DEAR DR. BLONZ: I see so much info online stating that canola oil, also called rapeseed oil, is not fit for human consumption, even after manufacturers address the toxic substances found in the original seed. This information says not to believe the canola proponents, insisting that this oil can cause blindness and other severe health problems. What are your feelings on this? Could this be the initial stage of another trans-fat-like trend -- something that people should avoid now, rather than waiting for all the chips to fall? -- R.H., San Francisco

DEAR R.H.: Misinformation on the internet can be like a pesky weed that keeps coming back. An already-debunked item gets found by a search engine and passed around anew, forcing a replay of the “Who do you trust?” game. I am glad that you wrote, because we each have the responsibility to exercise due diligence and find out the facts before we spread a bogus message of fear to others.

One way is to use a search engine, searching for the term in question, coupled with the term “urban legend” in quotes. Another is to limit your search to academic sites (those ending with .edu) or ones known to be evidence-based, such as berkeleywellness.com (I am on their editorial board). You can find Berkeley’s take on canola myths at tinyurl.com/yd865u5k.

Doing these searches for “canola” would have filled your pantry with more rational takes on the anti-canola nonsense. There is nothing wrong with canola oil; it does not contain, nor represent, an impending “trans-fat-like” dark spot on our food supply.

DEAR DR. BLONZ: You had recently reassured a reader who questioned the safety of cooking raw chicken in a slow cooker. I have another question about my son’s method for cooking chicken on the grill. He puts frozen chicken breasts on the hot grill and cooks them for about 15 minutes, turning frequently. He believes that the meat stays juicier than if he started with thawed pieces. I have eaten his grilled chicken, which did, indeed, seem to be quite moist. It appeared to be adequately cooked; at least, I did not suffer any ill effects. But is this a safe method of grilling? -- G.T., Pinole, California

DEAR G.T.: It can be safe if done carefully, but I don’t see the advantage here. Your son, the chef, has to walk the line between an overcooked, leathery outside and undercooked meat at the center. The thicker the piece of meat, the smaller the gap between these extremes. It’s all a matter of timing and a quick hand on the flipper. Constant attention is the name of the game. Lowering the grill temperature can provide more time for the heat to penetrate. It would also help if you had a good meat thermometer, and a grill that allows you to cook with indirect heat.

It is best to check the meat before you eat, checking the thickest part of the largest pieces. Undercooked chicken has a translucent quality to it. Care is also needed to avoid under- or overcooking when you start with poultry at refrigerator temperature, but it is much easier than starting with frozen. The USDA information page on freezing and food safety is at tinyurl.com/y9axm7qd. Their recommended minimum temperature for cooked poultry is 165 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.

DEAR DR. BLONZ: I read an article saying that a large consumption of spinach can cause kidney stones. This is one of my favorite vegetables, so I want to know if this is something I need to be concerned about. -- S.T., Fremont, California

DEAR S.T.: Spinach is one of my favorite foods, as well. I am not sure what the article meant by a “large consumption” of this healthful food, but here is some information to put the issue in perspective.

Spinach, along with a number of other leafy greens and plant foods, contains varying levels of oxalic acid, a naturally occurring organic compound produced by these plants. There are also mineral elements in these plants, and when oxalic acid reacts with one of these, such as calcium, it becomes calcium oxalate -- an insoluble salt. There are different types of kidney stones (also called urinary calculi), but calcium oxalate is the predominant composition of these solid particles. The reason calcium oxalate stones are such a menace when they form in the kidney is that they block the ducts involved with the production and elimination of urine.

With spinach, we have a vegetable that does indeed contain oxalic acid, and it also contains calcium. One half-cup of spinach contains about 100 milligrams of calcium, but spinach is not really considered to be a good source of dietary calcium. This is because substances need to be in a soluble form to pass through the absorptive surface of the intestines. When eaten, the calcium in spinach is likely to get tied up as calcium oxalate, which means it is unlikely to get absorbed.

Compare this to kale, another leafy green. Kale contains calcium, but it only contains a fraction of the oxalic acid found in spinach. Thus, kale is considered a good source of calcium.

Spinach does have a bit more oxalic acid than calcium, so some of the oxalic acid excess can be absorbed. It is important to appreciate that oxalic acid is present in many foods, and it does not cause kidney stones to develop in an otherwise healthy individual. If, however, your body has displayed any tendency to form oxalate kidney stones, spinach would be on a “foods to avoid” list.

So, how to proceed? Assuming you are in good health, that there is no history of kidney stones in your family, and that your physician has expressed no concerns that you have a tendency to develop kidney stones, it seems dubious to avoid spinach on the mere chance that you “might” become a stone former.

For more information about kidney stones, see tinyurl.com/y7becp5d.

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 doctor says I need more fiber in my diet, and recommends a fiber supplement. But it’s expensive, and I’m on a limited retiree budget. The affordable option (I hope) is a combination of oat bran (a soluble fiber) and wheat bran (an insoluble fiber), mixed into whatever else I eat. I have read that both types of fiber are needed. Is that true? And if so, how much of each should I consume daily? Should another kind of fiber, like psyllium seed husks -- which are the basis of the dietary supplements -- be added to the mix? If so, how much? -- F.S., Casa Grande, Arizona

DEAR F.S.: At present, the typical American diet contains about 12 to 15 grams of dietary fiber per day. We should double that, bringing our intake up to 25 to 30 grams per day. Do some checking to see where you stand.

Sources of both soluble and insoluble fiber should be part of your diet, yes; if your diet contains fruits, vegetables and grains, you have this covered.

Taking a fiber supplement may work for constipation, but why strain your budget with supplements when you can get your supply naturally, from nutrient-rich whole foods? No better way to start the day than with a high-fiber, whole-grain cereal with added dried fruits, such as raisins or dried berries.

Read more on fiber at tinyurl.com/ycje978z.

DEAR DR. BLONZ: Is it necessary to use extra-virgin olive oil to get all the health benefits? We found that the flavor of the extra-virgin oil we were getting was often too strong or bitter for our taste, so we switched to ordinary olive oil. What are we missing health-wise, if anything, by not using extra-virgin oil? -- J.N., Hayward, California

DEAR J.N.: “Extra-virgin” signifies the least processed of the oils extracted from the olive. This type of oil contains the highest amount of phytochemicals, which protect the oil -- a vital energy source for the olive seed -- and can help us, as well. But it is important to understand that there are wide varieties of flavors in extra-virgin oils; they vary according to the types of olives, and where in the world they are from, and how they have been grown, harvested and stored.

This being said, extra-virgin will always be the most flavor-intense oil from any variety or batch. Olive characteristics do vary, so I encourage you to visit a store where they do olive oil tastings. Another option is to look online for stores that offer tasting notes for their various oils. You will find more options than you might have imagined.

Bottom line, though, is that irrespective of whether extra-virgin oil has more health assets, it makes no sense to use it if the flavors are not enjoyed.

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.