Jan 30 2014

Nutritional Content of Produce

This is a frequent question I receive that I have yet to address – is the nutritional content of our produce diminishing over time? The claim that our produce is less nutritious is often used as a reason to justify routine vitamin supplementation, and various other dubious health claims, or recommendations to eat locally or eat organic.

The answer is a clear, “it depends” followed by, “it’s complicated.”

There are three levels to this question I want to address: is the nutritional content of produce decreasing over time; if so, what’s the cause; and what should we do about it?

The most often study I see cited is this 2004 study by Davis et al – they examined the nutrient content of 43 crops from 1950 to 1999. They found:

As a group, the 43 foods show apparent, statistically reliable declines (R < 1) for 6 nutrients (protein, Ca, P, Fe, riboflavin and ascorbic acid), but no statistically reliable changes for 7 other nutrients. Declines in the medians range from 6% for protein to 38% for riboflavin. When evaluated for individual foods and nutrients, R-values are usually not distinguishable from 1 with current data. Depending on whether we use low or high estimates of the 1950 SEs, respectively 33% or 20% of the apparent R-values differ reliably from 1. Significantly, about 28% of these R-values exceed 1.

While significant, these results are not as bad as presented by those citing the study. Of the 13 nutrients followed, 7 showed no change, and 6 showed a decline, ranging from 6-38%. It’s interesting that when looking at individual nutrients in individual crops, no significant difference was found. The declines only emerge when grouping the data.

So, while it seems there is a real decline in some nutrients (slightly less than half those tested), the overall impact on nutrition seems minor. You can still get plenty of vitamins and minerals from eating your vegetables.

Variables Affecting Nutritional Content

For the declines that were detected, what is the cause? This is where things get very complicated. Those citing a single dominant cause, for example soil depletion, never cite any specific evidence to back up that interpretation. The authors of the study suggest that the primary reason likely has to do with the varieties of crops that are being grown.

The best discussion of the topic I found was this paper from Harvard:

By the time fruits and vegetables reach your kitchen counter – whether from a stall at a local farmers market, or the supermarket produce department – several factors determine their nutritional quality: the specific variety chosen, the growing methods used, ripeness when harvested, post harvest handling, storage, extent and type of processing, and distance transported. The vitamin and mineral content of fruits and vegetables depends on decisions and practices all along the food system – from seed to table – whether or not that system is local or global.

Blaming any single variable is fallacious. Just eating locally may not make a significant difference, for example.

There does seem to be a consensus that Davis’s explanation is likely a significant contributor to changes in nutritional quality. Farmers have favored over the years varieties that are most profitable and convenient – that grow quickly and produce large and pretty produce. However, these traits may come at the expense of things like flavor and nutritional quality.

Another factor for which there seems to be agreement is that for some produce picking them early so that they will transport better, and allowing them to ripen after picking, also can compromise nutritional content.

Therefore a local farmer’s market may contain heirloom varieties with inherently better flavor and nutrition, picked that day and fully ripened on the plant.

A factor which does not seem to matter is whether or not the produce is grown “organically.” I use the scare quotes because I am against the use of the false dichotomy that the “organic” label encourages – it is a suite of practices that should be looked at individually. In any case, decades of studies of organically vs conventionally grown produce has not demonstrated any significant difference in terms of health or nutrition.

Another variable that people often believe is important but isn’t is canned vs frozen vs fresh. A comprehensive study found essentially no difference in nutritional quality among these various methods. Canned goods, which often have a bad rap, were just as nutritious as fresh or frozen.

What about raw vs cooked? Heavy cooking can deplete some vitamins and minerals, but raw is not always best. Some vegetables are actually more nutritious if steamed – the light cooking breaks down cell walls and allows for greater absorption of nutrients.

What to Do?

