Study finds beneficial blood-fat effects from both omega-3 sources; nuts’ heart benefits may flow as much from other nutrients as from their “weak” omega-3s
by Craig Weatherby
Loma Linda University sits about 40 miles east of Los Angeles, amidst Southern California’s nut-growing region.
This respected health sciences institution was founded in 1905 by the Seventh-day Adventist church, whose members strive to eat diets high in whole plant foods and low in refined foods and meats.
- New study compares blood-fat effects of walnuts and salmon.
- Walnuts and salmon produced different beneficial impacts on blood fats.
- In addition to “weak” omega-3s, the heart benefits of walnuts may flow from other factors.
Unsurprisingly, epidemiological (diet-health) studies find that Seventh-day Adventists rank among the healthiest people in North America.
The Adventists’ uncommon diets
—combined with generous funding from various California nut-growers’ groups
—have helped make Loma Linda University a leading center for studies on the health effects of nuts.
These studies suggest that nuts are hearth healthy, probably due to three major factors: fiber, antioxidants, and polyunsaturated fats.
Funding-source induced bias does not appear to be a factor, since many studies from other institutions support these findings.
For example, see our 2006 report: “New Studies Confirm Popular Nuts as Conspicuously Healthful.”
And in 2007, researchers from Harvard, Spain, Loma Linda, and Penn State published an analysis review of four U.S. epidemiological studies, as part of a USDA-sponsored scientific symposium on nuts and health.
Their analysis showed that people with the highest nut intake are about one-third (35 percent) less likely to die from coronary heart disease (CHD), due primarily to a decrease in sudden cardiac death… the same kind of heart-related death that fish oils appear to deter most effectively.
As the international team wrote, “Clinical studies have evaluated the effects of many different nuts and peanuts on lipids [blood fats], lipoproteins [cholesterol-carriers], and various CHD risk factors, including oxidation, inflammation, and vascular reactivity. Evidence from these studies consistently shows a beneficial effect on these CHD risk factors.” (Kris-Etherton PM et al 2007)
Somewhat surprisingly, even though regular nut consumption adds about 250 calories per day, nut consumers weigh no more than nut-avoiders (King JC et al. 2008). This is probably due to the satiating effects of the fats and fiber in nuts.
Walnuts and fish seen as complementary cardio-protectors
As we reported in 2006, a study from Loma Linda University showed that eating walnuts adds to the benefits seen with eating salmon. (See the subsection titled “Study #3: Walnuts complement heart-health effects of salmon” in the article, “New Studies Confirm Popular Nuts as Conspicuously Healthful”)
In March of this year, German researchers reported the results of feeding people plant and animal sources of omega-3s, which produced distinctly different effects on their blood fats and cholesterol, with fish-source omega-3s (EPA and DHA) outshining the sole plant-source omega-3, called ALA (Egert S et al. 2009).
Now, a new Loma Linda study compares the different effects that walnuts have on people’s blood-fat and cholesterol profiles
—a key heart risk factor
—compared with fatty fish.
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 “Walnuts’ heart benefits…,” below).
Associate professor Sujatha Rajaram, Ph.D., and her colleagues at Loma Linda recruited 25 adults with mildly high cholesterol and triglyceride levels and randomly assigned them to eat one of three tightly controlled diets, each of which contained the same number of total calories:
The diet trials lasted for four weeks, whereupon all the participants switched over to eating another of the diets.
- Control diet (contained no nuts or fish)
- Walnut diet (providing 42.5 grams of walnuts per 2,388 calories consumed)
- Salmon diet (providing 113 grams of salmon twice a week)
The Loma Linda researchers report that people on the walnut diet enjoyed significant reductions in total and LDL cholesterol levels, compared to the salmon and control diets.
The walnut diet also out-performed the salmon diet when it came to two other beneficial effects:
However, the salmon diet raised HDL (“good”) cholesterol levels more than the control or walnut diets.
- Reduced the ratio of total cholesterol to HDL cholesterol (a major predictor of reduced heart risk)
- Reduced the ratio of apolipoprotein B cholesterol to apolipoprotein A-I cholesterol
As expected, the salmon diet also lowered participants’ blood levels of triglycerides, compared to the control and walnut diets.
The researchers measured no significant reductions in total or LDL cholesterol in the fish groupwhich is unsurprising, because fish and fish oil have never been shown to do either of these things.
