Since many of the physiological adjustments are dependent on changes in body composition, we will first examine that before considering the adaptations themselves.

Body composition. Major changes in body composition occur with loss of body mass. Lean and fat tissue are almost inevitably lost together, although the proportions of each will differ widely. The greater the energy deficit and the lower the initial body fat level, the greater will be the percentage of fat-free mass (FFM) or muscle mass lost as the percentage of total weight loss.

For a very fat person, on the other hand, dieting is likely to be more effective for fat loss because of the greater stores available.

A more restrictive diet (500kcal v 1200kcal) will result in a greater proportion of lean mass being lost because the body simply cannot pull large amounts of energy out of the fat stores in a hurry. The lean mass represents the ‘quick release’ calorie compartment of the body so more energy is taken from the breakdown of muscle tissue. General estimates for ratios of lean to fat mass loss by obese people on reasonable diets according to English obesity expert Dr John Garrow, are about 25:75, i.e. 25 per cent lean body mass (LBM) to 75 per cent fat loss. This is used as the standard estimate for big people.

Myth-information. Individual foods such as grapefruit have been claimed to have special fat burning’ potential. There is no physiological reason why this is so, nor any positive evidence to this effect.

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more body water than women.

These proportions change with age, degree of muscularity, fitness levels and a range of other factors, but they generally represent the difference between the sexes. Each gram of fat is the equivalent of around 9 kcal of energy. Hence, a person with 15kg of body fat will have the equivalent of 135 000 kcal of potential energy. To put this in perspective, for a person who weighs 70kg, it requires about 100 kcal of energy to walk 1km. It also requires around 2000 kcal of energy to keep the average sized person alive for a day. This is called the resting metabolic rate (RMR). So theoretically, fat stores provide enough energy to keep the average person alive for around 60-70 days. For the average person to perform normal daily activity and to meet energy requirements of metabolism, a daily consumption of around 2000-2500 kcal of food is required.

Glucose (a basic form of carbohydrate) is the other main source of energy used by the muscles. This is a more immediate source of fuel than fat in that it can be used in the absence of oxygen. An analogy would be the difference between using paper (glucose) and wood (fat) as fuels in a fire. Paper is quick to start, but also burns out quickly. Wood is slower to get going, but is a much more effective form of fuel over a longer period.

Glucose is present in the body in three main locations: liver, muscle and blood. In the blood it circulates as glucose and in the liver and muscle it is stored as glycogen, which is a series of glucose molecules joined together. Total storage volumes in each of these locations is shown in

In contrast to fat, glycogen has to be stored with water. Each gram of glycogen is stored with about 3 grams of water, making it very bulky as an energy store.

Although this storage capacity can be increased, and perhaps even doubled through various nutritional techniques such as carbohydrate loading, glucose stores can’t be relied upon for long term survival in times of food shortages. Indeed, if we were to store as much glycogen as provides the equivalent energy of fat stores in the body, humans would need to be the size of elephants to accommodate the volume of glucose and water! Fat, therefore, is a very efficient and valuable store of energy.

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Rick, a 46-year-old barber from Rockville, Maryland, admits that he has a passion for eating. But until he joined Weight Watchers in 1990, he had never exercised. “I got the message right away that I couldn’t lose weight and keep it off without working out,” he says. “So a week after I joined, I started ] walking.”

Back then, Rick weighed 240 pounds. He could barely walk for 15 minutes without tiring. But he stuck with it, gradually working his way up to 45 minutes—about 3 miles—every day. By the end of that year, he had lost more than 50 pounds.

More than a year later, still buoyed by his success, Rick decided to step up his exercise program. “I didn’t want to worry about every little thing that I ate,” he explains. “I figured that if I switched from walking to running, I’d burn more calories.” In fact, he started running the day that he successfully quit smoking, April 14,1992.

“At first, I thought that by running, I could cut my workout time a little,” Rick says. “But then I got addicted to running. My workouts were twice as long as when I was walking.”

Now, Rick runs for about an hour every day, covering roughly 7 miles. He also goes to a gym three times a week.

While Rick’s workouts may seem demanding, they’re the price that he’s willing to pay for the freedom to enjoy his favorite foods. “You have to strike a balance between the amount of food that you eat and the amount of exercise that you do to keep your weight pretty much the same,” he says.

Rick’s eating habits have improved, however. These days, he says that eating healthfully and exercising regularly are as natural for him as overeating and smoking used to be. And those 50 pounds that he lost never came back. “My only regret is that I waited so long before making these changes,” he says.

WINNING ACTION

Pick your battle plan. Consume more calories than you burn, and you’ll gain weight. Consume fewer calories than you burn, and you’ll lose. It’s that simple. You just have to decide whether you want to focus on reducing your calorie intake from foods or on burning more calories through exercise. Or if you want, focus on both. Just do what feels right for you.

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