What, then, is the average consumer to do with all this information. I think the bottom line is this – the most nutritious produce is the produce you will actually eat. Even the worst fruits and vegetables still have a higher nutrient density than other types of food. If affordable and convenient produce allows you to eat more, that is more important than slight incremental gains in some nutrients (but not others) by obsessing over the details. If precut veggies afford you the time to prepare veggies for dinner after a long day at work, then don’t worry about the slight decrease in nutrients that precutting causes.

But, if you want to maximize the nutrient density of your produce, there are some simple things you can do. First and foremost, eat a variety. The main difference to pay attention to is color, as produce color often reflects their nutrients. When picking individual fruits and vegetables, deeper colors may indicate denser nutrients.

If you have the time and resources, buying produce that was picked recently, allowed to ripen on the plant, and did not have to travel far will give a boost to the nutrient density. Such produce is also likely to be more flavorful, and if you enjoy them more you are likely to eat more (or get your kids to eat more).

If you have the time and inclination, growing some of your own produce can give you access to heirloom varieties that you can pick when fully ripe, right before you consume them.

Fresh, canned, or frozen are all fine – whatever is most convenient and cost effective for you.

I don’t think the organic label is worth paying premium prices for. This is a marketing scam or ideology, in my opinion. I do think we should incorporate best practices in farming, and not worry about arbitrary and highly politicized labels.

The Farming Industry

I do think, however, that the farming industry has been moving toward monoculture (reliance on single varieties at the expense of local varieties) and cultivars that are optimized for profit rather than flavor or nutrition.

Monoculture is a problem on multiple levels, but perhaps worst is that it leaves our agriculture vulnerable to blight and pests. If you plant millions of the same exact variety, something will evolve to eat it. The most sustainable solution is to utilize a large number of varieties. Even if farmers plant mostly the most profitable types of produce, they should mix in other varieties.

Another solution is for farmers to cultivate (by whatever method – I won’t go down that rabbit hole here) varieties that reintroduce improved traits for flavor and nutrition while maintaining the advantages of mass production. That would be a win-win. Obviously if this were easy, they would already be in wide use. It seems like this is worth some investment in resources.

Conclusion

I want to emphasize the bottom line – fruits and vegetables are the most nutrient dense foods we eat and should be a major part of everyone’s diet. Differences in the various types and methods of producing and processing fruits and vegetables have an overall small impact on their nutrient density. It would be counterproductive to sacrifice the amount of fruits and vegetables consumed (because of expense or invonvenience) because of attempts to have small gains in their nutrient density.

 

Share

23 responses so far

23 Responses to “Nutritional Content of Produce”

  1. evhantheinfidelon 30 Jan 2014 at 11:33 am

    I love posts like this, Dr. Novella! Out of curiosity, does anyone know whether or not it’s better to get the cheaper, less nutrient-dense varieties of vegetables and eat more, or to pay more money and get the more nutrient-dense veggies? Obviously, expense isn’t always an indicator of quality, but the question has more to do with quantity vs. quality for the same cost.

  2. zorrobanditoon 30 Jan 2014 at 12:12 pm

    Thank you for your sensible evaluation of the label “organic.”

    There are several different ways that foods can gain that label (that is, there are different groups which hand out this designation) and some are more honest than others. In one case I learned from a client that the label “organic” was openly for sale: pay the certifying body a large fee, and suddenly your product is organic. I am hoping this practice is not widespread, but be aware that it exists.

    I would prefer not to eat foods soaked in pesticides, but beyond that things get pretty murky. As you point out, there are a lot of different aspects to “organic” farming, and almost no one is prepared to be entirely candid with the consumer.

    The one thing we can be sure of is that “organic” produce will be more expensive. Whether the designation is worth the higher price is a good deal more doubtful.

  3. mvucakon 30 Jan 2014 at 12:52 pm

    When looking at frozen vegetables, are there significant losses in nutrients that occur when the vegetables are initially frozen then allowed to thaw and then frozen again?

    If there are, can we be reasonably confident that frozen vegetables stay frozen until they reach the consumer?

