DEAR DR. BLONZ: Please help settle a family debate. It is my impression that when vegetables are boiled with no lid on the pot, some nutrients leave with the steam. My son says that all the nutrients stay in the cooking water. -- J.A., Hayward, California

DEAR J.A.: Your son is much closer to accuracy, but there is one nutrient that does, indeed, exit with the steam: water! The steam/water itself is a nutrient, which means you and your son both have some claim to correctness.

The cooking process can cause a breakdown of some vitamins, but these are not lost with the steam. For an article on how cooking affects nutrients, see b.link/xrz7zcd.

DEAR DR. BLONZ: This is a follow-up to your recent column on repelling mosquitoes. When we went camping years ago, we learned that Avon Skin So Soft Bath Oil worked well to repel mosquitoes. We liked using it rather than applying insect repellents that contained other chemicals. This could be a good option for young children. -- G.F., San Ramon, California

DEAR G.F.: After my piece on how a particular dietary supplement was ineffective against mosquitoes, I received several notes about Avon Skin So Soft Bath Oil. I recall when the rumors emerged, years ago, that this product could repel mosquitoes; it became a go-to product for many summers and was difficult to find.

Studies were undertaken to verify its efficacy, using a sample population to assess the oil's benefits. The studies failed to find a significant difference in the performance of the oil and a placebo substance. There are various possible explanations for this: 1. The product is indeed ineffective as a mosquito repellent; 2. The placebo selected was equally effective, so there was no difference between the two; or 3. There were other characteristics -- whether genetic, cosmetic or something else -- that were unequally distributed between the groups and these impacted the results.

The bottom line is that the mosquito-repellent effect has not been confirmed. To Avon's credit, the company has never promoted this as a feature of the bath oil product. Consumer Reports has also discussed the issue: see b.link/sajmfx2.

All of that being said, some people may experience good results when using this product to repel mosquitoes, and there is no reason to stop if you are having success.

We do not yet fully understand the individual and combined factors that entice or repel mosquitoes. Any of these can play a role in our odor, and therefore our attractiveness to bugs: what we have recently eaten; the detergent or fabric softener used on our garments; the moisturizers, sunscreens or deodorants on our skin; when we last bathed or exercised; even our stress levels.

It is a wildcard; better to rely on our individual observations of what works for us.

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 your opinion of weight-loss products that claim they shrink belly fat by reducing the level of cortisol in the body? The message is that this approach can help one lose 10 to 20 pounds using all-natural means. Is this correct, and is there a particular product or system that works? -- S.F., Denver

DEAR S.F.: Social media and the commercial airwaves are overweight with cortisol-reducing ads replete with their hefty doses of misinformation and puffery. Their assertions might even sound plausible -- that's how ads are designed -- but that's as far as it goes. Elevated cortisol, including its prolonged use as a medication, is, indeed, associated with elevated abdominal obesity. Evidence of these products' efficacy is not available. The boasts and testimonials on these products are often from those with financial interests in them.

Cortisol, also called hydrocortisone, is an essential hormone made by the adrenal glands located atop the kidneys. It is referred to as one of the three "stress hormones," which includes cortisol, epinephrine (adrenaline) and norepinephrine. Our stress hormones rise when physical or emotional stressors confront the body. Norepinephrine helps rev things up in response to stress, while cortisol helps calm things down. They play a role in various aspects of metabolism, including inflammation, appetite, glucose metabolism and blood pressure, and all of their responses are tailored to the situation the body is facing.

The anti-inflammatory hormone in the group, cortisol, helps prevent tissue destruction associated with inflammatory conditions that include some types of arthritis and autoimmune diseases, as well as asthma and problems associated with organ transplantation. Cortisol can be prescribed as a medication for certain health conditions prone to inflammation.

Don't assume that any product can actually shrink your midsection without providing evidence that it works the way it claims. Typically, such products take elements of the body's stress response out of context, claiming their ingredients affect metabolism in a way that lowers the cortisol level, causing the body to shed belly fat. Simply put, there is no evidence that these products can accomplish their stated goals.

When checking out the range of belly-fat/cortisol products on the market, I found that some contain stimulants, others contain laxatives, and yet others rely on a combination of proprietary ingredients with no obvious mechanism. What they all share is a lack of objective clinical evidence to back up what they claim.

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 behind the advice that saving oranges until they are sweeter may result in them losing their vitamin C? Oranges that are picked too early may not have any. Should I avoid oranges with a greenish tint, which indicates they were picked before they were ripe? -- S.B., Scottsdale, Arizona

DEAR S.B.: Some fruits, such as bananas and stone fruits, including avocados, contain enzymes that remain active after harvest; they break down complex carbohydrates into simpler, sweeter-tasting sugars. This isn't the case with oranges, however, which are harvested at the peak of ripeness. What that means is that when it is picked, an orange is about as sweet as it will ever be. It is also when its vitamin C content is the highest.

Don't look at the color as being an indication of ripeness. Oranges can often "regreen," which is a process unrelated to ripeness or taste -- the overall color is more a reflection of the temperature before harvest than of the flavors locked inside. Although oranges will keep for a few days at room temperature, the best storage method is to keep them in the refrigerator. When an orange begins to shrivel, its nutrient value has begun to decline. The juiciest fruits, incidentally, are the ones that are heaviest for their size.

DEAR DR. BLONZ: A friend told me to take guarana pills for alertness, better concentration and faster learning. But I have heard that guarana is also used as a cure for erectile dysfunction. Could you tell me if I should try this? -- D.P., Nashville, Tennessee

DEAR D.P.: Guarana comes from the seeds of a South American shrub. The claimed effects you mention -- at least the ones associated with alertness and better concentration -- stem from the fact that guarana has a high concentration of naturally occurring caffeine -- higher even than the coffee bean, the kola nut or cacao (cocoa).

There is no reliable evidence to support the use of guarana (or caffeine) for erectile dysfunction (ED). Given the financial success of pharmaceutical drugs designed for ED, it is not surprising to find herbal supplements claiming efficacy in this area, lack of evidence notwithstanding. For a review of dietary supplements touted as effective for erectile dysfunction, see b.link/54hps9e. Guarana is not even on the list.

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.