Pomegranate juice ads claim its antioxidants fight free radicals, but it may not really do that, and they may not be foes 05/25/2017
Ads for pomegranate juice seem to be everywhere.
The video versions feature antioxidants — in the form of red dragons and warriors — raring to fight free radicals.
But the reasons why antioxidant-rich plant foods benefit health are more complex and nuanced than those cartoonish ads would have us believe.
And free radicals may not be the villains portrayed in those juice ads and by the "free radical theory of aging", which is often portrayed — inaccurately — as settled science.
Before we get to recent research that undermines those ads and that theory, let's quickly review the chief players: free radicals and antioxidants.
What are free radicals and antioxidants?
The term “free radical” refers to any molecule that's unstable and prone to “oxidizing” — stealing electrons from — nearby molecules.
This explains why a chemical that stabilizes free radicals — typically by giving them an electron — is commonly called an “antioxidant”.
If your body harbors free radicals in amounts larger that your own internal antioxidant network can control, the resulting “oxidative stress” can damage your cells and their DNA.
Oxidative stress is typically caused by one of three things:
- Chronic inflammation from any cause.
- Exposure to high levels of air or water pollutants, pesticides, and other toxic chemicals.
- Diets — such as the standard American diet — laden with a pro-inflammatory excess of sugars and polyunsaturated vegetable oils high in omega-6 fatty acids.
If you're healthy, your water and air are reasonably clean, and you eat a reasonably healthy diet, you’re unlikely to suffer the excess of free radicals that produces damaging oxidative stress.
Antioxidant vitamins may not help much
The clinical trials published to date don’t show that supplements like vitamin C, vitamin E, and beta-carotene discourage development of major diseases.
That said, most of the trials haven't lasted long and were conducted in people with existing health conditions, so future research may modify that picture.
And, there's abundant epidemiological evidence suggesting that diets rich in whole plant foods (fruits, vegetables, and whole grains) help protect heart, metabolic, and brain health.
Unlike single, isolated antioxidant vitamins, whole plant foods provide multiple antioxidants of various types — most of which exert beneficial "nutrigenomic" effects on our genes — plus healthful fibers.
Foodborne antioxidants: The complex, nuanced reality
There’s good evidence that pomegranates provide significant health benefits.
Of course, the same is true of berries, greens, and other colorful fruits or vegetables, tea, cocoa, coffee, extra virgin olive oil — and other rich sources of antioxidants (polyphenols and carotenoids).
But antioxidant-rich plant foods exert little direct effect on free radicals or oxidative stress in the body.
That's because only tiny proportions of the antioxidants in foods get into your bloodstream, and they're unlikely to directly neutralize free radicals.
This explains why, in 2012, the USDA stopped displaying the so-called “oxygen radical absorbance capacity” (ORAC) of the foods in its widely used nutrient database.
The federal agency said this change was “due to mounting evidence that the values indicating antioxidant capacity have no relevance to the effects of specific bioactive compounds, including polyphenols, on human health.”
Instead, the health benefits of pomegranates and other plant foods stem from the so-called “nutrigenomic” effects that occur in reponse to the tiny proportions of their antioxidants that enter the bloodstream.
The effects include stimulation of the body’s own internal antioxidant network, and of genes that help control inappropriate, unhealthful inflammation.
Critically, the body operates on a delicate balance of oxidizing reactions and opposite "reducing" reactions, and if antioxidant-rich foods could directly affect that balance, the results could be very harmful.
Free radical theory of aging takes another hit
The “free radical theory of aging” was first proposed in 1956 by biologist Denham Harman, Ph.D.
Our cells can usually control free radicals, and repair any damage they cause.
Harman hypothesized that aging results when our internal antioxidant defenses falter, or face a burden of poorly controlled free radicals big enough to produce oxidative stress.
He envisioned a vicious cycle in which free radicals weaken the immune system over time, thereby impairing its ability to control free radicals.
Although Harman’s theory seems to make sense, it’s suffered from a shortage of persuasive evidence.
Here's how Randolph Howes M.D., Ph.D. — the first recipient of the award for excellence in oxidation medicine — summarized the reasons for skepticism:
“A half century of data demonstrates its lack of predictability and it has not been validated by the scientific method. Widespread use of antioxidants has failed to quell the current pandemic of cancer, diabetes, and cardiovascular disease or to stop or reverse the aging process.” (Howes RM 2006)
Ongoing research has further undermined Dr. Harman's hypothesis, and we reported on one sign of trouble in Worms Weaken “Radical” Aging Theory.
And research published over the past two years combines to further undermine the credibility of Harman’s core idea.
That evidence comes from fruit flies and roundworms — creatures with whom we share many of the same genes, and which age in similar ways.
Let’s scrutinize two recent studies that call Dr. Harman’s seemingly plausible theory into serious question.
Study #1: Free radicals may be longevity allies
Three years ago, researchers from Canada’s McGill University found that free radicals promote longevity in roundworms (Yee C et al. 2014).
Studies in roundworms earned the Nobel prize for the scientists who discovered the process known as “apoptosis”, or cellular suicide, which serves to eliminate damaged and pre-cancerous cells.
The McGill team discovered that this same mechanism — when stimulated in the right way by free radicals — reinforces a cell’s defenses and lengthens its lifespan.
In other words, an excess of free radicals that doesn’t kill a cell seems to make it stronger.
Study co-author Siegfried Hekimi described the implications of their finding this way:
“We have turned this [free radical] theory [of aging] on its head by proving that free radical production increases during aging because free radicals actually combat — not cause — aging. In fact, in our model organism [the roundworm] we can elevate free radical generation and thus induce a substantially longer life.”
Study #2: Free radicals may not be as destructive as believed
Proteins are critical players in most of the key processes in our bodies.
So, it’s been assumed that high levels of free radicals harm health and accelerate aging by damaging proteins and impairing their functions.
But surprising evidence published two years ago by scientists from Imperial College London revealed that proteins can survive exposure to free radicals unscathed (Menger KE et al. 2015).
“Clearly, the cell can cope with the presence of free radicals,” said study co-author Helena Cochemé. “Our findings are surprising, and go against the [assumptions in the] field.”
Dr. Cochemé and her colleagues analyzed hundreds of proteins in young, middle-aged, and old fruit flies, to identify the amounts and identity of proteins that undergo oxidation by free radicals as the creatures age.
As she said, “What’s really surprising is that the oxidation status of the proteins was the same in both young and old flies. This suggests that cells have a built-in protection system.”
Reducing the calories fed to rodents and other animals is proven to improve their health and extend their lifespans. And protein oxidation alerts cells to environmental stresses, such as a lack of food.
So Dr. Cochemé’s team compared the oxidation status of proteins in a group of flies that had been fed much less than normal to a group that was fed a normal diet.
Starvation simultaneously lengthened the flies' lifspans and dramatically increased the proportion of proteins that became oxidized — a finding that undermines the free radical theory of aging.
As Dr. Cochemé said, “We have to go back to the drawing board to find out the underlying mechanism [of aging].”
Stay tuned ... we'll keep our eyes on this field of research, whose findings hold important implications for health and aging, and the roles that antioxidant-rich plant foods can play in both.
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