The quality of food is so important to everyone these days and many are growing their own to have better control over nutrient density. Lots of different gardening styles like organic, permaculture and regenerative promote their system as the best way to keep nutrient density high.
How much of this information is true? What can a backyard gardener do to grow more nutritious food?
In this post I will help you understand what nutrient density really is, and I’ll help you weed through a lot of the gardening myths that claim to grow high density food.
What is Nutrient Density?
There is no simple answer to this question.
The National Cancer Institute defines it this way, “Food that is high in nutrients but relatively low in calories. Nutrient-dense foods contain vitamins, minerals, complex carbohydrates, lean protein, and healthy fats”.
That seems like a logical definition, but doesn’t all garden produce contain vitamins, minerals, complex carbohydrates, lean protein, and healthy fats? Sure they do. By this definition anything we grow in the garden is nutrient dense – that’s not much help.
The US Department of Agriculture defines a nutrient-rich food index (NRF) based on 9 nutrients to encourage (protein; fiber; vitamins A, C, and E; calcium; iron; potassium; and magnesium) and 3 nutrients to limit (saturated fat, added sugar, and sodium). The idea being that you should eat fewer calories and still get high amounts of the things your body needs. But what about all the other things in food, like antioxidants and phytochemicals? Are they not important?
Without going into this in more detail, there is no single accepted definition of nutrient dense food. Several systems are used and new ones, like nutrient profiling, are being developed because all of the current systems have flaws. Keep in mind that vegetables contain thousands of chemicals and in many cases we still don’t know what role they play in our health. Without that knowledge it is really impossible to define which nutrients are most important to us.
If you see the term “bionutrient” it means the same thing as nutrient density.
The Important Nutrients are the Ones You Need
A slice of white bread contains about 100 micrograms of vitamin E and a slice of brown bread contains 350 micrograms. Some would conclude that whole wheat has a higher nutrient density than white bread. But what if white bread had a higher level of calcium? Which one is more nutrious?
Salmon is considered to be a high nutrient density food, because a 100 gram piece of wild salmon contains 2.8 grams of omega-3. But Omega-3 is not even one of the nutrients considered important by the NRF index.
Once a fruit or vegetable is picked, its vitamin C content starts to drop and for this reason fresh vegetables are considered to have a higher nutrient density. However, the average person in the US already gets enough vitamin C in their diet. Eating food with higher levels of vitamin C are of little value since the excess can’t be used by the body. So should vitamin C even be counted when measuring nutrient density?
These are just some of the problems with defining nutrient dense food and if we can’t clearly define it, how can gardeners expect to grow food with a higher density?
Why is Nutrient Density Important?
Some of the current focus on nutrient density stems from a global fallacy, namely that our soils are being depleted of nutrients. It is therefore believed that todays food is much less nutritious than 50 or 100 years ago.
I had a close look at this in, Is Soil fertility Decreasing? and found that the science does not support the idea that our soil is less fertile today. Food grown today is as nutritious as it has ever been, and in some cases it is more nutritious.
Claims by Gardening Groups
There is a lot of advice for growing higher density food and each gardening style, or technique makes similar claims.
“organic gardening will boost nutrient density”
“bokashi composting increases nutrient density”
“bionutrient gardening produces nutrient dense food”
They generally talk about their gardening technique and then discuss and define nutrient density in a superficial way. Finally, they make some unfounded claims that their technique increases nutrition. Unfortunately they never provide any references to verify this, in part, because such references do not exist.
It is known that a healthier soil, containing a good amount of nutrients and organic matter, will produce food that is more dense. Many of these gardening techniques focus on improving soil health and so they will result in better quality food but there is nothing special about any of these techniques that make it better than the others.
Does Organic Gardening Increase Nutrient Density?
Organic gardening is the most popular and best established technique that makes claims and some people even equate “organic” with “nutrient density”, which is definitely wrong.
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.
Measuring Nutrient Density in Food
How does a gardener know when they have achieved the goal of growing more nutrient dense food?
One web site suggests that, “When you consume fruits and vegetables that are nutrient dense you feel like you have just bitten into the best fruit or vegetable on the planet. Your body jumps for joy as you take another bite”. Wow – it’s that simple! What complete nonsense.
Many suggest that a Brix refractometer can be used to measure nutrient density, but it can’t. For more on this see my post called, Nutrient Density – Can it be Measured With a Brix Refractometer? If anyone recommends using a refractometer for this purpose, don’t listen to any of their gardening advice.
Some groups are now suggesting that hand held spectrometers, like NIR, could be used by farmers and gardeners. But that is unrealistic at this time because these techniques do not distinguish the nutrients of interest from those of no interest.
Testing all the nutrients in food can be done in a lab, but even there it is not a trivial process. A gardener has no way to measure nutrient density. That means you can’t compare one variety of vegetable to another or one growing condition to another, to see which one produces a higher density. You can only do things in the garden and hope it works.
