Vitamins conveniently fall into two classes, fat soluble and water soluble, which describe a chemical attribute: compounds either dissolve in water or in fat, and those two solvents don’t mix. When you add vinegar, which is a water-based liquid, to oil, they form separate layers. But beyond a chemical trait, this classification gives you some idea of how the vitamins function and how they’re handled by the body. From a practical standpoint, solubility determines if a vitamin can be stored in the body and how easily it’s lost from the body and, for that matter, from foods during processing or preparation. It also gives you a tiny clue as to the foods that might contain them.
Solubility and Vitamin Clues in Foods
Let’s start with how solubility tells you where to look for vitamins. A vitamin has to be dissolved in some part of a food to be contained within it, and in the case of fat-soluble vitamins, the food has to contain at least a moderate amount of fat to be a good source of one of these vitamins. One exception to this rule of thumb is a food that has been fortified with a fat soluble vitamin, such as skim milk which contains no fat. Milk naturally contains a fair amount of fat, 8 grams in one cup to be exact, and a significant amount of vitamin A. When manufacturers remove the fat, they put back in the lost vitamin A and also throw in some vitamin D. Other examples include commercial products like breakfast cereals. These cereals are made from various grains which don’t naturally contain fat soluble vitamins such as vitamins A and D.
Another exception to our rule is when a food contains a precursor of fat soluble vitamin A, such as beta-carotene and other carotenoids. A precursor, sometimes called a provitamin, is a compound that the body can convert into an active vitamin. The most significant food sources of vitamin A precursors are highly colored fruits and vegetables, which tend to be very low in fat. You can eat lots of fruits and vegetables for practically no dent in your daily fat budget and get loads of carotenoids, which your body can turn into active vitamin A as you need it.
Knowing the solubility of vitamins also tells you about how easily these nutrients may be lost in food preparation, most of which occurs with the addition of water and when heating foods. In general, fat soluble vitamins are fairly well retained during food preparation, largely because they don’t dissolve in water. In contrast, water soluble vitamins readily dissolve into the water used in cooking. This is one reason why the Southern practice of using pot liquor, liquid remaining after cooking foods like vegetables, to make soups and stews is a smart idea; the water soluble vitamins that escaped into the water during cooking are recycled back into something you can eat instead of being poured down the drain. Heat is a problem for many water soluble vitamins, more so for some than others. Vitamin C, folate, and riboflavin are among the touchiest vitamins. The following are tips to cut down on nutrient losses from foods during food preparation.
Food Preparation and Storage
- Use fresh produce as soon as possible after purchase, as naturally contained enzymes destroy nutrients as the produce continues to ripen.
- Avoid soaking produce in water for long periods of time.
- Leave skins intact on produce when possible (if you must peel, use a peeler to remove the least amount of flesh, since nutrients are often concentrated between the skin and flesh).
- Cut produce after washing if possible; cut into larger pieces rather than small pieces because more juice (high in water soluble vitamins) is lost with more cutting.
- Return milk in opaque plastic jugs to the fridge as soon as possible since riboflavin is readily destroyed by exposure to light; for the same reason, don’t store pasta and other grains in glass containers (glass is okay if stored in the cupboard).
- Keep juices tightly covered both in fridge and out because vitamin C evaporates into the air.
- Steam vegetables rather than boil in large quantities of water microwaving and stir-frying are also better than boiling.
- Add vegetables to boiling water, rather than placing in water and then bringing to a boil; quickly reduce heat to a simmer.
- Limit cooking time and avoid high temperatures for all foods.
- Never rinse boiled grain products such as pasta because vitamins will also be rinsed off; to avoid stickiness, add just a touch of olive oil.
The Solubility Factor Inside the Body
In general, water soluble vitamins are not stored in the body’s tissues to any great extent, so you need them every day. These vitamins are also readily excreted by the kidneys, which means that when you consume more than you need, the excess ends up in the urine. While this seems wasteful, especially if the excess amount came from supplements for which you probably paid an average of 10 to 50 cents for each tablet, you can be somewhat assured that you won’t accumulate toxic amounts. In contrast, the body can store fat sol,uble vitamins for long periods of time and not excrete them in case of an excess. People don’t often realize that too much of a good thing, even vitamins, can actually kill you!
A favorite story that college nutrition professors regale students with when they get to the vitamins lecture is the one about the Arctic explorers and polar bear livers. It seems that some of the first explorers to those cold wastelands ran out of food supplies and were forced to rely on what they could find around them for sustenance. The only edible food was an abundance of polar bear livers, which are even higher in vitamin A than other types of liver. Because they ate so much, and vitamin A is not excreted, some of them died from vitamin A toxicity-quite a vivid illustration, albeit unlikely to occur in the average town, of the potential toxicity of vitamins. Similarly, vitamin D has a fairly low toxicity range. But those are fat soluble vitamins, which one would expect to possibly cause problems.
Conventional wisdom had suggested that, in sharp contrast, water soluble vitamins were harmless in excessive amounts, as the body was able and willing to dump the overage into the daily urine for excretion. But recent studies and clinical experience have shown that excess amounts of some of the water soluble vitamins can have undesirable effects. A common example is niacin, which is modestly effective in lowering blood cholesterol. The amount needed to lower cholesterol greatly exceeds the RDA, and the nutrient mega dose of up to 100 times the RDA acts like a drug in the body. The megadose produces what are called pharmacological or drug effects, and besides lowering cholesterol, it may also cause liver damage and stomach ulcers. While the water soluble vitamins are not quite as lethal as some of the fat soluble ones, excesses can cause physiologic problems. We’ll explore the potential problems of each vitamin in the upcoming chapters.
An overview of vitamins would be remiss if we neglected to mention the impostors which crafty marketers slip into everything from shampoo to “high-energy snack bars.” If scientists did discover a new vitamin, you’d hear about it on the 6:00 P.M. news before the story made it into print. But some of these fake vitamins sound like the real thing, like vitamin B one of the “newly discovered” vitamins. Following is a brief list of some perennial impostors:
- Bioflavonoids, vitamin P
- Gerovital H-3
- Laetrile, vitamin B
- Nucleic acids
- Pan gamic acid, vitamin B
- Provitamin B complex