DEAR DR. BLONZ: I continue to hear that high-fructose corn syrup is a dangerous food additive that is much worse than regular sugar. Is this true? -- J.B., Walnut Creek, California

DEAR J.B.: Let's take a look at high-fructose corn syrup (HFCS) and compare it to "regular" sugar, also known as sucrose. Both are composed of the same two simple sugars (monosaccharides): glucose and fructose. In the case of sucrose, the two simple sugars are bound together, but in HFCS, they are not.

This is an important characteristic, because fructose on its own is about 1.4 times as sweet as glucose. When bound to fructose as part of a sucrose molecule, the sweetness is less potent. Honey is also a 1:1 blend of glucose and fructose, but with honey, as with HFCS, the two are not bound; this explains why honey tastes sweeter than sucrose.

The creation of HFCS begins with cornstarch, which is not noticeably sweet. Cornstarch is made up of long chains of glucose molecules all bound together. Cornstarch gets converted to corn syrup by breaking apart the individual glucose molecules. This gets done using a starch-digesting enzyme, similar to what goes on in our body when we eat starches.

Corn syrup then gets converted to HFCS through the use of a specialized enzyme that converts glucose into fructose. Not all the glucose is typically converted, and the percentage in the final product depends on its intended use. A typical HFCS is about 55 percent fructose, 45 percent glucose. It is called a "high"-fructose corn syrup because standard corn syrup is primarily glucose.

How does HFCS compare to sucrose? A study in the July 2007 issue of the American Journal of Clinical Nutrition looked at whether HFCS might not satisfy like other sweeteners, which could then lead to excess consumption (and an increased risk of obesity), but it found no differences between HFCS and sucrose. In the same journal in May 2008, they looked at the effects of beverages sweetened with HFCS, sucrose, fructose and glucose. The study reported no differences in a number of physiological measures, including 24-hour blood glucose, insulin and triglyceride levels. Another study in the December 2013 issue of Nutrition Research reported no significant difference in the metabolic effects of HFCS versus sucrose at low, medium or high levels of consumption.

With HFCS, you get more sweetness per unit weight. It is also less expensive than cane or beet sugar, which explains why it's found in so many processed foods. Using a sweeter sweetener could translate to fewer calories for an equivalent level of sweetness.

I consider HFCS to be just another sweetener; there is no evidence that it is worse than regular sugar. The issue with any caloric sweetener relates to the level of consumption.

My bottom line is that HFCS is not a dangerous food additive -- just don't overdo it, as should be the case with any caloric sweetener. This is especially true where soft drinks are concerned.

The idea of balance may not be sexy, but its powers hold considerable sway over our life and well-being. Our biochemistry is a continuous, complex system of chemical interactions. When there is a lack of whole foods and variety, and an excess (or deficiency) of one substance, it can influence how the body reacts, and ultimately how it performs. Toss in medications, stressors or ongoing health conditions, and things become even more complicated. This is true whether we are speaking about sweeteners or any other components in our diet.

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: Do oils that are left at room temperature become more susceptible to oxidation? When I began to refrigerate my cooking oils, they became thick and seemed to almost coagulate. How serious is this, and what exactly is at risk? -- A.B., Philadelphia

DEAR A.B.: Oils, by definition, are liquid at room temperature, whereas fats are solid. (Room temperature is typically considered to be 68 degrees F.) It's natural for an oil to become thick and cloudy as it chills. This results from the crystals that form as the oil changes from liquid to solid. No doubt you have noticed that the oil clears up when it returns to room temperature.

The greater an oil's degree of unsaturation, the colder the temperature needed to start crystalline formation. This means that oils high in polyunsaturates, such as corn, sunflower, soy or safflower, will be clear when your monounsaturated olive oil has begun to cloud. Fats with higher levels of saturates, such as butter, lard or coconut oil, will be in a solid, crystalline form at room temperature.

Storing oils in the refrigerator does not harm them. Refrigeration may actually be the preferred storage method for unfiltered, unrefined oils. (Most oils are refined; the label will usually say.) Unrefined, unfiltered oils can contain compounds that make them less stable, and thus benefit from refrigeration.

