Did you know peanuts are not nuts at all? They actually belong to the legume family, with beans and peas. Unlike "real" nuts, which grow on trees, peanuts grow under the ground. Yet they look like and have a nutritional composition akin to tree nuts – and they're cheaper, too, so they dominate the budget mixed nut varieties.
Peanuts have a bad reputation for being high in fat and bad for health, but this is mainly due to our appetite for the roasted and salted variety. As a raw product, peanuts are high in protein and fibre and contain heart-healthy monounsaturated and polyunsaturated fat, vitamin E, magnesium and niacin.
Walnuts are rich in omega-3 fats – a 30g handful of walnuts has 1800mg of omega-3s. There are two types of omega-3 fats – the kind found in plants (including walnuts) and the kind found in oily fish. Plant omega-3s are important in heart health.
The trick to walnuts is getting the walnut out of its shell without breaking the two nut kernels inside. This is something of an art. A nutcracker works, but not everyone has one, and it can do a lot of damage to the nut kernels. There's a simpler method, according to the Australian Walnut Industry Association. All you need is a teaspoon: simply put the handle end in the depression where the walnut was attached to its stem and twist.
If you're buying them in the shell, look for ones that are heavy for their size, and with intact shells. Shelled walnuts should be plump and crisp. If they're packaged, look for airtight packaging and buy the ones with the longest time remaining on the best-before date.
Store walnuts in an airtight container in the refrigerator or freezer. They should keep in the fridge for four months (six months in the freezer). Walnuts that have been stored for too long go rancid – which makes them bitter.
Beware the added fat
While investigating brands of mixed nuts, we looked into the types of oils most manufacturers use for roasting. It's not always obvious when the nuts contain added oil. The word "roasted" or the term "oven baked" could spell the presence of added oil in the form of "vegetable oil". Under the food standards code a manufacturer is not obliged to identify the specific oil used. The good news is that the oil used by most of the manufacturers we looked at is from a healthy vegetable source, such as sunflower oil. The bad news is that there is no guarantee that a nastier oil isn't used in other products.
And the added salt
Although we excluded salted varieties of nuts from our investigation, they dominate the market, often chosen for flavour. But the salt in these products offsets some of the heart health benefits derived from the nuts. A high salt diet is strongly linked with increased blood pressure and hypertension – a risk factor for heart disease and stroke. Some brands of salted nuts contain as much as 780mg of sodium per 100g, a far cry from what is considered low salt (less than 120mg sodium per 100g). If you're interested in salted nut varieties, check the back of the pack, aim for less than 400mg per 100g and limit your intake.
Many products display health and nutrient claims on the packaging, which can be a great education tool, but watch out – you could be paying more for no additional benefits. The health claims on the pack do not mean you are getting a more nutritious nut, they're just exploiting the natural properties of the product. Compare the prices and look beyond the packaging.
Although there's no such thing as an unhealthy nut, no two nuts are equal in nutritional composition. Almonds and walnuts are particularly prized. Almonds tend to have high levels of nutrients across the board and walnuts are high in the omega-3 ALA (alpha linolenic acid).
Studies show that including nuts in a meal may reduce the rise in blood glucose levels after you've eaten. A review of evidence conducted by industry nutrition organisation Nuts for Life suggests that eating a 30–50g serve of nuts five times a week is enough to reduce your risk of heart disease up to 50%, lower total cholesterol levels by 10% and the risk of diabetes by 27%. Nuts have also been linked to a lower body mass index (BMI); despite their high energy and fat content, nuts have the amazing power of satiety but our bodies don't absorb all the fat they contain.
Nuts are a rich source of monounsaturated and polyunsaturated fats, which help control cholesterol.
- Macadamia nuts are highest in monounsaturated fats, which promote "good" cholesterol.
- Walnuts are the richest plant-based source of the omega-3 ALA, containing 100% of the adequate intake for women and 63% for men in just 13g (about five walnuts). Omega-3 can reduce the risk of heart disease.
Nuts are a good source of protein, which can help control appetite. They also provide the amino acid arginine, which the body turns into nitric oxide, causing blood vessels to dilate and remain elastic.
- Almonds contain the highest amount of arginine and provide the second-highest amount of protein after pistachios.
Fibre keeps the digestive system work on a regular cycle and can reduce cholesterol levels by preventing re-absorption in the gut. It also helps you feel fuller for longer.
- Hazelnuts contain the most fibre (10.4g/100g), followed by pistachios (9g/100g) and almonds (8.8g/100g).
Nuts provide a good hit of essential minerals, including magnesium, copper, zinc, selenium and potassium – all of which can play a role in protecting your heart. Magnesium also has protective properties against diabetes, high blood pressure and CVD – all factors in metabolic syndrome.
- Brazil nuts are highest in magnesium and selenium (an antioxidant).
- Cashews are highest in zinc and copper.
- Pistachios are highest in potassium (which can help control blood pressure).
Vitamin E is a tocopherol – an antioxidant that can stop cholesterol from sticking to artery walls, which can lead to atherosclerosis, the leading cause of heart attack and stroke.
- Almonds are by far the nuts highest in vitamin E.
Nuts contain plant sterols, which have been proven to reduce cholesterol absorption.
- Pistachios contain the highest amount of plant sterols, followed by almonds and pinenuts.
'Good' fat still = kilojoules
Sure, nuts have a reputation for being high in fat, but it's not as simple as that. You may be happy to learn you won't absorb all the fat in nuts, but don't use that as an excuse to nibble your way through a whole pack just yet. Although nuts are full of vitamins and "good for you" fats, fat is the most energy-dense nutrient, providing 37kJ per gram (by contrast, carbohydrate provides 16kJ per gram). So even if you don't absorb all this energy, you're still going to get a big kilojoule hit.
The bottom line is that a small handful of nuts a day (about 30g, or 26 almonds) as part of a healthy diet will provide the health benefits you want without expanding your waistline.