In many ways, life today is much healthier than it was in the past. But for too many modern Americans, the advantages of medical technology are outweighed by unhealthy habits that are all too common in our society.

One of the biggest problems lies in our modern diet. For tens of thousands of years, our human ancestors lived in conditions where food was scarce and precious. So our bodies have evolved to extract as much energy as possible from the food we eat, to burn only what’s needed, and to store the leftovers as fat to protect us from starvation.

Over the past century, however, food has become astonishingly plentiful. Unfortunately, now our problem is not a lack of food, but too much food, or too much of the wrong kind of food.

Americans today are eating more than ever before. In restaurants and at home, our portion sizes (the amount of food we eat at one sitting) have gotten larger and larger over the past few decades. For example, in many fast-food restaurants, what was called a large order of French fries 30 years ago is the smallest size available today. A typical bagel has grown to about twice its original size and is smeared with nearly a whole package’s worth of cream cheese. All-you can-eat buffets and huge servings at popular restaurant chains have trained us to believe that when it comes to food, more is always better. (Think of how many times words like “extralarge,” “jumbo,” “king-size,” and “supersize” pop up on menus and food packages and in advertisements.) Unfortunately, more food also has more calories—and calories add up fast: If you tack on just 150 calories to each of your meals (that’s about the number of calories in a 12-ounce can of soda or half a candy bar), you’ll take in over 164,000 extra calories per year. That’s enough to put on 47 pounds of fat!

We’re not only eating more than before—we’re also eating worse. Many popular foods today are highly processed, full of unhealthy saturated and trans fats, refined sugars and flours, excess sodium, and countless additives and preservatives. Fast foods and pre-packaged supermarket foods are thebiggest culprits. These foods are also typically low in vitamins, nutrients, antioxidants, and dietary fiber—all of which improve health and fight against cancer and heart disease. Too many Americans rely far too heavily on these products and not enough on fresh, whole foods such as fruits, vegetables, beans, nuts, fish, and lean meats.

All these poor and excessive food choices have consequences, including rampant obesity. “Obese” means “extremely overweight.” In 2001, more than 20% of Americans were obese—nearly twice the rate from just a decade earlier. Obesity is dangerous because it leads to poor circulation, heart disease, high blood pressure, diabetes, heat exhaustion, and a lot of other problems. It is estimated that as many as 300,000 deaths per year in the U.S. are related to obesity. A recent report by the Centers for Disease Control said that obesity is ready to overtake tobacco as America’s leading cause of pre-ventable death.

Apart from playing a role in obesity, a poor diet can affect us in other ways. Diets that are high in unhealthy fat and low in fiber, essential nutrients, and antioxidants have been linked to several kinds of cancer. Poor dietary choices can also cause bad forms of cholesterolto build up in your arteries, increasing your blood pressure and eventually leading to a heart attack. Improper nutrition can lower your body’s natural defenses against disease and make you feel sluggish and weak. It’s hard to believe, but many Americans are both obese and undernourished at the same time!

Besides taking more calories in, we’re burning fewer calories off than ever before. Over a century ago, your great-great-grandparents expended lots of energy every day, by lifting heavy loads, working in fields or in factories, building and fixing things with their hands, and walking almost everywhere they needed to go. Even housework used to be a vigorous workout. It was a hard life, but all that challenging physical activity helped to keep their bodies fit.

Nowadays, many of us can get through a whole day scarcely lifting a finger. We wake up and get right into a car, bus, or subway that takes us to work. We might spend the entire working day behind a desk or a counter, moving only a few steps at a time. People who work in factories or in the home have many kinds of machines that do the hardest work for them. At night, we can order a pizza delivered to our front door and eat it while watching TV— using a remote control so we don’t even have to get up to change the channel!