The South Beach Diet Supercharged: Faster Weight Loss and Better Health for Life (6 page)

In a 2007 study conducted at the University of Guelph in Ontario, researchers had women in their early twenties do an interval training program consisting of 10 sets of 4 minutes of hard cycling with 2 minutes of rest between each set. After seven 1-hour sessions over 2 weeks, all eight women in the study showed a 36 percent increase in fat burning. This finding held true for women who were fit, as well as for those who were less fit. So much for the myth that you can’t burn fat working at a high intensity! The women also showed a 13 percent improvement in cardiovascular fitness, which means their hearts and lungs were better able to send oxygen to working muscles, which is important whether you are working out or simply going about your daily activities.

Burning calories is critical to shedding pounds and maintaining a healthy weight. And on the calorie-burning front, interval training is the clear winner. A landmark study conducted by Darlene Sedlock, PhD, and her colleagues at Purdue University found that it took only 19 minutes for a high-intensity exercise group to burn the same 300 calories that it took a low-intensity group 30 minutes to burn. Even more interesting, the high-intensity group continued to burn more calories long after the exercise period ended, compared with the low-intensity group.

In another study, conducted jointly by Baylor University and the University of Alabama, researchers compared continuous low-intensity exercise performed for 60 minutes to a high-intensity interval training program alternating between 2-minute periods of work and recovery, also for 60 minutes. The participants were eight women between ages 23 and 35. Researchers found that the interval training protocol burned 160 more calories per day than the low-intensity training method, or about 800 calories more per week when the exercises were performed five times a week.

The point is that if you want to burn more calories, you need to work out with greater intensity. But don’t worry, we’re not telling you this so you feel compelled to get on the treadmill for an hour a day. In fact, we’ve already seen some excellent results with women we’ve put on our 20-minute-a-day Interval Walking program. Not only have they lost excess pounds, but they’ve lost them in trouble spots like the waist and hips.

Studies also reveal that interval training is more effective for normalizing blood sugar and correcting bad blood fats (such as LDL, or low-density lipoprotein, cholesterol, and high triglycerides) than conventional exercise, making it ideal for cardiovascular health. This means that interval training is a wonderful choice for people at risk of developing prediabetes and diabetes. And it’s particularly effective for burning away belly fat, the dangerous visceral fat that is the bane of many men and women in midlife.

There’s yet another reason interval training is preferable to conventional training: It prepares you better for living in the real world. Consider this. Do you take your training heart rate when you leave the house in the morning and stay at that level for the whole day? Of course not. You’re constantly speeding up and slowing down as you go about your activities, whether you’re getting up from a desk, running for a bus, or chasing after a toddler. Our lives are actually built around interval activities. Therefore, an ideal fitness program should prepare you for the kinds of physical demands you encounter every day. And interval training does just that.

How Interval Training Works

How does interval training work? It switches your metabolism into high gear and increases your demand for energy (calories) so that you burn more calories and fat. Think of your body as a car. When you drive in stop-and-go traffic, you burn a lot more gas than when cruising along at a constant speed. With gas prices so high these days (let alone our desire to use less fossil fuel), that’s the last thing you want to do when you’re driving. But it’s exactly what you
do
want to do to burn maximum calories and fat during exercise. And that’s how interval training works. Every time you work hard and then slow down, you waste energy and use up calories. And what it’s costing you are those extra, unwanted pounds.

Debunking Those Exercise Myths

Many of you have heard metabolism mentioned in connection with weight loss, but unfortunately, few people actually understand what metabolism is all about. If you want to look great in your bathing suit, fit back into your “thin” clothes, prevent diabetes, and maintain a healthy weight for life, you need to know how to make your metabolism work for you, not against you. So bear with me while I give you a brief lesson on metabolism.

In a manner similar to how your car runs on gasoline, your cells run on a substance called adenosine triphosphate, or ATP, which is made in all the cells of the body. You need energy from ATP to run your body’s systems as well as to perform your day-to-day work. ATP is, in a sense, your only energy source, and it’s replenished by the food you take in daily, as well as the fuel stored in your body as fat or glycogen (the storage form of sugar). ATP is what’s converted into the energy you need to contract your muscles and perform all of your bodily functions. Using ATP for energy is analogous to burning coal in a furnace to run a steam engine. The burning coal heats the water that makes the steam that propels the engine.

At the peak of endurance training, athletes like Lance Armstrong require roughly 6,000 to 9,000 calories a day to keep their muscles working for extended periods of time. It seems like these elite endurance athletes must spend most of their nonexercise, nonsleeping time eating just to keep up with their training muscles’ demand for energy. For most of us, however, all the fuel we need for a regular exercise and weight loss program is easily consumed in the healthy meals and snacks we should be eating every day.

Another key point to understand about metabolism is that there are two types, and each one burns different fuels. Aerobic metabolism requires oxygen to make ATP and can use both sugar and fat as fuel. Anaerobic metabolism doesn’t use oxygen to make ATP and burns sugar and a compound known as creatine phosphate, which is made in the cells, for fuel.

If the words
aerobic
and
anaerobic
are familiar to you, it’s because we also use them to categorize different types of exercise. Aerobic activities (sometimes called cardio), which can be done for a long duration, include walking, cycling, rowing, and working out on a treadmill or an elliptical trainer. Since these are done at a relatively low intensity level, you can usually maintain your performance using the aerobic systems of the body. Therefore, by breathing more deeply and more frequently and having your heart beat faster, you can deliver sufficient blood and oxygen to supply your muscles’ needs without accumulating excessive waste products that can fatigue your muscles. Anaerobic activities, such as weight training, jumping rope, and sprinting, work muscles at a high intensity and consequently require energy faster than the aerobic systems can supply it, even though they’re working as hard as they can. The result is that your working muscles rapidly build up waste and tire out. Therefore, anaerobic exercise cannot be sustained for long, and you’re forced to reduce activity to a level where aerobic metabolism once more dominates.

There are several misconceptions about exercise in general and anaerobic exercise in particular. One of the biggest myths is that you can burn fat only by doing aerobic exercise. This idea is based on a misinterpretation of the fact that fat is an aerobic fuel, and it has led to a second, more insidious myth: When you work at a high-intensity anaerobic level, such as during interval training, you shut down your fat-burning machinery. This is simply not true; it’s based on a misconception about how your metabolism operates. We were once taught that the body can be in only one mode of metabolism at a time—either aerobic (burning sugar and fat) or anaerobic (burning sugar and creatine phosphate).

In reality, as you exercise, your body slides freely between aerobic and anaerobic metabolism. Depending on the activity, your body may favor one type over the other, but it’s never exclusively in aerobic or anaerobic mode. You’re never actually burning just sugar, fat, or creatine phosphate. You’re burning all three fuels simultaneously. But, depending on your activity, you’re burning more of one than another.

When you do interval training, you’re repeatedly moving from high-intensity work to low-intensity work, and you’re also moving along the metabolic spectrum. You can’t maintain a high-intensity level for too long because you’ll get tired. Tiredness occurs for several reasons: First, you rapidly burn through your high-energy fuel, creatine phosphate, while you’re still burning sugar and fat. Second, your muscles make lactic acid and a number of waste products, which contribute to fatigue. So, to cope with this fatigue, you slow down and move into your low-intensity recovery period. During this recovery period, you’re not only burning off lactic acid as fuel, you’re also using fat and carbohydrates aerobically to replenish creatine phosphate and ATP. This allows you to do the next high-intensity spurt and continue to burn more fat and calories.