DEAR DR. BLONZ: I wanted to know what you think about the frequently hyped health-promoting qualities of juicing, and about juicing machines in general. Do you get more nutrition from using a juicer than from simply eating the same fruits or vegetables? -- F.S., San Jose, Calif.

DEAR F.S.: Fresh juices can be a healthful food, but there is no reason to believe that you can "juice" away your health problems as many infomercials might have you believe. So, as with the juicers themselves, it's important to know the difference between substance and pulp.

There is a wide range of juice "prescriptions" for various ills. To help with arthritis, for example, one author might tout a pineapple juice formula, while another swears by broccoli, kale and spinach, and yet another recommends bean sprouts, carrots and cucumbers. Each recipe will have positive attributes, but there is no basis to believe that any of them will cure any of the various types of arthritis.

A focus on curing disease tends to overshadow the larger value of juicing. We would be better off getting refreshment from fresh vegetable or fruit juices instead of soda. Juices provide wonderful flavors and they contain valuable nutrients and phytochemicals not found in soda. For example, 12 ounces of fresh carrot juice contains about 100 calories and is loaded with healthful phytochemicals. Fresh apple, pineapple or melon juices yield flavor and aromas unmatched by other beverages.

The benefits of consuming more fruits and vegetables are indisputable, and it's a lot easier to drink a dozen carrots than to eat them. But because juice (without pulp) doesn't have fiber, the goal should be to have juice in addition to, not instead of, fresh fruits and vegetables. And while juicing proponents might swear juice gives you all the food's essential goodness except the fiber, it's unclear what proportion of the nutrients are left behind with the pulp.

There are three basic types of juicers. Extractors, the most popular kind, grind the food with a high-speed spinning disc that traps the pulp. They often have an ejector that deposits the pulp in a convenient bin. Masticator-type juicers chew up the food at a slower speed and make juice by mechanically pressing the ground-up produce against a screen. Finally, there are specialized blender/juicers that grind the entire fruit or vegetable. This is the one type of machine that doesn't remove the pulp; the juices from these machines retain the food's fiber. The tradeoff, however, is that the output can end up as slush rather than juice.

You'll find the greatest price variation among the juice extractors. The different price tags -- from about $50 to more than $300 -- reflect the power and noise level of the motor, as well as pulp capacity and cleaning ease. The masticator and blender/juicers tend to be in the $200 to $500 range. There's no "best" method; it's all a matter of taste and pocketbook.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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: There has been no clear clinical evidence that food causes behavioral issues in children. I am interested in your thoughts on this issue. -- R.D., Los Angeles

DEAR R.D.: The role of food allergies in childhood behavior remains controversial, but it is not unreasonable to at least consider this as a possibility when other avenues have been unproductive. It is essential, however, that one proceeds cautiously, calling upon a clinician experienced in this area.

One issue is that the connection between the behavior and the offending substance(s) might not be readily apparent. You have to consider what happens if the wrong substance is blamed, or if one simply turns to generalities, such as blaming all food additives. Such cases can give rise to changes in parental behavior that can then act as programming for the child: "You shouldn't eat that, it will make you sick." It can all turn into a march down an unproductive road with ever-growing limits placed on the child's ability to eat and enjoy life.

The ironic thing is that a parent might observe improvements in a child's behavior even if the wrong substance is identified. Such changes might take place because they are expected -- the essence of the placebo effect. You haven't accomplished much if the underlying problem was not allergy-related or if it was caused by an item not originally suspected. If the symptoms resurface, other foods or food categories might get added to the "banned" list, further restricting the child and the parents.

I raise this scenario to highlight the importance of a reasoned, systematic approach. Parents can assist the process by maintaining a diary of foods consumed and reactions observed; this aids the experienced health professional in compiling a list of the likely suspects for further testing.

Once suspects are identified, testing in a controlled clinical environment is essential to remove any possible bias from all concerned parties. A gold-standard often relied upon is the double-blind, placebo-controlled food challenge. I would encourage you to discuss this with a physician. I often refer people to an excellent review article, "Manifestations of Food Allergy: Evaluation and Management," which appeared in the January 1999 issue of American Family Physician.

DEAR DR. BLONZ: One of my favorite times of year is when the new crop of potatoes comes to the market. My question has to do with the nutritional value of these fresh potatoes. I checked the USDA database, which says that a medium-sized baked potato, or a similar amount of French fries, is supposed to contain about 17 milligrams of vitamin C. You have mentioned that heat destroys vitamin C, among other nutrients. If this is the case, how can these "heated" potatoes still be a good source of vitamin C? -- J.J., San Diego

DEAR J.J.: The high heat involved in the preparation process does indeed destroy a number of vitamins, including vitamin C and thiamin (vitamin B1). That level of vitamin C does reflect a reduction from the amount in the raw potato. French fries will have a bit less due to their increased surface area.

A good source for any nutrient is one that provides between 10 and 19 percent of the daily value for that nutrient. An excellent source is one that provides at least 20 percent of the daily value. Seeing as the daily value for vitamin C is 60 milligrams, one serving of "heated" potatoes would actually be an excellent source.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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 recently went on a detox/cleansing diet routine, complete with a drink and pills, that was recommended by my close friend. I was able to drop almost 10 pounds in a few days. It was incredible until the intensive part of the routine was over, and the weight began to return within a week. Did I do anything dangerous to my body? Was there anything I could have done so that the weight stayed off? -- G.M., San Jose, Calif.

DEAR G.M.: The goal of losing "weight" can actually be a bit deceptive, because the number on the scale can vary for many reasons. More appropriately, the goal should be to reduce excess body fat. Some regimens can be very successful at taking off pounds, while failing to make any significant dent in our stores of unwanted body fat.

As the body's most calorie-dense material (nine calories per gram), fat is our main form of energy storage. Whenever the intake of calories exceeds the demand at the moment, all the excess, whether from carbohydrate, fat or protein, gets converted to fat and then shuttled away to storage. That means that at mealtime, the flow is toward storage, while between meals the flow is from our fat stores to the working muscles and organs.

A pound of body fat is estimated to contain about 3,500 calories of potential energy. It is reasonable to consider, therefore, that the number of calories burned has to exceed dietary intake by something in the neighborhood of 3,500 for every pound of body fat to be lost.

In the 2010 Dietary Guidelines for Americans, adult men reported an average daily intake of 2,640 calories, while women reported consuming an average of 1,785 calories each day. These numbers can vary according to age, body size and level of activity, but you can see that even if one were to cut one's food/calorie intake by half, it's difficult to lose much more than a couple of pounds of body fat a week.

How to explain your results? Cleansing routines often talk about pounds of "toxins" clinging inside your intestines, but there is not much evidence to support such claims. What is known is that there is usually a quantity of fecal matter in queue for normal elimination. Any "cleansing routine" that includes laxative ingredients will cause a temporary -- albeit dramatic -- weight loss due to the physical weight of this matter. If it also contains diuretic ingredients, the cleansing product can cause a loss of water weight; again, a temporary effect. Neither of these are the same as weight loss that involves a decrease in body fat from the adipose stores. Once the cleansing regimen is finished, the body reestablishes balance and the numbers on the scale return to where they were.

Success takes determination and a good plan. There has never been a quick fix that has withstood the test of time. Relying on a cleansing diet drink, or diet pills, does not bode well for long-term chances. Better to find a plan that includes a healthy, balanced diet, a good selection from all the food groups and a solid activity component. By tweaking your food choices, lowering calories and increasing activity, your new routine can bring lasting success.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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.