DEAR DR. BLONZ: The parents of our son’s soccer team bring the halftime refreshments. Typical items are water and orange slices. Recently a parent brought sweetened juice-flavored drink packets that he claimed would be better than water because they would drink more. It wasn’t a sports drink. An animated discussion followed. It has all been resolved, but I wanted to know your thoughts. -- M.V., Walnut Creek, California

DEAR M.V.: Our bodies work best within a narrow temperature range. There are automatic processes designed to conserve body heat when temperatures fall. If our core body temperature drops, we instinctively reach for some kind of cover or warm layer; if it drops too low, we begin to shiver, which is a purposeful activity that takes advantage of the heat given off by working muscles. But when we engage in continuous physical activity, it’s an excess of heat that becomes the issue. When that happens, the body’s largest excretory organ -- the skin -- assumes center stage.

Small blood vessels dilate near the skin’s surface to radiate heat into the ambient air. The skin will dampen with perspiration, purposely losing heat through the water’s evaporation. With a long, intense workout, electrolyte loss -- mostly sodium, but also potassium -- can become an issue. These minerals are normal elements in bodily fluids and flow out with perspiration, helping to explain the salty nature of skin that has been sweating.

Being overheated and short of water at the same time will place an extra burden on the heart: It’s forced to work harder to pump blood into the working muscles while also pushing fluids out to the skin surface to maintain the cooling process. If the body is not well-hydrated, it can begin to overheat, which can impact athletic efforts as well as the post-workout recovery. In the extreme, it can progress to a dangerous condition known as heatstroke.

Being well-nourished before the event, and resupplying what’s being lost in the process -- including water, energy and electrolytes -- can help during the workout and afterward. Plain water is fine for shorter efforts, such as those under an hour, and adding oranges provides flavor and a source of energy and nutrients from real food.

Sports drinks, which usually include sweet flavorings and some electrolytes, do encourage young athletes to drink more; this works well for those who play sports for extended periods of time, or who sweat excessively. That parent was correct in saying that some sugar can improve palatability and encourage consumption.

Beverages with added sugar are not cast in a positive light these days. But this is an exception, in that the muscles are at work. A small amount of sugar in a drink can help performance by helping maintain blood glucose, a key source of energy for muscles involved in athletic efforts. But “small” is the operative word here, as too much sugar slows absorption and leads to bloating and cramping.

Sweetened juice drinks not specifically designed as sports drinks can be too sweet, tend to contain artificial colors and flavors, and are unlikely to include electrolytes (check the Nutrition Facts label).

Water and oranges make practical sense for team events, such as your son’s soccer games. For individual athletes, I favor homemade sports drinks made from water and fresh fruits. My recipe can be found at: tinyurl.com/krkj8mx.

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 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.