Reasons for wanting to lose weight rapidly range from wanting to look good for a wedding, to qualifying for a sports activity.
The vicious cycle of crash diets
Losing weight quickly sounds like a good idea, but is it healthy or helpful?
When the human body consumes less energy than it requires, it uses its stored energy.
At rest, the body uses a mix of fat and glucose for fuel. The central nervous system uses only glucose for energy.
When a person starts fasting, the body begins to use up its glycogen stores, the body's store of glucose. Humans mainly store glycogen in the cells of the liver and the muscles.
When the glycogen runs out, the body starts breaking down amino acids from proteins in the body to make glucose.
Glycogen holds water, so losing glycogen or protein means losing water. The weight lost is in water, not fat.
To lose one pound, a person needs a calorie shortage of about 3,500 kilocalories. Chronic dieting can make the body more efficient at holding onto weight. This can cause a reduction in the number of calories burnt in a day.
Why does the metabolism slow down?
The body's metabolism slows down for several reasons.
The goal of the body is to survive, not to lose weight. During a crash diet, the body goes into survival mode. The hypothalamus, a region in the brain, realizes that fat stores have changed. It decreases metabolism to replace the lost fat.
As amino acids break down into glucose, protein is lost. This means that lean muscle tissue is also lost. Having less muscle slows the metabolism.
As weight loss slows, the crash dieter loses motivation, abandons the diet, goes back to the habits that led to excess weight in the first place, and puts on more weight.
This happens because, with the slow rate of metabolism, the brain is telling the body to store every possible reserve of energy in fat. Feeling disappointed, the dieter may eat more.
Research shows that it is better to focus on habit changes, not dieting, for weight loss.
Healthy habits lead to weight loss
To lose weight quickly but healthily, a person needs good nutrition, good quality sleep, and exercise. Healthy weight loss is about adopting a lifestyle that is realistic in the long-term.
According to the Centers for Disease Control and Prevention (CDC), evidence suggests that people who lose about 1 to 2 pounds per week are better at keeping weight off.
How many calories do I need?
Calorific requirements depend on many factors, including general health, lifestyle, sex, height, size, and age. A tall, 22-year-old marathon runner requires more calories than a small, sedentary 70-year-old woman.
Aerobic exercise such as running is a good way to use up calories.
Losing weight may start with determining how many calories your body needs to maintain its current weight.
According to the United States Department of Agriculture (USDA), a moderately active woman over 25 years needs 2,000 calories a day, and a moderately active man, 2,400 calories.
If one pound of body weight equals 3,500 calories, a person's calorie intake will need to be 500 less per day than the recommended daily requirement in order to lose one pound in one week.
To lose two pounds, a person's daily calorie intake must be 1,000 less than the daily requirement.
A calorie deficit does not just mean eating less.
An alternative is to increase calorie expenditure through additional activity. This is often easier and healthier than lowering the calorie intake.
Exercise burns calories. A person who reduces their food intake by 600 calories, and then burns 400 calories a day in exercise could lose 2 pounds in body weight in one week.
Regular exercise is vital for maintaining good health and muscle tone during weight loss, and to help prevent future weight gain.
What type of exercise is best for weight loss?
A combination of aerobics and resistance training can contribute to effective, long-term weight loss.
Aerobic exercise, often called cardio exercise, includes brisk exercise that promotes the circulation of oxygen through the blood and raises the heart beat. Examples include cycling, swimming, running, and brisk walking.
Resistance training includes exercise that induces muscle contractions and builds strength, anaerobic endurance, and the size of skeletal muscles. It increases strength and muscle mass.
Aerobic exercise burns more calories than resistance training. However, a combination is recommended, because resistance training helps to maintain your muscle mass, and people with more muscle burn more calories per minute, even while resting.
Resistance training does not necessarily involve heavy weights. Lighter weights can achieve similar goals.
What is the best diet for weight loss?
There is no best diet for weight loss. Changing lifestyle habits is the best way to achieve successful weight loss that can be maintained. The goal is to identify those habits that are leading to poor food and exercise choices, and then focusing on changing those habits.
Choose a heart-healthy or Mediterranean diet with plenty of fruits and vegetables.
Diets, such as The Zone, Atkins, and South Beach, can help people to lose weight. Followed carefully, and according to instructions, a person can lose weight while still consuming essential foods. Often however, once a person quits the diet, they often resume their old way of eating, and they regain the weight.
A low-glycemic index diet focuses on helping people to choose carbohydrates that digest slowly rather than quickly.
Foods are assigned an index number from 1 to 100, 100 being pure glucose. The glycemic index ranks carbohydrates according to how they affect blood glucose. Low-glycemic index foods take longer to absorb.
The individual feels satisfied for longer and is less likely to overeat.
A low-carb diet severely limits carbohydrate intake, often to a maximum of 20 percent of caloric intake, but the dieter consumes more protein and fat.
One study has shown that people on a low-fat diet use less energy while resting, compared with those on a low-carb or low-glycemic index diet. This indicates a higher risk of gaining weight in future.
Other research concludes that, as long as a diet is heart-healthy and lower in calories, regardless of whether the focus is on low fat, low carbohydrates, and so on, the person will lose weight.
A heart-healthy diet is low in saturated fat and trans fats, and high in dietary fiber.
Evidence suggests that the Mediterranean Diet can help with weight loss. It may also be beneficial for maintaining a healthy body weight, and physical and mental health.
The role of sleep
A study of 70,000 people found that getting enough sleep can help to lose weight and maintain a healthy body weight. Women who did not sleep at least 7 hours a night were 30 percent more likely to put on 33 pounds over a 16-year period. Other studies have supported the findings.
Weight loss is not just a question of eating less. It needs a combination of a healthy, well-balanced diet, exercise, and good quality sleep.