Nuts have a role to play in preventing heart disease, lowering cholesterol and boosting fertility, so why don’t we eat more of this tasty and beneficial food?
“My sister was driving,” says Lowry, “and I thought, ‘I just need to stop for a minute,’ because I almost couldn’t breathe.” In her fifties at the time, Lowry had experienced the pain before and was sure it was just another bout of bad indigestion. “I knew if I said to her, ‘I’ve got a chest pain,’ she’s going to freak out, which she did.”
Lowry’s sister cancelled the shopping trip and rushed her to a doctor. The doctor couldn’t categorically state whether Lowry was having a heart attack. As a precaution, he insisted on having her admitted to hospital overnight for further tests, before referring her for a follow-up when she returned home to Gisborne.
Cardiovascular disease is New Zealand’s, and the world’s, leading cause of death. It’s estimated that every 90 minutes, one New Zealander dies from heart disease. In 2010, it caused one in four deaths worldwide – which includes all diseases of the heart and circulation, including coronary heart disease, atrial fibrillation, heart attack, congenital heart disease and stroke.
It is possible to reduce heart-disease risk by managing a number of factors, including smoking, high blood pressure, high cholesterol, inactivity, diabetes, poor nutrition and excessive alcohol intake.
Before her trip to Hawke’s Bay, Lowry’s GP had done routine blood tests that revealed she had raised cholesterol. “He basically said, ‘What medication should I put you on?’” However, Lowry wasn’t keen to go on drugs as her first response and instead asked her GP if she could try reducing her cholesterol by changing her diet.
Lifestyle changes, such as eating a healthy diet and getting regular physical activity, can prevent up to 80% of premature heart disease, strokes and diabetes.
However, Lowry says, her GP wasn’t particularly enthusiastic about her trying dietary changes. “He just said, ‘Oh, you can try it.’” But he sent her on her way without offering any specific advice.
The fact that Lowry’s doctor didn’t mention anything about simple dietary changes, such as eating nuts, which have been shown to reduce cholesterol, would come as no surprise to University of Otago associate professor Rachel Brown.
Brown heads the university’s nut research group and has co-authored a number of studies looking at the benefits of nuts to cardiovascular health. More recently, the group has investigated the perceptions of health professionals and the general public in regard to nuts.
“We saw that nut consumption was quite low and wanted to know why, what people thought of nuts and what made them eat them,” says Brown. “And also, the health professional perceptions of nuts, because often they’ll be the ones to say whether you should eat them or not.”
In one survey, they found less than 4% of New Zealanders have received advice from a health professional to eat more nuts. However, more than half of the survey respondents said they would eat more nuts if they were advised to do so by a dietician or doctor.
When Brown’s research team surveyed New Zealand GPs, they found less than half of them offered a message consistent with the Heart Foundation’s guidelines, namely, that we consume 30g (a small handful) of raw nuts a day to improve diet quality and reduce several risk factors associated with heart disease.
That advice applies especially to people for whom nuts will have a direct effect on their high blood cholesterol. However, Lowry had no idea that nut consumption could lower blood cholesterol and heart-disease risk and nor did 40% of New Zealanders in one of Brown’s surveys. And it’s far from guaranteed that they’ll hear this information from a health professional any time soon – when Brown’s team surveyed a range of health professionals, including dieticians, practice nurses and GPs, they found only 55% of GPs would recommend patients increase nut consumption, compared with 63% of practice nurses and 83% of dieticians. In addition, 39% of New Zealand GPs reported that they would never discuss nut consumption with their patients, irrespective of the patients’ health condition.
Nuts and cardiovascular disease
There’s certainly no lack of evidence about the benefits of nut consumption for heart health.
“Nut consumption is related to a reduction in ‘bad’ LDL cholesterol and the risk of heart disease,” says Brown. “And that tends to be shown in epidemiological studies, where we follow groups for years, and in clinical trials when we give people nuts and their cholesterol comes down.”
Nuts – both peanuts and tree nuts – are rich in a variety of important micronutrients, including folate, niacin, vitamin E and vitamin B6. They’re also rich in a number of macronutrients, such as monounsaturated and polyunsaturated fatty acids and dietary fibre, as well as phytoestrogens, phytochemicals and essential minerals, including copper, magnesium, potassium and zinc.
The nutrients and good fats in nuts may explain why observational and clinical trials have consistently shown that people who eat nuts regularly have a lower risk of heart disease and premature death.
A 2013 study published in the New England Journal of Medicine, based on data from 76,464 women involved in the US Nurses’ Health Study (1980-2010) and 42,498 men in the Health Professionals Follow-up Study (1986-2010), found that nut consumption was inversely associated with total mortality for both women and men. More directly, there were specific relationships between nut consumption and a reduced risk of death as a result of heart disease, respiratory disease and cancer.
A similar study in the US, using data from 20,742 men involved in the US Physicians’ Health Study, discovered an inverse association between nut consumption and the risk of death from heart disease and all-cause mortality.
