Close your eyes and picture 110 million obese people waddling around America’s sidewalks. You’ll probably want to keep your eyes closed.

Such is the scenario suggested by a new study projecting that 42 percent of American adults will be obese by 2030. That’s 32 million more than today’s 78 million.

Of course, they probably won’t be waddling. They’ll be in their cars in the fast-food drive-through lane, as they are now. Recall that independent filmmaker Morgan Spurlock (“Super Size Me”) gained 24.5 pounds after one month of eating exclusively at McDonald’s.

Something no less than a “major public health intervention” is needed, according to Eric Finkelstein, a health economist with the Duke University Global Health Institute and lead author of the study.

What this means is anyone’s guess, but it isn’t far-fetched to infer that a government-mandated health care system eventually would necessitate a government-mandated diet to control costs.

In another study, Finkelstein and the Centers for Disease Control and Prevention estimated that obesity costs about $147 billion per year, accounting for about 9 percent of all medical expenses. An obese person, defined as carrying an extra 30 pounds, costs about $1,400 more in medical expenses per year than a person of healthy weight.

No one wants to make overweight people feel worse than they do. Fat is indeed a plague, and most of us struggle to varying degrees.

About 12 renegade pounds out there love me so much they never want to be far away. If I drop my guard for so much as a month (that is, eat like a normal person), they jump on me like a June tick.

At this point, we make the necessary disclaimer that some people are blessed with hummingbird metabolisms (and we hate them), and others are genetically inclined toward fatness. Genetic inclination isn’t a life sentence, however, and personal responsibility can’t be excluded as contributing to most fatty outcomes.

These days, responsibility isn’t only about pushing away from the table, but it means educating oneself, reading food labels and going to a little extra trouble.

Getting fat has never been easier, of course. Food is plentiful and convenient, and the bad stuff is tasty and cheap. At the end of long day, it’s easier to buy a Happy Meal than to shop and prepare a balanced dinner. And who wants to hear the little darlings protest when presented with cauliflower instead of calzone?

Out of sheer exhaustion, we fool ourselves into thinking children should have a say in what they eat. And, never-minding all the studies, diets, consultants and excuses, we know that the mystery of non-medical obesity isn’t really so mysterious.

In a word, it’s about sugar, including hidden sugars such as high-fructose corn syrup, a liquid sweetener that seems to be in nearly everything. Because it is six times sweeter than cane sugar, HFCS is cheaper to use and also has preservative, as well as fattening, attributes.

A 2010 Princeton University study found that rats that drank HFCS gained considerably more weight than rats eating sugar, though their caloric intake was the same. On average, Americans consume about 60 pounds of HFCS per person per year, according to the study.

Here’s the simple explanation: Refined or simple sugars and their cousins — high-glycemic carbohydrates (think white bread and potatoes) — cause the pancreas to produce high levels of insulin, which cause the body to store excess sugar not used for energy as fat. The liver in turn is induced to produce cholesterol.

We love high-glycemic carbs because they make us feel good by spiking our blood sugar. But what goes up must come down — with a thud. When our blood sugar inevitably plunges, we feel tired, ornery and hungry — and we repeat the cycle.

Low-glycemic foods (think apples and collard greens), on the other hand, release energy at a steady, less-dramatic rate, and our blood sugar stays reasonably level. Less sugar means less insulin means less fat means leaner bodies means better health.

Oh sure, eating with such attention to the glycemic index ruins your life. You won’t have any friends, and your children will hate you. You’ll spend all your time alone weighing four-ounce cuts of fat-free meat, sautéing spinach and picking flaxseed out of your teeth, but you’ll be thin. Best of all, you won’t need to go to the doctor as often, or rely on federal food marshals to tell you what to eat.

Kathleen Parker is a Pulitzer Prize-winning syndicated columnist and a member of Washington Post Writers Group. Email at kathleenparker@washpost.com.