When it comes to antioxidant power, blueberries get most of the buzz.
But that's always been a distorted picture of reality, for four good reasons.
First, a food's “antioxidant capacity” is probably not a reliable measure of its actual health-enhancing potential … see our sidebar, “The truth about food-source ‘antioxidants'”.
Second, the antioxidant capacity of berries runs behind that of raw (non-Dutched) cocoa, dark chocolate, extra virgin olive oil, and herbs and spices such as parsley, cilantro, cumin, basil, turmeric, sage, and rosemary.
Third, each kind of berry appears to offer distinct benefits, with no one berry being clearly superior to the rest.
The truth about food-source “antioxidants”
Certain chemicals in plant foods – namely, polyphenols and carotenoids – are commonly called “antioxidants” because they behave that way in test tube experiments.
When researchers add polyphenols, carotenes, and carotenoids to test tubes containing the unstable oxygen compounds called free radicals, they neutralize those potentially damaging molecules.
However, these “antioxidant” compounds do not exert direct antioxidant effects in the body… at least not to a significant extent.
Instead, polyphenols and carotenoids appear to exert so-called “nutrigenomic” effects on gene switches (e.g., transcription factors) in our cells.
These nutrigenomic effects tend to moderate inflammation and stimulate the body's own antioxidant network … which includes enzymes, lipoic acid, CoQ10, melatonin, and vitamins C and E.
The richest known food source of polyphenols are raw (non-alkalized / non-“Dutched”) cocoa and dark chocolate, culinary herbs and spices, berries, plums, prunes, tea, coffee, extra virgin olive oil, beans, and whole grains.
Carotenoids abound in peppers, carrots, yellow-orange squashes, shrimp, krill, and wild salmon.
Cocoa, chocolate, and tea are the richest sources of particularly promising polyphenols called flavanols. Extra virgin olive oil is uniquely rich in a highly beneficial group of polyphenols called tyrosol esters (i.e., hydroxytyrosol, oleuropein, oleocanthal, and more).
Finally, antioxidant content and capacity can vary quite widely within a single berry species.
For example, wild blueberries are higher in antioxidants than cultivated ones, while berries that grow wild in higher latitudes (e.g., Alaska and Scandinavia) have more than berries grown in warmer climates.
Now, the results of a joint U.S.-Irish clinical study confirm earlier evidence that strawberries offer special cardiovascular benefits.
U.S.-Irish trial finds strawberries very heart-healthy
The story began six years ago, with a series of small clinical studies from Oklahoma State University, the USDA, and universities in Canada, Italy and Iran.
All but one of these small trials involved people who were either obese or had metabolic syndrome or diabetes (Basu A et al. 2009; Basu A et al. 2010; Zunino SJ et al. 2012 ;Moazen S et al. 2013; Alvarez-Suarez JM et al. 2013).
In all cases, the subjects were assigned to consume strawberry powder … and they enjoyed significant reductions in all or most of several key risk factors for cardiovascular disease:
Small, dense LDL cholesterol
Oxidized (damaged) cholesterol
Oxidative stress (free radical levels)
Ratio of total cholesterol to HDL cholesterol
Adhesion molecules (which promote arterial plaque)
And a new U.S.-Irish clinical study shows that diets rich in strawberries exert beneficial effects on three important risk factors:
That last finding is especially important because having high levels of small, dense LDL cholesterol is truly dangerous.
By way of contrast, it's now clear that it's not necessarily unhealthful to have “high” total cholesterol levels, or high levels of “regular” (large, light) LDL cholesterol.
The new clinical study comes from researchers at Oklahoma State University and Queen's University of Belfast in Northern Ireland (Basu A et al. 2014).
Oklahoma State's Dr. Arpita Basu and her co-workers recruited 60 adults with excess fat around their belly (“abdominal adiposity”) and high blood cholesterol and triglyceride levels.
The participants were randomly assigned to drink one of three beverage s daily for 12 weeks (four months):
Low-dose strawberry drink (25 grams per day)
High dose strawberry drink (50 grams per day)
Strawberry-flavored “control” drinks that contained no actual strawberries.
