DEAR DR. BLONZ: I have questions about foods sold in plastic containers at my local store. Can a microwave be used to defrost chicken and beef broths in these containers? These foods are produced in small quantities, sold only at this store, and have no markings aside from a label indicating the food inside. Should I be concerned about plastics leaching into the food? -- B.B., Portland, Oregon

DEAR B.B.: Many different materials are used in food packaging, and there may be cause for concern if a substance migrates from the packaging into the food it contains. These are referred to as incidental food additives, and are regulated by the Food and Drug Administration. Attention is required if a food-packaging substance is found to be harmful, but there should also be concern if the packaging affects the food's quality, appearance or shelf life. Two concerns with plastics are bisphenol A, also known as BPA, once common in can-lining materials and plastics, and plasticizers known as phthalates. (More about BPA at b.link/dzukfd, and phthalates at b.link/skx9fz5e.)

Your local store packages its minimally labeled foods in plastic containers, then stocks them in their freezer for sale. Foods prepared in a retail establishment and sold only in that establishment are exempt from the requirement to display nutrition labeling. (For more on this, see b.link/6ex3bwrr.)

But that does not absolve you of the need to know how to treat these foods and their containers appropriately -- especially as they may be sold in single-use containers unsuitable for the microwave.

Check for a "microwave-safe" symbol on the carton or label before putting that container in the microwave. "Microwave-safe" is usually an icon with horizontal wavy lines. (For examples of food and equipment symbols, including those signifying "microwave-safe," see b.link/hdsuug2b. For more on general microwave safety, see b.link/js6iw9yw.)

If you don't see the "microwave-safe" symbol, it's best to assume the container is not microwave-safe. What to do with that store-packaged frozen broth? Defrost it in your refrigerator. You can also use a brief hot-water bath to loosen up the contents and then transfer it to a designated microwave-safe container for the rest of the defrosting in the fridge.

If the container has a symbol of a 5 in a triangle, often with a "PP," it is made from polypropylene, which is generally considered microwave-safe. Still, it's best to find those squiggly, microwave-safe lines. The responsibility is on the consumer to check with the store to verify that they use microwave-safe containers. You can encourage the store to post information about the containers they use.

One final point: Containers, particularly plastic ones, do not have an indefinite life span. Discard single-use containers after the contents are gone, and toss any plastic container if it shows signs of cracking or discoloration.

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 had to stop my caffeine intake due to a health condition. It took a few days to stop the annoying headaches, and I wondered what caused them. Things have now settled, but I do miss my coffee. I have a question about a caffeine-free energy drink: The ingredients list shows "guarana," which has me wanting some clarification before trying it. Thanks for any advice you might provide. -- T.I., San Jose, California

DEAR T.I.: The headaches you experienced relate to the way caffeine works: how the body adapts to its chronic presence, and what happens with abrupt withdrawal, which is what you went through. In addition to caffeine, a key biochemical in this scenario is adenosine, a compound found in all living cells that plays many roles and is part of the genetic building blocks of DNA and RNA. As a neurotransmitter, higher levels of adenosine cause feelings of sleepiness. Receptors on cell surfaces bind to adenosine to make this happen. Caffeine blocks the adenosine receptors, which keeps us alert. After days of regular caffeine intake, the body compensates by adjusting the number and sensitivity of its adenosine receptors. Not everyone responds to this process with the same efficiency, which explains how some people can consume coffee with dinner without it affecting their ability to fall asleep at night.

When a regular caffeine user abruptly stops, the body becomes hyper-responsive to adenosine because caffeine is no longer present. It is believed this is responsible for the withdrawal headache and other discomforts associated with the sudden absence of caffeine. People who stop their regular caffeine consumption when fasting for blood tests, medical procedures or religious holidays know this sensation. Consuming caffeine, of course, would reverse it, but that's not always an option. It has been suggested that continued caffeine consumption may be as much about avoiding the withdrawal effects as any enjoyment of the caffeinated beverage itself. As a coffee drinker who enjoys my morning brew, I find this a bit disingenuous, but I acknowledge a bit of subjectivity here.

As for your energy drink: Guarana (Paullinia cupana) comes from the seeds of this South American climbing shrub. Guarana seeds have a high concentration of caffeine -- more than twice that of coffee beans, the kola nut or cacao (cocoa), which makes it a useful ingredient in energy drinks. Often referred to as guaranine, or natural caffeine, guarana is misleadingly characterized as "caffeine-free." The seeds of the guarana shrub produce caffeine as part of their phytochemical defense against insects and animals dining on the plant and its seeds. For these tiny natural poachers, the level of caffeine in one seed can be deadly, but our size provides us with greater tolerance. Marketing guarana as "caffeine-free" is deceptive. Glad you checked things out.

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.

(Note to Editors: Dr. Blonz is away this week. This column originally appeared on Oct. 19, 2021.)

DEAR DR. BLONZ: I wonder if you could comment on a family discussion. My father-in-law often eats an entire bag of potato chips at one sitting -- a 10-ounce bag, not an individual 1-ounce bag. He says that his body can only absorb so many of the calories that he eats at once, and that the rest will just pass on through. In this way, he claims he will actually absorb fewer calories by eating the whole bag at once than if he ate just a portion every day until it was gone. Is this true? -- K.B., via email

DEAR K.B.: There is some logic to your father-in-law's position: namely, that in some circumstances, there can be inefficiencies in caloric absorption when the body is dealing with an uncharacteristic dietary overload. The backstory, however, can help complete the picture.

The human body is oriented for efficiency, avoiding any waste of calories and other resources whenever possible. Muscles, for example, require energy (calories) even while at rest. (Think of the analogy of gas consumption by an eight-cylinder car at idle versus a four-cylinder car.) Working muscles adapt to our activity routines, increasing their mass to meet the demands of habitual load. The converse is also true: Muscles shrink when decreased activity becomes the new norm.

Similar adjustments occur with digestion -- system-wide adaptations to what, when and how much we regularly eat. This helps explain why we tend to get hungry at our typical mealtimes and why we might be at greater risk for indigestion when eating at unusual times, such as after traveling through several time zones. This also explains why abrupt, radical shifts in the foods we eat might not "go down easy," even if the change is toward more healthful fare.

Does the above suggest that having a 10-ounce bag of chips -- the equivalent of 10 1-ounce servings -- at one sitting might be an acceptable strategy? Hardly. Downing that full bag will result in increased blood levels of the chips' food components -- approximately 90 grams of fat, 160 grams of carbohydrate and 1,500 mg of sodium. All of that will be waiting in the queue for absorption, and it is complemented by few, if any, healthful assets.

Fat, carbs and sodium are not the snack-food elements you want to accentuate, even if absorption isn't happening with 100% efficiency. What fails to be absorbed ends up traveling the rest of the way through the intestines, bringing nutrients to areas where they're not often seen. This can result in indigestion, gas and other negative effects. And if the bag of chips is consumed within a couple of hours of another meal, the digestive and absorption machinery will already be up and running -- robbing the assumption of caloric wastage of its heft.

A sizable load of fat, carbohydrates and sodium, from a processed food with few healthful assets, increases elements associated with many chronic diseases. So even if you feel you can defend the action using a caloric-inefficiency rationale, health logic argues that you are not doing yourself any favors.

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.