DEAR DR. BLONZ: I have tried intermittent fasting, but I want to know your thoughts on going on a multi-day complete fast for energy, cellular renewal, detoxification and immune system strength. Water would not be stopped, only all food. Thanks. -- A.K., Raleigh, North Carolina

DEAR A.K.: The idea of fasting has been around for a long time and is an integral part of many religions. The origins are intertwined with ancient beliefs that fasting leads to a purification of the soul or spirit. I appreciate your qualifying complete fasting from intermittent fasting, where you only eat during specific times or a limited number of hours a day. This is a more nuanced area with varying approaches and evolving research (for more on intermittent fasting, see the article at: b.link/8pp5ue6).

Up front, let's understand that when you stop eating, your supply of energy and raw materials, as well as the rate of tissue repair, all decrease. Glucose (blood sugar) is the preferred fuel for the brain and nervous system. It is the only fuel that the red blood cells use, and it is the body's primary source for instant energy. Glucose allows you to transition from resting to running without first taking deep breaths to increase the level of oxygen in your blood. There are small stores of a form of glucose in the liver and muscles, but it doesn't last very long. When in short supply, the body craves glucose to the point that it breaks down its muscles and organs to get at the specific amino acids it can modify into glucose (glucogenic amino acids).

Daily protein intake provides amino acids to replace worn-out cells, but during a fast, the body must recycle its amino acids. It comes up short because some are recruited to form the needed glucose. During the first days of a fast, approximately 75 grams per day of the body's protein gets used to satisfy our need for glucose; this slows tissue growth and repair.

One of the claimed benefits of fasting is that not eating allows the digestive system to rest, thereby freeing energy to help the body detoxify and improve overall health. This is illogical. Normally, about 10% of dietary energy is used to digest, absorb and metabolize what's in food. Fasting for this purpose would be like quitting your job to save commuting expenses.

As for detox claims, toxins are often fat-soluble compounds that distribute themselves throughout the stored fat in the body while awaiting elimination. With a fast, the mobilization of fat calories can result in increased blood levels of these unwanted substances and contribute to the general weakness experienced. There is much to consider. A healthy diet and lifestyle are important goals, and many paths can take you in that direction. I encourage you to look behind rosy portrayals of total food fasting as critical to that objective.

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 been focusing on whole foods and reducing my consumption of processed fats in my diet, as well as that of my family. I do want to address the diets of my children, aged 9 and 14, and what they need in their diets. -- C.P., Chicago, Illinois

DEAR C.P.: It's essential to appreciate how certain fats are vital to our good health; this applies to both adults and children. Essential fatty acids (EFAs) play a crucial role in combating major maladies, including heart disease, high blood pressure, rheumatoid arthritis, intestinal disorders, psoriasis and complications associated with diabetes. For you and your family, understand that habits formed in childhood set the stage for later years, and your example goes a long way.

Currently, we are aware of two types of primary EFAs: omega-3 and omega-6. The omega-3 EFAs are found in fish oils but can also be obtained from flaxseed (also known as linseed) and, to a lesser degree, in walnut and canola oils. The fish containing high levels of omega-3 include salmon, mackerel, tuna, sardines, anchovies and herring. For more, see b.link/ubluccbx.

The omega-6 EFAs are derived from vegetable seed oils, such as corn, soy and safflower. We have learned that the body uses EFAs to produce powerful, hormonelike compounds called prostaglandins (PGs). These PGs help determine how the body operates. I encourage you to resist the overload of toxic misinformation regarding seed oils on social media. For more on omega-6, see b.link/d5cd8md.

The typical American diet tends to be high in the omega-6 EFAs and too low in dietary omega-3s. This is an important point because while both EFAs are essential, they have dramatically different health effects.

For example, a heart attack is caused when a blood clot blocks the flow of blood through an artery. The omega-6 PGs tend to encourage blood clotting, while those made from omega-3s inhibit the process. Experiments have shown that including more omega-3-containing fish in the diet results in blood clots forming at a slower rate, and the incidence of heart attacks can be reduced.

Blood pressure is another topic of interest. It's beginning to look as if the PGs coming from the omega-3s can help moderate high blood pressure. Both high blood pressure and blood clotting are involved in many long-term health complications seen with diabetes. Three recent reports highlight the potential benefits that insulin-dependent diabetics may experience by consuming more fish.

Having sufficient EFAs in the diet may also play a role in two disorders involving the immune system. In separate controlled studies, symptoms of rheumatoid arthritis and ulcerative colitis improved when volunteers were fed high levels of omega-3 EFAs; in this study, it was in capsule form.

Omega-3 fats also have potential as an anti-cancer agent. While PGs produced from omega-6 have some ability to increase tumor growth in experimental animals, those from omega-3, such as those found in fish oil, do not. What we continue to learn about omega-3s is that they have numerous benefits.

Don't get the idea that one EFA is good and the other is bad. We need them both. The problem with essential fats is that the typical American diet is out of balance, and you can work on educating the family about its long-term significance.

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: What is known about how our digestive system can renew itself? Can materials normally eliminated end up stuck for several months and cause various problems? There are "cleanse" services that provide colonics to unclog and resolve these issues, and I would like information about whether there are benefits to undergoing this procedure. -- F.S., San Jose, California

DEAR F.S.: There is misinformation on this topic, often from those selling products or services that they claim address specific problems. The cells lining our digestive tract don't last long. This is crucial, because they are constantly exposed to mechanical stress, digestive enzymes, microbial interactions or unwanted substances that have been consumed or formed from breakdown products, or medications detoxified by the liver and deposited into the digestive system for elimination. The ongoing renewal helps maintain gut integrity, optimize nutrient absorption and support our healthy microbiome.

Different sections of the digestive system have varying rates of cell renewal. The cells lining the stomach turn over every two to three days due to the wear and tear of its harsh, acidic environment. In the small intestine, we have cells (enterocytes) responsible for breaking down food and absorbing nutrients; these cells are replaced every two to five days. In the large intestine, where the microbiome calls home, turnover is slower and can take four to five weeks. This delay makes sense as we want more stability for our microbiome.

Claims that undigested waste and toxins can get stuck for months and need to be routinely flushed using colonics are based on pseudoscience, not objective evidence.

Now, there are specific medical conditions that can affect the ability of food to move through the digestive system, referred to as digestive motility. These are uncommon clinical conditions that require clinical diagnoses. (For a discussion of various health conditions affecting motility disorders, see b.link/ngpgfet.)

As a general rule, after food has been consumed, it will, under normal circumstances, exit the body within three days. Claims of months- or years-old waste typically come from detox product marketing or downright pseudoscience to encourage your interest in their colon cleanses or supplements. Conditions like severe constipation, intestinal obstruction or medications or conditions impairing motility could result in delayed elimination -- but not monthslong accumulation in an otherwise healthy system.

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.