After four months, the two strawberry-beverage groups showed “dose-dependent” drops in total cholesterol, total LDL cholesterol, and small LDL cholesterol.
The term “dose-dependent” means that these three cholesterol measures dropped more in the volunteers who drank 50 grams daily, compared with those who drank 25 grams per day … though the results were statistically significant only in the high-dose group.
In addition, blood levels of a known marker of oxidative stress (from free radicals) called MDA dropped by similar degrees in both of the “real” strawberry groups.
No effects were found on other markers of cardiovascular health, including HDL cholesterol, adiposity (belly fat), triglycerides, blood pressure, or blood glucose levels.
As the authors wrote, this was the first time a randomized controlled trial found that strawberries could lower total cholesterol, total LDL cholesterol, and small-dense LDL cholesterol levels in obese people.
In addition, both doses of the real strawberry beverage displayed antioxidant effects, in the form of decreased oxidation of blood cholesterol.
We hasten to add that the results of this trial and the earlier strawberries trials must be confirmed in larger studies.
And it seems unwise to assume that sweetened strawberries – such as the sugary strawberry in commercial yogurt, preserves, and jams – would bring the same benefits, given the known risk that sugar poses to cardiovascular health.
Instead, add organic, unsweetened strawberries to cereal, yogurt, smoothies, salads, and more.
The study was partly funded by the California Strawberry Commission.
Alvarez-Suarez JM, Giampieri F, Tulipani S, Casoli T, Di Stefano G, González-Paramás AM, Santos-Buelga C, Busco F, Quiles JL, Cordero MD, Bompadre S, Mezzetti B, Battino M. One-month strawberry-rich anthocyanin supplementation ameliorates cardiovascular risk, oxidative stress markers and platelet activation in humans. J Nutr Biochem. 2014 Mar;25(3):289-94. doi: 10.1016/j.jnutbio.2013.11.002. Epub 2013 Nov 27.
Basu A, Betts NM, Nguyen A, Newman ED, Fu D, Lyons TJ. Freeze-Dried Strawberries Lower Serum Cholesterol and Lipid Peroxidation in Adults with Abdominal Adiposity and Elevated Serum Lipids. J Nutr. 2014 Mar 26. [Epub ahead of print]
Basu A, Fu DX, Wilkinson M, Simmons B, Wu M, Betts NM, Du M, Lyons TJ. Strawberries decrease atherosclerotic markers in subjects with metabolic syndrome. Nutr Res. 2010 Jul;30(7):462-9. doi: 10.1016/j.nutres.2010.06.016.
Basu A, Wilkinson M, Penugonda K, Simmons B, Betts NM, Lyons TJ. Freeze-dried strawberry powder improves lipid profile and lipid peroxidation in women with metabolic syndrome: baseline and post intervention effects. Nutr J. 2009 Sep 28;8:43. doi: 10.1186/1475-2891-8-43.
Jenkins DJ, Nguyen TH, Kendall CW, Faulkner DA, Bashyam B, Kim IJ, Ireland C, Patel D, Vidgen E, Josse AR, Sesso HD, Burton-Freeman B, Josse RG, Leiter LA, Singer W. The effect of strawberries in a cholesterol-lowering dietary portfolio. Metabolism. 2008 Dec;57(12):1636-44. doi: 10.1016/j.metabol.2008.07.018.
Moazen S, Amani R, Homayouni Rad A, Shahbazian H, Ahmadi K, Taha Jalali M. Effects of freeze-dried strawberry supplementation on metabolic biomarkers of atherosclerosis in subjects with type 2 diabetes: a randomized double-blind controlled trial. Ann Nutr Metab. 2013;63(3):256-64. doi: 10.1159/000356053. Epub 2013 Dec 6.
Zunino SJ, Parelman MA, Freytag TL, Stephensen CB, Kelley DS, Mackey BE, Woodhouse LR, Bonnel EL. Effects of dietary strawberry powder on blood lipids and inflammatory markers in obese human subjects. Br J Nutr. 2012 Sep;108(5):900-9. doi: 10.1017/S0007114511006027. Epub 2011 Nov 9.