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Delving into the nutritional differences of food sourcing
On a daily basis, we are challenged to make decisions about the foods we eat. Not only are we challenged by the food choice itself (salmon burger or beef? fruit or vegetable?) but we also are continuously faced with countless options on the shelves of the grocery stores we frequent. Even mega retailers like Walmart and Target now offer organic, grass-fed, or wild-caught options. Marketers of food products are well aware of the influence these words have on our product selection, and loudly proclaim all that they are able to on their product packaging. But a look at the nutritional information panel doesn’t show us many differences between these products and their conventional counterparts on a line-by-line comparison, which leaves us wondering if we are really getting the increased health benefits we hope for from these often more expensive options. A look at some recent studies assessing common options provides some insight – some of which may be surprising – which may make us think even more deeply about the choices we make, and why we are making them.
Organic versus conventional production
Phytobiome. Apples, the fruit we associate with “keeping the doctor away,” sadly are consistently on the Environmental Working Group’s (EWG) “Dirty Dozen” list due to the high level of pesticide residues found on them. One of the things that pesticides affect is the plant phytobiome – the microbial community found not only on the plant, but also that of the soil, insects, nematodes, and other plants that come in contact with it. Much like the microbiome in humans, a high level of diversity amongst the microbes found on plants may help improve resistance to disease and reduce overgrowth of pathogens – which also translates to these benefits when the fruit is consumed by humans.
One of the core taxa found in the organic apples was Lactobacillus, while the potentially pathogenic flora Escherichia-Shigella was only found in the conventional apples.
Recently, it was shown that apples cultivated by organic processes have a significantly more diverse microbiota, with differences in the microbiome of the fruit pulp standing out as the tissue that exhibited the most dramatic difference. The seeds, which also exhibited a greater microbial diversity in the organic apples, had the greatest abundance of bacteria, and their microbiome most closely resembled that of the fruit pulp. Much like humans, there is vertical transmission of the microbiome in plants, further validated by this study’s finding. In addition to these findings, of particular interest was the fact that one of the core taxa found in the organic apples was Lactobacillus, while the potentially pathogenic flora Escherichia-Shigella was only found in the conventional apples.
Polyphenols. Polyphenols are compounds including flavonoids and phenolic acids that are found at high levels in plants, and help protect them from damage by ultraviolet radiation and pathogens. Intuitively, one might expect organic and biodynamic farming techniques to facilitate the plant’s production of these protective compounds as the plant is not protected by application of potent pesticide agents.
Organic farming techniques were shown in one multi-year study to contribute to apples having a higher level of polyphenols and antioxidant activity, although climate and related growing conditions had a greater impact. A follow-up study did not show differences in bioavailability of apple polyphenols in humans with consumption of conventionally versus organically grown apples on either a short- or long-term basis. An additional investigation into the impact of consumption of apples produced by these two farming methods found that both deliver similar antioxidant protection.
Organically or biodynamically farmed fruit had a higher level of polyphenols in seven of 14 studies, and only three of the 14 showed higher levels with conventional farming techniques.
A 2017 review of studies assessing the impact of agricultural management techniques on plant polyphenol content reinforced these findings, also offering additional insights. A review of several studies found that the application of nitrogen-containing fertilizers and high soil nitrogen availability led to a lower level of polyphenols being produced by the plant. In their assessment of numerous studies related to farming technique, it was found that the organically or biodynamically farmed fruit had a higher level of polyphenols in seven of 14 studies, and only three of the 14 showed higher levels with conventional farming techniques. A similar assessment of vegetables and grains by this team found that nine of 25 crops had a higher level of polyphenols in the organically or biodynamically farmed option, while the majority of the studies showed no difference between them.
Salmon: wild-caught vs. farmed
Salmon is well known as a dietary source of the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Another nutrient that is found at high levels in salmon is astaxanthin, a carotenoid that salmon bioaccumulate from the food that they eat. Astaxanthin is responsible for the pink to reddish hue not only of salmon, but also of krill, shrimp, and even flamingos.
Surprisingly, studies have not shown that wild-caught salmon is necessarily a better source of EPA and DHA, with some investigations even showing that farm-raised salmon contain higher levels of these fatty acids. However, the omega-3 content of salmon is highly dependent on the feed that they eat. Much of farm-raised salmon is fed a “finishing diet” that is high in these essential fatty acids for the last weeks before slaughter to ensure they are present in the final product that we consume, but this is not guaranteed. Interestingly, genetic variations also play a role in the amount of EPA and DHA found in salmon – which in the future we may anticipate will lead to the farm-raising of salmon known to have particular genetics to further enhance their essential fatty acid content.