Instead, the long-chain omega-3s in fish oil are proven to lower the combined levels of all forms of cholesterol except HDL (“good”) cholesterol. And in terms of reducing risk of heart-related deaths, this effect is proven more beneficial than lowering total or LDL cholesterol.
(Unfortunately, the Loma Linda team’s report did not include the relative abilities of walnuts and salmon to lower all non-HDL cholesterol.)
Clearly, walnuts deliver significant beneficial changes in blood chemistry, with heartening implications for cardiovascular health.
But it seems unlikely that such significant benefits can be attributed to the presence in walnuts of small amounts of a “physiologically inefficient” omega-3 fatty acid called ALA.
Here’s the scoop.
Walnuts’ heart benefits rely on more than their relatively “weak” omega-3s
Compared with diets high in saturated animal fats, diets higher in polyunsaturated fats (omega-6 and omega-3) are generally hearth healthier.
(The story is more complex that this, as we’ve reported. See “Cholesterol Fiasco Undermines Accepted Theory” and “Comic Critique of the Heart Disease Consensus.”)
Omega-3 fatty acids come in two different forms, which also differ in their ability to enhance human health.
The two kinds of omega-3s occur in two different groups of foods:
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”).
- Short-Chain “Green” Omega-3s (ALA): Leafy green veggies such as spinach, walnuts, flaxseed, and canola oil.
- Long-Chain “Marine” Omega-3s (EPA and DHA): Aquatic foods such as fish, shellfish, and algae, and eggs from hens fed extra DHA.
But researchers and health authorities worldwide agree that the long-chain “marine” omega-3s found in fish and fish oil are substantially more beneficial to human health.
To ensure optimal health, people who consume little fish or fish oil need to eat lots of the plant foods highest in short-chain omega-3s (ALA).
This is because the body can only convert a small portion of short-chain omega-3s (ALA) obtained from foods into the long-chain omega-3s required to sustain life and health (EPA and DHA).
Accordingly, it’s much easier to meet your omega-3 needs—and ensure optimal health—through fish or fish oil supplements.
This is why the FDA-approved heart-health claim for omega-3s applies only to foods or supplements that contain long-chain omega-3s (EPA and DHA), extracted from fish or algae, and why only DHA (not ALA) is approved as a fortifying supplement added to infant formulas.
As the authors of the 2007 review of epidemiological evidence on nuts concluded, the beneficial effects that the (mostly omega-6) polyunsaturated fats in nuts exert on blood fats, artery health, and heart rhythms cannot explain the large heart-risk reductions associated with nutty diets.
The authors of that international review suggested that other nutritional factors in nuts add considerably to their heart-health benefits.
These were their comments, to which we’ve added some clarifications in brackets :
“…in addition to a favorable fatty acid profile [high in polyunsaturated omega-6 fats], nuts and peanuts contain other bioactive compounds that explain their multiple cardiovascular benefits… plant protein and fiber… potassium, calcium, magnesium, and tocopherols [vitamin E compounds]; and phytochemicals such as phytosterols, phenolic compounds [potent antioxidants], resveratrol [potent antioxidant], and arginine [from which the body makes artery-relaxing nitric oxide] (Kris-Etherton PM et al. 2007).
Unsurprisingly, the new study from Loma Linda University affirms prior indications that “green” plant-source omega-3s in walnuts and leafy greens exert beneficial effects on blood fats and chemistry.
And its results help define the ways in which the effects of plant-source “green” omega-3s differ from those exerted by long-chain “marine” omega-3s.
- Egert S, Kannenberg F, Somoza V, Erbersdobler HF, Wahrburg U. Dietary alpha-linolenic acid, EPA, and DHA have differential effects on LDL fatty acid composition but similar effects on serum lipid profiles in normolipidemic humans. J Nutr. 2009 May;139(5):861-8. Epub 2009 Mar 4.
- King JC, Blumberg J, Ingwersen L, Jenab M, Tucker KL. Tree nuts and peanuts as components of a healthy diet. J Nutr. 2008 Sep;138(9):1736S-1740S.
- Kris-Etherton PM, Hu FB, Ros E, Sabaté J. The role of tree nuts and peanuts in the prevention of coronary heart disease: multiple potential mechanisms. J Nutr. 2008 Sep;138(9):1746S-1751S. Review.
- Rajaram S, Haddad EH, Mejia A, Sabaté J. Walnuts and fatty fish influence different serum lipid fractions in normal to mildly hyperlipidemic individuals: a randomized controlled study. Am J Clin Nutr. 2009 Apr 1. [Epub ahead of print]