Why eating nuts WON’T make you fat, experts reveal

Nuts have long had a reputation as diet wreckers—too fatty, too calorific, too moreish. But new research is turning that idea on its head.

One recent trial found that when young adults ate a breakfast containing 50g of walnuts, they not only felt sharper but actually performed better on memory and reaction tests later that day.

Another analysis of weight-loss studies showed that including nuts in calorie-restricted diets didn’t hinder progress—in fact, in some cases people who ate them lost more weight than those who didn’t.

It’s not the first time nuts have impressed scientists.

Over the years, studies have linked them to lower rates of diabetes, heart disease and even depression, as well as better fertility and improved brain function in later life.

Yet despite decades of evidence, they still don’t feature heavily in public health campaigns—and many people remain wary of them, worried that the calories will outweigh the benefits.

In reality, experts say the opposite is true. A daily handful can provide a powerful mix of protein, fibre and healthy fats that not only fills you up but also helps protect long-term health.

To find out which varieties deliver the most benefits, and how much we should really be eating, we spoke to nutritionists Grace Kingswell and Dr Emma Derbyshire.

Why nuts won’t make you fat 

At first glance, it makes sense to be cautious. A small handful of almonds contains more than 150 calories, while Brazil nuts are among the fattiest plant foods you can buy.

But research shows those calories don’t behave in the same way as the empty kind found in biscuits or crisps.

Studies by the US Department of Agriculture have shown that we don’t absorb all the fat in nuts. Around a fifth of the calories in almonds and walnuts never make it into the bloodstream, because the fat remains locked inside their fibrous cell walls and passes straight through the digestive system.

‘Nuts are incredibly nutrient-dense, but the body doesn’t utilise every calorie they contain,’ says nutritionist Grace Kingswell. ‘That’s why they don’t have the same impact on weight gain as other high-fat foods.’ 

Their unique mix of protein, fibre and unsaturated fat also keeps hunger in check and stabilises blood sugar—meaning people are less likely to reach for snacks later.

A review of weight-loss trials last year even found that participants who included nuts in their diets sometimes lost more weight than those who cut them out.

In other words, far from being diet-wreckers, nuts can actually support weight control when eaten in sensible portions—roughly 30g a day, or a small handful.

More than just a snack

Once the weight myth is set aside, the range of benefits is striking. 

‘Nuts are a great source of fibre, vitamin E, antioxidants and minerals—but more importantly, they work on multiple systems in the body at once,’ says nutritionist Grace Kingswell.

Vitamin E, abundant in almonds and hazelnuts, is a powerful antioxidant that helps protect cell membranes from damage. 

Higher intake from food has been linked in several large studies with slower age-related cognitive decline. 

Walnuts and pecans, meanwhile, are high in polyphenols that dampen inflammation, a driver of heart disease and diabetes.

There are reproductive benefits too. A Spanish clinical trial found men who added two handfuls of mixed nuts to their diet every day for 14 weeks improved sperm count, motility and morphology. 

Other research suggests women who eat nuts regularly are less likely to experience problems conceiving, possibly because of the role omega-3 fats and selenium play in hormone balance.

On top of this, regular nut consumption is associated with lower blood pressure, reduced risk of type 2 diabetes and even a modest lift in mood—thought to be due to their effect on neurotransmitters like serotonin.

Not all nuts are created equal, though. From the brain-boosting power of walnuts to the thyroid-friendly punch of Brazil nuts, each type brings something different to the table…

Walnuts boost brainpower

Walnuts are especially rich in omega-3 fatty acids, protein and polyphenols. 

A University of Reading study found that when young adults added just 50g of walnuts to breakfast, they enjoyed faster reaction times and sharper memory throughout the day. 

Omega-3 fats are already thought to help shield against Alzheimer’s disease and stroke, and the Reading trial was the first to show even a single serving of walnuts could deliver a measurable mental boost.

Brazil nuts pack a punch

Brazil nuts are one of the richest sources of selenium, a key nutrient for thyroid health. 

Just three provide a full day’s requirement—but Kingswell warns against overdoing it, since too much selenium can be toxic. 

Despite being high in saturated fats, Brazil nuts also contain magnesium, copper and phosphorus, and a small study even suggested a single monthly serving could lower cholesterol faster than statins. 

Public health nutritionist Dr Emma Derbyshire adds that older adults in particular often fall short on selenium, making Brazil nuts a useful addition in moderation.

Almonds help the gut

Almonds stand out for fibre, with a 30g serving providing around 4g—helping boost gut health, immunity and digestion. 

They’re also rich in vitamin E, which has been linked to lower risks of heart disease and even some cancers, though more large-scale research is needed to confirm these effects. 

Nut butters under scrutiny

Nut butters have surged in popularity. Almond, hazelnut and pistachio butters are marketed as healthier swaps for peanut butter, and indeed they provide protein, fibre and good fats. 

But not all spreads are equal. ‘There are a lot of nut butters on the market that are full of palm oil or sugar,’ says Kingswell. 

‘It’s important to look for one that’s 100 per cent nuts, with maybe just a pinch of salt.’ 

Whole nuts, she adds, remain slightly higher in fibre and may be better for blood sugar control.

Because nut butters are so concentrated, it’s easy to eat far more than you realise—a tablespoon can contain the equivalent of several handfuls of nuts, meaning calories mount quickly. 

Kingswell also notes that peanuts in particular are prone to mould, which can produce toxins linked with immune problems and, in rare cases, cancer. 

Brazil nuts should also be limited to avoid excess selenium.

Easy ways to add them in

Still, for most people, the benefits far outweigh the drawbacks. 

Dr Derbyshire says: ‘Nuts are great as they are, but they can be paired to further improve nutrient absorption and balance.’ 

Pairing them with berries or oranges, she explains, enhances the iron absorption from nuts, while sprinkling them on top of yoghurt can provide ‘an array of complementary amino acids, known as protein synergy.’

Kingswell added that activating nuts—which involves soaking them overnight and then slowly dehydrating them in the oven—can make the nutrients more bioavailable and easier to digest. 

Because they are naturally low in carbohydrates but high in fibre and healthy fats, nuts also make an ideal snack for people looking to manage blood sugar or improve their diet.

‘Despite decades of diet advice and campaigns, we are still not better off when it comes to our nutrition and this includes brain and immunity nutrients,’ she says. 

‘We need t get back to the basics of snackin on and cooking nutrient-dense fresh foods and minimising sugary, fatty snacks. 

‘In an ideal world, people should be able to get all the nutrients they need from their diets.’