What are weight loss and gain?

Quick Answer
Weight loss occurs when more energy is expended than ingested, while weight gain occurs when more energy is ingested than expended; both conditions may exist as a consequence of changes in diet or physical activity or of physical or psychological disease.
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Process and Effects

Whether a person gains or loses weight is dependent on the balance of energy expended versus energy ingested. Thus, weight is determined by how many kilocalories are in the foods eaten and how many kilocalories of energy are expended. Normal day-to-day fluctuations in weight are typically minor changes attributed to shifts in body fluid and are not related to energy balance (input versus output). Input kilocalories refer to those from fat, protein, carbohydrates, and alcohol. Although alcohol is not considered an energy-yielding nutrient, it provides 7 kilocalories per gram. Output kilocalories are used to maintain the body’s basal metabolism; to chew, digest, and process food; to fuel muscular activity for physical exercise; and to help the body adapt to environmental changes. When energy intake exceeds output, a person gains weight. When energy output exceeds intake, a person loses weight.

Body weight is determined by the amounts of body fat, water, lean tissue (muscle), and bones. Ideally, what people want to lose when dieting is body fat, not lean tissue. It takes approximately 3,500 excess kilocalories to store a pound of body fat, whereas approximately 2,000 to 2,500 kilocalories are required to gain one pound of lean tissue. Any excess food kilocalories—whether from fat, carbohydrates, protein, or alcohol—can be converted into body fat. There is no limit to body fat stores.

During periods of caloric deficit (meaning that input is less than output), a person will lose weight. A deficit of 500 kilocalories per day translates into a loss of about one pound per week. Not all the body weight lost is fat. During a deficit or fasting, the body draws on stores to provide energy. During the first four to six hours without eating, either while sleeping during the night or while awake and active during the day, the body draws its energy primarily from liver carbohydrate stores called glycogen. If no food is consumed after these periods, the body begins to break down muscle (also called lean body tissue) as fuel. Although people lose weight under these circumstances, it is the result of muscle loss and fluid shifts, not fat loss. Body fat supplies fuel during fasting but cannot prevent muscle wasting unless a regular supply of carbohydrates is present. The fat used during fasting is not efficiently metabolized and can cause medical problems if the fast continues for more than a few days. Fat loss can be accomplished by eating balanced regular meals that contain fewer kilocalories than those typically eaten.

Caution should be used before an individual undergoes either a weight loss or a weight gain plan. Starvation diets or very low kilocalorie diets and meal skipping are not wise. These diets promote water and muscle loss, not a steady body fat loss. A reduction in kilocalories of about 500 per day will promote safe, effective fat loss without medical hazards. The central nervous system cannot use stored body fat as fuel, making prolonged fasting a dangerous practice. By consuming a balanced diet that contains all five food groups in moderate portions, exercising, and modifying poor dietary behaviors (such as snacking while watching television), an individual can achieve lasting weight loss. Nutrient-dense foods—those that are low in kilocalories and fat yet still contain ample amounts of vitamins and minerals—should be chosen. Understanding the kilocaloric content of foods is not always necessary if a person uses exchange lists (diabetic exchanges), which are portion-controlled groupings of foods with similar energy contents that can be used to form an adequate diet. Exercise is important because it not only tones the body but also allows for more energy expenditure. Research has shown that regular exercise speeds up the basal metabolic rate, which also helps control weight.

Usually individuals seeking weight gain want to gain muscle, not body fat. Weight gain of this type can be accomplished by physical conditioning and a high kilocalorie diet. The amount of muscle gained is under hormonal control. In healthy individuals, an excess of 700 to 1,000 kilocalories per day is sufficient to add 1 to 2 pounds per week. This excess must be accompanied by exercise training, however, or only body fat deposits will increase.

Healthy individuals desiring weight gain need to exercise and to ingest more kilocalories in order to increase muscle size. Consuming more kilocalories can be problematic, especially for athletes. These individuals must take time to eat perhaps five to six times per day. These individuals should eat more kilocalorically dense foods—the exact foods avoided during weight loss. Emphasis should still be placed on nutrient-wise choices, not simply empty kilocalories. If someone is underweight, increasing fat in the diet is not considered a major heart disease risk because the fat will prevent muscle wastage.

Complications and Disorders

Not all weight gain or loss is voluntary. Weight changes can be warning signs or consequences of disease. Several diseases are frequently accompanied by severe weight loss and wasting, such as acquired immunodeficiency syndrome (AIDS), cancer, colitis, chronic obstructive pulmonary diseases (such as emphysema), cystic fibrosis, and kidney diseases. Wasting is characterized by decreased muscle mass and depleted fat stores. This is a result of inadequacies in both kilocalories and nutrient intake. Lack of appetite, termed anorexia, could be a consequence of disease, drug therapy, or both, complicating a person’s desire to eat. Severe weight loss is compounded by other nutrient losses caused by diarrhea, loss of blood, or drug interactions. Individuals with AIDS can experience extreme weight loss, perhaps losing up to 34 percent of ideal body weight.