Studies have not shown that wild-caught salmon is necessarily a better source of EPA and DHA, however, it contains higher levels of natural astaxanthin, a potent antioxidant.
Astaxanthin, on the other hand, may prove to be a distinguishing feature setting wild-caught salmon apart from that which has been farmed. Wild salmon primarily feed on krill and copepods, which take in astaxanthin by consuming the microalgae Haematococcus pluvialis, the main source of natural astaxanthin. Much of the astaxanthin used in the fish-farming industry is produced by synthetic processes or yeast, which affects the stereoisomers of astaxanthin found in these products – so much that it has been considered for use as a marker for certification of salmon sourcing.
Natural astaxanthin, produced by H. pluvialis, has been shown to be 20 times more potent than synthetic astaxanthin in eliminating free radicals. Wild salmon primarily contain the 3S,3′S astaxanthin isomer (the main form produced by H. pluvialis), modest amounts of the 3R,3′R isomer (the main form produced by yeast), and very little of the 3R,3′S isomer (the main form found in synthetic astaxanthin).,, Not surprisingly, wild-caught sockeye salmon is the best dietary source of natural astaxanthin, providing approximately 1 mg/ounce of flesh.
Nitrites and nitrates
Nitrite and nitrate are important compounds found in food, used by the body to produce nitric oxide (NO). Although there are two pathways by which the human body produces NO, the reduction of nitrate to nitrite by nitrate-reducing oral bacteria, and the subsequent reduction of nitrite to NO is a very important pathway. Although we often think of nitrites and nitrates as substances found in processed meats that we should try to avoid, they actually are found at a far higher level in green leafy vegetables, and are particularly important for supporting healthy vasodilation in the human body.
Processed meats. Misconceptions surrounding nitrites and nitrates have led to a considerable amount of deceptive marketing by companies with their advertising for products like nitrite-free bacon or organically cured sausages. Despite using alternate processes to produce nitrites, these products still contain them. The nitrites found in processed meats act as an antioxidant and antimicrobial and are necessary to prevent botulism, bacterial overgrowth, and lipid oxidation. They are why these products have a shelf-life much longer than non-processed meat options. In products advertised as “nitrite-free,” rather than adding sodium nitrite, celery salt (which contains nitrate) and a starter culture of bacteria that converts nitrates to nitrites is added. The challenge with this approach is that the level of protective nitrites is highly variable—the nitrate content of celery salt is variable; the bacteria activity is variable—giving the final product an unknown safety profile.
Despite using alternate processes to produce nitrites, “nitrite-free” or naturally-cured meat products still contain them.
In cured and processed meats, the potential problem is actually nitrosamine, not nitrites and nitrates. However, in conventional meat-curing processes, when manufacturers add sodium nitrite to these products, they also add ascorbic acid or a structural analog known as erythorbate, compounds that prevent nitrosamine formation. The addition of ascorbate and erythrobate to naturally-cured products is not allowed – which may further contribute to a questionable safety profile of these products.,
Vegetables. Approximately 80 – 85% of nitrates consumed in the diet are from vegetable consumption. Vegetables that are high in nitrates include beetroot, leeks, lettuce, spinach, arugula, and celery. Fortunately, plants sources of nitrates and nitrites also contain high levels of antioxidants that naturally inhibit nitrosamine formation like ascorbate and erythorbate do.
The level of nitrites and nitrates found in plants dramatically varies, potentially by a factor of 10 or more, and is affected by factors including genotype, soil conditions, growth conditions, and storage and transport conditions. A recent survey of several nitrate-containing vegetables purchased in multiple major cities, located in different geographical regions of the U.S., including both conventional and organically-labeled products, found that of the plants surveyed, the conventionally grown product often had a higher level of nitrates than the organically-grown counterpart. For comparison, in the conventionally grown products (averaged for all cities) the level of nitrates in broccoli, cabbage, celery, lettuce, and spinach were 394, 418, 1496, 851, and 2797 mg/kg of fresh weight, versus 204, 552, 912, 844, and 1318 mg/kg in their organically-labeled counterparts. The differences between the organically grown and conventional products may be partly attributable to the use of nitrogen-containing fertilizers for the production of the conventional produce, in addition to the other many variables previously mentioned.
Clearly, the food sourcing debates have many considerations with regards to the health benefits we derive from the foods we eat (in addition to many other factors not mentioned in this article). For many, this may drive purchases back to local sourcing, where the many aspects of production can be fully known and even viewed by visiting local farms or by cultivating one’s own produce and animal products.
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Dr. Carrie Decker
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