There is a lot of information out there about the best foods to help us lose weight, prevent cancer, fight inflammation – the list goes on. In fact, for everything about our health we try and improve, there’s someone out there with a new theory on how to do it. But what does the science say?
Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to give you the evidence-based approach to take the mystery out of the best way to live a healthier, longer life.
If antioxidants were the star of a big budget movie, they would probably be wearing a cape. Why? Because they rescue us from oxidative stress. Antioxidants are compounds that help defend your cells from damage caused by free radicals. And yes, that also sounds like a movie too. In our first story we dive into some of the benefits of antioxidant-rich fruits and vegetables.
According to the latest from the CDC, the rates of all of our top ten killers have fallen or stabilized except for one: suicide. Accumulating evidence indicates that oxidative free radicals may play important roles in the development of various neuropsychiatric disorders, including major depression.
For example, in a study of nearly 300,000 Canadians, greater fruit and vegetable consumption was associated with lower odds of depression, psychological distress, self-reported mood and anxiety disorders and poor perceived mental health. They conclude that since a healthy diet comprised of a high intake of fruits and vegetables is rich in antioxidants, it may consequently dampen the detrimental effects of oxidative stress on mental health.
But that was just based on asking how many fruits and veggies people ate. If you measure the levels of carotenoid phytonutrients in nearly 2,000 people across the country, a higher total blood carotenoid level was associated with a lower likelihood of elevated depressive symptoms, and there appeared to be a dose-response relationship, meaning the higher the levels, the better people felt.
Lycopene, the red pigment predominantly found in tomatoes, but also present in watermelon, pink grapefruit, guava, and papaya is the most powerful antioxidant amongst the carotenoid family. In a test tube, it’s about 100 times more effective at quenching these free radicals than vitamin E, for example.
And in a study of about a thousand older men and women, those who ate the most tomato products had about half the odds of depression. The researchers conclude that a tomato-rich diet may have a beneficial effect on the prevention of depressive symptoms.
Higher intake of fruits and vegetables has been found to lead to a lower risk of developing depression, but if it’s the antioxidants can’t we just take an antioxidant pill? No; only food sources of antioxidants were protectively associated with depression. Not antioxidants from dietary supplements. Although plant foods and food-derived phytochemicals have been associated with health benefits, antioxidants from dietary supplements appear to be less beneficial, and may, in fact, be detrimental to health. This may indicate that the form and delivery of the antioxidants are important. Alternatively, the observed associations may be due not to antioxidants, but rather to other dietary factors, such as folate, that also occur in fruits, vegetables, and plant-rich diets.
In a study of thousands of middle-aged office workers, eating lots of processed food was found to be a risk factor for at least mild to moderate depression five years later, whereas a whole food pattern was found to be protective. Yes, it could be because of the high content of antioxidants in fruits and vegetables but could also be the folate in greens and beans, as some studies have suggested an increased risk of depression in folks who may not be getting enough.
Low folate levels in the blood are associated with depression, but since most of the early studies were cross-sectional, meaning a snapshot in time, we didn’t know if the low folate led to depression, or the depression led to low folate. Maybe when you have the blues, you don’t want to eat the greens.
But since then, a number of cohort studies were published following people over time, and low dietary intake of folate may indeed be a risk factor for severe depression, as much as a threefold higher risk. Note this is dietary folate intake, not folic acid supplements, so they were actually eating healthy foods. If you give people folic acid pills they don’t seem to work. This may be because folate is found in dark green leafy vegetables like spinach, whereas folic acid is the oxidized synthetic compound used in food fortification and dietary supplements because it’s more shelf-stable, but it may have different effects on the body, as I explored previously.
These kinds of findings point to the importance of antioxidant food sources rather than dietary supplements. But there was an interesting study giving people high-dose vitamin C, also known as ascorbic acid. The vitamin C, but not placebo group experienced a decrease in depression scores, and also greater FSI. What is FSI? FSI evidently stands for penile-vaginal intercourse, an acronym that makes no sense to me.
But evidently, high-dose vitamin C improves mood and intercourse frequency, but only in sexual partners who don’t live with one another. In the placebo group, those not living together had sex about once a week and those living together a little higher, once every five days, but with no big change on vitamin C. But those not living together on vitamin C, every other day! The differential effect for non-cohabitants suggests that the mechanism is not a peripheral one, meaning outside the brain, but a central one; some psychological change which motivates the person to venture forth to have intercourse. The mild antidepressant effect they found was unrelated to cohabitation or frequency, so it does not appear that the depression scores improved just because of the improved FSI.
Açai berries are touted for their antioxidant power, but does that translate into increased antioxidant capacity of our bloodstream when we eat them? Let’s find out.
