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Potatoes: Good for the Mood, but Do They Really Cause Lung Cancer?

Clearly the take-away message is not to replace sweet potatoes with Snickers bars or eat a stack of bacon, lettuce and tomato with mayonnaise without the bread.
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Decades ago, while staying with friends in Stockholm, we were introduced to their version of a midnight snack: steamed new potatoes on a bed of fresh dill. Karin, a medical doctor with a doctoral degree, and Bengt, her equally well-educated medical doctor, Ph.D. husband and we ate these tiny potatoes after returning to their home following a concert. And despite the late June sun never quite setting, we were able to fall asleep quickly and rest soundly, probably because eating the potatoes increased the soothing, soporific events of serotonin.

Had we only known then what a recent research publication has claimed a few weeks ago, we would never have let a potato touch our lips. Obviously our hosts, despite their scientific credentials, were not aware that potato eaters may increase the risk of lung cancer. A study asserting that potatoes and other carbohydrates with a high glycemic index ("GI"), are a risk factor for cancer was still in the future. Indeed as we sat eating our deliciously tender, dill-flavored potatoes, their high glycemic index was of little concern to us. At that time, the only people concerned with the glycemic index of foods were diabetics and their health care givers, as the GI of foods was involved in determining to insulin requirements. Now it is impossible to escape this concept as the GI of foods seems to affect every aspect of our health (at least according to self-appointed nutritional experts).

GI refers to how the rise in sugar (or glucose) levels in the blood two hours after a particular carbohydrate in a specific quantity is eaten on an empty stomach. Foods that cause glucose levels to rise quickly are called high GI foods and include potatoes, white bread, Fruit Roll-Ups, white rice, and Gatorade. Foods bringing about a slower rise have a moderate GI: Snickers bars, ice cream, macaroni and cheese, chicken nuggets, peanut M&M's. The foods associated with a slow rise in blood sugar levels, such as lentils, soybeans, peanuts, cashew nuts and prunes have a low GI.

This means is that the GI depends on high rapidly carbohydrates are digested. Adding fat, protein and/or fiber to a carbohydrate food will slow down its digestion and decrease the GI. This is why a Snickers bar or pizza loaded with melted cheese would have a much lower GI than bread or steamed rice.

Insulin is released as soon as glucose enters the circulation and pushes the glucose into the cells where it is used for energy. Diabetics sometimes have too low glucose levels and need to consume a food or beverage with a high GI to elevate their glucose levels quickly. Not doing so may cause them to become unconscious. Endurance athletes may also consume a high GI food during a sporting event because their muscles have run out of the energy producing glucose and they want the energy immediately, not at the end of the race. Sometimes, eating a high GI food has an almost immediate positive effect on mood the same as what we experienced with our midnight potato snack. Serotonin is made soon after glucose enters the bloodstream and its increased activity soothes and subdues stress, lowers anxiety and calms. When our clients in our weight management center worried about binge eating, we suggested they eat a rapidly digested carbohydrate similar to those eaten by endurance athletes to switch on serotonin's ability to brake the appetite.

So what does all of this have to do with cancer? The unexpected finding from a study done at the University of Texas Anderson Cancer Center that there is a "49 percent increased risk of lung cancer among people who consume the most foods with a high GI, compared to people who consume foods with a lower GI..." (presumably people who eat Snickers bars rather than rice). Does this mean that diabetics, endurance athletes, and people seeking serotonin's help in curbing their excessive food intake are more likely to get lung cancer?

Well as it turns out, unlikely if they were educated beyond high school. "Participants who had less than 12 years of education were 77 percent more likely to develop lung cancer than those in the lowest GI group," according to the results. This means that our Swedish friends are probably not likely to develop lung cancer from their midnight snacks of potatoes, having had considerably more than 12 years of education. But it still leaves unanswered the question of why someone who out of necessity or choice has less education will be more vulnerable to this type of cancer? What else were they eating or not eating?

Few of us live solely on high glycemic index potatoes as did the Irish during the early 1800s. It has been estimated that by the middle of the 19th century, about one third of the entire population was totally dependent on the potato and in some regions, the potato was the only food eaten. Obviously diets must include large quantities of vegetables, fruits, high fiber carbohydrates, low fat dairy products and lean protein. But one effect of the study linking a high GI with lung cancer may be a move to include high fat ingredients in foods because that lowers the GI. Clearly the take-away message is not to replace sweet potatoes with Snickers bars or eat a stack of bacon, lettuce and tomato with mayonnaise without the bread. Let us hope that in the near future, the headlines of a study will announce, "Moderation in all that is eaten is the best way to good health."