The term lettuce does not designate a variety of salad. It’s the generic name of a series of vegetable plants with generally green leaves eaten raw in “salad” or cooked. A large number of lettuce varieties are grown in the world.
History of lettuce
For millennia, hunter-gatherers harvested lettuce belonging to one or the other of the dozens of wild species of Lactuca. If one relies on paintings appearing on tombs dating from 2 500 years before our era, a primitive form of romaine lettuce was perhaps already cultivated by the Egyptians at that time. The leaves were not consumed, judged to be too bitter, but the seeds were used for its medicinal properties and edible oil was taken. However, the first documents concerning lettuce cultivation date from the year 450 before our era. The species L. Serriola, native to the Mediterranean Basin and the Middle East, would be the ancestor of all the forms of L. sativa that we consume today. The ancient Greeks were said to have been the first to be domesticated.
The first species of lettuce quickly formed a high stem on which small, very bitter leaves were grown. At first, the Romans sought to alleviate this bitterness by subtracting the plant from the light during part of its growth (as is still done today for endive). Then, by selection, they obtained shorter-stem varieties and larger leaves, which were less quickly seeded and were less bitter. In the first century A.D., they had selected a dozen varieties, some of which were commonly consumed. Like many other greens, they ate it gladly raw, seasoned with oil and vinegar. However, in the Middle Ages, people began to see the raw vegetables with a bad eye. The consumption of raw lettuce will reappear in Western Europe in the sixteenth century only, after a long period when it was only served cooked, in stews and pies.
The lettuce will cross the Atlantic ocean with Christopher Columbus to bring seeds on his first trips to America. Until the middle of the twentieth century, we will cultivate and consume all types of lettuce, of which many varieties are now not found.
The introduction, in 1941, of the iceberg (a firmer and bigger variant of the European Batavia) completely transformed the markets. Finally, people came to find a lettuce supporting the constraints of industrial culture, survived long trips destined to make it cross a continent, even an ocean, and kept infinitely longer than any other known varieties.
Since then, iceberg lettuce dominates North American market (it held 73% of the market in 2000) and is in the process of imposing itself in Europe, although it is significantly less nutritious than other varieties. However, for some years its consumption has declined to the benefit of other varieties, the Roman in particular.
Lettuce health profile
The lettuce comes in multiple varieties: curly, lettuce, Boston, iceberg, romaine … and even the asparagus lettuce. It is certainly consumed in salad, but also braised or in soup! Beautiful coincidence, its antioxidants are better absorbed when accompanied by a source of fat, for example an oil vinaigrette.
The benefits of lettuce
Cancer. Some studies have associated the consumption of lettuce with the decrease in the risk of being affected by different cancers. In one of them, the consumption of lettuce several times a week has been specifically associated with a lower risk of lung cancer.
Neurodegenerative diseases. According to an in vitro study, compounds contained in lettuce, particularly in romaine lettuce, would have neuroprotective effects and could help prevent the onset of certain neurodegenerative diseases, such as Alzheimer disease. However, clinical studies will be needed to confirm these effects among humans.
Blood lipids. A study among rats indicated a diet with a fifth of lettuce allowed to decrease their blood cholesterol. Another study among mouses showed a diet rich in fat and cholesterol to which red-leaf lettuce was added decreased the blood concentration of total cholesterol, “bad” cholesterol (LDL) and triglycerides. Among humans, no data have been published on the effect of lettuce consumption on blood lipids.
Several epidemiological studies have shown that high consumption of vegetables and fruit decreases the risk of cardiovascular diseases, some cancers and other chronic diseases. The presence of antioxidants in vegetables and fruits could play a role in these protective effects.
Red curly lettuce and their antioxidant
Curly lettuce (red and green) would contain larger amounts of antioxidants (phenolic compounds and beta-carotene) than romaine and Boston lettuce. The latter still contain more than iceberg lettuce. Iceberg lettuce would contain 13 times less carotenoids than leaf lettuce. In general, red lettuce contains more antioxidant compounds than green color ones. The environmental factors to which lettuces are subjected during the harvest season vary the amount of antioxidants contained in this vegetable. However, these variations influence less the amount of antioxidants than the variety of lettuce consumed.
What does the lettuce contain?
Lettuce contains various phenolic compounds, mainly quercetin, as well as phenolic acids (caffeic acid and coumaric acid). These antioxidant substances protect the body cells from damage caused by free radicals.
Eating fresh or prepackaged lettuce?
Eating fresh lettuce would increase the presence of some antioxidant compounds in the bloodstream. Used to prolong the shelf life of the food, the modified atmosphere bag would not completely preserve the active antioxidant compounds of the lettuce.
However, research has revealed green lettuce has a low antioxidant power and little effect to prevent the growth of cancer cells in vitro. Red lettuce would be the only one with high antioxidant power. However, regular consumption of lettuce, regardless of color, still provides a significant contribution to phenolic compounds, which are beneficial to health.
