DEAR DR. BLONZ: You often discuss oxidation when dealing with health issues, and I wonder how this applies to foods when they’re exposed to air. Please explain more about how oxidation works. I also want to know if it is an issue with foods like carrot sticks and mushrooms, which now come cut and ready to use. -- R.W., Anderson, South Carolina

DEAR R.W.: Oxygen is essential for life; much of this comes from its ability to react with other substances. Something combining with oxygen undergoes “oxidation,” and when complete, it’s been “oxidized.”

“Antioxidants” are thought of as beneficial because oxidation is associated with bad things, but it’s important to understand that oxidation is integral to health. Our body gets most of its energy when fats are oxidized in a predetermined way inside a designated part of the cell, and oxidation is also a key player in our bodily defenses. Virtually everything we’re made of required oxidation at some point during the construction process.

Oxidation, therefore, should not be considered evil; it only becomes problematic when it takes place at the wrong time and place. We have systems set up to stop this using antioxidant substances; some are made by the body, while many come from our diet. Plant foods are the primary sources of dietary antioxidants. This makes sense, as they evolved systems that allowed them to flourish while exposed to the oxidizing rays of the sun. Curiously, antioxidants tend to work by being more attractive to oxygen: They take the oxygen “hit” first, to shield the substance they are designated to protect. From this, you may understand why having a diet that’s high in oxidizable fats while relatively low in antioxidant plant foods is a recipe for problems.

As to the other specifics of your question, fresh fruits and vegetables are living tissues, and they continue to breathe after harvest. There is no need to avoid ready-cut produce, but it pays to be a smart shopper. A couple of destructive processes are at play.

Plant cells contain enzymes that are tucked away until the plant food is sliced or peeled. At that point, the enzymes are liberated, and are free to act on the food. This is what causes apples and bananas to brown when cut -- a process called enzymatic browning.

Oxidation is another way that foods can break down. Cutting or slicing does expose cut surfaces to air and oxygen, but the effects can vary according to the type of food, and the way in which the food is cut, packaged, and stored. There can be changes in quality and some loss of nutrient value, but these will be minor due to the fact that vegetables (and fruits) are low in fat, and they contain their own antioxidants to help stave off damage. When damage is excessive, the food becomes unattractive and unpalatable.

Companies that do this type of minimal processing make use of low temperatures, special washes, and “oxygen-scavenging” systems to slow breakdown. There is even active packaging and controlled atmospheres that can safely maintain product freshness.

Ready-to-eat products are more expensive, but the convenience can be worth the price, provided the product is wholesome and fresh. Be sure to observe freshness dating and let your eyes be your guide to ensure you are getting the best product.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 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 often see xanthan gum in the ingredients lists of salad dressings and chocolate syrup. There are other types of gums in processed foods as well. My naturopath said that if these are eaten, the gums can build up in the intestines and cause problems. Is that true? -- S.F., New York City

DEAR S.F.: Vegetable gums such as agar, locust bean gum, tragacanth, xanthan gum, and pectin are used as food additives to help with texture and spreadability, and provide a slippery “mouthfeel” such as the one generally associated with butter and similar products.

These compounds are built like a carbohydrate, but they’re constructed in a way that digestive enzymes cannot attack, which means they stay too large to be absorbed and won’t directly contribute calories. There is no evidence or reason to believe that gums build up and cause toxic reactions at the levels consumed as additives in foods. If the testing prior to their approval had revealed such evidence, they would have never been approved as additives. But gums can be acted upon by the flora in our large intestines, so there is a chance consuming them will produce brief, minor digestive effects, including gas and laxation.

You mentioned xanthan gum in particular, which is made from a specially fermented corn syrup, itself made from corn starch. It was created at a USDA research station in Peoria, Illinois, as part of a project to find new uses for surplus corn. Xanthan gum helps to thicken the texture of food, and it has proven to be quite versatile. Aside from syrups and salad dressings, it is found in puddings, sauces, baked goods and desserts. Because it is made from corn, xanthan gum should be avoided by individuals allergic to corn, but aside from that, there do not appear to be any problems associated with its use.

