I hope you are safe and well. In this edition of Verified, we investigated antioxidants in food with Metafact nutrition editor Dr Tim Crowe and many other experts. Tim wrote a consensus article concluding: ‘Antioxidants in food are not as important as they’re made out to be’.
Here are the takeaways I learnt from Tim and many other experts on Metafact:
Antioxidants do serve important roles in our body and diet is an important source of them to maintain health.
Antioxidants are not just one molecule, our supply can come via many different vitamins and minerals. Plant-based foods are rich in antioxidants and also contain thousands of other plant chemicals that likely benefit our health more than antioxidants alone.
Evidence suggests antioxidant supplements do not work as well as the naturally occurring antioxidants in whole foods such as fruits and vegetables.
Antioxidants found in so-called superfoods [like goji berries, blueberries or pomegranate juice] are no more effective than those in regular fruit and vegetables.
Be very wary of antioxidant supplementation (see 3.) as evidence shows it can be harmful.
Experts say there’s too much hype on antioxidants. Save your money on supplements or superfoods - just maintain a diverse diet with lots of fruits and vegetables.
You can read our detailed review below, but remember to share this to your friends and colleagues where they can subscribe for free to the Metafact digest:
Mini-review on 'antioxidants' in food
Green Tea. Dark chocolate. Red wine. Pomegranate juice. We hear they have loads of health-boosting ‘antioxidants’ from food marketers. It’s a good excuse for us when something delicious can have healthy properties. So what does the evidence say about antioxidants in food? Are they important? Should we seek antioxidant-rich food or supplements?
What are ‘antioxidants’?
Antioxidants are certain types of molecules that protect other molecules from a chemical process called oxidation. Oxidation is very common and important for us to live. Glucose for example, a sugar from the food we consume, is oxidized by the oxygen we breathe which gives us the energy to live. Food preservatives are a type of ‘antioxidant’ as they prevent the oxidation process and food spoilage.
In our body, however, the oxidation process can damage important molecules in our cells, including DNA and proteins. Antioxidants are important since they can prevent or reduce this damage. Uncontrolled oxidation is typically caused by highly reactive molecules known as ‘free radicals’.
What are ‘free radicals’?
Free radicals are unstable molecules that can damage cells. Antioxidants help mop up excess free radicals. The body can cope with some free radicals and even needs them to function effectively. However, the damage caused by an overabundance of free radicals over time may become irreversible and lead to certain diseases including heart disease and some cancers.
Having an imbalance of electrons makes the free radical unstable and places the body in a state of oxidative stress. Oxidation can be accelerated by stress, cigarette smoking, alcohol, too much sunlight, pollution and other factors. Oxidative stress and an excess of free radicals can lead to damage of:
Nucleic acids leading to cancerous changes
Membrane lipids and LDL-cholesterol in arteries
Enzymes which repair cell structures
Other proteins such as collagen
So where does our supply of antioxidants come from?
Antioxidants come from many different vitamins and minerals like vitamin C, vitamin E, beta-carotene and selenium. “Generally our body makes most of its antioxidant enzymes in the right amounts needed” says Professor Margreet Vissers from the University of Otago, but our diet is also important.
Vegetables, fruit and tea are sources of dietary antioxidants. Even though chocolate and red wine also contain antioxidants, consuming them to increase antioxidant status is not recommended” says nutrition scientist from North-West University Dr Cornelie Nienaber-Rousseau. “However, microgreens [like basil, coriander or kale] are very good sources of antioxidants or phytochemicals”. Plant-based foods are rich in something called phytochemicals—"plant chemicals"—many of which also have antioxidant properties that interact importantly.
For example, Vitamin C is an antioxidant, while a phytochemical called hesperetin (found in oranges and other citrus fruits) restores the vitamin C to its active antioxidant form. Carotenoids (such as lycopene in tomatoes and lutein in kale) and flavonoids (such as anthocyanins in blueberries, quercetin in apples and onions, and catechins in green tea) are also antioxidants (Source).
Are antioxidants good for you?
Antioxidants can short-circuit the damage caused by free radicals so it seems logical that the more antioxidants a person eats, the healthier they will be. But that is unclear since not all antioxidants are beneficial says Dr Homer Black, biochemist from Taylor College of Medicine:
A number of epidemiological studies (principally case-control) have found inverse associations with carotenoid levels (both dietary intake and blood levels) and cancer risk. However, clinical trials have failed to substantiate such a relationship and one even found an 18% increase in lung cancer among male smokers receiving beta-carotenoid supplements. Recent experimental evidence seems to indicate that beta-carotene, per se, acts as a pro-carcinogenic agent in UV-carcinogenesis when provided as the only carotenoid and phytochemical in the diet.
