Fruits and Vegetables Reaching an Alarming State of Nutrient Depletion
What if our food has been getting less and less nutritious? What if modern intensive farming methods — many of which solved malnutrition problems when they were first introduced — have affected the mineral and vitamin content of what we eat? Could having a constant supply of varied produce and introducing genetically modified foods be compromising nature’s goodness?
Whether it be vegan, low carb, paleo, or any other diet, the quest for the healthiest method of eating shows no sign of abating, yet all have considerable controversy. We know more than ever about what food does to the body and the importance of antioxidants, healthy fats and a low glycaemic index.
Things have changed so much since the wisdom of our ancestors was lost or ignored. Wild dandelions, once a springtime treat for Native Americans, have seven times more phytonutrients than spinach, which we consider a “superfood.” A purple potato native to Peru has 28 times more cancer-fighting anthocyanins than common russet potatoes. One species of apple has a staggering 100 times more phytonutrients than the Golden Delicious displayed in our supermarkets.
Were the people who foraged for these wild foods healthier than we are today? They did not live nearly as long as we do, but growing evidence suggests that they were much less likely to die from degenerative diseases, even the minority who lived 70 years and more. The primary cause of death for most adults, according to anthropologists, was injury and infections.
Some of the most eye-catching work in this area has come from Donald Davis, a now-retired biochemist at the University of Texas. In 2011, he compared the nutrients in US crops from 1950 and 2009, and found notable declines in five nutrients in various fruits, including tomatoes, eggplants and squash. For example, there was a 43 per cent drop in iron and a 12 per cent decline in calcium. This was in line with his 1999 study — mainly of vegetables — which found a 15 per cent drop in vitamin C and a 38 per cent fall in vitamin B2.
Fruit and vegetables grown have shown similar depletions. A 1997 comparison of data from the 1930s and 1980s found that calcium in fresh vegetables appeared to drop by 19 per cent, and iron by 22 per cent. A reanalysis of the data in 2005 concluded that 1980s vegetables had less copper, magnesium and sodium, and fruit less copper, iron and potassium.
Genetically modified organisms (GMOs) in food have also alarmed researchers on distinct differences between organic and GMO produce. Higher antioxidant levels, lower pesticide loads, better farming practices all lead to a more nutritious end product when choosing organic over GMO foods.
For example, tomatoes grown by organic methods contain more phenolic compounds than those grown using commercial standards. That study — published in the Journal of Agricultural and Food Chemistry — analysed the phenolic profiles of Daniela tomatoes grown either using ‘conventional’ or organic methods, finding that those grown under organic conditions contained significantly higher levels of phenolic compounds than those grown conventionally.
Other findings published in the Journal of Agricultural and Food Chemistry showed that organically produced apples have a 15 percent higher antioxidant capacity than conventionally produced apples.
Davis and others blame agricultural practices that emphasise quantity over quality. High-yielding crops produce more food, more rapidly, but they can’t make or absorb nutrients at the same pace, so the nutrition is diluted. “It’s like taking a glass of orange juice and adding an equal amount of water to it. If you do that, the concentration of nutrients that was in the original juice is dropped by half,” says Davis.
But the idea that modern agriculture produces crops that are less nourishing remains controversial, and “then and now” nutritional comparisons have been much criticised. The differences found may be down to older, less accurate methods of assessing nutrition, and nutrient levels can vary widely according to the variety of plant, the year of harvest and the time of harvest.
Contrary to frequent claims that there is no evidence of dangers to health from GM foods and crops, peer-reviewed studies have found harmful effects on the health of laboratory and livestock animals fed GMOs. Effects include toxic and allergenic effects and altered nutritional value.
Other studies have sought to get round this by comparing old and new varieties of a crop grown side by side. In 2011, researchers at the US Department of Agriculture measured the concentrations of 11 minerals in 14 commercial varieties, or cultivars, of broccoli launched between 1950 and 2004.
They found no clear relationship between mineral levels and the year that a particular cultivar was released, but there was evidence of a dilution effect:bigger broccoli heads favoured today had lower levels of some minerals relative to a 1950 variety called Waltham 29. But, as the study also noted, Waltham 29 is less tough than modern cultivars and so would be unlikely to succeed if grown in the same way.
