If you want to change your weight, there’s good news: your metabolic rate isn’t fixed for life. Metabolism can and does change over time, and you can take steps to speed it up or slow it down. If you intend to start gaining weight, see your doctor before you begin to hammer out details of a healthy plan to follow.

Losing weight requires you to eat fewer calories than you burn, so it seems logical that eating no calories would lead to the quickest loss. Fasting, however, does not speed up your metabolism -- and may actually backfire by slowing down your metabolic processes to compromise your ability to successfully drop pounds.

Lipase is an enzyme that is found in several different places in the body, including the pancreas, intestines, and liver. In the pancreas, lipase helps in digestion of food by breaking down components of fat called triglycerides into smaller molecules that can be easily absorbed. According to the website Healthline.

You can't actually calculate your body mass index, or BMI, using your waist and hip measurements. These two measurements are used to calculate your waist-to-hip ratio, or WHR, which can be helpful for determining whether you're carrying your weight in a healthy way.

When you weigh yourself, the scale cannot differentiate between muscle, fat, water, bone or internal organs. In fact, a scale doesn't know if you are human being or a bag of rice. If you have recent weight gain, it's important to know if it's muscle or fat.

The average weight for men of different heights varies by country, and the average isn't necessarily a healthy weight. Two men of the same weight and height may also look very different, depending on how much of their weight comes from muscle versus from fat.

When you can't determine the height of a patient, upper arm circumference can help calculate his body mass index. Body mass index, or BMI, gives a caregiver an estimation of a patient's body fat level.

Many medical providers use body mass index, or BMI, to assess your weight and health risk. BMI is a calculation of a person's weight in kilograms divided by the square of his height in meters. A BMI below 18.5 is considered underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight and 30 or above is obese.

The average body mass index (BMI) in men between the ages of 20 and 74 has increased from 25.1 in the early 1960s to 27.9 between 1999 and 2002, the last year there was a National Health and Nutrition Examination Survey. Men 75 and over weren’t sampled until 1988, but their BMI has also increased.

Your prostate gland -- found at the base of your bladder -- is normally the size of a walnut. It can become larger with age, causing uncomfortable urinary symptoms such as the sensation of being unable to completely empty your bladder.

The breasts are made up of a series of structures called lobules, connected to the nipple by a series of ducts, and surrounded by fat and connective tissues. Lactation, the release of milk from the breast, occurs upon the maturation of cells within the lobules.

ATP is short for adenosine triphosphate, a crucial chemical in human metabolism that has been called "chemical currency" because the cells use it as a direct source of energy.