Nuts may be mightier than they look.
Nuts also boast other bioactive chemicals, such as phenolics and phytosterols.
They might be diminutive and beige, but nuts are chemically complex and, thankfully for us, delicious.
Exactly how nuts guard our hearts is up for debate, but there are some theories: some believe that it might be because they improve blood lipid levels and reduce the risk of weight gain, and others think it's due to their anti-inflammatory effects.
However they manage this feat, it is pretty well-established that eating nuts reduces death from heart disease. But very few scientists have looked at the relationship between specific types of heart disease and nut consumption.
Which facets of CVD are particularly sensitive to our nutty companion's sword?
Dissecting a nut eater
A group of nut enthusiasts from the Karolinska Institutet in Stockholm, Sweden, recently set out to crack the shell of this tricky question and examine the nutty kernel within. Their findings are published this week in the journal Heart.
When investigating how a certain food affects the average human, you need a great deal of data before you can draw any conclusions.
In this case, the team had access to data from 61,000 Swedish people aged 45–83, who had filled out food frequency questionnaires. Each was tracked for 17 years, or until they died.
From the data available to them, the scientists got a glimpse of the inner lives of your average nut lover.
According to the questionnaires, compared with people who never ate nuts, those who did tended to lead more healthful lifestyles: they were less likely to smoke tobacco or drink alcohol, they were leaner and more physically active, and they ate more fruits and vegetables.
Also, the nut brigade was less likely to have a history of hypertension and more likely to be highly educated.
Herein lies the difficulty with researching the impacts of food on a population: what's protecting the nut lovers' hearts — the active lifestyle, the reduction in alcohol, or the occasional cashew? Did the lean physique and love of vegetables come before the nut habit, or after?
Hearty benefits of nuts
But when other variables were taken into account — including lifestyle factors, diet, family history, and diabetes — many of the links disappeared in a puff of statistical smoke. However, even once the analytical playing field had been leveled, some heart-based benefits did remain.
After controlling for a plethora of other factors, people who included nuts in their diet still had a significantly lower risk of A-fib, which is an abnormally fast and irregular heartbeat.
Eating a handful of nuts one to three times per week reduced the risk of A-fib by only 3 percent, but eating nuts three or more times every week lowered the risk by 18 percent.
A significant relationship between eating nuts and heart failure was also found after controlling for lifestyle variables, but it was less consistent.
They showed that eating a moderate amount of nuts was linked to a 20 percent reduction in heart failure risk. Weirdly, those who ate more than a moderate amount of nuts did not benefit from the protection.
A simple and effective intervention?
As with any study such as this, it is observational and cannot, therefore, prove cause and effect — the old chicken and egg scenario.
In this case, however, the researchers had access to a heroically large dataset, giving their findings much more weight. But, as they note, you can never know whether it's the nuts or other related behaviors that are making the difference.
The study authors write:
"Nut consumption or factors associated with this nutritional behavior may play a role in reducing the risk of [A-fib] and possibly heart failure."
These latest findings add to the growing evidence that there's something about nuts that our hearts appreciate. The study authors believe that they might be an easy and cost-effective way to improve general health across the board.
"Since only a small proportion of this population had moderate (about 5 percent) or high (less than 2 percent) nut consumption," they say, "even a small increase in nut consumption may have large potential to lead to a reduction in incidence of [A-fib] and heart failure in this population."
So, whether you're mad about macadamias or ambivalent about almonds, you may as well have a few handfuls of nuts each week; your heart will probably thank you for it.