Knowing what nutrients comprise a well-balanced diet, in what foods to find them, and in what quantities to eat them are some of the first steps to good health. Applying this knowledge by eating nutrient-rich foods and incorporating physical activity into your schedule at any stage of life are the greatest investments you can make in sustaining good health.

Although healthful eating may lower your risk for certain diseases, there are no guarantees that adhering to the tenets of good nutrition will prevent an illness from developing. Science has shown that not all diseases or disorders are associated with what you eat. However, statistics do show that lifelong food selections may influence the risk for some diseases.

Research continues to evaluate and clarify the role that diet and nutrition play in the promotion of health and in the development of obesity, high blood pressure, diabetes mellitus, coronary artery disease, osteoporosis, cancer, and other illnesses. The nutritional recommendations for prevention of many diseases are similar.

Obesity

If obesity were merely a matter of aesthetics, it would be of less concern. But obesity is a health issue.

It is associated with an increased risk of diabetes, lipid abnormalities, coronary artery disease, high blood pressure, certain cancers (such as breast, colon, and gallbladder in women and colon and prostate in men), stroke, degenerative arthritis, respiratory problems, sleep disturbances, and gallbladder disease.

Obesity places a huge burden on society in terms of lost lives, ongoing illnesses, emotional pain, discrimination, and economic cost (nearly $100 billion annually). The most ominous burdens posed by being overweight are reduction of the quality of life and shortening of life span.

The likelihood of dying early (compared with the average age at death of all people in the population) progressively increases the more overweight you are. Diseases caused by obesity are the second leading cause of preventable deaths in the United States.

With countless diet programs and products promising to help you shed pounds, losing weight should be easy. Simply eating too much and not being active enough are the causes of most overweight problems. But you also know it is hard to lose weight and even harder to keep it off.

The cause of overweight and obesity is a chronic imbalance of calories ingested and calories burned. Genetic and environmental factors also contribute to obesity. Americans spend more than $33 billion a year on weight-loss products and services, but they are losing the “battle of the bulge.”

Despite the great desire of Americans to be thinner, they have become more obese. Some have even declared that the United States has an “obesity epidemic.” It is estimated that more than 50 percent of adult Americans are overweight. The prevalence of obesity also is increasing in several other countries.

“Overweight” and “obesity” are terms that often are used interchangeably, but they have different meanings. “Overweight” refers to having excess body weight compared with the norm for a person’s height, but the term does not account for what tissue is making up the weight.

For example, athletes are often overweight according to weight-for-height tables because they have increased muscle mass. However, for most people, overweight means having too much fat. “Obesity” refers to body fat in excess of what is healthful for an individual.

In healthy women, an acceptable level of body fat ranges from 25 to 35 percent. In contrast, an acceptable range of body fat in men is from 10 to 23 percent.

The number of calories used by an individual is determined by three factors: basal metabolic rate, the thermic effect of the food eaten, and the calories used during physical activity. The basal metabolic rate is the amount of energy needed to maintain bodily functions when an individual is at rest.

This component accounts for 60 to 75 percent of the daily calorie requirement in sedentary adults. The major determinant of the basal metabolic rate is the amount of fat-free mass in the body. Muscle is one example of fat-free mass.

Resistance (strength) training can increase the amount of muscle and therefore increase the basal metabolic rate. Resistance training also can help prevent the loss of lean mass that normally occurs with aging.

Men tend to have more muscle than women and therefore burn more calories. The thermic effect of food is the energy required to digest, metabolize, and store nutrients. The thermic effect of food accounts for about 10 percent of the total daily calorie use.

The number of calories burned during exercise can vary tremendously depending on the amount of exercise performed.

For most so-called sedentary persons, the activities of daily living (such as walking, talking, and sitting) account for 15 to 20 percent of the daily calorie use.

Should You Lose Weight?

How do you determine whether you are overweight or obese? Scientists can use sophisticated tests to measure body composition. However, these are not necessary for most individuals. You can measure your change in weight over time. Alternatively, you can calculate your body mass index (BMI) and determine its relationship to health risks.

There are risk factors that indicate a predisposition for obesity. Among these risk factors are the following: Body mass index (BMI)—BMI is defined as your weight (in kilograms) divided by the square of your height (in meters).

The advantage of BMI over bathroom scales and weight-for-height tables is that it normalizes weight for height and helps determine whether you have a healthful or unhealthful percentage of total body fat. People who should not use the BMI for determining health risks include competitive athletes and body builders.

Their BMI will be high because they have a larger amount of muscle. BMI is also not predictive of health risks for growing children, women who are pregnant or lactating, and frail, sedentary older adults. A BMI from 19 to 24.9 is associated with a minimal to low health risk.

A BMI from 25 to 29.9 is considered overweight and is associated with moderate health risks. A BMI of 30 or higher is considered obese and is associated with a substantially greater risk for development of various diseases. Extreme obesity is a BMI of more than 40.

Body shape—Increasing attention has been focused on the distribution of body fat as a potential indicator of health risk. Specifically, excess fat in the abdomen is associated with an increased risk for development of various metabolic illnesses, including diabetes mellitus, increased blood lipid levels, and high blood pressure.

In contrast, people whose excess fat is located in their lower body (hips, buttocks, and thighs) seem to have minimal or no increased risk of these diseases. Upper-body obesity also is associated with an increased risk for coronary artery disease, stroke, and certain cancers.

Therefore, it can be helpful to assess your health risk by measuring your waist circumference. A measurement of more than 35 inches in women and 40 inches in men is associated with increased health risks, especially if you have a BMI of 25 or more.