DEAR DR. BLONZ: I have some questions about some steaks I recently purchased. They looked really good in the store: a fresh, bright red. The date on the package also indicated that they were fresh. When I got home and opened the package and trimmed the steaks a bit, it became obvious that the middle of the steaks were brownish; only the outside surfaces were red and fresh-looking. The steak didn’t have a bad smell. I have never seen anything like this before. I returned the steaks and got my money back, no questions asked, but also no answers. What could have caused this? Was the meat “stressed”? Was it spoiled, and then treated somehow to look fresh? -- W.B., San Bruno, California

DEAR W.B.: Color and general appearance help determine the appeal of any food product, including meats. Meat is muscle tissue, and when working in the body, it is normally dark-red to purple in color. When exposed to oxygen, a chemical reaction takes place that causes it to turn bright red. This phenomenon is referred to as “bloom,” and involves a reaction with myoglobin, a muscle protein. Below the surface, or even on the bottom of the package, the color can be darker because the reaction hasn’t yet taken place there.

If a cut of meat that has bloomed is allowed to sit out, exposed to the air, a second reaction can occur, causing the red color compound of the meat to oxidize and turn brown. This is not necessarily a sign that the meat is of poor quality, but in time, the flavor will deteriorate.

Interestingly enough, once meat has bloomed, the length of time it stays red can depend on the antioxidant content of the meat. Studies have found that upping the vitamin E content of the animal’s diet can increase the time in bloom.

In general, butchers cut enough to satisfy turnover. They can use an overwrap film to limit air exposure, or even flush packages with a mixture of oxygen and carbon dioxide. All this causes the meat to bloom more slowly. The cutting and packaging processes are coordinated with the time it takes to get the meat into the display case and sold.

Products that turn brown on the surface can be trimmed, allowing a new layer to bloom. But in your case, the meat was red on the surface, but dark all the way through. This would seem to indicate that something was awry. It could very well have been due to stress, as you suggest, but there may have been other factors as well. In any event, it made perfect sense to take it back.

DEAR DR. BLONZ: What are good foods for magnesium? -- C.B., York, Pennsylvania

DEAR C.B.: Magnesium is an essential element needed for normal bones -- in fact, half of our bodies’ magnesium is in our bones -- but also required for normal nerve transmission, muscle relaxation and normal heart rhythm. Good dietary sources include avocado, nuts, bananas, legumes, whole grains, dark leafy greens, milk and oysters.

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 an issue with the term “carbohydrates.” I think of vegetables and fruits as “good” carbohydrates, and starchy foods as “bad” ones. In one of your recent articles, you said that the common after-Thanksgiving sleepiness was caused by the carbohydrates traditionally consumed with that meal. My question is, do the carbohydrates in vegetables cause the same reaction in the brain? And why do we lump all these foods into one category? -- M.T., via email

DEAR M.T.: To answer your question, we will need to cover some basic concepts. Carbohydrates are also referred to as “saccharides,” which comes from the Greek word for “sugar.” They are substances made up of carbon, hydrogen and oxygen. It is helpful to think of each individual carbohydrate unit as a chain link. When the “links” exist singly, they are referred to as monosaccharides; two examples are glucose and fructose. Two links joined are referred to as disaccharides, and these include sucrose (a glucose link joined to a fructose link), lactose (glucose joined to galactose) and maltose (glucose joined to another glucose). Monosaccharides and disaccharides are also referred to as “simple sugars.”

When the links are joined in complex, branched chains of varying lengths, you have a polysaccharide, also known as a “complex carbohydrate.” The main examples are the starches.

It takes a digestive enzyme to break each bond that joins carbohydrates together. This is a critical step, as the human body does not effectively absorb or metabolize carbohydrates unless they have been broken down into their individual “links.” Glucose and fructose, being monosaccharides, require no enzymatic action. Sucrose is rapidly broken apart. As a result, both of these are rapidly absorbed and will have a greater impact on raising blood sugar levels.

Starches are found throughout the plant world, and they exist in various branched configurations. (Interestingly, wood is made of carbohydrate links similar to starch, but they are bound together in a different way. Unlike starch, the human body doesn’t produce an enzyme to break apart or digest wood’s carbohydrate links.)

Now let’s return to the tiredness issue, which relates to the speed at which blood glucose rises after a meal. Blood glucose rises faster when we eat sugar than it does with starch. With the carbs in vegetables, it does not rise as rapidly, but as the structure of starches can vary, it will rise faster with some starches than with others.

The measure of how fast glucose rises for various foods is called the glycemic index. The other concept at issue is glycemic load, which factors in the total amount consumed. Check glycemicindex.com from the University of Sydney for a list of the glycemic indices of different foods; it also has a way to determine glycemic load.

The bottom-line response to your question: By virtue of the fact that it refers to chemical structure, you will have to accept the term “carbohydrate” as applicable to all its sources.

For more on carbohydrates, check the article at goo.gl/7lT0Ae.

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 there significant differences in health effects between roasted and raw nuts? A raw-foods proponent at a local natural food store said that a half-cup of raw peanuts has 430 calories, but when roasted and processed into peanut butter, a half-cup will contain 780 calories. I expressed my skepticism, but wanted your take. -- J.S., Walnut Creek, California

DEAR J.S.: When roasting nuts, or any food, a series of chemical reactions takes place that can enhance the flavor and odor. With nuts, this can be accomplished with or without oil. Dry-roasting (without added oil) is done in specially designed ovens and utilizes hot air. Salt, paprika or other flavorings can be added as desired.

Because over half the weight of a nut, and over 70 percent of its calories, come from its fat content, dry-roasting results in only a nominal decrease in overall fat content. A flavored roasted nut can contain less fat per serving than a raw one because some of the weight is taken up by the added flavors and coating. Regarding nutritional value, any high-heat process will destroy some of the folate and thiamin (vitamin B1), but the other nutrients remain.

Raw peanuts have similar tastes with slightly different texture and flavors, but there will be comparable fat content to roasted nuts. With raw nuts, there is a slightly higher risk of microbiological contamination, so they are not recommended for immune-compromised individuals. Any raw peanuts should be stored in the refrigerator in a well-sealed container. Purchase from sources that use bulk containers where the newest nuts are added on top, with the nuts being purchased exiting at the bottom.

Finally, that comment about the caloric content of raw peanuts versus peanut butter is misleading. There will always be air in a cup of peanuts that is not found in a similar volume of peanut butter. If, however, you were to compare similar weights of these two foods, the caloric content would be comparable.

DEAR DR. BLONZ: Can you explain why vitamins and minerals expire? -- S.H., Arlington Heights, Illinois

DEAR S.H.: Vitamins are reactive compounds that play an integral role in the wide array of chemical reactions that comprise our metabolism. While mineral supplements tend to be quite stable, vitamins can slowly lose their potency over time. The factors that encourage breakdown are humidity, temperature, and light. Formulas that contain fat-soluble nutrients tend to break down the fastest.

The best way to store products is in a tightly sealed container in a cool, dark place. Many supplements include moisture-absorbing capsules or packets to help maintain product quality. Product expiration dates indicate when the vitamins can be assured of full potency, assuming, of course, that the product has been appropriately stored.

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.