When Does High Metabolism Slow Down?

Chemical changes that occur in living cells provide energy to execute physiological functions necessary to sustain life. These processes are collectively referred to as metabolism. It plays a major role in weight gain and loss but is commonly misunderstood. Metabolism only occurs as fast as your body requires and may be altered if you initiate lifestyle changes.

Sleep and Obesity

Because of decreased physiological activity during sleep, metabolism slows. For example, heart and respiration rates, cognitive activity and body-system operations occur at reduced rates during periods of sleep. In addition, the "International Journal of Obesity and Related Metabolic Disorders" published a study in March 2002 revealing that metabolic rates in obese women are reduced compared to rates of normal-weight women. The researchers concluded that metabolic rates not only decline when sleeping but are related to your amount of fat and lean mass.

Lack of Muscle

Muscle expends more energy, or burns more calories, than fat. In November 2005, "The American Journal of Clinical Nutrition" published a study that reiterated that your metabolic rate is largely affected by your muscle mass or lack thereof. The researchers recruited 150 Caucasian male and female subjects and assessed their age, gender, hormones present in the blood, bone density and fat and lean mass. Researchers observed a 63 percent explainable variation in basal, or resting, metabolic rates attributable to fat-free mass. The evidence suggested that 1 kg of lean tissue increased the basal metabolic rate five times more than 1 kg of fat tissue.

Age and Increased Body Fat

Your age, gender, bodyweight and composition affect your metabolic rate. Around age 35 to 40, your body's fat-free mass decreases and your fat mass increases, causing your metabolism to slow and requiring a decreased caloric need. Without adopting healthy habits, you will notice a negative shift between your lean muscle mass and fat mass -- meaning you will lose muscle and gain body fat. You can prevent this by engaging in cardio and strength-training exercises and consuming a healthy diet consisting of lean protein, whole grains, water, fat-free dairy products, fruits and vegetables.

Lack of Nutrition

People battling the bulge might skip meals, particularly breakfast, engage in fad diets or severely restrict their caloric intake. If you employ calorie restriction as a means to lose weight, your body will operate as economically as possible and will only expend as much energy as is needed to sustain life. When you revert to old eating habits or healthy, new ones, you will exceed your body's caloric needs and will gain weight if you are not engaging in physical activity or exercise. You might become nutrient deficient or malnourished, which can have serious health repercussions, such as a heart arrhythmia or an impaired immune system.

Preventing Metabolic Decline

You may prevent the decline of your metabolism by consuming healthy meals and snacks and participating in physical activity or exercise. Keeping fat at bay only occurs when your energy expenditure equals or exceeds your caloric intake. If your calorie consumption exceeds your energy needs, you will pack on the pounds. Expending more energy than you consume causes a deficit and weight loss. Eat three healthy meals and two snacks or six mini-meals daily to maintain a feeling of satiety and avoid overeating. This will also keep your blood-glucose levels balanced, warding off midday fatigue and hunger. Water accounts for approximately 66 percent of your bodyweight and aids metabolism at the cellular level, so drink 64 oz. of water daily.