The higher the proportion of polyunsaturates, the greater the tendency to oxidize. Highly polyunsaturated oils such as fish oil or flaxseed oil tend to be sold in dark containers with instructions to refrigerate them after opening.

The risk is minimal when you leave refined oils out, provided you follow some simple guidelines.

Oils should be kept out of the sunlight and away from any source of heat. The container should be sealed when not in use. If you buy more than you expect to use in four months, consider splitting the large size into smaller portions, refrigerating the unused bottles until needed. Whenever an oil is stored in the refrigerator, keep the container well-sealed to prevent it from picking up undesirable odors. If an oil is going to be reused, such as storing frying oil between uses, let the oil cool a bit and strain it through multiple layers of cheesecloth sufficient to remove all food particles.

Understand that any oil can go rancid if subjected to excess heat, or if stored incorrectly or kept too long. An oil that has gone rancid will have a noticeable and unpleasant smell and taste, and it will ruin your food.

As a nutritional aside, plant oils are the energy source for the seed, and, especially when unrefined, they have their own protectants. These include polyphenols, tocopherols (vitamin E) or other antioxidants. You will find more of these in oils that are unrefined or unprocessed, such as extra virgin olive oil.

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: What are the facts about goji fruit? I have heard people say that it can boost the immune system, contribute to longevity and cure cancer. -- B.B., via email

DEAR B.B.: Goji fruit is a type of berry known also as the wolfberry (Lycium barbarum). It is a native of China and is actually a member of the tomato family. Goji is a fruit that matures in the sun and, like all such fruits, it contains nutrients and antioxidant phytochemicals. This is a general theme in nature: Fruits, berries, vegetables and even some grains that grow and mature in the sun need to possess an arsenal of protectants for the plant to survive.

There's no scientific evidence that goji, or products made from it, can cure cancer, boost the immune system, increase longevity or improve other bodily functions. It is simply a fruit, a type of food we should be having every day.

When something is new and "exotic," there tend to be promotions laced with overstatement. These are usually promotional statements put forth by people who stand to benefit from the sale of the products. (It is interesting that in some cases, such products have unpleasant flavors and must be enhanced with apple juice or other natural sweeteners.)

We are open to persuasion by marketing techniques that target health situations that affect our lives. Rather than being skeptical and objective and asking "Why?" we get cajoled into asking, "Why not?" When you want to believe something because you hope it'll help you or someone you love, you become an easy target.

Please understand, I am not saying that such foods have no value. But there's no evidence that, by eating them, you'd be doing anything extra that couldn't be accomplished by having widely available berries or other types of healthful fruits.

DEAR DR. BLONZ: I am concerned about the BPA lining of metal cans. Is it more beneficial to eat tuna that is packed in glass than metal? -- R.B., Walnut Creek, California

DEAR R.B.: No problem with glass, but no need, either -- there are several companies that use BPA-free cans. Trader Joe's is one of them. Others are Wild Planet, Crown Prince, Vital Choice and Whole Foods brand (check individual cans of any of these brands before purchasing, just to be sure). And tuna is also sold in BPA-free pouches. Look for tuna caught pole-and-line or by trolling, as these methods result in fish with a lower risk of mercury. If you eat a lot of tuna, do some research at tinyurl.com/q3gojw2. Learn more about BPA at tinyurl.com/ngpzoks.

DEAR DR. BLONZ: I used to take niacin pills when my doctor recommended them to lower my blood pressure. I often experienced the "niacin flush" you described. I usually took the pills in the morning. One afternoon, on the way home from work, my ankles and lower legs began itching incredibly. When I got home I had rashes on my legs (which sounds like the experience your reader N.L. had). My doctor said I had an allergic reaction to the niacin and should stop taking the pills immediately. I never had the experience again. I realize this doesn't prove a direct connection between the niacin and my skin's reaction; however, my doctor's prognosis and your statement regarding allergic reaction would seem to be in conflict. -- D.M., via email

DEAR D.M.: Niacin is an essential nutrient that is integral to our metabolism -- we can't do without it. The niacin "flush" reaction to elevated doses is not an allergic reaction. The "allergy" terminology might have been used by your doctor for the sake of simplification.

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.