And there lies the rub. Even if the arrival of intensive agriculture has meant that our vegetables contain slightly less nutrients than those our grandparents ate, it has also led to a huge increase in food supply, which has undoubtedly had a positive effect on our diet and health.
“Some evidence suggests that some nutrients have fallen, particularly trace elements such as copper in vegetables,” says Paul Finglas, who compiles nutritional data on UK food at the Institute of Food Research in Norwich. “Foods are now bred for yield, and not necessarily nutritional composition. But I don’t think that is a problem, because we eat a wider range of foods today than we did 10 years ago, let alone 40 years ago”.
Other crops are also getting subtly less nutritious. The introduction of semi-dwarf, higher-yielding varieties of wheat in the green revolution of the 1960s means that modern crops contain lower levels of iron and zinc than old-fashioned varieties.
Each fruit and vegetable in our stores has a unique history of nutrient loss, and there are two common themes. Throughout the ages, our farming ancestors have chosen the least bitter plants to grow in their gardens. It is now known that many of the most beneficial phytonutrients have a bitter, sour or astringent taste. Second, early farmers favored plants that were relatively low in fiber and high in sugar, starch and oil. These energy-dense plants were pleasurable to eat and provided the calories needed to fuel a strenuous lifestyle. The more palatable our fruits and vegetables became, however, the less advantageous they were for our health.
And as farmers strain to feed ever more mouths in the face of environmental change, the problem may become worse. Last year, researchers at Harvard University warned that crops grown in the future will have significantly less zinc and iron, due to rising levels of carbon dioxide from fossil fuel use. The team grew 41 different types of grains and legumes, including wheat, rice, maize, soybeans and field peas, under CO2 levels crops are likely to experience 40 to 60 years from now. They found that under these conditions, wheat had 9 per cent less zinc, 5 per cent less iron and 6 per cent less protein than a crop grown at today’s CO2 levels. Zinc and iron — but not protein — were also lower in legumes grown under elevated CO2.
A 2003 study evaluated the nutritional content of broccoli kept in conditions that simulated commercial transport and distribution: film-wrapped and stored for seven days at 1 Â°C, followed by three days at 15 Â°C to replicate a retail environment. By the end, the broccoli had lost between 71 and 80 per cent of its glucosinolates — sulphur-containing compounds shown to have cancer-fighting properties — and around 60 per cent of its flavonoid antioxidants.
Many kinds of mass-produced fruit and veg — most famously tomatoes — are picked unripe so that they bruise less easily during transit. They are then sprayed with ethylene to ripen them. Some studies suggest that tomatoes harvested early have lower antioxidant activity and less flavour. “If a fruit is left on a plant until the end of its life cycle, it’s able to recycle all the energy from the plant,” says Wagstaff. “If you pick it early you truncate that process and get less sugars into the fruit, which are needed to bind the nutrients.”
Supermarket tomatoes are often labelled as “vine-ripened”, but that doesn’t always mean what you hope, she says. “It may be ripened on the vine but the vine may not have been attached to the plant.” However, Wagstaff stresses that the downsides of early picking are small and an unavoidable consequence of consumer demand. “If you pick a tomato that you have grown at home, it tastes fabulous because it’s absolutely ready to eat,” she says. “But there’s no way you could do that at a commercial level because of the bruising that would occur if ripe fruits were transported through a typical supply chain. There has to be a compromise somewhere.”
Another complication is that each method of shipping and storing foods has different effects on the compounds they contain. Vitamin C, for example, breaks down in the dark, whereas glucosinolates — found in vegetables like broccoli and cabbage — deplete in the light. “That’s one of the problems with horticulture,” says Wagstaff. “By its very nature you have an enormous diversity of genera and species. In an ideal world, each one would have a tailored supply chain.”
Peas can lose half of their vitamin C in the first 48 hours after harvesting, but if frozen within 2 hours of picking they retain it. “Frozen peas are much more nutritious than peas you buy ready to shell,” says Catherine Collins, principal dietician at St George’s Hospital in London. What’s more, frozen foods often have fewer additives. “Freezing is a preservative,” she says.
