The Chicago Tribune has reported in 2013 that
Most produce loses 30 percent of nutrients three days after harvest
I've seen an ad a few times recently that says "Produce loses most of its nutrients just a few days after harvest". I found this hard to believe and didn't know where to find an answer, except maybe here.
Does some produce loses ~1/3 of it nutrients shortly after harvest?
If so, which?
The Chicago Tribune article references the following infographic from The Land Connection: https://www.thelandconnection.org/wp-content/uploads/2019/03/local_food_seasonal_calendar-health-benefits1.jpg
I've cropped the relevant section, here:
The quoted "Most produce loses 30 percent of nutrients three days after harvest" seems to refer to the text towards the bottom of that section, "Day 3. A majority of fresh vegetables have lost at least 1/3 of their nutrients."
The infographic has two sources listed in this section; Rich Pirog et al "Food, Fuel and Freeways" and IFR Extra Ltd. The Food, Fuel and Freeways paper is solely about food miles, and makes no mention of nutritional value. I've found mention of the IFR research quoted in several newspaper articles; it ultimately seems to stem back to a study they were commissioned to undertake by Birds Eye, the frozen food producers, to see if an earlier study, "A comparison of the vitamin C content of fresh and frozen vegetables" by D.J.Favell, (published in 1998 but written in 1996) was still relevant.
Looking at that study we can finally answer the question; the study was from the mid 90s, the only nutrient tested for was vitamin C, and the only vegetables tested were peas, UK; green beans, Italy; spinach, Germany; broccoli, UK; and carrots, Austria. Looking at the graphs from the study:
We can see that the roughly 1/3 loss of vitamin C after three days seems accurate for the peas, beans and broccoli stored at ambient room temperature, though not for the chilled vegetables or the carrots. The vitamin C in the spinach did drop off a lot more sharply.
Yes, produce can lose a variety of nutrients just a few days after harvest, albeit the rate and extent of this nutrient degradation depend on the specific nutrient and storage conditions.
Undoubtedly heat is the prime cause of nutrient losses, particularly ascorbic acid, thiamine, folic acid and the amino acid lysine. Vitamin C and some B vitamins degrade rapidly, especially if storage conditions are not optimal.
"Losses in B vitamins during transportation and storage of fresh fruits and vegetables are documented, with thiamin and vitamin B-6 being quite sensitive to heat and light[...] with losses due to blanching and freezing in the range of 20–60%."
Hence, the best strategy to keep nutrients high is temperature control, as:
Foods containing low moisture levels, rarely suffer appreciable nutrient losses even in prolonged storage at or below -10°C. Some high-moisture foods may sustain nutrient losses even at -1O°C, or lower.
Polyphenolics, primarily found in the skins of fruits like peaches, pears, and apples, also decline with storage and processing. Fat-soluble nutrients such as vitamins A and E and the carotenoids (including lycopene) are sensitive to heat, light, oxygen,and pH.
On the other hand, some nutrients like fiber are not affected much:
Fiber is relatively insensitive to thermal processing or freezing, so the fiber content is very similar in fresh and processed fruits and vegetables
Minerals are likewise stable. This stability is expected since minerals are relatively inert and not sensitive to degradation by thermal processes.
Most information above comes from Maximizing the Nutritional Value of Fruits & Vegetables UC Davis article and Effects of Storage on Nutritive value of Food from University of Maryland.
From a more quantitative perspective we can run a query like this using Wolfram API:
api_wolframcloud_com__jit_plugin.getWolframCloudResults({
input: "ResourceFunction[\"NutritionReport\"][\"100g vegetable\", \"ASCIITable\", \"NutritionProperties\" -> {EntityProperty[\"Food\", \"FatLabel\"], EntityProperty[\"Food\", \"AbsoluteTotalProteinContent\"], EntityProperty[\"Food\", \"AbsoluteTotalCarbohydratesContent\"], EntityProperty[\"Food\", \"AbsoluteVitaminAContent\"], EntityProperty[\"Food\", \"AbsoluteVitaminB6Content\"], EntityProperty[\"Food\", \"AbsoluteVitaminB12Content\"], EntityProperty[\"Food\", \"AbsoluteVitaminCContent\"], EntityProperty[\"Food\", \"AbsoluteVitaminEContent\"], EntityProperty[\"Food\", \"AbsoluteVitaminKContent\"], EntityProperty[\"Food\", \"AbsoluteThiaminContent\"], EntityProperty[\"Food\", \"AbsoluteFolicAcidContent\"], EntityProperty[\"Food\", \"AbsoluteCalciumContent\"], EntityProperty[\"Food\", \"AbsoluteIronContent\"], EntityProperty[\"Food\", \"AbsoluteMagnesiumContent\"], EntityProperty[\"Food\", \"AbsolutePotassiumContent\"], EntityProperty[\"Food\", \"AbsoluteSodiumContent\"]}]"
})
That will get us average nutrient content for 100 grams of vegetables :
| Property | Value |
|---|---|
| Fat Label | 2 g |
| Absolute Protein Content | 8 g |
| Absolute Carbohydrate Content | 300 μg |
| Absolute Vitamin A (RAE) Content | 0.1 mg |
| Absolute Vitamin B6 Content | 0 μg |
| Absolute Vitamin B12 Content | 5 mg |
| Absolute Vitamin C Content | 0.6 mg |
| Absolute Vitamin E (alpha-tocopherol) Content | 20 μg |
| Absolute Vitamin K Content | 0.07 mg |
| Absolute Thiamin Content | 0 μg |
| Absolute Folic Acid Content | 20 mg |
| Absolute Calcium Content | 0.6 mg |
| Absolute Iron Content | 20 mg |
| Absolute Magnesium Content | 200 mg |
| Absolute Potassium Content | 70 mg |
If we further group it by category, we can can get the total nutrition for 100 grams of vegetables, with nutrients summed and grouped by category:
| Category | Total Value (mg) | Percentage of 100g | Percentage of Total Nutrients |
|---|---|---|---|
| Fat | 2000 mg | 2.00% | 17.81% |
| Protein | 8000 mg | 8.00% | 71.25% |
| Carbohydrate | 0.3 mg | 0.0003% | 0.003% |
| Vitamin | 25.79 mg | 0.0258% | 0.23% |
| Mineral | 360.6 mg | 0.3606% | 3.21% |
We can see that on average, vegetables are mostly protein, which is quite heat resistant. This calls into question the statement that "Most produce loses 30% of nutrients three days after harvest" because, on average, less than 30% of the nutrients that vegetables are made of the sort that are heavily affected by thermal processes.
The loss of vitamins in harvested vegetables over time is well documented.
Just a quick search in Google Scholar found:
This study from Korea measured vitamin C levels in lettuce and found it lost 39% of vitamin C after 3 days left at room temp and 59% after 10 days in the fridge.
Canadian study looked at Vitamin C levels in fruits and vegetables and found "In general, degradation of vitamin C is a function of time."