The lettuce also contains carotenoids, mainly beta-carotene and lutein, but also different types of xanthines (e.g. zeaxanthin), according to the variety. These compounds would have antioxidant properties and the consumption of carotenoid-rich foods would be related to a lower risk of developing certain cancers. Some studies have observed consumption of lettuce increased the concentrations of beta-carotene in the blood, as well as the concentrations of zeaxanthin and beta-cryptoxanthin in the blood among women after menopause.
Salad and vinaigrette, a winning combination
Carotenoids including beta-carotene are better absorbed in the body when a small amount of fat is consumed at the same time. A study showed consumption of a salad (consisting of romaine lettuce, tomatoes, carrots and spinach) provided a greater amount of carotenoids in the blood when accompanied by regular dressing rather than a fat-free or reduced-fat dressing. The lipids contained in the vinegar sauce would allow carotenoids to be more readily released from plant membranes, making them more available for better absorption in the body.
Each variety of lettuce contains a different amount of fiber, of which about 15% to 35% is found in soluble form. Romaine lettuce is the richest, followed by curly lettuce, iceberg and Boston. Soluble fibers are well known for their beneficial effect on blood fats, those of lettuce would have some lowering power.
All varieties of lettuce, with the exception of iceberg lettuce, contain high amounts of vitamin K. This vitamin, necessary among other things to blood coagulation, can be produced by the body in addition to be found in certain foods. People taking anticoagulant medications, for example those marketed under the names Coumadin, Warfilone and Sintrom, must adopt a diet whose vitamin K content is relatively stable from one day to the next. Lettuce is part of a list of foods must be consumed at most once a day and in a maximum quantity of 250 ml (1 cup) each time. It is highly recommended for people under anticoagulation to consult a dietitian/nutritionist or physician to learn about vitamin K food sources and to ensure that the most stable daily intake is possible.
Choice and conservation
The leaves must be firm, without reddish discoloration at the end and without rotting at the base.
Refrigerator. From a few days to one week in the vegetable drawer. Preferably keep in a perforated plastic bag. Avoid the proximity of apples, pears and bananas that emit ethylene, a gas that causes the rotting of lettuce.
Freezer. The cooked lettuce can freeze, but not the fresh.
Long live the great air!
Lettuce grown in the open air would have higher content in phenolic compounds compared with those grown in greenhouse. A study conducted in Brazil showed hydroponic lettuce contained a little less carotenoids than classic cultured lettuce.
White-seeded lettuce (there are browns and blacks) needs light to germinate. It will not be covered with soil, but it will be packed well against the moist soil so it does not dry out.
A plant of fresh climate and short photoperiod, it is mainly grown in spring and autumn. During the summer, peolpe will be able to try the culture of the roman variety, slightly less sensitive to the heat. It will be protected against burning rays with a shade, leaving only 50% of the light to be filtered. People can also make successive seedlings of lettuce to be cut every 2 weeks, and harvest the leaves when the plant is very young before it has time to go into seed. Finally, some cultivars are relatively resistant to seed growth.
Fatten the soil well and water often to quickly bring the plants to maturity.
To obtain early production, start the seedlings in bins within 6-8 weeks before the last freezing. Transplant 3 or 4 weeks later to the ground (the plant is not afraid of freezing). Protect against the wind and the great colds with a geotextile fabric.
Ph: 6.0 to 7.0
Spacing: from 10 cm to 15 cm for the lettuce to be cut, from 15 cm to 20 cm for the others. When the seedlings expand to touch, delete 1 of 2.
Irrigation: contrary to what is recommended for most vegetable plants, lettuce prefers frequent, but superficial watering.
Insects: at the end of the season, aphids are to be feared, especially because they are vectors of the mosaic virus, against which there is nothing. Treat with insecticidal soap as soon as they appear. Slugs can also cause problems. Limit their proliferation with diatom earth, egg shells or containers filled with beer and arranged at the foot of the plants. Garlic extract has also been shown to be effective against this gastropod.
Diseases: it’s possible to limit the burn of the leaf edge and root rot by making sure that the air circulates well between the plants and watering frequently, superficially.
Ecology and environment
Lettuce is one of the vegetables receiving the largest amount of chemical treatments herbicides, insecticides and, above all, fungicides during its growth. This encourages several people to look for organic products which, alas, are generally more costly. Organic growers lose a large proportion of their lettuce because of the diseases and insects that are attacking them, which inevitably leads to an increase in the retail price.
Various solutions are currently being experienced in order to reduce the frequency and intensity of these attacks. Biofimugation, for example, consists of burying in the soil, the year before growing lettuce, plants with antifungal properties, particularly the brassicas (cabbage family).
Another approach is to practice on seeds energy healing techniques used by some practitioners to treat human beings. This highly controversial practice would aim to strengthen the immune defenses in the plant’s DNA. The technique has been experimented with some success, although on a small scale.