Why it isn’t always the most nutritious option
You may have heard about the “benefits” of eating uncooked vegetables, fruits, and herbs. A growing number of raw food gurus believe that heating plant foods above a certain temperature “kills” vital nutrients.
But this ridiculous theory ignores basic biology, which tells us that understanding the nutrient composition of foods is just half the battle. The other half relates to how the nutrients in foods are digested in the gastrointestinal tract, absorbed into the bloodstream, and transported throughout the body’s tissues.
A new study on a rather innocuous subject—involving the type of dressing you should put on your salads—reminded me of this key point. What it illustrates is that “raw” food doesn’t necessarily translate into the most nutritious food.
Why digestion is crucial, especially with plant-based foods
Science continues to reveal the nutritional constituents and other active phytochemicals in plant foods. And one thing researchers have discovered is disheartening, to put it mildly.
Over recent decades, analyses by the United States Department of Agriculture revealed steadily declining nutrient levels in conventionally grown produce. This unfortunate turn of events is primarily due to industrial-scale agricultural practices (use of chemical pesticides, over-farming, etc.) that deplete the soil.
Mass-produced foods have also been selected and bred over the years for appearance, abundance, shelf life, and other commercial factors, without regard to the most important factor: nutritional value. And this trend was in place long before the latest disaster of genetically modified foods.
Which is why now, more than ever, it’s vital to ensure the nutrients remaining in plant foods are adequately absorbed by the people eating them.
But modern medical science has only recently begun focusing on digestion and all the related factors that influence virtually every aspect of health and illness.
So researchers are now “discovering” what the ancient traditions of Ayurvedic and Chinese medicine have known all along. In order for plant foods to act as medicines, they need to be digested properly.
Breaking down bacteria’s role in digestion
In basic terms, raw plants have the highest levels of raw nutrients, but they’re typically hidden behind the strong double-walls of plant cells. These walls allow plants to withstand being in nature 24/7. They can’t come in from the elements, or into the shade from the sun because they often are the shade.
In woody plants and grasses, strong cellulose fibers provide great and enduring strength. That’s why humans use lumber to build structures or grasses to weave baskets—because these materials stand the test of time.
Cellulose is also found in plant foods. But neither humans nor animals can digest this substance, which is perhaps the most prevalent carbohydrate in nature. However, there are certain bacteria that can break down cellulose.
Termites and other insects that “eat” wood have this type of bacteria in their GI tracts.
Grazing animals (like cattle, sheep, and goats) also house bacteria in their stomachs that can digest cellulose. Which, in turn, converts an indigestible plant product into highly nutritious and bioavailable meat and dairy for human consumption.
Additionally, grass-fed dairy and meat products are associated with lower rates of heart disease and other illnesses (contrary to politically correct agendas to label meat as unhealthy).
Probiotic bacteria can also break down cellulose in vegetables for human consumption. (Fruits don’t usually need to be broken down that much for digestion.)
These bacteria ferment cellulose-rich plants like cabbage into foods such as sauerkraut or kim chi, so their high content of vitamin C and other nutrients can be easily digested and absorbed into the human bloodstream. I often think of these kinds of foods as “prebiotic,” since they support a healthy microbiome in the GI system.
So probiotic bacteria acting outside of the GI tract, in nature, is just as important as probiotics inside the GI tract.
The most nutritious ways to cook plant foods
There’s another way to break down vegetables’ hard-to-digest, double-walled cells: cooking. But when it comes to preserving nutrients, not all methods of cooking are equal.
You can boil the heck out of cabbage, onions, and carrots and still have some nutrients left in these hardy vegetables—but it’s otherwise not recommended for more delicate vegetables.
Excessive heating over prolonged periods (like boiling) breaks down all of the contents of many plants—including nutrients. But it’s possible to heat these plants just enough to break down the double-walled cells to allow the nutrients to get out, without completely destroying them.
