DEAR DR. BLONZ: Is there truth to the “raw foods” movement’s claim that cooking kills the natural living enzymes in foods, including vegetables, and that this creates poisons in our bodies? -- R.V., Berkeley, California

DEAR R.V.: The concept of “living enzymes” is misleading, in that enzymes are not living substances. Rather, they are a type of protein in living cells that speeds up chemical reactions, helping to change other things without being changed themselves.

In our bodies, enzymes not only work on digesting food, but they are involved in most aspects of our metabolism, which can be thought of as the processes associated with life. Enzymes have unique characteristics that determine how and when they become active. For example, if our blood sugar (glucose) is normal, one set of enzymes becomes active to process incoming nutrients. But if blood sugar is elevated, another set of enzymes gets the call. It is a remarkable system, all designed to ensure that things get handled in the most appropriate way for a given situation.

Like us, plants contain enzymes that play a part in their metabolisms. Inside plant seeds, enzymes can remain inactive for years, springing into action when conditions favor a need for their participation in the chemical reactions involved with the development of the new plant. Heat can indeed destroy plant (or any) enzymes, but it is important to appreciate that plant enzymes are there for the plant -- not for us.

A normal, healthy body makes its own enzymes as needed to digest the foods we eat. One of the initial stages of the human digestive process subjects foods to the acid environment in the stomach, which breaks down enzymes, treating them like other proteins that might be in the foods we just swallowed.

The heat of cooking helps make certain foods easier to digest, and it can make certain plant nutrients more bioavailable for our bodies. The idea of cooking being inherently negative because it “kills” anything alive in food is a bogus spin. Eating cooked food does not “poison” our body. Overcooking, the use of excess heat, can destroy some of the nutritive value of food -- and it can, if taken to an extreme, create mutagenic and carcinogenic substances. But that is not what we are talking about here.

By all means, we should enjoy eating fresh, raw, wholesome plant foods as part of a varied, healthful diet. But we should do so because we like the flavors and textures of the foods -- not because we fear that cooking creates poisons.

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: Are flaxseeds an appropriate source of omega-3 fats? I have been buying and sprinkling ground flaxseed on my cereal, and also using it in baking. My concerns are a couple of conflicting bits of information that I found. One is that raw flaxseed is toxic until it is heated, and the other is that flaxseed oil is NOT toxic until it’s heated. What’s that all about? Is it OK to continue baking with ground flaxseed in muffins, bread, etc., instead of eating it raw? Or should I stick to unheated ground flaxseed, or simply use flaxseed oil? -- F.S., Lodi, California

DEAR F.S.: Lots of flax to go over here (sorry, couldn’t let that slip by). The fatty acids in flaxseed are highly unsaturated -- more so than most other vegetable oils. The greater the degree of a fat’s unsaturation, the greater its susceptibility to oxidation, because the unsaturated bond is a point of vulnerability. (Read more on fats at b.link/oils56.) When food fats become oxidized, they lose their nutritive value and become rancid, which also messes with their taste, aroma and mouthfeel. Now, don’t overreact here, as this oxidation is not the same as becoming toxic, and a healthy body can handle this to a degree.

Exposure to the “oxidizing” rays of the sun, and to air, help make oxidation more likely, and heat also facilitates these reactions. All this explains why storing fats in sealed containers in a cool, dark place makes sense.

Now we tie in the concept of the antioxidant, which is a substance that prevents oxidation by being more attractive to oxygen -- sort of a biochemical “take me first” ethos. It also speaks to the unique value of extra virgin olive oil, with its own antioxidants, and to the healthfulness of a plant-based, whole-foods diet, which provides naturally occurring antioxidants to the body.

The flaxseed also has protectants, the primary being the protective seed coat that keeps the oil safe inside. The seed coat is so strong that most intact flaxseeds tend to pass right through our digestive systems. Inside the flaxseed are also several antioxidants -- nature’s way of helping assure the viability of the seeds once planted. The healthful components of the flaxseed become available to us once the seeds are cracked or ground, but that process also increases the susceptibility to oxidation. This is why ground flaxseed should be stored in airtight containers and kept in the refrigerator once opened.

An issue relating to toxicity is the fact that flaxseed contains cyanogenic (cyanide-producing) compounds. Their mere presence does not make flaxseed dangerous; it all comes down to the amount of the compounds and the health of the consumer. Cyanogenic compounds are present in several other foods, and they cause problems primarily in malnourished individuals. The cyanogenic compounds in flaxseed are more a concern for livestock, where very large amounts are consumed. Heat can help in that situation, because it breaks down the compounds into harmless substances.

As for purified flaxseed oil, that would provide you with the omega-3s of flax, but not its naturally present fiber or phytochemicals. You would avoid the cyanogenic compounds -- not much of a risk at the levels consumed -- but the risk of rancidity would remain.

If you are interested in using flaxseed oil, look for a brand that contains all the beneficial compounds found in the intact seed, including the phytochemicals known as lignans. Flaxseed oils, particularly when purchased as liquids, should be stored in the refrigerator or freezer.

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 have purchased some wild turbot fillets, and the nutrition chart reads: “Total fat 6 grams, saturated fat 2 grams, trans fat 0 grams.” Please explain the breakdown of the fat content in this fish, as I had thought it was a good source of unsaturated fat. Obviously, it is not the same as the fat in red meat, but is it “good” fat? It also has 210 calories per serving, which seems like a lot. -- F.S., Concord, California

DEAR F.S.: Naturally occurring fats and oils tend to be mixtures of saturated, monounsaturated and polyunsaturated fatty acids. The most prevalent fat is the one that generally gets associated with the identity of the food.

For example, olive oil is considered monounsaturated, but about 10 percent of its fat is saturated, and 13 percent is polyunsaturated. The same goes with fish, which is generally thought of as polyunsaturated, some with omega-3s, but they also contain saturated and monounsaturated fatty acids. And then there’s lard. We might classify it as saturated, but in actuality, it is approximately 45 percent monounsaturated, 11 percent polyunsaturated, and only about 39 percent saturated fat -- much of it stearic acid, a saturated fat that has been found to have a neutral effect on blood lipid levels.

My point here is to not get all worked up about such labels, and focus instead on the overall quality and variety of the foods you eat. Speaking generally, fish are good food, but your question about whether the fats in this particular fish are “good” relates more to personal taste than anything else.

The calories provided seem quite modest. You can also compare this with other fish or food options. Check out nutritiondata.self.com, where you can compare the nutrient contents of foods and portion sizes and see a Nutrition Facts label for your selection. It also provides a breakdown of the different types of fatty acids and other nutrients in your selected foods. Another option is the USDA database (ndb.nal.usda.gov), which provides a library of branded and generic options.

DEAR DR. BLONZ: Why is there palmitate in powdered milk? -- M.B. San Jose, California

DEAR M.B.: When a compound has “palmitate” as part of its name, it means that it is made with palmitic acid, a saturated fatty acid found in palm oil.

In milk fortified with vitamin A, or retinol, that nutrient is combined with palmitic acid, and the resulting compound is called either “vitamin A palmitate” or “retinol palmitate.” The amount of palmitate in powdered milk is negligible. It is only there as an “escort” for the vitamin A added to the product.

You might see palmitate in other compounds as well, such as ascorbyl palmitate, which is a combination of palmitic acid and vitamin C (ascorbic acid).

Consider also that the human body can synthesize its own palmitic acid. Palmitate makes up about 25 percent of the fats found in breast milk, and it’s also present in human lung surfactant -- a substance that coats the inside of our lung surfaces and allows us to breathe.

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.