Thus, with illness a vicious cycle occurs: A lack of adequate food energy promotes the risk of infection; infections require more food energy for healing, further depleting energy reserves; and patients lose more weight, placing them at greater risk for subsequent infections. Extreme weight loss makes AIDS patients prone to other infections, which subsequently compromise weight status because more kilocalories are needed to combat these infections. Similarly, patients with cancer, colitis, and chronic obstructive pulmonary disease who experience weight loss become nutritionally compromised, placing them at risk for infections and delayed wound healing. Extra kilocalories are required to support the labored breathing accompanying chronic obstructive pulmonary disease. People with emphysema, a type of this disease, are often too weak to ingest enough food to prevent weight loss. Diseases of the gastrointestinal tract magnify poor nutritional status because energy-yielding nutrients cannot be absorbed.

Weight loss is also a symptom of cystic fibrosis. Cystic fibrosis is a genetic disorder that affects the pancreas and lungs. Individuals with this disease become malnourished because the normal release of pancreatic digestive enzyme secretions is impaired and because of high nutritional needs to combat lung infections. In an effort to clear congested lungs, individuals with severe cystic fibrosis cough so forcefully that frequently they vomit any food substances that they were able to consume.

Treatment for illness-related weight loss is complex. Individuals do not always want to eat, for both physical and psychological reasons. More frequent meals, higher fat intakes, and even special nutritional supplements are required. In severe cases, intravenous solutions, tube feedings, and hyperalimentation (feeding higher-than-normal amounts of nutrients through tube feeding or veins) may be implemented.

Sudden, dramatic weight loss could be a sign of dehydration. Athletes exercising during hot weather must pay attention to weight loss after practice and replenish fluids immediately. Rapid weight loss in teenagers, especially girls, may be attributable to eating disorders such as anorexia nervosa (self-induced starvation) and bulimia (periods of binge eating followed by intentional vomiting, or purging). Being underweight increases the risk of infections and often causes infertility in women.

Patterns of weight gain or loss are important indicators of childhood growth. Rapid changes may signal illnesses or psychological problems that have manifested themselves as overeating or undereating. Tracking weight gain during pregnancy is also important. Gaining weight too rapidly may be a sign of fluid imbalance forewarning pregnancy complications. Weight gain may precipitate insulin-dependent (type 2) diabetes mellitus. Although people with this type of diabetes are overweight, they are hungry because the energy that they ingest cannot enter the body’s cells; consequently they continue to overeat, fostering further weight gain. The location of excess weight on the body is also important. Individuals who gain excess weight in the waist area are considered to be at risk for hypertension, type 2 diabetes, and other disorders.

Perspective and Prospects

It is now well known that weight loss, the predominant goal of people with nonmedical weight-related concerns, cannot usually be achieved and sustained by dieting. It is estimated that one-fifth to one-third of the otherwise healthy adult population in the United States is “on a diet” at any given time. Going on a diet is not the way to get control of weight. Diets can produce weight loss; they rarely produce weight control over the long term. Repeated cycles of weight loss through deprivation of favorite high-calorie foods and weight gain when the motivation to tolerate this deprivation wanes, so-called yo-yo dieting, are hazardous. The cycles usually reduce individual metabolic rates, reduce lean tissue, discourage the individual, and make subsequent weight loss extremely difficult.

Weight management is a long-term endeavor resulting from myriad short-term decisions. Success comes with setting and achieving realistic goals. Family or group support, positive and tolerant attitudes, regular meals representative of all food groups, and behavioral modification will sustain healthy weight. Twenty to thirty minutes of exercising the large muscle groups, every other day, can prove a modest, effective way to burn fat and increase one’s metabolic rate. It also produces more lean muscle tissue, a goal for both dieters and gainers.

Whether weight gain or loss is the goal, healthful eating habits require one to make wise choices and understand that weight control is a lifestyle, not a quick fix. Individuals experiencing a weight gain or loss who are not voluntarily altering exercise or food intake should have a thorough physical examination to determine the root cause. In June 2013, the American Medical Association voted to classify obesity as a disease. The decision spurned a nationwide conversation about obesity treatment and prevention. In addition, it led some members of the United States Congress to consider expanding Medicare coverage to include weight-loss drugs and weight-reduction treatments.


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