Nutrient Levels in Retail Grocery Stores, or Why You Should Be Buying Your Groceries from Walmart

A counterintuitive conclusion

Cross-posted from Twitter.

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I've done some digging into nutrient levels in retail grocery stores (specifically where I should shop if I want nutritious food) and learned some insane things.

Source: Challenges in the Diagnosis of Magnesium Status

1) It's a well-documented phenomenon that nutrient levels in produce have been declining for decades. The average mineral content of calcium, magnesium, and iron in cabbage, lettuce, tomatoes, and spinach has dropped 80-90% between 1914 and 2018.

There are several reasons for this, but most of them are due to modern agricultural practices. These reasons include: selective breeding, soil depletion, synthetic fertilizers that provide basic nutrients necessary for plant growth but not others that would make them nutrient-dense, higher CO2 levels in atmosphere diluting nutrient content in plants, over-irrigation washing away nutrients from soil, and long storage times.

2) If all you care about is nutrient content, SPEED is the only factor that matters. That means time between being picked and ending up in your mouth. Price doesn't matter, organic doesn't matter, marketing hoo-ha about how fancy the produce is doesn't matter. Literally just speed. Fresh spinach loses almost ALL of its vitamin C within 7 days of harvest when stored at 68°F (20°C). When stored at 39°F (4°C) which is about fridge temp, it loses 75%. The apples you buy at the grocery store can be up to a *year* old since they've been harvested, especially if you are not buying them in season.

Taste, texture, and smell are not good indicators of nutrient content, because you can't tell how long it has been since it's been harvested. Modern shipping and storage methods can be deceptive, combined with practices like spraying strawberry fragrance on otherwise bland strawberries so you think you're buying the good stuff (yes some places actually do this).

In general, it can help to eat in season, but due to the globalized supply chain...it's always in season *somewhere*. But how long did it take to get to you? You don't know. Even if it's in season where you are, how do you know if that's not from *last* season? Again, you have no idea.

3) Think for a moment: what store do you think sells the most nutritious produce? Your local farmers’ market? Whole Foods? Trader Joe’s must be decent, right? Nope, it’s Walmart. Because of their scale and insanely efficient supply chain, they can get things from the farm (wherever it is in the world it's growing in season) to the store where you can buy it, really really fast. Oh, and for the lowest cost.

I wanted to believe every time I splurged on fancier produce, I was actually getting something better. But this is what the data comparing 18 major US retailers showed — Walmart consistently outperformed.

I learned this from talking to Brent Overcash, co-founder of a startup called TeakOrigin, which specialized in testing nutrient content in groceries from retail grocery stores. For years, every week, his team would walk into grocery stores, buy thousands of produce items the way normal consumers would, and bring them back to the lab to assess nutrient content. They’d go to Whole Foods, Trader Joe’s, Costco, Wegmans, Sprouts, Waitrose, farmers’ markets, and many more retailers. The “winner” varied depending on the specific type of produce/brands/exactly what week it was, but Walmart tended to come out on top. The more important point is that price and taste and organic certifications had no impact on the actual nutrient density.

They raised ~$5M and did a decade of research with labs full of analytical chemists where they used a combination of molecular spectrometry, HPLC, GC/MS, TGA, and wet chemistry methods. With 800+ million data points, the USDA and FDA at one point told them they had the world’s largest dataset of dynamic nutrition data. They’re no longer around, but had branches in California, Boston, and the UK just a couple years ago.

It went out of business because no major grocery store wanted to partner with them, because the transparency would hold these retailers accountable for *so many things* the consumers aren't even currently aware of. Things like how Whole Foods centers their entire branding around fresher, higher quality produce that's better for you, but when he actually tested some expensive apples they were selling from a local orchard advertised with handwritten chalkboard signs, it had so little nutrient content it was barely detectable on their lab-grade machines. He called the orchard because he was curious, under the guise that he was interested in picking some apples for the season. They said, "Oh sure, you can do that, but our first harvest isn't for another 6 weeks." That means it had been a year since the apples he bought were actually picked. This is actually industry standard, made possible by storing them at low temperatures and spraying a gas called 1-MCP which blocks ethylene (a gas naturally produced by the apples that makes them ripen) by binding to the same receptors.

I asked him: Are farmers’ markets any better, since we're getting the produce directly from local farmers? And he said basically there's huge variance. If you walk into a booth and that vendor is selling over 5 types of produce, there's no way they all ripened at the same time. They may not even all be grown by them. Once, he actually saw a vendor at Boston farmers’ market selling carrots from Target! He could tell from the packaging because he used to work for them. Turns out when a produce delivery is refused by the grocery store, the truck owner is then responsible for getting rid of that produce, and they usually drive to a “food hub” where bulk produce is bought and sold just to recoup some of the costs. That is one possible source of the mysterious farmers’ market carrots they were pawning off as homegrown.

Now, I'm not saying you should *stop* shopping at non-Walmart places. There are a lot of factors other than nutrient density that influence a purchasing decision. The fancy, expensive produce might taste better, smell better, and be better for cooking. It may come from farms where there are better wages and working conditions. There might be fewer pesticides. But again, for nutrient content, speed is the only thing that matters.

I want to do something about this, but it’s an issue way bigger than I can tackle alone. From the way we do modern farming, to the complete lack of transparency on the retailer's end (and vested interests in keeping it that way), to the government's lack of interest in enforcing this transparency for the sake of consumers...the problem runs deep and I'm tired man. And so is Brent, who’s retired and doing woodworking in his studio these days, living the good life.

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Side note on frozen produce: The post above is about fresh produce only. A potentially appealing alternative may be buying frozen produce, which on average has equal or higher nutritional content than fresh. This is because frozen produce is picked at peak ripeness then frozen shortly after, locking in most of the nutrients at the expense of appearance/texture/flavor. If it’s been blanched (i.e. exposed briefly to hot water or steam to preserve quality of produce by killing enzymes that cause loss of flavor, color, and texture) before freezing, some nutrients like Vitamin C, B1, and folate are definitely lower because of heat sensitivity and being water soluble so they leach out into the blanching water. Pretty much all frozen veggies are blanched first, and stuff like berries/fruit aren’t. The rest of the nutrients are quite stable, and knowing which ones are lost means you can supplement in other ways. Fresh produce is picked before peak ripeness to accommodate for ripening during storage and transport, and the nutrients degrade as it sits on shelves and in refrigerators before it is eventually prepared.

It’s also great that it’s more convenient, and I think frozen produce unfairly gets a bad rap. The only thing I would change is the plastic packaging because I don’t like microplastics in my food. I would avoid heating or microwaving produce in its original plastic packaging.

One thing to be aware of is frozen berries (or produce that isn’t blanched before freezing) that have been imported. In 2022-2023, New Zealand had a hepatitis A outbreak from frozen berries imported from Serbia so they advised people to boil/cook their berries before refreezing or eating. Some countries have more lax sanitation standards and contamination can happen in processing facilities. Furthermore, freezing doesn’t kill viruses! For stuff like berries which aren’t cooked before they’re eaten, you can more easily get sick. It’s less of a concern for berries sourced from within the US, Canada, Australia, most of the EU – but Australia has had 2 of the same hep A outbreaks so I’d just keep it in mind.