DEAR DR. BLONZ: Something that is hyped with intermittent fasting and ketogenic diets is that they promote autophagy, which is described as cleaning out, detoxifying and renewing the body. I remain curious whether and to what degree this might be true, and how it works. -- F.S., Tulsa, Oklahoma

DEAR F.S.: The adult human body is remade regularly by way of cell replacement; directions for this are in our genes. But, to work as programmed, there must be access to raw materials, nutrients, and available energy when and where needed (especially vital during pregnancy and growth spurts).

In adults, turning over the fastest are the red blood cells and the cells lining the mouth and gastrointestinal tract; this helps explain why nutrient deficiencies or other medical or medication issues tend to be felt in these areas first. Regarding other parts of the body, the cells of the liver turn over faster than muscle cells, which turn over faster than bone cells.

The point to remember is that while autophagy renews, it does not make us "new and improved" -- our bodies remain governed by our genes, the foods we eat and the lifestyle we lead -- check out b.link/x555gk.

The materials for the rebuilding come from essential nutrients in the foods we eat, along with those provided by the body's recycling system. Autophagy (aw-TAHF-uh-gee), which translates literally as "digesting oneself," is the process of cell breakdown that facilitates the disposal of unwanted cellular debris while holding on to substances suitable for reuse. Sounds great -- so who wouldn't want eating plans that promote cell renewal?

Autophagy's expression is not fixed -- it gets prioritized according to the needs of the moment, as efficiently as possible. For example, suppose the body hasn't been getting enough of a particular essential mineral. The body's response is to be more conservative with what it has, and the kidneys become stingy in allowing that mineral into the urine. Autophagy aligns with such priorities to facilitate the availability and reuse of any materials in short supply.

Nutrient intake stops during a fast, and with a ketogenic diet you may not get the full complement of the body's nutritional needs. One thing both diets cut is carbohydrate intake.

Digestible carbohydrates get converted to glucose, which is the only fuel that can be burned by our red blood cells and is the brain's preferred fuel (the brain uses about 70% of the glucose in the blood for its energy). The body has a minimum blood glucose level; if sufficient amounts are not in the foods we eat, the body breaks down resources to support the minimum level. This is potentially lifesaving as, unlike fat, glucose is the only substance that can release its energy without oxygen. It explains how we can walk up a hill or stairs without first taking deep breaths to increase the oxygen level in the blood. After several steps, the body has you breathing deeper as it shifts to burning fat for energy.

The bottom line is that autophagy is a complex process that should not be spun as an eating plan to promote cell renewal. Keeping your body supplied with its essential nutrients through a plant-based, whole food, healthful diet will keep this process functioning properly to help achieve normal cell turnover, in which the body recycles the good stuff and takes out the trash as needed.

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 no thyroid problems, but during a recent lecture on iodine, the presenter described a simple test to determine if you are deficient. It involved buying some iodine antiseptic and painting it inside your forearm or thigh. If you wake up the following day and the iodine is still visible, it indicates your body has sufficient iodine. But if the dark color has faded, it indicates your body is iodine-deficient. I wanted your thoughts. -- H.T., Scottsdale, Arizona

DEAR H.T.: Iodine is an essential trace element needed for thyroid hormones, which are substances that help regulate the metabolism. The daily value for adults is 150 mcg, but it is higher during pregnancy and breastfeeding (more on iodine from the NIH at b.link/chse3n).

Absorbed iodine travels in the blood and gets removed by the thyroid, a butterfly-shaped gland at the front of the neck below the larynx. If the body were chronically iodine-deficient, the thyroid gland would enlarge to do a more efficient job of grabbing iodine from the blood. At this point, a condition known as goiter would have developed, including a noticeable bulge in the lower throat area. Iodine is plentiful in the ocean, but is not well-distributed on land. In the U.S., areas where iodine deficiency was common in the early 1900s -- including the Great Lakes, the Appalachian Mountains and the inland Northwest -- came to be known as the "goiter belt." In the 1920s, as a public health measure, the government encouraged manufacturers to add iodine to table salt -- a move that drastically reduced the incidence of goiter.

On a side note, iodine has a connection to nuclear accidents, which often involve a release of radioactive iodine (radioiodine) into the environment. Radioiodine can be absorbed by the body and destroy cells in the thyroid and elsewhere. An iodine deficiency makes one particularly vulnerable to such damage. While those in an area with a radiation emergency are advised to evacuate, another protection can be to take a potassium iodide supplement, which would satisfy the body's need for iodine and protect the thyroid from that danger.

Today, it's uncommon for anyone eating a varied diet to suffer from an iodine deficiency, especially when iodized salt is used. Food containing iodine is limited to seafoods, crops grown in coastal areas and dairy or meat from animals that graze on feed that's supplemented with iodine.

Now, back to your question. There are established, reliable ways to determine whether your body is iodine-deficient, and the method you describe would not be on that list. The procedure you describe, sometimes called an "iodine patch test," is unreliable. Iodine applied to the skin can be absorbed, and it can happen more rapidly if there is a severe deficiency, but the iodine will also lose its color when it converts to (colorless) iodide, a process that can occur irrespective of the level of iodine in the body. That patch test may work under some circumstances, but it is not considered a reliable indicator of your iodine status.

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 keep reading about "buying locally." I can see the good in that it would involve fewer resources, but it seems that if you buy all your food from your area, you wind up with the nutrients only from that area, and might miss others. I am curious about the possible benefits of getting food that is grown all over the world. -- B.K.

DEAR B.K.: "Seasonality," where we are limited to foods available during periods in which they are harvested, is less of an issue in today's fully stocked supermarkets. Much depends on where you live; there is less impact in a state like California, where vast agricultural resources and temperature-controlled transportation methods keep fresh produce available throughout the year. But even with bountiful harvests, there will be periods during which specific foods may not be available. (One of my favorites is dry-farmed Early Girl tomatoes, which are around only a few months of the year. To my palate, no other tomatoes come close.)

Store shelves remain full as grocers purchase fresh foods grown worldwide and organically grown produce available from the Southern Hemisphere when it's winter in the north. We should support local agriculture by buying locally and patronizing farmers markets when possible. Quality can vary, as some regions do a better job with specific foods than others; this is often based on cultural traditions perfected over generations. As for potential health benefits, nutrients reflect more the quality and variety of what you eat rather than where it was grown.

DEAR DR. BLONZ: After I get my dietetics degree, I am considering graduate school, with the goal of working for a food company to develop nutritious foods with less processing, ideally by using controlled atmospheres. I want to develop, test and promote various food products, create new recipes and improve existing ones. Would getting a graduate degree in food science or nutrition be more beneficial? I would appreciate your opinion since this is your area of specialty. -- J.D.

DEAR J.D.: A dietetics degree will provide a foundational understanding of how nutrients work in the body. A graduate food science degree would seem logical if you want to work in the food industry. In addition to learning essential information about food production science, you would be more marketable when looking for a job. Consider a school with food science and nutrition departments; some may have these combined. The Institute of Food Technologists may be a good resource. This professional organization is based in Chicago, and it provides information about careers in the food industry (ift.org).

As you compile a list of possible schools, check online for a list of faculty research interests. Academic departments' successes depend on their faculty's strengths, and reviewing their interests is an excellent way to see how a department is oriented. In graduate school, you will take the required coursework, but will be associated with a professor to guide you on projects. You'll be ahead of the game if you find a school with one or more faculty members that either speak to your current interests, or describe an area of research you want to pursue.

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.