A few weeks ago, I ran into a regular reader of this column, and we talked about a recent article. As we said our goodbyes, I asked her if she had any requests for future columns.

She said, "I still don't have that good-carb, bad-carb thing down pat. Could you write more about that?"Honoring that request makes sense. First, consuming one rather than the other often determines whether weight is lost or gained. Second, a recent CDC report revealed that the obesity rate in U.S. adults increased by about 8 percent in the last decade.Third, and possibly most importantly, this escalation continues the trend of obesity increasing in U.S. adults despite serious efforts in the last 25 years or so to prevent further progression. In the early 1980s, about 1 in 6 adults were determined to be obese, or seriously overweight.Now the rate is nearly 2 in 5, still trending upward, and chowing down on too many bad carbs is to a large degree responsible. As a result, knowing what carbs are good and bad is essential, but what factor determines these designations?Chemical bonds.But to keep this column from reading like a chemistry book, think in these terms. All food ultimately used as energy gets broken down into glucose, a simple form of sugar. Foods that mainly consist of other simple forms of sugar get converted into glucose quickly and get called bad carbs.The name developed because this quick conversion increases your blood sugar rapidly, and your hormonal system reacts by secreting an excessive amount of insulin. The insulin whisks away the blood sugar, but secreting too much of it means too much blood sugar gets whisked away.So about 90 minutes later, you feel just as hungry as before you ate the bad carbs, ultimately establishing a cycle of overeating. Consuming bad carbs, however, does more damage than adding body weight.You'd think that the glucose created from the bad carbs, fuel essentially, would get used by your muscle cells to provide energy throughout the day. But, too often, it doesn't work that way.Yes, insulin transports the glucose to the muscle cells initially, but unless you've just expended a significant amount of physical energy or have gone a long period without food, your muscle cells are hesitant to accept large amounts of glucose at once. If denied entry to the muscle cells, the shipment of fuel gets rerouted to the fat cells and is immediately accepted.Any sugar-sweetened beverages and processed foods that feature processed grains - white breads, pastas, cookies, cakes, most varieties of pizzas, finger-food snacks, and bagels - contain high amounts of simple carbs that break down easily and therefore earn the bad-carb label.But not all carbs break down this quickly. Some have more complex chemical bonds, hence the term complex carbohydrates. When you consume these, your blood sugar increases moderately and so does your insulin secretion.Both of which are very good for you; thus the name: good carbohydrates.While acceptance of any glucose still is best accomplished within a half an hour or so of exercise, energy from good carbs stands a greater chance of not turning into energy stored as fat for other reasons. The composition of complex carbs and the thermic effect of food (TEF) are the two most germane to this explanation.Besides the more complex chemical bond, the relatively high amount of dietary fiber in most complex carbs, aka good carbs, reduces the chance you store those calories as fat, for dietary fiber cannot be stored by the body in any way. It simply moves through the digestion system, which in itself provides numerous health benefits, and then gets passed.In a sense, eating fiber means free calories.Additionally, moving that fiber through your system means your body works harder than moving simple carbs. Harder work means more calories are expended in digestion. More calories expended mean there are fewer to store as fat after the demands of the muscle cells have been met.Unprocessed grains and vegetables are seen as the best good carbohydrates.While some experts remove potatoes from this list because they score high on the glycemic index, there's an easy way to mitigate that: bake the potatoes and then be sure to eat them with a meal that includes a high-quality protein source. Protein takes longer time to digest than any type of carb and all food commingles during the digestive process, so a single baked potato should not adversely affect blood sugar levels if consumed as part of a well-rounded meal.While there are a few exceptions, keeping good carbs and bad carbs correct in your mind can be as simple as understanding the different types of oatmeal. The best type to consume is unprocessed, but that takes longer to cook, so people opt for the instant.But the instant is processed, meaning that the grain has been broken down, which speeds up the digestive process.Which is exactly what you don't want to do if you're worried about gaining weight.Moreover, virtually all instant oatmeals contain added sugars, giving you additional calories that stimulate your taste buds but do not satiate your hunger.