By Dr. Royal Lee
Summary: Dr. Royal Lee discusses the nutritional value of potatoes, explaining that much of that value is lost when they are cooked. “We may estimate that 25 percent of the vitamins are lost in cooking either by heat or leaching. The loss of vitamin C is particularly fast….” In addition, he says, “the cooked potato contains no enzymes, as all enzymes are destroyed by heat.” One such enzyme, studies showed, helps relieve constipation, while others are even more precious. “One of the enzymes found in raw potatoes is phosphatase, which promotes assimilation of calcium and iron in particular; another is tyrosinase, an essential component of the vitamin C complex and associated directly with the function of the adrenal glands.” (Dr. Lee often referred to raw potatoes and raw mushrooms as the best food sources of tyrosinase available.) Lee gives tips on conserving potatoes’ nutrients when cooking them and instructs readers to be sure to add lemon juice to freshly extracted potato juice, which keeps the juice from oxidizing and turning black. From Let’s Live magazine, 1958.[The following is a transcription of the original Archives document. To view or download the original document, click here.]
The Use of Raw Potatoes
The Irish peasantry refer to their beloved potatoes as “bog apples.” This is a useful term to remember because it implies that potatoes, like the apple, may be eaten raw and, also like the apple, help “keep the doctor away.” But while hardly an American meal passes without serving cooked potatoes, this same food served in the raw state is a rarity.
Good for Overweight
“Eat potatoes instead of bread” is good advice for the overweight who are constantly engaged in the battle of the calories. Pound for pound, potatoes furnish about one-third less calories than bread—so we may eat three times as much on a caloric basis. (There are about 100 calories per medium-sized raw potato, which is much less than a serving of spaghetti, pie, or cake.) In addition its superior digestibility and food value as a source of protein, vitamins, and minerals make it ideal for reducing the caloric intake without sacrifice of many essential food factors.
Copeland said, “To eat is human; to digest divine.” While the quality of potatoes is greatly [affected] by the conditions under and the soil in which they are grown, an analysis shows they are generally about 75 percent water, 15 percent starch, 1–2 percent protein, and 2–3 percent mineral salts. However, the nutritive value cannot be [assessed] on the basis of analysis alone. It is necessary to know the extent to which the various constituents are digestible. Reports show that 95 percent of the potato’s calories are digested, 70–85 percent of its nitrogenous material is absorbed (40–60 percent of that is in the form of protein), and 97 percent of the iron is present in “available” form (McCance and Widdowson, 1942). Potatoes have very little fat or sugar and are high in potassium, phosphorus, and calcium. The richer they are in protein, the more waxy they are; the higher they are in starch, the more mealiness they have when cooked.
The portion of the potato [immediately] under the skin contains almost twice the solids as the central portion. [Unfortunately] the removal of 20–25 percent of the potato’s total weight upon peeling is not uncommon. In addition, if peeled potatoes are boiled in water, 20 percent of the solid constituents may be dissolved and so lost. This loss is practically eliminated if potatoes are boiled with their skins intact. Cutting the potato causes cell damage and the liberation of an enzyme that destroys vitamin C to some extent (ascorbic acid oxidase). We may estimate that 25 percent of the vitamins are lost in cooking either by heat or leaching. The loss of vitamin C is particularly fast in heat. [Storing] cooked potatoes, even under refrigeration, causes over 50 percent loss in twenty-four hours, and practically all the vitamin C [is gone] in 72 hours. Ninety percent of the vitamin C may be lost in mashed potatoes in 30 minutes if they are kept hot.
It thus becomes evident that a 50 percent loss of nutrient value is a conservative estimate of the deficit caused by the ordinary methods of preparation of this important food.
Tips on Conserving
Cooking in salt water conserves more vitamin C than cooking in unsalted water. The presence of calcium salts in the water (hard water) tends to conserve this vitamin. There is a greater loss of solid constituents if the potatoes are started in cold water than if they are dropped into boiling water. One tablespoon of vinegar or lemon juice [added] to a quart of water helps prevent blackening and may have additional beneficial effects. When extracting the juice of potatoes, lemon juice should also be added.
Sprouted potatoes are inferior in quality to unsprouted ones. The potato skin is only six to ten cells thick, yet it contains about 9 percent of the protein and acts to prevent the loss of solid constituents in cooking.
Baked potatoes should be pricked or broken open as soon as they are removed from the oven to let the heat and steam escape. This prevents them from becoming soggy. It is a good idea to insert a stainless steel skewer through the potato while baking; this conducts heat into the center, and thus less baking is required.
The cooked potato contains no enzymes, since all enzymes are destroyed by heat. There is an enzyme in raw milk that prevents constipation and an enzyme in raw potatoes that does the same thing, according to clinical reports. Certainly a piece of raw potato before retiring can do no harm, and it has produced beneficial results in cases of chronic constipation. The farmer who reduces his potato intake when he comes to the city may notice that his head “pounds” after meals. Quite possibly this is due to a reduction in his ordinary intake of potassium—the mineral that promotes normal heart rhythm. One of the enzymes found in raw potatoes is phosphatase, which promotes assimilation of calcium and iron in particular; another is tyrosinase, an essential component of the vitamin C complex associated directly with the function of the adrenal glands.
The best potatoes come from Maine, where the crops are rotated with oats and clover, the clover ploughed under as green manure. The soil is abundantly supplied with decomposed shale rock. While potatoes can be grown on almost any soil, the muck or peat soils are often used, and since these soils may be comparatively virgin, we have a good chance of obtaining good potatoes. Of course it is recognized that one should try to obtain potatoes that have not been exposed to commercial fertilizer and poisonous insecticides.
By Dr. Royal Lee. Let’s Live, 1958.