DEAR DR. BLONZ: I support the importance of having whole foods in our diets. But I am troubled by constantly reading that the soil is depleted of minerals -- the same minerals we assume will be present in our foods. If that’s the case, the produce we eat might not be providing our bodies with the nutrients we need. However, it is my understanding that produce requires certain nutrients to grow to proper size, shape, color, taste, etc. Therefore, it seems illogical to me that the produce of today would not have the same nutrients as it would have had in previous eras with “non-depleted” soil. Please advise. -- S.T., Arlington Heights, Illinois

DEAR S.T.: You can think of plants as miners, pulling the mineral elements required for their growth out of the soil. Add water, energy from the sun, and the appropriate climate, and the game is on.

You are correct in your assumption that if a mineral needed by the plant is unavailable, the plant will fail to thrive; it is doubtful such produce would ever find its way to the market. That indeed makes it incorrect to think that today’s fruits, vegetables or grains would provide any less of the essential nutrients than the same varieties of these plants had provided in the past.

Mineral elements are key here, because unlike humans, plants synthesize their own vitamins. So vitamins will definitely be there, as required by the plant, and will be available for us after the food is consumed, digested and absorbed.

There is another layer to this question, however, as nonessential minerals in the soil can also end up in a plant. Whole foods grown in iodine- or selenium-rich soils, for example, can have more of these nutrients than the same type of food grown in soils with lesser amounts of these minerals.

What gets pulled in can differ from plant to plant and mineral to mineral -- even among different varieties of the same fruit, vegetable or grain. The plant’s overall nutrient content can also vary according to the time of the growing season and the length of time the plant has had to grow. This means that a plant picked green may not have the same nutrient content as one allowed to ripen on the vine.

It is difficult to speak with any statistical certainty, because we don’t have records of nutrient content from the produce of a hundred years ago. Based on what we know, however, it’s likely that the amounts would be comparable.

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 kept up with a group of my high school friends through social media. Back then, we went out for the same sports and all had comparable body types, heights and weights. This past New Year, we made an agreement to measure and compare our caloric intakes, checking with online food composition tables. To our surprise, we found that we each eat just about the same number of calories every day. Despite all this, our weights and body shapes have now changed, in some cases rather dramatically. It was frustrating for me, as I have one of the larger waistlines in the group. How is it that people with similar caloric intakes can end up with such different weights? Four of us have been exercising together on and off for about 10 years. -- F.S., Brooklyn, New York

DEAR F.S.: Food composition tables, now available online through the U.S. Department of Agriculture (ndb.nal.usda.gov) and commercial sites (nutritiondata.self.com), provide information about what’s in the foods we eat. Remember that the calories they list for a given portion are nothing more than calculations of “potential energy.” The efficiency with which a fixed number of calories is utilized can vary from body to body. It’s similar to the way miles per gallon varies between the different models and conditions of automobiles.

For example, one’s basal metabolism -- the calories used while the body is at rest -- rises as the amount of muscle in the body increases. This is because muscle is “active tissue.” Fat tissue, by contrast, is not very active. Using the automobile analogy, this would be similar to how a car with an eight-cylinder engine burns more gas at idle than one with a four-cylinder engine.

Other factors include age, sex, genetic makeup, level of physical activity and the efficiency with which one digests and absorbs food. All these play into the way a given number of calories will affect a particular body at a particular period of life.

We get away with much during our youth, particularly if we are physically active. But if we scale back the exercise during our transition to adulthood, we will find our measurements advancing with the years. This becomes more likely if our dietary habits fail to change with the times. Exercise not only burns up calories, but can also increase the amount of muscle in the body, and that additional muscle mass burns more calories even when you are at rest.

As is true with most aspects of life, some people have to work harder to accomplish the same goal. Where weight is concerned, though, one’s value system should not get bogged down with comparisons to others. Rather, we should be focused on doing the best we can with what we’ve got -- or at least starting the process with that as our goal.

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: My grandmother used to encourage us to eat the inner white part of the orange skin, saying that it is a secret part of the food that has special qualities. Dutifully, I have followed this advice for a lifetime. Finally, realizing that the science behind nutrition was not as well known in her day, I have come to question the advice’s worth. What, if anything, is the value of this part of the orange? -- S.N., Lombard, Illinois

DEAR S.N.: Your grandmother’s advice may not have been drawn from research findings of the day, but it does reflect an intuitive appreciation for citrus fruits, and whole foods in general.

The entire orange contains a number of naturally occurring compounds that have been associated with disease prevention in humans. But please note that simply because a substance can be found in a food, that doesn’t mean there is enough of it to have a significant beneficial effect in our bodies. These are compounds that evolved to protect the fruit’s seeds, as well as the flesh that the seeds rely upon for sustenance until they get their first sprouts into the sun and begin producing their own energy.

Aside from the vitamin C that we associate with citrus, there are a number of substances in the peel and in the white inner portion, or albedo, of the citrus peel. The list includes bioflavonoids, limonene, glucarate, pectin and soluble fiber. If you consume the outer part of the peel, expect it to contain residues from any sprays used by the grower -- so select your citrus provider carefully and scrub the fruit before eating. Citrus zest is quite flavorful and is often used for culinary purposes, but only use zest from well-washed, organically grown fruit.

Other fruits and vegetables offer similar types of protective substances, but science is still in the discovery stage about their range of potential health benefits for us -- along with how they might work together, and what effective doses would be. I salute your grandmother’s whole-food wisdom.

DEAR DR. BLONZ: There are many half-and-half products in my dairy case. Some are pasteurized, and others are ultra-pasteurized. What is the difference? -- D.C., San Jose, California

DEAR D.C.: Pasteurization and ultra-pasteurization are heat treatments designed to reduce the presence of potentially harmful microorganisms. The two differ in the amount and duration of heat used.

Pasteurization heats a dairy product to 160 degrees F for 15 seconds, while ultra-pasteurization heats the product up to 280 degrees F for up to 3 seconds. The higher heat used in ultra-pasteurization eliminates more bacteria and results in a more shelf-stable product. Once opened, however, both types of products require refrigeration.

Ultra-pasteurization is not widely used because the high heat can affect flavor, so the process is usually reserved for products such as half-and-half or whipping cream. However, ultra-pasteurized milk can be found in remote areas, or in stores that don’t sell a high volume of dairy products.

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.