  4. Factoidjunkieon 30 Jan 2014 at 1:04 pm

    Sensible post to a highly debated topic. Thanks very much.

  5. ccbowerson 30 Jan 2014 at 1:09 pm

    “I think the bottom line is this – the most nutritious produce is the produce you will actually eat.”

    This is the bottom line, and is the response I give when people try to point out differences between fruits and vegetables. Having 25% more of vitamin “X” is meaningless when 25% of 0 = 0.

    Also, when comparing 1950 produce to current produce, there is a huge advantage in that we have many more options available to us now. Even looking at apples alone, there are a couple dozen available in my area alone, and in 1950 there were probably only a handful.

  6. Steven Novellaon 30 Jan 2014 at 2:12 pm

    cc – I meant to make that point but forget. We now have year round access to a wide variety of fruits and vegetables – never before available in human history. This variety and access far outweighs the reported decrease in nutrition density. That’s the positive side of the trade-off of large scale farming and shipping.

  7. eeanon 30 Jan 2014 at 3:54 pm

    Really surprised that canned vegetables retain so much of their nutrition. I had heard that they lose a lot, and it makes sense given that frozen & fresh tastes so much better. But I guess that’s all just differences in texture?

    It might take a study analyzing health outcomes of canned vs frozen vs fresh to really convince me that canned veggies are as nutritious. My prior is “canned food is squishy and the wrong color”. Given our general ignorance of nutrition (it certainly seems like we should be able to produce helpful multivitamins, that we can’t is somewhat telling) just analyzing the chemical composition of food isn’t really enough. Especially since the study you cite was about best bang-for-buck, not directly addressing the question of nutrition of canning food.

    > never before available in human history

    Sitting here in the perpetual spring of the Bay Area that seems unlikely. And moreso the tropics might have fruit of one kind or another year round. Plenty of humans throughout history have been smart enough to not live in a Connecticut-like climate. :)

  8. Steven Novellaon 30 Jan 2014 at 4:21 pm

    eean – it is the number of choices that is unprecedented. You can get produce from around the world.

    The PlosOne study did not just look at nutrition for cost, but nutrition density – nutrients per 100 calories, and these were the same canned, fresh, or frozen. Essentially, keeping the vegetables sealed prevents significant loss of nutrients.

  9. TheFlyingPigon 30 Jan 2014 at 4:35 pm

    My problem with canned foods isn’t about loss of nutrients, it’s about the added extras. Heavy syrup in canned pineapples or salt in canned beans can make canned foods unhealthy, even if nutrients haven’t been compromised.

  10. dbeon 30 Jan 2014 at 5:03 pm

    I’d like to know how much this factors in, but do they compensate for the size of the vegetable? I can’t access the full article. Bear with me. I may just be crazy.

    Imagine that you’re comparing an “old” pear and a “new” pear for potassium. You can’t use “grams K per pear” unless all pears are the same size. So it would be “ppm” or “mg per 100g” or something similar.

    So you could end up with this situation: the old pear is small and has 10mg of K in the entire pear. The new pear has 10mg of K in the pear but this new awesome variety of pear is 20% larger. It’s got 20% more water, fiber, and sugar, but the same amount of K. So a comparison of mass-equivalent samples would show the new pear to have a loss of K. Even though, nothing has been “lost”. You just have more of everything else.

    I know the abstract says “adjusted for differences in moisture content” but that’s a little vague.

    Anyway thanks for the article and the analysis.

  11. rezistnzisfutlon 30 Jan 2014 at 5:21 pm

    The cultivar of a particular crop can make a big difference in taste and nutritional content, as well as growing conditions, soil conditions, fertilization methods, how much precipitation fell versus irrigation was done, what pests were prevalent that season and the methods used for controlling them, etc.. The variety and farming conditions are often ignored or overlooked when making a case usually for “organic” or “all natural”.