Use caution listening to advice from individuals who have a history of dubious statements.

DEAR DR. BLONZ: My question is whether adding a small bit of sugar -- say, a teaspoon or so -- changes the acidity of tomato sauce. My partner insists that is what happens, but I remain skeptical. If sugar caused this change, what would be the chemical reaction? -- S.T., Columbia, South Carolina

DEAR S.T.: Added sugar would help offset the dominance of the acid taste of a tomato, but it doesn’t react with or neutralize the acid in any significant way.

DEAR DR. BLONZ: I am soliciting your review of using Java tea for weight loss. One product says the tea contains natural fat-burning enzymes, and that these enzymes get absorbed and help release fat cells from storage areas. It says the tea also contains flavonoids that clean and unclog the large intestine’s mucous membranes, which, by themselves, can help you to lose 3 to 4 pounds within the first 48 hrs. Is there anything to this, or is it a myth and theoretical? -- R.P., Chicago

DEAR R.P.: While tea contains flavonoids, which are healthful phytochemicals, the rest is filed under “myth and theoretical.” Tea is a healthful beverage, but the bits about fat-burning enzymes and intestinal “mucous membrane cleansing” are nonsense.

Claims are easy to make, especially when you don’t back them up with objective evidence. Drink the tea if you enjoy it, but I wouldn’t waste my time or money if these claims are the only motivation.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 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: What makes a vitamin water-soluble? I know vitamins A, D, E and K are not water-soluble, and that B and C are. Does this relate to the fact that we do not store water-soluble vitamins in our body? -- H.T., Phoenix

DEAR H.T.: First, some history about what we now call vitamins. The work of Louis Pasteur (1822-1895) and Robert Koch (1843-1910) revealed that germs were responsible for diseases. Scientists then began working to identify the bugs behind every illness. Sanitation was found to be a key, and the “germ theory” of disease ruled the day. Some ailments, however, were found to persist even when sanitation was under control. The concept that what we ate, or failed to eat, was involved was not widely embraced, but as time went on, scientists began to investigate the role of diet.

The usual way to establish the essentiality of a nutrient is through an investigation of what happens when it is absent. Because vitamins are present (and needed by the body) in relatively small amounts, it was not until researchers had an ability to purify foods that they could know what, precisely, was being fed. Answers began to emerge when experiments started using purified diets that only contained protein, fat and carbohydrate. These nutrients, by themselves, did not support life; young animals failed to grow, and mature animals failed to maintain their body weight. It became clear that there were other essential substances.

As analytical procedures progressed, the different essential micronutrients were discovered. The first of these nutrients contained the element nitrogen, in the form of an amino group. It was assumed that all micronutrients would have a similar structure, and this new group was referred to as “vital amines,” or “vitamines” -- a word coined in 1911 by a Polish scientist named Casimir Funk. It was later determined that not all of these substances were built in the same way, but the name -- shortened to “vitamins” -- had already become part of scientific jargon.

An adult is about 60% water by weight. Water gets consumed, serves as the medium for biochemical reactions, then serves as the vehicle to help eliminate metabolic byproducts through the kidneys. By contrast, the body conserves fat by virtue of its role as the body’s concentrated source of metabolic energy.

When the vitamin discoveries began, it became convenient to classify these substances by whether they dissolved in water or fat. This classification was not based on whether the vitamins were stored; that was not known at the time. This system, however, has remained. Due to the constant turnover of water through the body, water-soluble vitamins are not effectively stored to any appreciable degree. Fat-soluble vitamins tend to get distributed in body fat, so they hang around for a while.

The fat-soluble vitamins include A, D, E and K, as you mentioned. The water-soluble vitamins include thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), ascorbic acid (C), vitamin B12, folate, choline and biotin.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 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.