For example, quickly sautéing vegetables in a saucepan, or in a Chinese wok, preserves delicious flavors, and enhances the bioavailability of nutrients for digestion. Quick steaming is another good option.
But what about salad greens that are typically eaten raw? There’s yet another important consideration about how to prepare them if you want to be sure you’re getting the most nutrition. Which leads me to the new study I mentioned earlier.
All dressed up and going places
You already know that leafy green vegetables are high in nutrients. But in order to absorb their abundant lutein, lycopene, and other carotenoids (including vitamin A), as well as vitamins E and K, you need to eat your greens with some fats, like cheese or oils.
Remember, these are fat-soluble nutrients, meaning the body can only absorb them in the presence of fats. (That’s also why you’re wasting your time trying to get vitamins A, D, E, or K in supplements that don’t include some oils in the formulation—they must be softgels or liquid preparations. One reason to steer clear of those worthless, one-a-day multivitamin pills.)
The new study found that eating a salad with soybean oil allowed the body to better absorb the fat-soluble nutrients I mentioned above.1 Furthermore, the study showed that the more oil is added, the more nutrients are absorbed.
The study involved 12 healthy women between the ages of 19 and 39. They were asked to consume foods that weren’t good sources of carotenoids and fat-soluble vitamins for four days. On the fifth day, they ate a salad of spinach, romaine lettuce, carrots, and tomatoes. It was dressed with differing amounts of soybean oil—0, 2, 4, 8, or 32 grams.
The researchers then measured the women’s blood-nutrient levels. They found that the women who consumed the most oil on their salads had the highest levels of carotene, lycopene, and vitamins A and K.
The lead researcher stated: “The best way to explain it would be to say that adding twice the amount of salad dressing leads to twice the nutrient absorption.”
Please note that these researchers used soybean oil, which I’d never recommend. Instead, use traditional olive oil. The study only showed the short-term benefit of this vegetable oil without observing the long-term hazards of soy—including genetic modification. But since the study was done at Iowa State University, the researchers were apparently more interested in supporting a local cash crop (soy) instead of olives, which aren’t grown there.
Nevertheless, the principle is the same—a vegetable oil dressing helps people better digest the nutrients naturally present in raw greens.
My favorite uses for plant oils
The current U.S. dietary recommendation is about two tablespoons of plant or vegetable oil per day—and I always recommend a high-quality olive oil. Of course, research on the Mediterranean diet shows that higher levels of olive oil are not only safe, but highly beneficial for your health as well.
When your pantry is well-stocked with olive oil, there’s never any reason to resort to bottled salad dressings full of sugars and other unhealthy ingredients. A simple dressing of olive oil with vinegar, or lemon juice, will do the trick. You can also add some mustard, pepper, and other herbs to taste. Keep olive oil on hand at all times for sautéing as well.
But do not be taken in by false claims about the quality of olive oils. I gave you a guide about which brands to choose in a November 2016 Daily Dispatch (“The scandal sweeping through supermarket aisles all across the country.”) You can access this in my archives at www.DrMicozzi.com.
To ensure your olive oil stays fresh, don’t buy more than what you would consume in about three months’ time.
This Spring, make your veggies tasty and nutritious
As Spring gets underway, take advantage of all of the healthy, fresh, locally-grown plant foods that begin to appear. Make sure you make the most of them when planning your meals. I recommend stocking up at your local farmer’s market or even planting your own garden (which is also great for exercise and soaking up precious vitamin D).
So whether it’s arugula or zucchini, don’t assume you’re doing yourself any favors by eating raw or undressed vegetables. Your body needs some help to absorb the healthy nutrients in these and other plant foods.
Give it a quick sauté or steam, and add some healthy olive oil. Not only will your food taste better, but you won’t get a “raw deal” when it comes to your nutrition.
1“Modeling the dose effects of soybean oil in salad dressing on carotenoid and fat-soluble vitamin bioavailability in salad vegetables.” Am J Clin Nutr. 2017 Oct;106(4):1041-1051.