    A beef tomato is going to taste differently and have a different nutritional profile than an early girl tomato. Early girl tomatoes grown in two different fields with different conditions will have different nutritional profiles. Often, the taste and perceived freshness of produce grown in one’s garden compared to what they get from the supermarket can typically be explained by the differing varieties, so when ignoring this, people often believe that what they’re growing is superior because they are growing it in their back yard, so modern agriculture must be flawed and detrimental.

  12. tmac57on 30 Jan 2014 at 7:11 pm

    TheFlyingPig- You should be able to find canned/jarred fruit that has ‘no sugar added’ if you look closely.Also most canned vegetables have a ‘no salt added’ choice,even in store brands.

    mvucak- I can’t comment on whether there is nutrient loss from frozen veggies that have thawed and refrozen,however,they are often inferior in taste,as they lose more moisture to frost,and get a kind of dehydrated appearance.
    One trick to avoid this,is to see if the veggies are frozen together in a chunk(bad),or move around freely in the bag as individual peas,beans, kernels etc. that is usually a good sign that they have not thawed and refroze.

  13. BillyJoe7on 30 Jan 2014 at 10:54 pm

    “an early girl tomato”

    Sounds delicious but…aren’t we a bit off topic!

  14. TheFlyingPigon 30 Jan 2014 at 11:21 pm

    tmac, thanks. The only one that has given me problems is finding low sodium beans. I love beans, but I’ve never found low sodium beans in grocery stores… and I’ve looked. Instead, I buy dry beans and cook them myself… this is time-consuming and they don’t last long – frustrating! I was about to respond to you with my failed efforts, but decided to ask google first. And I found that they do exist and get positive reviews in general! So, thanks for getting me to do what I should have done already.

  15. ConspicuousCarlon 31 Jan 2014 at 1:46 am

    I’m too lazy to actually do it, but it would be interesting to see a detailed breakdown of which foods were added at what time, along with their nutrition details.

    I would guess that maybe the newer imports were selectively appealing to our cruder indulgences, which tend toward high calorie and bland in other food groups (eg, white bread or frying oil). Maybe we are choosing apple and pear varieties which are sweeter and less zingy.

    I looked at the abstract, and I can’t figure out if the nutrient level was relative to weight of the food or calories. It said they accounted for water, but the amount of fiber can be different too.

  16. Bruceon 31 Jan 2014 at 4:42 am

    Thanks for this post Steve. It goes back to that mantra I have had in my head for years now and only recently realised was actually quite skeptical:

    “Everything in moderation.”

    A little bit of everything is much better for you than a lot of something, no matter how healthy it is.

  17. BillyJoe7on 31 Jan 2014 at 7:10 am

    “Everything in moderation.”

    Provided you don’t have obesity, diabetes, high cholesterol, high blood pressure, an inborn error of metabolism, a malabsorptive syndrome….
    In fact, I don’t know the statistics, but those who can have everything in moderation might actually be in the minority.

  18. QuiteDragonon 31 Jan 2014 at 9:32 am

    @BillyJoe7:

    I think it is reasonable to assume that what is meant is, “All things which are done, should be done in moderation”.

  19. tmac57on 31 Jan 2014 at 10:53 am

    I’d still like to see some studies done on juicing and nutrition.
    It has apparently again become popular (faddish) among the younger set. What little I’ve had of it was awful tasting (except fruit smoothies) and seems very troublesome (cleaning the apparatus) and costly to do. Plus,personally, I would much prefer steaming or sauteing my kale or greens,or eat them in a salad,rather than reducing them to yucky green glop.It also seems like most of the fiber is being removed in the process. The big attraction to it is apparently for perceived health reasons,but I suspect that it is not what it’s cracked up to be.Probably better than no veggies,but no better,or worse than traditional food preparation.

  20. zorrobanditoon 31 Jan 2014 at 1:40 pm

    @ BillyJoe7:

    “[Moderation is ok] provided you don’t have obesity, diabetes, high cholesterol, high blood pressure, an inborn error of metabolism, a malabsorptive syndrome….”

