lower cholesterol when we eat them in place of saturated fats.

The type of fats present varies between nuts. For example, walnuts are rich in polyunsaturated fats, whereas other types of nuts such as hazelnuts and macadamias have more monounsaturated fat.

What the evidence says

Even if the type of fat in nuts is good for us, they are still high in fat and calories. But this doesn’t mean we should be avoiding them to manage our weight.

Studies that looked at people’s eating habits and body weight over a long period have found people who regularly eat nuts tend to gain less weight over time than people who don’t.

Nuts are a healthier option for a snack than many processed alternatives.
From shutterstock.com

We see a similar pattern in clinical studies that asked people to include nuts in their diets and then looked at the effects on body weight.

A review of more than 30 studies examined the effects of eating nuts on body weight. It did not find people who ate nuts had increased their body weight, body mass index (BMI), or waist circumference, compared to a control group of people who did not eat nuts.

In fact, one study found that when people ate a pattern of food aimed at weight loss, the group of people who ate nuts lost more body fat than those who didn’t eat nuts.




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Let’s nut this out

There are several possible explanations for why eating nuts doesn’t seem to lead to weight gain.

  1. We don’t absorb all of the fat in nuts: The fat in nuts is stored in the nut’s cell walls, which don’t easily break down during digestion. As a result, when we eat nuts, we don’t absorb all of the fat. Some of the fat instead is passed out in our faeces. The amount of calories we absorb from eating nuts might be between 5% and 30% less that what we had previously thought.

  2. Nuts increase the amount of calories we burn: Not only do we not absorb all the calories in nuts, but eating nuts may also increase the amount of energy and fat we burn. It’s thought this may partially be explained by the protein and unsaturated fats in nuts, although we don’t yet know exactly how this occurs. Increases in the number of calories burnt can help us maintain or lose weight.

  3. Nuts help us feel full for longer: As well as fat, nuts are rich in protein and fibre. So, nuts help to keep us feeling full after we eat them, meaning we’re likely to eat less at later meals. Recent studies have also suggested providing people with nuts helps improve the overall quality of the types of foods they eat. This may be because nuts replace “junk foods” as snacks.

  4. People who eat nuts have healthier lifestyles in general: We can’t rule out the idea that eating nuts is just a sign of a healthier lifestyle. However, randomised controlled trials, which can control for lifestyle factors like eating habits, still find no negative effect on body weight when people eat nuts. This means the favourable effects of nuts are not just the result of nut eaters having healthier lifestyles – the nuts themselves play a role.




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Overall, the evidence suggests nuts are a healthy snack that can provide us with many of the nutrients our bodies need. We can confidently include the recommended 30g of nuts a day in a healthy diet, without worrying about the effect they will have on our waistlines.The Conversation

Elizabeth Neale, Career Development Fellow (Lecturer), University of Wollongong; Sze-Yen Tan, Senior Lecturer in Nutrition Science, Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, and Yasmine Probst, Senior lecturer, School of Medicine, University of Wollongong

This article is republished from The Conversation under a Creative Commons license. Read the original article.