What the public must understand is not all antioxidant mediated reactions are beneficial and antioxidants such as beta-carotene can, under certain conditions, act as a pro-oxidant.
Dr Tim Crowe confirms this:
Vitamin A as beta-carotene has been associated with a reduced risk of certain cancers, but an increase in others, such as lung cancer in smokers, if vitamin A is purified from foodstuffs.
So it seems important to be wary about taking antioxidant supplements.
“The notion that antioxidants per se have superpowers in terms of preventing or curing disease has been put to rest long ago” says Professor Jens Lykkesfeldt, a biochemist from the University of Copenhagen:
Clearly essential micronutrients such as vitamin C that are also antioxidants are good (essential) for you. However, the notion that antioxidants per se has super powers in terms of preventing or curing disease has been put to rest long ago. It is therefore important to distinguish between essential micronutrient that happens to be antioxidants (and are important for humans health) and other ‘generic’ antioxidants that very common in e.g. fruits and vegetables that are not individually essential.
Do antioxidants help cancer?
Consensus: Uncertain via 4 experts.
It’s unclear and controversial says Dr Homer Black, biochemist from Taylor College of Medicine:
The idea that antioxidants, consumed in green leafy and yellow vegetables, are cancer protectants arose from a 1981 epidemiologic study in which individuals consuming a greater amount of these vegetables were at a lower risk for cancer. As these vegetables were rich in carotenoids such as beta-carotene, and knowing that beta-carotene was a strong singlet oxygen quencher and antioxidant, it was proposed that this carotenoid, or related carotenoids, might act as a cancer preventive. Whether these carotenoids can reduce cancer risk is unclear and controversial.
Dr Cornelie Nienaber-Rousseau goes into more details about the uncertain cancer link:
Cancer patients often take antioxidant nutritional supplements during cancer treatment to alleviate treatment toxicities, improve long-term outcomes and replenish antioxidant status that declines during cancer treatment. However, summaries of the scientific studies on antioxidant supplements (beta carotene, vitamin A, vitamin C (ascorbic acid), vitamin E, and selenium) for prevention of cancers found no evidence that they prevent cancers (Bjelakovic et al., 2004). In fact antioxidant supplements (beta carotene, vitamin A, and vitamin E) seem to increase overall mortality (Bjelakovic et al., 2004; Bejelakovic et al., 2007) .
Fruits & vegetables are much more than just antioxidants
Polyphenols, not antioxidants, should take more credit says Dr Tim Crowe:
A brief reading about polyphenols on the Internet will bring up article after article highlighting that polyphenols are antioxidants and that explains their health benefits. Nutrition science though has well-and-truly moved on from using such simplistic language and concepts to describe how these thousands of polyphenols found in food work. They are much more than antioxidants. You need to step back and see the bigger picture. It should instead be about polyphenols and their multitude of benefits and actions in the body such as:
Regulating cell growth and death
Slowing down cancer cell proliferation
Altering glucose responses and insulin sensitivity
Increasing activity of enzymes involved in removing harmful substances from the body
Are antioxidants overhyped?
Consensus. Likely via 5 experts.
Experts suggest most of the hype on superfood antioxidants don’t match the science. Be additionally wary of antioxidant supplements as “intake needs to be controlled according to usage as some of these can be overdosed (Vitamin A, Vitamin E and selenium are toxic in high doses)” says Professor Vissers from University of Otago.
The good news is that the evidence seems to suggest that whole foods are more effective than supplements, Dr Tim Crowe says:
There is increasing evidence that antioxidants are more effective when obtained from whole foods, rather than isolated from food and presented in tablet form with some antioxidant supplements actually increase cancer risk.
“Antioxidants should preferably come from food and not be supplemented”, says Nutrition Scientist Dr Cornelie Nienaber-Rousseau.
What about superfoods? Dr Jacqui Adcock from Deakin University writes “Despite the marketing hype, antioxidants found in so-called superfoods [like goji berries, blueberries or pomegranate juice] are no more effective than those in regular fruit and veg, so you’re better off saving your money”.
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