DEAR DR. BLONZ: I want some perspective on a recipe known as “skinny soup,” which consists of cabbage, celery, onions, garlic, peppers, carrots, canned tomatoes and water. The rumor is that digesting this soup uses more calories than those found in the ingredients. It is also supposed to be anti-inflammatory. There are many different spins on this theme online, with an assortment of recipes out there. Any truth to this? -- C.N., Phoenix

DEAR C.N.: Small amounts of energy are indeed required for digestion, as well as for the conversion of proteins, carbohydrates and fats into different forms and structures. And our bodies’ metabolisms are not 100 percent energy-efficient; energy is lost, perceived by us as heat when our metabolism kicks into a higher gear. (Think about the heat you experience while exercising.) This also occurs during the digestive process after eating, a phenomenon referred to as the thermic effect of food, or TEF.

It is all part of the cost of bodily business. Once the body is in a “fed” state, the green light goes on to build, repair and put the excess away into storage; these are also functions that require energy, but are not 100 percent energy-efficient.

Foods with a low caloric density (few calories per unit weight), such as that soup, might indeed cause the body to burn more calories than they provide. The caloric difference, however, would not be that significant. However, if you get in the habit of substituting a low-calorie soup or salad -- or even a glass of water or a cup of tea -- for a more calorie-dense food, the net effects will certainly add up over time. That’s the real skinny. It’s not a magic soup; it’s just math.

As for the anti-inflammatory aspects, contributions to that element of the balance sheet would hold true for the healthful whole foods in the recipe -- as well as most other fruits, vegetables and whole grains, however they are consumed.

DEAR DR. BLONZ: This is another exceedingly hot summer, and as we all know, summer temperatures tend to soften fruits rather quickly. I have hesitated to refrigerate tomatoes for fear it would result in a loss of flavor. Is this a misconception, or should I go ahead and refrigerate? -- F.M., Hayward, California

DEAR F.M.: Refrigeration can slow the growth of many microorganisms, but it can also affect the quality of some foods. Tomatoes are best kept at room temperature, preferably in an airy location with moderate humidity. They should last about five or six days in these conditions. By placing the tomato in the refrigerator, you may delay it from going moldy, but flavor and texture are likely to be damaged in the process.

This is particularly an issue with flavorful homegrown varieties and those purchased at a farmers market. It may not be as much of an issue with store-bought tomatoes that have already been given a dose of refrigeration, as many markets store their produce in the cooler overnight.

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: Our new home has some olive trees that are bearing fruit. We all know how healthy extra-virgin olive oil is for us, but do we get the same health benefits from eating olives? -- J.T., San Jose, California

DEAR J.T.: As you may have inadvertently discovered if you sampled the fruit, olives are quite bitter coming off the tree. To be eaten, they need to undergo a curing process to remove this bitterness, caused primarily by a phytochemical called oleuropein.

Curing typically involves a solution of salt or lye (sodium hydroxide). Both of these leave the olives quite high in sodium: 15 grams of olives (three to five of them, depending on size) contains about 115 milligrams of sodium -- not surprising given that the olives are stored in salty pickling brine before purchase. In a pimento-stuffed olive, the sodium can be twice that amount.

By contrast, when olives are used for oil, the harvested fruit goes directly to the presses without treatment. The fatty acid profiles are similar between eating olives and extra-virgin olive oil. The phytochemicals are mostly similar, with one exception being the intentional decrease of the bitter oleuropein in the eating olive.

It takes a lot of olives to equal a comparable serving of oil. For example, a tablespoon of olive oil (about 14 grams) would contain 120 calories. It would take about 22 large black-pitted olives to match that amount of oil, but that number of olives would contain 644 milligrams of sodium.

I do enjoy eating olives, and there are countless varieties and flavors, but you have to keep in mind that it’s a high-sodium food. You can give your olives a series of fresh-water rinses before serving to reduce the level of sodium.

If you are interested in this topic, there is excellent information from the University of California at Davis (tinyurl.com/zeqp2lh). This page provides reading on different olive types, the curing process, and information on curing with water, which would certainly make a dent in the level of sodium.

DEAR DR. BLONZ: I’ve been having a strange reaction to all dairy, including lactose-free products. I react as if I’ve had three cups of coffee or other caffeine products. I cannot sleep, and sometimes I get a headache. What am I allergic to? -- T.M., via email

DEAR T.M.: Get this checked out with your health professional at your earliest opportunity. It could be a reaction to the protein or some other substance found in dairy products -- but whatever the issue might be, this is NOT something you should let slide. Until it is all sorted out, it’s best to keep dairy products off the menu. This includes reading the ingredient statements of any processed foods you use. There are many dairy ingredients aside from the obvious; see the hidden dairy “cheat sheet” at tinyurl.com/y9tmbw75.

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: At a recent luncheon, there was a talk at our table about healthy foods we include in our diets. A couple of my friends went on at unusual length about the endless health and curative powers of mangosteen. This is not a fruit I am familiar with. I would appreciate any information you may have about this substance and products made from it. I was rather skeptical, and I will pass on your comments. -- S.T., Concord, California

DEAR S.T.: The mangosteen is a fruit native to Indonesia and southeast Asia, but it can be grown in other tropical climates, including Hawaii. Like any plant that manages to flourish under the oxidizing rays of a tropical sun, the mangosteen has evolved to produce a complement of antioxidant phytochemicals. As with most tropical fruits, this one can be an excellent addition to the diet, but it is not widely available in the domestic produce aisle. As for its possessing “endless health and curative benefits,” this is more marketing than a reflection of evidence-based science.

There may indeed prove to be something special in the mangosteen, but I could find no convincing evidence from clinical studies. Regarding the fruit itself, it’s supposed to have a unique, enjoyable flavor that has been variously described as sweet or slightly sour, with undertones of vanilla, strawberry and peach. I will keep an eye out for reliable scientific studies, and will report back if there are any promising developments.

We have been down this road before with various fruits, vegetables and herbs. The more respectable commodities put funds into research on the popular produce du jour, and then wait for results before any grand health claims are made.

The bottom line is that there is no shortage of healthful foods, and they all deserve consideration for a place on your plate. Health claims should never outpace the hard science. Proceed cautiously, especially if the plaudits from your friends are associated with the use of mangosteen as a dietary supplement and not a whole food.

DEAR DR. BLONZ: I have been told not to heat food in the microwave in hard, plastic containers, as the plastic secretes a cancer-causing chemical when hot. Is this true? -- M.S., via email

DEAR M.S.: The major issue here is: Are you using containers that are specifically designated as “microwave safe”? That being the case, you are almost certainly in the clear. There may be troubling substances in certain plastics, but we are talking about levels that are very low -- well below any level for concern. There is an FDA article on microwave cooking that includes a discussion of containers at tinyurl.com/yc8z6ydl.

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.