This morning I drove past the new Krispy Kreme donut shop in Adelaide, people were lining up waiting for it to open. Ironically, this morning a paper was published in the British Journal of Nutrition entitled “Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analyses”.
Despite its title, this is yet another study that shows that there is little difference in nutritional content between organically grown food and conventionally grown food (see here and here for previous studies). There have been many attempts to measure the nutritional differences between conventional and organic food, with largely inconsistent results.
This is not surprising, as the nutritional value of foods is very variable, influenced strongly by local regional factors, variations in growing seasons and rainfall, ripeness of food when harvested and time of harvest. I’m writing this is South Australia, possibly the wine capital of Australia, where we know that having vines on the different sides of a hill will affect sugar and flavor of the grapes. Even different cultivars of the same crop may vary significantly in composition due to the factors above. Nutritional values of crops can vary from between 100% to nearly 200% (which should be kept in mind when the differences reported between conventional crops and organic crops run from 6-69%).
As well as issues relating to timing, seasons and cultivars, the definition of “organically grown” can vary significantly between and within countries.
To try and avoid these limitations, several studies have looked at large numbers of the single studies (a meta-analysis), and generally concluded that there is no meaningful difference between conventional and organic food (again see here and here).
The current paper by Baranski and colleagues in the British Journal of Nutrition follows in the footsteps of these large comparison studies, looking at the largest group of studies to date (343). The authors placed greatest weight on the best designed studies, with the clearest definitions of “organic”. Their findings are largely similar to previous meta-analyses, with only a handful of nutrients being statistically different between organic crops and conventional crops, and only one difference that is of plausible biological significance.
As many people choose more expensive organic produce over conventional produce believing it has better health impacts, I’ll look at a couple of selected nutrients to show what these figures mean.
Ascorbic Acid (Vitamin C)
Ascorbic acid is statistically significantly higher in organic crops compared to conventional crops. This means we are reasonably confident these differences are not due to chance alone. However, organic food has (on average) only 6% more ascorbic acid than conventional foods. Assuming a conventional apple has 8 mg of ascorbic acid, then you would need to eat 5.6 conventionally grown apples to get the recommended daily intake of ascorbic acid.
You would need to eat 5.3 organically grown apples to achieve the same recommended daily intake. As you can see the difference is insignificant in terms of people’s real food consumption.
Carotenoids are an important class of nutrient, beta carotene in particular as it is the precursor to vitamin A. There is about 50% more carotenoids in organically grown fruit than in conventionally grown fruit. Thus you would need to eat 7.5 conventionally grown apples to get the recommended daily intake of carotenoids, while you would only need to eat 5 organically grown apples to get the recommended daily intake of carotenoids.
But we don’t get the majority of our carotenoids from fruit, we get them from things like carrots and green leafy vegetables, and there is no difference in carotenoids between organically and conventionally grown vegetables. So there will be no biologically meaningful differences in the amout of carotenoids you get from conventional or organically grown food.
This is the general pattern we see, even when there is a statistically significant difference between conventional and organically grown produce, it makes no practical difference in terms of our consumption of these products.
Organic fruit has statistically more total antioxidants (around 20%) than conventional fruit, but there is no difference between organic and conventionally grown vegetables in antioxidant content.
Furthermore, while the overall antioxidant levels are higher in organic fruit, there is no difference in the important antioxidants phenolic acids, flavanones, flavones and flavanols, the major contributor would appear to be the carotenoids. As we have already seen fruit is not an important dietary source of carotenoids.
These small differences are unlikely to significantly affect health. This is a bit disappointing personally, as I spent some time researching the effects of antioxidants in Alzheimer’s disease models.
While consumption of antioxidant containing fruit and vegetables have been associated with better health outcomes, the antioxidants themselves do not appear to have any role in this effect (see also here, here and here), despite the number of television advertisements that exhort us to buy antioxidant enriched food. Indeed, the major finding is that high concentrations of fat soluble antioxidant vitamins are associated with detrimental effects.
One of the most convincing effects is an adverse effect of high levels of beta carotene. As we saw, organically grown fruits tended to be higher in carotenoids, but fruit consumption is unlikely to boost carotenoid levels to those associated with higher risk of death.
Organic foods have lower levels of certain kinds of pesticides, but since these are already well below the threshold for toxic effects, this is irrelevant to health. Organic food can be produced with pesticide, typically Pyrethrum (which has its own problems) and Bacillus thuringiensis toxin.
The levels of the toxic metal Cadmium were lower in organically grown cereals than conventional grown cereals. The levels in fruits and vegetables were no different whether they were grown organically or conventionally. Although most peoples intake of cadmium in conventional foods is below that associated with any health risk (unless they are eating food that has been grown on cadmium contaminated soil), this is one area where organic foods may have a larger margin of safety.
The Bottom Line
The bottom line though is that the whole organic vs conventional food is a pointless distraction. Australians don’t eat anywhere near enough fruit and vegetables, in fact only 5.5% of adults have adequate intake of fruit and vegetables. Worrying about whether having 25% more antioxidant in organic fruit is irrelevant when we don’t eat enough fruit and vegetables in the first place, if you eat the recommended amounts of fruit and vegetables you will have adequate nutrition with sufficient vitamins and antioxidants for healthy life, the minor differences between organic and conventional foods will have no impact at all.
As someone remarked to me this morning “people will line up overnight for a donut, no one lines up for a broccoli floret” . Therein lies the problem.