More recently, researchers have begun investigating whether higher consumption of nuts would benefit the cardiovascular health of people with diabetes. This group is of particular interest because, over time, the high blood glucose that occurs with diabetes can damage the blood vessels and nerves that control both the heart and blood vessels. Statistically, the longer you have diabetes, the more likely you are to develop cardiovascular disease.
Using data again from the Nurses’ Health Study and Health Professionals Follow-Up Study, US researchers recently investigated whether there was any relationship between nut consumption and heart-disease risk and deaths among type 2 diabetes patients. Their findings, published in Circulation Research in February this year, revealed a link between higher consumption of nuts, especially tree nuts, and a reduced risk of heart disease and premature death among those with the condition.
Nuts and cancer
The second leading cause of death worldwide, cancer, is a major health and social burden. One of the best ways to reduce our death rate from cancer is to prevent it occurring in the first place.
It’s estimated that a third of cancer cases could be prevented by a healthier diet containing plenty of wholegrains, vegetables, fruit and beans and limited amounts of red and processed meat, fast food, sugar-sweetened beverages and alcohol. More recently, nuts have been touted for prevention, too.
In a 2015 US review and meta-analysis, the regular inclusion of nuts in the diet was associated with reductions in certain cancers, including colorectal, endometrial, gastric, lung and pancreatic. However, researchers have highlighted the need for more data in order to dig deeper into the connection and see whether nuts really are responsible for a reduction in risk of these cancers.
But they note that there are plausible explanations for how nuts might prevent cancer. First, the vitamin E and selenium found in almonds and walnuts, as well as quercetin and resveratrol in pine nuts, are antioxidants.
Second, the vitamin E in almonds and hazelnuts can regulate cell differentiation and proliferation, and the quercetin and resveratrol in almonds and pine nuts, as well as polyphenols in walnuts, can inhibit chemically induced carcinogenesis.
In addition, the folic acid found in almonds and pine nuts can reduce DNA damage, and the resveratrol in pine nuts can regulate inflammatory response and immunological activity.
Nuts are also rich in dietary fibre and, in some cases, oleic acid – both of which are recognised as cancer protective.
Indeed, the World Cancer Research Fund’s 2018 report “Diet, Nutrition, Physical Activity and Cancer: A Global Perspective” noted there is strong evidence that foods rich in fibre, such as nuts, “probably” reduce the risk of colorectal cancer.
More recently, a large study led by researchers at Yale Cancer Center added weight to the suggestion that nuts might influence cancer outcomes. They tracked the diet and health outcomes of 826 colon cancer patients against 1846 healthy controls and discovered that the rate of cancer recurrence in those who ate nuts was nearly half that of those who didn’t.
People with stage III colon cancer who regularly eat nuts are at significantly lower risk of cancer recurrence and premature death than those who don’t, according to the study published in the Journal of Clinical Oncology. It found that people who regularly consume at least two 28g servings of nuts a week have a 42% improvement in disease-free survival and a 57% improvement in overall survival.
“Further analysis of this cohort revealed that disease-free survival increased by 46% among the subgroup of nut consumers who ate tree nuts rather than peanuts,” said the director of Yale Cancer Center and senior author of the study, Charles Fuchs. Tree nuts include almonds, walnuts, hazelnuts, cashews, and pecans, among others. In contrast, peanuts are actually legumes.
It costs peanuts
Even with all that good news about nuts, most New Zealanders still don’t eat them regularly. In New Zealand, Europe and the US, less than 8% of the population consume whole nuts on a given day, says Brown.
New Zealand’s mean population nut intake of 3.5g a day is well below the Heart Foundation’s recommended 30g.
So, why don’t we eat more nuts? Cost is often cited as a significant barrier. In Brown’s 2018 survey of the New Zealand public, the most frequently cited barriers to increasing nut consumption were cost (67%), potential weight gain (66%) and fear of eating too much fat (63%).
However, as Brown points out, it’s worth comparing the cost of nuts with other snacks. For instance, although 30g of raw almonds may cost 55-70c, that’s not much different from a banana at 57c, she says. A 40g packet of potato chips costs $1.49 and a cereal bar about 50c.
At the more expensive end of the scale are brazil nuts, macadamias and pine nuts, at $1.95, $2.10 and $2.37 respectively per 30g.
Peanuts provide good value for money at just 20c per 30g and could provide a more cost-effective “nut” option to benefit the health of budget-conscious shoppers.
Peanut butter is an affordable form of nuts, too, at about 36c per 30g serving. But as with whole nuts, a spread with no added sugar, salt or oil is the best option.
Even if nuts are affordable, that won’t necessarily shift more people towards eating them, says Brown. “A lot of people are worried that they’ll gain weight by eating nuts.”
In Lowry’s case, she wasn’t eating nuts when she was diagnosed with high cholesterol and she didn’t know that including them in her diet could reduce it. “Back then, I thought they were fattening and not good for you, so I wasn’t eating them.”
Although nuts are energy-dense and high in fat, there is considerable research showing that regular nut consumers tend to be leaner than non-nut consumers.
A 2015 analysis of data from the US National Health and Nutrition Examination Survey revealed that tree-nut consumption was associated with lower body mass index (BMI) and waist circumference.
