Walnuts top all other nuts when it comes to the quantity and quality of healthful, polyphenol-type antioxidants, according to a pair of Scranton University chemists.
The Pennsylvania-based scientists presented their findings at the 241st National Meeting & Exposition of the American Chemical Society.
“Walnuts rank above peanuts, almonds, pecans, pistachios and other nuts,” said Joe Vinson, Ph.D., the prominent plant-antioxidants expert who led the analysis (ACS 2011).
“A handful of walnuts contain almost twice as much antioxidants as an equivalent amount of any other commonly consumed nut. But unfortunately, people don't eat a lot of them. This study suggests that consumers should eat more walnuts as part of a healthy diet.” (ACS 2011)
"Antioxidants" from foods work on our genes to kill free radicals
For decades scientists and reporters have been talking about the antioxidants in foods.
The compounds they are referring to are polyphenols, which are usually labeled “antioxidants” because they display potent free-radical-fighting powers in the test tube.
But it's increasingly clear that polyphenols' apparent health benefits – including their indirect antioxidant effects – stem from their positive influences on genetic “switches” in our cells.
Such external influences on expression of genes are called “epigenetic”, which is Greek for “over genes”.
And the study of the epigenetic effects of food factors such as polyphenols and omega-3s is called “nutrigenomics”.
The nutrigenomic influences exerted by polyphenols appear to produce antioxidant and anti-inflammatory effects in the body.
Polyphenols exert both kinds of benefit via their indirect, epigenetic effects on our working genes … not through direct antioxidant or anti-inflammatory mechanisms.
In addition to polyphenols, nuts offer many beneficial nutrients in a convenient package … including protein, polyunsaturated fats, vitamins, minerals, and dietary fiber.
However, walnuts are the only nuts to offer large proportions of plant-form omega-3 fatty acids.
Most nuts are high in omega-6 fatty acids, in which the average American's diet is far too high relative to omega-3s, thereby creating a pro-inflammatory imbalance in the body.
But despite that hypothetical drawback, the health benefits of all nuts are clear … probably because the amount of omega-6 fats is small, relative to their ample amounts of beneficial, anti-inflammatory polyphenols.
Walnuts provide far more omega-3s than any other nut, and therefore offer a uniquely beneficial balance of omega-3s to omega-6s.
Walnuts rank high among the few major food sources of “short-chain” omega-3s, while salmon and other fatty fish are the only major food sources of “long-chain” omega-3s. See our sidebar, “Omega-3s: Not created equal”.
Thanks to the new finding that they're tops for polyphenols, walnuts may now deserve top ranking as the healthiest nuts of all.
Nuts are healthy snacks … and walnuts may take top honors
Reams of research link modest intake of nuts with reduced risks of heart disease, certain kinds of cancer, gallstones, Type 2 diabetes, and other health problems.
Surprisingly, scientists had not, until now, compared both the relative amounts and potencies of the antioxidants found in different nuts.
Professor Vinson's team filled that gap by analyzing the polyphenol profiles of nine different types of nuts: walnuts, almonds, peanuts, pistachios, hazelnuts, Brazil nuts, cashews, macadamias, and pecans (Vinson J, Cai Y 2011).
Walnuts had the highest levels of polyphenols … and the antioxidant/anti-inflammatory potency of the polyphenols in walnuts was highest among all the nuts.
Omega-3s: Not created equal
There's little doubt that the short-chain “green” omega-3s in walnuts and leafy greens bring cardiovascular health benefits (see “Walnuts Help Win Heart-Health War”).
But the body can only convert a small portion (two to 10 percent) of short-chain omega-3s (ALA) into the long-chain “marine” omega-3s required to sustain life and health (EPA and DHA).
This is why health authorities worldwide agree that the marine omega-3s found in fish and fish oil are substantially more beneficial to human health.
In the test tube, the polyphenols in walnuts were two to 15 times as potent as vitamin E in terms of their antioxidant effects.
And as Vinson said, “The heat from roasting nuts generally reduces the quality of the antioxidants. People usually eat walnuts raw or unroasted, and get the full effectiveness of those antioxidants.” (ACS 2011)
Even though nuts are calorie-dense, they are also packed with filling fiber and protein, which may help explain why nutty diets are not linked to weight gain.
A recent evidence review and large epidemiological study both found that nut consumption is associated with a significantly lower risk of weight gain and obesity (Sabaté J, Ang Y 2009; Bes-Rastrollo M et al. 2009).
Still, a little goes a long way. Dr. Vinson said it takes only about seven walnuts a day to get the potential health benefits uncovered in previous studies.
American Chemical Society (ACS). Walnuts are top nut for heart-healthy antioxidants. March 27, 2011. Accessed at http://portal.acs.org
Sabaté J, Ang Y. Nuts and health outcomes: new epidemiologic evidence. Am J Clin Nutr. 2009 May;89(5):1643S-1648S. Epub 2009 Mar 25. Review.
Vinson J, Cai Y. Presentation # 17 – Walnuts combine superior phenolic antioxidant content and proven health benefits. Tree Nuts, Sunday, March 27, 2011. 241st National Meeting & Exposition of the American Chemical Society. Accessed at http://abstracts.acs.org/chem/241nm/program/view.php