There are so many açai products on the market now, from frozen pulp in smoothie packs to freeze-dried powder and supplements. How is it eaten traditionally? Amazonian tribes cut down the tree, eat its heart, and then pee on the stump to attract a certain type of beetle that lays these monster maggots. And so, a few weeks later, you’ve got three or four pounds of these suckers; so, you can make some grub-kabobs. I think I’ll just stick with my smoothie pack.
“Despite being used for a long time as food” in the Amazon, only since the beginning of this century have “açaí berries been the object of scientific research.” Four years ago, I reviewed that research, starting with in vitro studies that showed that açai could kill leukemia cells in a petri dish at levels one might expect in one’s bloodstream eating a cup or two of açai pulp, or cutting the growth of colon cancer cells in half.
Unfortunately, subsequent studies published since then failed to find such benefit for that type of colon cancer, a different type of colon cancer, or an estrogen receptor negative form of breast cancer. An açai extract did appear to kill off a line of estrogen receptor positive breast cancer cells, but to achieve that level of açai nutrients in your breast, you’d have to sit down to like 400 cups of açai pulp.
That’s the problem with many of these petri dish studies: they use concentrations that you could never realistically achieve in your bloodstream. For example, açai berries may exert a neuroprotective effect, blocking the buildup of amyloid fibers implicated in Alzheimer’s, but only at a dose reached drinking maybe 2,000 cups at a time. Or, have an anti-allergy effect, or decrease bone loss at a mere thousand cups a day.
But, I also talked about a clinical study in which folks were asked to drink less than a cup a day of açai in a smoothie, and appeared to get significant improvements in blood sugar, and insulin levels, and cholesterol. Now, there was no control group, and it was a small study, but there’d never been a bigger study to try to replicate it, until now.
Same amount of açai, for the same duration, but no significant improvements in blood sugars, insulin, or cholesterol. Huh? Why did this study fail to show the benefits seen in the first study? Well, this study was publicly funded;” no conflicts of interest”, whereas the first study was funded by an açai company, which always makes you suspect that maybe the study was somehow designed to get the desired result. And, indeed, the study participants were not just given açai smoothies, but explicitly told to avoid processed meat (like “bacon and hot dogs”). No wonder their numbers looked better at the end of the month.
Now, the new study did find a decrease in markers of oxidative stress in the participants’ bloodstream, a sign of how antioxidant-rich açai berries can be. Those that hock supplements love to talk about how açai consumption can “triple antioxidant capacity;” “triple the antioxidant capacity of your blood.”
And, if you look at the study they cite, yes, there was a tripling in antioxidant capacity of the blood after eating açai. But there was the same, or even better, tripling after just plain applesauce, which was used as a control, and is significantly cheaper than açai berries or supplements.
In our final story we look at how antioxidant intake from foods, not supplements is associated with lower cancer risk.
The USDA recently removed their online antioxidant database of foods, concerned that “ORAC values were routinely misused by food and dietary supplement manufacturing companies to promote their products.” Supplement manufacturers were getting into my-orac-is-bigger-than-your-orac pissing contests, comparing their pills to the antioxidant superfood du jour, like blueberries. And, we know there’s lots of bioactive compounds in whole plant foods that may help prevent and ameliorate chronic diseases in ways that have nothing to do with their antioxidant power. So, I understand their decision.
So, should we just eat lots of whole healthy plant foods, and not worry about which ones necessarily have more antioxidants? Or, does one’s dietary antioxidant intake matter? We have some new data to help answer that question. “Dietary total antioxidant capacity and the risk of stomach cancer,” the world’s second leading cancer killer. A half-million people studied, and “dietary antioxidant capacity intake from different sources of plant foods was associated with a reduction in risk.” Note; they say dietary intake. They’re not talking about supplements.
Not only do antioxidant pills not seem to help; they “seem to increase overall mortality.” That’s like paying to live a shorter life. Just giving high doses of isolated vitamins may cause “disturbances” in our body’s own natural antioxidant network. There is hundreds of different antioxidants in plant foods. They don’t “act in isolation.” They work synergistically. Mother Nature cannot be trapped in a bottle.
Similar results were recently reported with non-Hodgkin’s lymphoma. The more ORAC units in food we eat per day, the lower our cancer risk may drop; though, antioxidants or not, greens were particularly protective. Going from eating like one serving of green leafy vegetables per week to more like a serving per day may cut our odds of lymphoma in half.
Should we be worried about antioxidant intake during cancer treatment, since that’s how most chemo drugs work by creating free radicals? According to some of the latest reviews, there’s “no evidence of antioxidant interference with chemotherapy.” And, in fact, they may actually “improve treatment response and patient survival.”
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For recipes, check out my “How Not to Die Cookbook.” It’s beautifully designed, with more than 100 recipes for delicious and nutritious meals. And all proceeds I receive from the sales of all my books goes to charity.
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