Studies have also shown that the addition of nuts to a regular diet typically results in no or very little weight gain. Randomised controlled trials involving pistachios have found similar results – that consuming them daily had no significant effect on body weight or BMI as compared with study participants who ate no nuts.
There are several plausible reasons that nuts don’t tend to lead to weight gain. Nuts are rich in unsaturated fats that may require more energy for our body to metabolise than saturated fats, so less fat is stored.
Certainly, there’s some evidence that nut consumption may increase the body’s metabolism.
Nuts may also simply lead to us feeling fuller, thanks to their unsaturated fat content, which means we end up eating less food overall.
Or it could be that we’re simply flushing the excess fat and energy down the toilet, says Brown. “When you chew whole nuts, they’re not fully broken down and some of the fat is not accessible because of the cell walls of the nut. So, you do have some appearing in the faeces.”
Another major issue for many New Zealanders is oral health. Brown’s nut research group surveyed 710 randomly selected people. Among this group, the most frequent reason given for avoiding nuts – given by 43% of respondents – was dental problems.
More than a quarter of health professionals surveyed by Brown and her colleagues reported that their patients didn’t want to eat nuts because their teeth couldn’t cope with them.
It’s a significant concern for people aged 65 and over, according to the Ministry of Health’s 2012 New Zealand Older People’s Oral Health Survey, with more than half the 2218 respondents having lost all their natural teeth. Even among those who did have teeth, nearly all had at least one tooth missing, and those who had some of their natural teeth were missing an average of 15.
Overall, that means the diet, nutrition and well-being of a substantial proportion of older adults may be affected by their oral health. Eating whole nuts while wearing dentures or partial dentures or with several missing teeth can be difficult, with potential for dentures to become dislodged and pieces of nut to get stuck under dentures or in the gaps of missing teeth.
Instead, a more comfortable option may be nut butters, either on toast or sandwiches or added to a smoothie and blended so there are no solid bits.
Fashion and fertility
Although social-media “influencers” rave about the health benefits of turmeric smoothies, kale salads and goji berries, that money would be better spent on a handful of nuts. Why has the humble nut been overtaken by the current crop of “superfoods”?
Auckland dietician Alice Gormack thinks food trends play a big part. “People like the latest fashion or fad or new product. Raw nuts are a basic food and they’ve been around forever. They’re not trendy, but they should be, because of the health benefits. And you don’t have to eat that many for them to have an effect.”
Gormack works for Fertility Associates, helping her clients optimise their health before they start fertility treatments. She has long advised them to eat about 30g of nuts a day, “preferably raw nuts, and to try to get the nuts to take the place of processed snacks, to provide a good degree of healthy fats, protein and also some fibre”.
Gormack’s advice is supported by studies such as the Spanish Fertinuts research project, which demonstrated the effect nut consumption has on sperm quality. The 14-week clinical trial involved 119 healthy men aged 18 to 35, who were allocated either a Western-style diet enriched with 60g of nuts or the same diet but without the nuts. The men who included nuts in their diet had an increased intake of total fat, monounsaturated fatty acids, polyunsaturated fatty acids, magnesium, vitamin E and total omega-3 and improved omega-3 to omega-6 ratio.
More importantly, the nut eaters had a significantly improved total sperm count as well as improved sperm vitality (the percentage of live sperm), motility (the percentage of sperm that move) and morphology (shape of the sperm). The researchers believe that these findings were at least partly explained by the reduced rate of DNA fragmentation in the sperm.
“It’s very positive stuff,” says Gormack, “especially for the one in seven couples who have trouble conceiving, because male factors are estimated to account for 40-50% of these cases.”
The results of the Fertinuts study build on the findings of a previous one that found eating 75g of walnuts a day for 12 weeks improved sperm vitality, motility and morphology, too.
That both studies used a 12-week intervention is no coincidence. “Sperm production takes about three months or 12 weeks,” says Gormack. “So, I tend to tell people we’ll start working on your diet a few months ahead of IVF treatment. Longer than that is even better, to improve overall health.”
Gormack advises both men and women to add nuts to their diet – for women it’s more a case of improving overall health and nutrient intake.
And the great thing about nuts, Gormack says, is that they’re quite a specific food group and easy to supplement into our diet.
Spread the love
“Different nuts have higher and lower amounts of micronutrients, which is why we recommend eating a variety of them,” says Brown. So, whereas two brazil nuts provide our daily selenium needs, almonds contain more vitamin E and hazelnuts offer more folate.
When it comes to healthy fats, most are high in monounsaturated fats, but walnuts are high in the omega-3 polyunsaturated fats. Those good fats aren’t linked to weight gain. In Lowry’s case, she only recently discovered, via a Facebook group, that nuts could have potentially reduced her high cholesterol. To what degree she’ll never know, as her doctor convinced her to start taking cholesterol-lowering medication after her Hawke’s Bay incident.
It seems the missing puzzle piece, when it comes to accessing the health benefits of nuts, is knowledge.
This article was first published in the October 5, 2019 issue of the New Zealand Listener.