DEAR DR. BLONZ: With the recent reports about food poisonings from fruits and vegetables, I wanted to know the best way to clean produce. Is water enough, or should I use more, such as a diluted solution of dishwashing liquid? -- J.D., Phoenix

DEAR J.D.: Fruits and vegetables can absorb liquids to varying degrees; this means that any fluid you use to wash your produce should be approved for food use. Dishwashing detergents, in general, are not. It is important to always clean your produce in potable, running water before eating. This will usually suffice, but if you desire a product that does more, you should seek out one specifically designed for produce washing.

DEAR DR. BLONZ: Please help me out with two unrelated questions. The first is: Is there anything to the theory I keep hearing that foods not indigenous to the area we live in will not be as nutritious? My second question is: What nutrients does the Mexican platano contain? -- M.S., San Diego

DEAR M.S.: Indigenous foods might be more familiar to our taste buds and to our digestive tracts, but in general, they don’t possess any special health attributes.

A 6-ounce Mexican platano, also known as a plantain, contains about 218 calories, along with 2.3 grams of protein, 57 grams of carbohydrate and less than a gram of fat. It is a vegetable, but it looks like a large, greenish banana with a mottled, rough peel. Plantains blacken when fully ripe, but can be broiled or sauteed at any degree of ripeness. They are a good source of dietary fiber and vitamin C, along with folate, carotene and potassium.

DEAR DR. BLONZ: I would like to express my opinion that your answer to the patient with low thyroid didn’t go far enough in explaining the importance of the thyroid hormone in overall health.

You stated that thyroid replacement “may be a reasonable option,” but did not discuss the potentially serious consequences of not following the physician’s instructions. Low thyroid levels can lead to fatigue, memory loss, weight gain, menstrual irregularities, fluid retention, hair loss and, in extreme cases, even coma.

If a patient has doubts about a physician’s advice, it’s always wisest to discuss the concerns with the physician, and, if doubts persist, to seek a second opinion. Patients should not ignore the physician’s advice without letting the physician know about their concerns. I feel that this additional information should be imparted to S.T. and your other readers. -- C.D., M.D.

DEAR DR. C.D.: Many thanks for the read, and for providing the added emphasis.

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 husband has only one kidney, working at 20 percent. To avoid dialysis, I work to keep all his food low-sodium and low-potassium. The sodium is easy; I changed from salt to cumin, coriander, cardamom, etc. Potassium is more difficult. There are about six vegetables he can have, and I work mainly with those.

That’s the background. Here is the question. The two lowest-potassium veggies are summer squash, in its green and yellow varieties. However, also on the “avoid” list are “nuts and seeds.” Emphasis here on SEEDS. Those squashes are about 50 percent seeds down their centers -- small seeds, soft seeds, but seeds nonetheless. So I lose about half of the veggie as I scoop out the seeds and discard them.

What do you think? The disabled kidney cannot handle seeds, and I want above all to save the kidney. Am I doing the right thing, or working too hard at it? -- H.K.

DEAR H.K.: Please accept my concern about your husband’s kidney issue, and my acknowledgment of his good fortune in having you as an advocate. I do not have the expertise to advise in specifics on this matter, but the National Kidney Foundation (kidney.org) has a “MyFoodCoach” tool designed for such issues. Find it by using the search bar on the organization’s website.

One final note: I encourage your vigilance in watching for indications in your husband that dialysis is becoming a necessary, lifesaving measure. See the resources at kidney.org/patients/peers/dialysis. I wish you both well.

DEAR DR. BLONZ: My question is about caffeine. Can it be diluted? If I drink a soda straight from the can, will it contain more caffeine than if I pour it over ice? Is there the same amount of caffeine in a 12-ounce cup of soda from a fountain as in a 12-ounce can? -- A.Q.

DEAR A.Q.: The two concepts involved are amount and concentration. Our sensation of taste relies on concentration, so a sip of saltwater from a container where one teaspoon of salt was dissolved in a cup of water will be perceived as saltier than a sip where a teaspoon of salt was dissolved in a quart of water. But if the entire cup or quart were consumed, the body would be receiving the same amount of salt -- and the 2,325 mg of sodium it contains. (Yep, that’s how much sodium is in a teaspoon of salt.)

Similar to sodium, the effect of caffeine is based on the dose, not the concentration. There will be comparable amounts of caffeine whether or not the drink was diluted with ice. (Soda fountains mix flavored syrups with a common supply of carbonated water. For the sake of comparison, it must be assumed that the concentration of ingredients and proportions in a fountain soda are similar to those found in the can.)

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: A local store was selling butter in the dairy section, but it was not refrigerated. Then, while at a friend’s house, I saw that she kept her butter at room temperature year-round. Her thought was that butter is saturated fat, so there was nothing that could go wrong, plus it makes the butter easy to spread. She does not feel there is any danger in this practice. I know it is wrong and unhealthy, but I cannot articulate to her the reason why. I would also like to pass something on to my local store. -- K.E., Hayward, California

DEAR K.E.: Storing butter at room temperature, exposed to air, will invite spoilage. The issue is that fats can react with oxygen in the air. As this happens, the fats become rancid; they develop “off” flavors and are no longer healthy to eat. It is a gradual process, and the reaction is slowed considerably at refrigerator temperatures.

It is true that saturated fatty acids tend to be more resistant to this type of breakdown, but they are not immune. Even saturated fats can oxidize and turn rancid. It is also important to consider that while most people think of butter as entirely “saturated,” this is not the case. According to the USDA, butter fats are 68 percent saturated, 28 percent monounsaturated and 4 percent polyunsaturated.

As a fat becomes rancid, it develops a foul, unappealing taste. However, there are degrees of rancidity, and one cannot always identify low levels, especially when present in dishes with strong flavors. Another insidious fact is that eating food with oxidized fats will not bring on food poisoning-like symptoms. Rather, the effects are cumulative, and thought to play a role in the risks of cardiovascular disease, cancer and aging.

You help prevent spoilage by keeping fats in well-sealed containers that prevent exposure to air, and by storing them in an appropriate low-temperature environment.

There is also a chance that butter might be affected by yeast and mold organisms in the air. Ongoing storage at room temperature would make butter vulnerable to this type of attack, as well.

My final spread: You won’t have to toss the butter if you accidentally leave it out overnight, and it is reasonable to take it out before mealtime if you want a softer spread. But the habitual storing of butter at room temperature is not recommended. If kept in an airtight container, such as a crock or butter keeper, the butter can be kept out for a few days, but even this method is not recommended with indoor temperatures that rise about 70 degrees F.

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.