The statement that beets help build the blood, and detoxify it, can be found in numerous books and websites about juicing, body detox, and other assorted food faddist publications. It is a nonsense proclamation borne entirely of superstition, probably based on the deep red color of beets and nothing more. Many other foods and herbs have been claimed to be blood builders as well.
There is no one food that, by itself, builds your blood. Good nutrition and an adequate intake of iron are all you need to maintain healthy red blood cells, unless you have chronic anemia caused by another condition.
Other foods that have been claimed to build the blood are spinach, Swiss chard, dandelion greens, turnips, Brussels sprouts, blackberries, blueberries, elderberries, raspberries, carrots, celery, pomegranates…this list goes on and on, but beets are one of the oldest foods to traditionally be associated with blood building. Curiously, besides the dark leafy greens, some of the foods highest in iron are left out: red meat, liver, eggs (yolks), raisins, prunes, shell fish (oysters, clams, etc), beans, and peas. However, all the proposed blood builders are a good addition to a varied diet.
Beets, themselves, are a fairly good source of iron but they pale in comparison to the iron-rich foods listed above. For instance, a 1/2 cup serving of baby Lima beans contains well over twice the amount of iron as an equivalent serving of cooked beets. Beets are high in other minerals and vitamins, and may contain other useful phytonutrients.
Beet roots are, however, high in oxalic acid, and so people who are prone to kidney stone or urinary stones have been warned to avoid over-consumption of beets and other foods with high levels of this compound. Oxalic acid combines with calcium to form calcium-oxalates, which build up as crystal deposits in a condition known as hyperoxaluria. However, dietary restriction of oxalic acid has not been shown to have an appreciable affect on the condition as dietary oxalic acid contributes little to the condition. Although no plant food should be consumed in much greater levels than any other plant food, beets are nutritious and, although they have no magical effects on our health, that we know of, there is probably little reason to fear them, either.
There has never been any legitimate scientific association between beets and any special affect on the blood. Such myths are usually passed down from ancient herbalist traditions, where the action of a plant was associated with it’s color. Beets can range in color from a deep purple red, through red, pink, yellow, and white. The red color in beet roots are caused by a combination of violet colored betacyanins and yellow colored betxanthines, and the ratio of these determine whether the beets are red, orange, pink, or yellow. This has no relationship to the building of blood in the body. There have been some investigations into the antioxidant effect of beet juice and its possible anti-tumor effect in vitro.