DEAR DR. BLONZ: Processed foods, even some that brag about their "all natural" ingredients, often choose to add food coloring. Where do natural and artificial food colorings come from? What does "FD&C" stand for when used to describe a color on the label? How concerned should I be over the safety of food coloring? -- B.B., Los Angeles

DEAR B.B.: The use of food colors is controversial because their purpose is to change the appearance of a food into one that is more acceptable to the consumer. It's nothing new, as archaeologists have identified the use of cosmetic colors dating back as far as 5,000 B.C. Research has shown that if the colors of a food look wrong, people have difficulty detecting specific tastes. One classic study, for example, demonstrated that some volunteers couldn't correctly identify strawberry flavoring when it was tinted green. And in a classic 1970s experiment, volunteers were fed a meal of steaks, peas and french fries under lighting conditions that masked their appearance. A number of volunteers became ill when the lights were raised at the end of the meal to reveal a blue steak, red peas, and green French fries.

One rationale for the use of colors in processed foods is that natural color compounds tend to be destroyed during processing. When used as additives, however, natural colors are rarely "natural" to the food in which they're used. Rather, they are color-rich chemicals that come from animal, vegetable or mineral sources, and this is what allows them to be called "natural." Artificial colors, by contrast, tend to be made from petroleum-based substances.

The components of natural red food coloring, for example, can be extracted from beets, but it also can come from carmine, a crimson pigment from the shell of a Central American insect. Both are considered "natural" red colors, and they're used in everything from fruit drinks to candy to strawberry ice cream.

If a color comes from a natural source, it is exempt from certification. By contrast, every batch of an artificial color must be certified safe by the Food and Drug Administration before it can be used. The FD&C in the name of an artificial color stands for the Food, Drug and Cosmetic Act, the 1938 legislation that gave the government the authority to regulate the dyes used in foods, drugs and cosmetics. The artificial colors used in foods are identified by number and appear on the ingredient statement as, for example, "FD&C Blue #2." A complete list of FD&C colors can be found at tinyurl.com/oenz94w.

The safety issue is complicated. In general, food colors have a good safety record, but over the years a few "numbers" have been taken off the market when they were found to cause cancer in animal experiments. Keep in mind that unrealistically large amounts of the chemical are often used to provoke cancer in these experiments, while only minuscule amounts of colors are ever used in foods. Other issues include an ongoing debate about an association between artificial colors and hyperactivity in children.

The big picture here is that color additives don't provide any health value to a food, the main mission being to make a processed food appear more natural or wholesome. There is no real basis to recommend them. The fact that you don't find food color additives in whole foods, such as fruits, vegetables and grains, speaks volumes.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I am interested in your thoughts on linoleic acid. I've been collecting linoleic acid research these past few years, and what I've learned thus far paints a grim picture. I believe we should be cutting this fat out of our diets. I found that reducing my soybean oil intake (which I did in 1994) and peanut butter intake (in 2009) has done my body a world of good. -- D.B., via email

DEAR D.B.: Linoleic acid is an essential fatty acid. This means that it is needed for normal health, but the human body cannot make sufficient amounts on its own. As a result, linoleic acid needs to be provided in the diet.

But how much? Just because something is essential does not mean it should be consumed to excess. For example, there is reasonable evidence that a strict vegetarian (or even vegan) diet contributes to health, but that does not mean that we should overdo it with meat-free junk like candy, beer and potato chips. Balance and whole foods are the key, and this is also the case with the fats we consume.

Linoleic acid is the primary polyunsaturated fatty acid in nuts and seeds. Vegetable oils made from these will be high in this fatty acid. Unless there is specific negative evidence -- such as what was learned about the need to avoid industrially produced trans fats -- we do ourselves a disservice when we become overly fixated on individual food components.

That said, you don't want to overdo it with any fat, whether it is lard, coconut oil, fish oil, vegetable oil or even olive oil. The mix of healthful whole foods is what works. Think of them as a system perfected over time by nature.

Fats are the most concentrated form of caloric energy in nature; plants use fats as an energy source to nourish their seeds during the critical development period before the plant can begin to make energy on its own. That makes fats, and the maintenance of their wholesomeness, a vital project for a successful plant. The plants that have succeeded have evolved to produce their own set of "essential" protectants. These phytochemicals keep the elements, such as the oxidizing rays of the sun, or the invasion of insects or bacteria, from destroying their energy supply or doing other types of damage that can threaten their survival and propagation.

When you eat a whole food, you get the entire package, including these protectants. When you eat a variety of whole foods, you get a variety of protectants. Contrast this with fabricated foods that are formulated to achieve a particular taste, texture, appearance, functionality and shelf life -- not to survive or reproduce. Be less concerned about linoleic acid and more focused on making it just one of many fats in your healthful diet. Toss in an active lifestyle with limited stress, and you would definitely have something. Check out my online book that goes aisle-by-aisle through the supermarket for more information about food choices. It is available free of charge at blonz.com/guide.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Can you tell me how long eggs are still usable, after the best-by date on the carton? Are they safe to use in recipes? What about eggs purchased at a farmers' market, where there is no date on the carton? -- T.D., Lafayette, California

DEAR T.D.: Eggs that have a U.S. Department of Agriculture grading need to display the day of the year (from 1 to 365) on which the eggs were packed. Egg cartons often display an expiration date, as well -- the month and day after which they can no longer be sold, but are still safe to eat. Assuming they have been under refrigeration, you have about four to five weeks after the pack date during which the eggs are considered fresh and safe.

The expiration date will pass during this period. If purchasing eggs at a farmers' market, be sure to ask the vendor for the pack date. It is likely that there will be a dating system on any container for a perishable item such as eggs. Then make sure you note this date (or the date you purchased the eggs) on the carton you take home.

As time passes, eggs will gradually lose some of their qualities. In a fresh egg, the yolk is compact and stands high, and the white stays close to the yolk. As the weeks pass, the yolk and the egg white begin to spread, and the yolk sac becomes more fragile. Anyone who eats eggs sunny-side-up or over easy will notice that it doesn't take much to rupture the yolk of an older egg. These are the results of subtle changes in the egg albumin, the protein in the egg, but this does not have a significant impact on the egg's nutritional value. Over time, though, these changes can affect how an egg performs in certain recipes.

Use the freshest eggs for poaching or frying, as older ones will be more runny. If you want your egg to be whipped for volume, such as in a meringue or a cake, it's OK to use a "middle-aged" egg. Older eggs will perform fine if they are going to be used in a batter. If you are making hard-boiled eggs, older ones are preferred, as it is easier to take the shell off an older egg than a fresh one.

If the expiration date is long gone and you have concerns, it is always best to discard the eggs. If you do end up using eggs near, or just after, their expiration date, be sure to cook them well. That is always the best way to eliminate any bacteria that might have taken up residence. The USDA has a booklet on how to buy eggs, and there is more detailed information at eggsafety.org.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.