“Any loss of nutrients must be weighed against the fact that these products may encourage people to eat better overall.”
Similarly, processing has become a maligned word in the context of food, but there are some cases where it enhances a food’s health benefits. In fact, you arguably get more benefits from processed tomatoes, such as in purees, sauces or ready chopped in cans, than fresh.
Although salad leaves that have been picked and stored for several days before being eaten are a bit less nutritious than a freshly harvested lettuce, chilling and using packaging to reduce oxygen exposure may slow the nutrient loss. And any loss of nutrients must be weighed against the fact that these products may encourage people to eat better overall.
“There is a chance that ready prepared vegetables may have a lower content of some vitamins,” says Judy Buttriss, director general of the British Nutrition Foundation in London. “But if their availability means that such vegetables are consumed in greater quantities, then the net effect is beneficial.”
The bottom line is that although aspects of today’s food production, processing and storage might make what we eat a bit less nutritious, they are also making foods more available — and this is far more important. The majority of us consume far less fruit and vegetables than we ought to. We eat too much fat, sugar and salt and not enough oily fish.
“The most important thing you can do is eat more fruits, vegetables and wholegrains, and cut down on highly refined, human-made foods, vegetable oils and added sugars,” says Davis. “If you’re worrying about nutrient losses from cooking or whether your food is straight from the farm — those differences are minor compared to the differences you’d get from eating unprocessed foods.”
What’s really on your plate
Beef from cattle reared outdoors on grass is less fatty and contains more omega-3 fatty acids than cattle reared indoors and fed mainly grain. However, consumers preferred the taste of latter, according to a 2014 study.
Today’s pasta might be less nutritious thanks to modern, fast-growing wheat varieties introduced in the 1960s. Levels of zinc, iron and magnesium remained constant in wheat grain from 1865 to the mid-1960s, then decreased significantly as yields shot up.
Carrots from the 1940s contained less than half the vitamin A levels of carrots grown in the US 50 years later. The reason? A preference for more orangey carrots. The colour comes mainly from the pigment beta-carotene, which the body can use to make vitamin A.
Milk from cows reared the old-fashioned way — mainly feeding on grass outdoors — has a better nutritional profile of proteins, fatty acids and antioxidants than milk from cows reared indoors and fed intensively.
Humans have been making bread for 10,000 years, but the way we do it has changed dramatically in the last half-century. In 1961, a new method of mass-producing bread was devised at the Chorleywood laboratories, just north of London. It used extra yeasts, additives called processing aids and machinery to slash fermentation times, so a loaf could be made in just a few hours. Around 80 percent of bread consumed is now made this way.
But there are concerns that such methods have altered the digestibility of bread, and this may explain why many people with irritable bowel syndrome and gluten sensitivity name bread as a trigger. For a significant subset of those with IBS, the condition is thought to be linked to gut bacteria reacting to fermentable foods, causing gas and bloating.
Last year, Jeremy Sanderson at King’s College London and colleagues compared the effects of fast and slow-fermented breads on gut microbiota from donors with IBS and those free from it. They found that sourdough bread — which is left to rise for several hours using its natural yeasts — produced “significantly lower cumulative gas” in the IBS donors’ microbiota than fast-fermented bread. The theory is that if bread is left to ferment for longer, its carbohydrates will reach the gut in a predigested state and gut bacteria won’t react so much. “If you under-ferment bread and add a lot of yeast, it’s hardly surprising this will set up problems for people who have a problem with fermentation in their gut,” says Sanderson.
Slow-fermented breads may benefit other groups too: sourdough produces a lower glucose response in the body than other breads. What’s not yet clear is whether eating slow-fermented breads would lead to a general improvement in the gut flora of healthy people. “That’s difficult, but it’s a reasonable hypothesis,” says Sanderson. “After all, bread-making probably evolved to match what the gut could cope with.”
If modern, high-intensity farming is causing food to lose some of its goodness, could organic food offer an alternative? For many consumers the answer is yes.
About the Author
Marco Torres is a research specialist, writer and consumer advocate for healthy lifestyles. He holds degrees in Public Health and Environmental Science and is a professional speaker on topics such as disease prevention, environmental toxins and health policy.
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