Despite their generally calorie-rich diets, many Americans don't get optimal amounts of key nutrients. 

The nutrients most often lacking include omega-3s, vitamin D, vitamin K, certain B vitamins, and polyphenol “antioxidants” from vegetables, fruits, beans, whole nuts, and whole grains. 

Foods are the best sources of all nutrients, and only whole, unrefined foods contain a full complement. (See “Whole Foods Seen Superior to Supplements” and “Michael Pollan's In Defense of Food”). 

But supplements can help ensure optimal health, and irresponsible claims that the average American's diet provides enough of all important nutrients defy loads of published evidence. 

Thanks to the influence of genetics, overall diet, and gender, humans differ when it comes how well they absorb and utilize nutrients … including the omega-3s in seafood and supplements. 

The results of a small clinical study suggest that vegetables – especially dark green varieties – may enhance the absorption and cardiovascular benefits of the omega-3s in seafood and supplements. 

Do veggies boost the efficacy of omega-3s?
The new study comes from scientists from the University of California, Davis and the USDA's Agricultural Research Service (O'Sullivan A et al. 2013). 

They recruited 83 people of African ancestry for a double-blind, randomized, placebo-controlled trial. 

(By the way, it's not certain that the results seen in this small sample of African-Americans would apply to other ethnic groups, but it seems likely that they would.)

Each participant was randomly assigned to one of two supplement regimens for six weeks:
  • Corn/soybean oil (placebo) capsules
  • Omega-3 fish oil capsules (2 grams of omega-3 EPA + 1 gram of omega-3 DHA). 
The researchers administered questionnaires to gauge each subject's average diet, and took blood samples to test omega-3 levels in their red blood cells. 

Each participants' diet was assigned scores for each of several food groups, based on the 2005 Healthy Eating Index, which assesses how closely a person's diet conforms to official U.S. guidelines. 

At the beginning and end of the trial, the scientists measured three risk factors for cardiovascular disease: 
  • Blood triglyceride levels (lower is better) 
  • VLDL cholesterol particle size (smaller is better) 
  • LTB4 levels. When produced in excess, this messenger chemical sustains chronic inflammation and promotes cardiovascular disease (Labat C et al. 2013; Di Gennaro A et al 2013). 
After six weeks, the 41 people in the omega-3 group showed either small or large increases in their omega-3 EPA blood levels: 
  • Low responders (13 people) – small rise in omega-3 EPA levels 
  • High responders (28 people) – large rise in omega-3 EPA levels 
And when the scientists compared the diets of the two omega-3 subgroups, they detected statistically significant links between these volunteers' diets and changes in their omega-3 EPA levels

Critically, the scientists also found links between the omega-3 group's individual diets and the extent of positive changes to the three cardiovascular risk factors.

Diets richer in orange vegetables, dark green vegetables, and legumes (beans), were linked to higher omega-3 levels and greater desirable changes.

The strongest link was between dark-green vegetables – such as spinach, kale, and broccoli – and higher responses to omega-3 supplements

As the authors wrote, “Although further work will be required … this study has generated an intriguing and unexpected hypothesis for diet interactions in the context of omega-3 fatty acid supplementation.” (O'Sullivan A et al. 2013)

Why would greens boost the efficacy of omega-3s?
The study authors proposed two possible answers to this question.

First, they point out that fruit and vegetable consumption reduces oxidative stress, which may damage omega-3s in the body: 
“… it is conceivable that lower vegetable intake induces a pro-oxidative state that may diminish omega-3 availability ...” (O'Sullivan A et al. 2013) 

This seems possible. However, unlike isolated omega-3s, the omega-3s in animal and human cell membranes are not easily oxidized: see “Fish Oil Oxidation Fears Prove False, Again”. 

Second, they note that the fiber and polyphenol “antioxidants” in plant foods influence the composition of microbes in the human gut, which influences how we metabolize omega-3s and other fatty acids: 
“… diets rich in dark-green vegetable may modulate gut microbiota and in turn influence fatty acid availability and cellular composition in humans.” (O'Sullivan A et al. 2013)

Their second proposed explanation seems more plausible than their first one, given the fast-growing evidence that gut microflora exert strong influences on human health and metabolism.

We'll watch for any longer, larger follow-up trials … but in the meantime, it makes sense to enjoy plenty of dark, leafy greens, which bring their own bountiful health benefits (see the Vegetables & Beans section of our news archive. ).

  • Di Gennaro A, Haeggström JZ. Targeting leukotriene B4 in inflammation. Expert Opin Ther Targets. 2014 Jan;18(1):79-93. doi: 10.1517/14728222.2013.843671. Epub 2013 Oct 4. 
  • Labat C, Temmar M, Nagy E, Bean K, Brink C, Benetos A, Bäck M. Inflammatory mediators in saliva associated with arterial stiffness and subclinical atherosclerosis. J Hypertens. 2013 Nov;31(11):2251-8; discussion 2258. doi: 10.1097/HJH.0b013e328363dccc. 
  • O'Sullivan A, Armstrong P, Schuster GU, Pedersen TL, Allayee H, Stephensen CB, Newman JW. Habitual Diets Rich in Dark-Green Vegetables Are Associated with an Increased Response to ω-3 Fatty Acid Supplementation in Americans of African Ancestry. J Nutr. 2013 Nov 20. [Epub ahead of print]