DEAR DR. BLONZ: Please explain the difference between fats, oils, serum lipids, cholesterol and triglycerides. My main question is about a close friend with high blood cholesterol who is now on a statin, which brought down their lipid profile into the normal range: Is there any reason, except for weight gain, why they should not eat high-fat, high-cholesterol foods? -- M.K., Chicago

DEAR M.K.: We can discuss these components and the general impact of diet, but discussions about health issues relating to blood lipids and medications should be with your physician.

"Lipids" is an umbrella term for a group of chemicals, including fats and oils (both made of fatty acids), waxes and steroids. Each type of lipid has a particular chemical structure that distinguishes it from the others. Although the terms "fats" and "oils" tend to be used interchangeably, the difference is that the former are solid, while the latter are liquid at room temperature. All lipids share one characteristic: They cannot dissolve in water, but will dissolve in organic solvents, such as mineral spirits or cleaning fluids. Triglycerides are also lipids; they're the form in which fats and oils are packaged in the body. (For more on dietary fats, see b.link/s2fd25z.)

Cholesterol, a type of steroid, is a waxy, fatlike substance with a complex structure resembling a honeycomb. It is an essential structural element in every body cell. Unlike fats and oils, the body does not use cholesterol for energy; it is a raw material used to make hormones, including estrogen and testosterone.

However, whether due to a genetic predisposition, poor diet and lifestyle or some other factor, cholesterol can become elevated. Taking a cholesterol-lowering drug, such as a statin, provides a means to help correct that element of imbalance in the body. (Read more about statins at b.link/8wsa7ak.) If you're prescribed such medication, by all means, use it.

Medications to control an elevated blood cholesterol level should not be considered a "license to eat" and live in an unhealthful manner. It is not correct to assume that a pharmaceutically lowered cholesterol level fixes the problem -- medication can help, but it does not absolve us of the responsibility to treat our bodies with care.

The takeaway, and the message for your friend, is to consider it a worthy goal to adopt diet and lifestyle changes that might help reduce the need for such medications.

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: 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.