    Let’s pull this apart. People who are obese should indeed heed the counsel to moderation; if they had done so in the past they would not be obese. Never too late to start, though. If so many of us were not obese the incidence of diabetes would be much lower, as would high cholesterol and high blood pressure.

    Anyway, we’re talking about fruits and vegetables here, not chocolate cake. (Which anyway is ok IN MODERATION.)

    I don’t really think that the proportion of the population who can and should eat normally is a minority. (Perhaps the proportion who do eat normally, but that is another discussion.)

  21. Bruceon 31 Jan 2014 at 2:37 pm

    I guess, all I am trying to say is that extremes are bad, in diets, in religion, even in skepticism and logic.

    Obviously, if you have a condition, you need to take that into account, but the average person does not in general need to go to extremes to stay healthy.

  22. zorrobanditoon 31 Jan 2014 at 2:50 pm

    @Bruce, very sensible.

    All the data we have suggests that we are omnivores, that is, animals who can and do eat about everything we can get that doesn’t eat us first. Our long survival and great success as a species suggest that we have made this strategy work for us over the long term.

    In our current wealth of choices, a group of opinions has arisen to the effect that we cannot eat this, we cannot eat that, we must conform to this or that strict regimen to maintain good health, when the data suggests that what we really need to do is to eat a variety of good foods, a balance, always in moderation, and that we need not trouble ourselves too much with being picky. Some individuals genuinely must not eat certain things. The majority of us need not concern ourselves with this beyond realizing that we do need a balance of nutrients, a balance which is not actually that hard to achieve.

  23. BBBlueon 01 Feb 2014 at 2:34 pm

    Local is not better, but for some produce items, it can mean tastier at certain times of the year.

    “Organic” is more of a philosophy than a measure of wholesomeness, so eat organic if you want, but don’t let pseudoscience keep you from eating conventional too.

    The only minor quibble I have with Dr. Novella’s comments is about the risks of monoculture, which I think are slightly overstated. Once upon a time, when late blight of potato triggered the Great Famine and mass emigration from Ireland, coffee rust in Sri Lanka made tea-drinkers out of the British, and the boll weevil decimated cotton crops in the American south; agriculture was ill-equipped to handle the risks of monoculture. From the perspective of evolutionary ecology, polyculture makes sense, but not often from an economic perspective in developed nations where modern cultural practices, plant breeding, integrated pest management practices, and programs to detect and manage or eradicate invasive species have minimized those risks. (Many of the advances in our understanding of human disease during the second half of the 19th and early 20th century had parallels in agriculture.) Furthermore, farmers often don’t put all their eggs in one basket and do grow multiple crops or multiple varieties of the same crop to spread risk; they just don’t do it within the framework of polyculture.

    Subsistence farming in developing nations is a different matter. What if a corrupt, authoritarian government compels farmers to grow a particular cash crop and those farmers are dependent on the government to import and provide the staples they need to survive? Technology-poor farmers under those circumstances are much more susceptible to the vagaries of nature and their government, and they often benefit from polyculture, or at least they would, if they were not forced to do otherwise. So yes, it depends.

    As for developing varieties to reintroduce (or introduce) improved traits for flavor and nutrition while maintaining advantages of mass production; that is the Holy Grail and it’s an important subject to every farmer and plant breeder I know. I could write volumes on the challenges and hypocrisy associated with that topic. Suffice it to say that the best thing a consumer can do is vote for what they want by buying lots of it and complain directly to store managers or the producers themselves when they are disappointed by what is offered.

    The unfortunate thing about all of this is that concerns over organic versus conventional, local versus not, high-profile cases of foodborne illnesses, etc., all seem to have the effect of reducing overall consumption of fresh fruits and vegetables, and therefore, the net effect is a less-healthy average diet.

    Dr. Novella is spot-on with his conclusion, which I will paraphrase: Don’t sweat the details, just eat lots of fresh fruits and vegetables.

Trackback URI | Comments RSS

Leave a Reply

You must be logged in to post a comment.