More importantly, online anecdotal information is useless unless it is backed up by lab analysis.
What Does Science Know About Growing Nutrient Dense Food?
There have been a lot of studies that compare growing vegetables in different soils or with different fertilizers, and in many cases some nutrients have been measured. But I was not able to find a single such study that measured “nutrient density”, probably because it is not really defined.
Allen V. Barker, from University of Massachusetts has been studying nutrients in various vegetables and found the following.
Eighteen lettuce cultivars including butterhead, romaine, and loose-leaf, were tested for calcium levels and found that loose-leaf had the highest levels and romaine the lowest. Synthetic fertilizer produced higher levels of calcium than organic fertilizer. Modern cultivars produced larger heads than traditional cultivars, but the calcium concentration was the same in both groups.
The title of this study was, “Nutrient Density in Lettuce Cultivars Grown with Organic or Conventional Fertilization with Elevated Calcium Concentrations”. It does clearly mention calcium but starts out talking about nutrient density. I find the title misleading since it is not measuring nutrient density; it only measures calcium.
In cabbage, Baker found similar results. Crop production was greater with the chemical or organic fertilizers than with the compost. The mineral nutrient content (P, K, Ca, Mg, Na, Fe, Zn, Mn, Cu, Mo and B) was not affected by the fertilization method and, modern and heirloom cultivars had similar values. There was significant differences in cultivars.
Similar results were found in tomatoes (P, K, Ca, Mg, Na, Fe, Zn, Mn, Cu, Mo and B). “Differences in nutrient concentrations between modern or heirloom cultivars or among fertility treatments were small or non-significant. Differences among individual cultivars for each element were large with some cultivars having nearly twice the concentration of nutrients”. On average heirloom tomatoes produced smaller fruit than hybrids. Some believe that this means heirlooms have more concentrated nutrients, but that is not the case. The concentration of nutrients remains the same, for all fruit sizes.
In a greenhouse hydroponic study, synthetic fertilizer increased the levels of nitrogen, potassium, magnesium, and iron in lettuce when compared to organic fertilizer, but organic fertilizer had the highest phosphorus.
A review of literature on grain production shows that minerals can be increased by adding higher levels of synthetic or organic fertilizer. “The most effective fertilization could be via soil (for zinc and, to some extent, copper), foliarly (for iron) and by adding fertilizers to the irrigation water (for iodine).”
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.”
Antioxidant production in tomatoes is affected by environmental conditions including temperature, light and water, as well soil nutrients and the time of harvest, but much of the details on this are still unknown.
These are some conclusions that have been reached.
- Organic is not more nutritious than conventional gardening.
- Heirlooms, as a group, are not more nutritious than hybrids.
- Increasing fertilization increases minerals in food and may increase other nutrients.
- Nutrient density varies significantly among cultivars.
Much of the information about nutrient density is still unknown. Why then, is there so much advice given out in gardening circles?
Is Fresh More Nutrient Dense Than Old?
This is commonly suggested to encourage backyard gardening; “fresh picked vegetables are more nutrient dense”, but that is not entirely true.
Some water soluble vitamins do decompose quickly and therefore are higher in fresh food. However, minerals don’t decompose. Your lettuce has just as much calcium, in a month from now as it has today. Fiber decomposes very slowly and proteins are not going to change quickly either.
Fresh is a bit better for some nutrients, but not for many of them.
Is GMO Better Than Traditional?
GMO cultivars are not acceptable to many gardeners and they don’t even have access to them, but they can produce higher nutrient density. For example, Golden Rice has been specifically engineered to have a higher vitamin A content.
I’ll predict that in future, gardeners will have access to and accept, engineered seed that is more nutritious.
Is Home Grown More Nutritious?
One of the main reasons gardeners grow their own food is so that they have access to more nutritious food. Convenience, great taste and perceived lower costs are other reasons.
Is home grown more nutritious?
Claims that growing organic, or using heirlooms leads to higher nutrition are not supported by science. Compost and organic fertilizer is not better than synthetic fertilizer in this regard.
Selecting cultivars based on their ability to produce higher nutrition does work, but there is a problem. Except for the couple of studies mentioned above we don’t have this kind of information, and even for lettuce, cabbage and tomatoes, this information is not provided when you buy seeds. Gardeners really don’t have access to this information, unless of course they read my post and then study the above links.
Home gardens do provide fresher food but it is not more nutritious, except possibly for a few select nutrients.
Nutrition in fruits and vegetables is mostly dependent on soil quality (nutrition) , environmental conditions and cultivar selection. Most gardeners don’t test their soil and have little control over the climate. They also have no way to measure nutrient density. The only thing they can do is select better cultivars, but they can’t do that until this information is made more available.