There are many reasons why people grow their own food including freshness, taste and nutrition. It is commonly believed that home grown food is more nutritious than store-bought food. That organically grown food is more nutritious than conventionally grown and that heirloom varieties are more nutritious than modern day varieties.
Is any of this true? What can you do to improve the nutrition of your home grown food?
What is Nutrient Dense Food?
Nutrient dense food is food that contains a lot of nutrients. That seems simple enough but it’s not because we don’t know which nutrients are being discussed?
Traditionally, nutrition dealt with mineral nutrients like zinc and iron. We then started including vitamins, proteins, and carbohydrates and now people are talking about antioxidants. It’s common to measure Brix and equate that with nutrient density. I have discussed Brix in another post called Nutrient Density – Can it be Measured With a Brix Refractometer? In summary, Brix measures sugar and is not representative of any other nutrients.
Science has now identified many other nutrients that are important for good health, include omega fatty acids, carotenoids, folates and fiber. Using AI technology a company called Brightseed has documented 1.2 million different nutrients in food.
This all sounds great but there is a big problem. How do you quantify “nutrient density”? Do you only look at vitamins? Do you include all nutrients? Sugar is a nutrient – should it be included? We don’t even know what most nutrients do in our bodies. You can’t compare two tomatoes for one million compounds and determine which one is more dense, although many reports incorrectly do just that. The reality is that there is no accepted method for quantifying nutrient density. You can’t compare two fruits and say one is more dense than the other. You can however, select a fixed list of nutrients and compare the fruit based on that list, but this has its own issues as I have described in The Myth of Growing High Nutrient Density Food
Even with this limitation, lets see what effect different gardening practices have on nutrition.
Is Todays Produce Less Nutritious?
Lots of articles make this claim and there have been some studies that concluded this to be true, but on closer review that data is not complete enough to come to this conclusion. There is no good evidence that todays food is less nutritious than 50 or 100 years ago.
Is Soil Depleted of Nutrients
One of the common reasons given for todays “less nutritious food” claim is that our soil has been used too much and is low in nutrients. This sounds plausible since every year plants remove minerals from the soil and so there is less remaining. The problem is that except for some macronutrients, the level of minerals is not significantly lower in soil and the macronutrients are being replaced with fertilizer. The level of organic matter has gone down but that trend is being reversed with techniques such as low-till agriculture.
If soil was low on certain nutrients, you would expect yields to be dropping. The opposite is true, yields continue to increase. The idea that the mineral content of soil is dropping does not have much scientific support.
Is Nutrition Affected by Fertilizer Type or Quantity?
Many people claim that synthetic fertilizer grows food with “hollow calories” resulting in less nutritious food. Dr. Allen V. Barker has looked into this, testing tomatoes, cabbage and lettuce. He found that synthetic fertilizer and organic fertilizer produce food of equal nutritional quality, based on measuring mineral nutrients. Compost however, produced food with lower levels of minerals, probably because the nutrients are released into soil very slowly. I discuss this issue in the this video.
The type of fertilizer does not matter, but the quantity does. Higher amounts of fertilizer produce food with higher nutrient levels.
Are Heirlooms More Nutritious?
As a group, heirloom fruits and vegetables are not more nutritious (mineral nutrients) than modern cultivars. However, specific cultivars can be significantly more nutrition than other cultivars in the same group. So some heirlooms are more nutritious than other heirlooms and some modern cultivars are more nutritious than others.
The problem gardeners have is that such information is not readily available when buying seeds.
Is Organic Food More Nutritious?
Five different green vegetables were analyzed for β-carotene, vitamin C and riboflavin content. “The findings showed that not all of the organically grown vegetables were higher in vitamins than that conventionally grown.”
There have been numerous studies that show organic food is not better tasting, nor is it more nutritious than food grown by traditional means. Organic food is not more dense.
Is Ripe Food More Nutritious?
There is no doubt that nutrients change during the ripening process. A study looking at blackberries found that anthocyanin pigments increased during ripening and were highest in overripe fruit. However, total phenolics showed a slight decrease while antioxidants showed a slight increase. The degree of change varied by cultivar.
“The vitamin C content of a red (i.e., ripe) bell pepper is 50% higher than that of a green bell pepper, while the vitamin A content is almost 10 times higher.”
Green bananas contain a lot of resistant starch that we can’t digest, but it is beneficial to our gut bacteria. As the banana ripens this starch is converted to more digestible starch and sugar which is a beneficial nutrient for people who have limited access to food. Unripe bananas might actually be better for us.
The level of most minerals doesn’t change very much as fruit ripens. So the amount of potassium in a green banana is likely to be the same as in a ripe one. In either case it is not as high as people think.
As tomatoes ripen the concentration of reducing sugars, carotenes, ascorbate, rutin, and caffeic acid derivates increased, but the concentration of titratable acidity, chlorophylls, and chlorogenic acid content decreased. Sugars and acids that are important for taste did not change much with different ripening temperatures but metabolites with antioxidant properties were very sensitive to temperature. Increased light enhanced ascorbate, lycopene, carotene, rutin, and caffeic acid derivates and decreased oxidized ascorbate and chlorophylls. The ripening process is much more complex than reported in popular sources.
Ripe food may be more nutritious, but it really depends on the nutrient that you are trying to maximize. Remember that there are over a million nutrients and so far science has studied very few of them.
Taste and Color
Food quality is determined by a number of factors including taste, appearance, texture, and nutrition. Taste is not a good indicator of the nutritious value of a food. We tend to like sweeter food and reject bitter food, but the bitterness in food is due to nutrients that may be important for our health.
Darker vegetables may contain more antioxidants. “For example, black beans contain more antioxidants than white beans. That being said, white beans have higher levels of iron, potassium, and protein than black beans do.”
How Can Gardeners Increase Nutrient Density
The following are things you can do to improve nutrient density.
- Check research papers to see which cultivars are more nutritious.
- Keep soil nutrient levels higher, i.e. use more fertilizer.
- Keep plants properly watered. A well grown plant should produce better quality food.
- Provide the right amount of sun. Many gardens today don’t have enough sun, so place plants in the sunniest spot you have.
The reality is that you have no way to tell if a food is more nutritious and contrary to a lot of online misinformation, you have few options to increase nutrition. So don’t sweat it. Grow the foods you love and enjoy them.