Although it isn't necessarily easy, you can change your metabolism. Unfortunately, these changes can go both ways. While many people would prefer to speed up their metabolism, it's also possible to slow it down. The speed of your metabolism stems largely from genetics, so any alterations are likely to be relatively small. You'll probably have to make multiple changes to have a significant effect on how many calories you burn each day.
Calorie Consumption and Metabolism
Cutting your calorie intake can slow your metabolism, especially if you drastically reduce calories to try and lose weight quickly. Restricting calories signals to your body to slow your metabolism; your body senses that you're not getting enough food, so it lowers your calorie burn to preserve your fat stores. This could make it harder for you to lose weight. If you're a woman, make sure you eat at least 1,200 calories per day, and if you're a man, get at least 1,800 calories from your diet. If this doesn't help you lose weight as quickly as you'd like, try adding more exercise instead of eating less so you don't mess up your metabolism.
How Body Composition Alters Metabolism
Your body composition -- the ratio of fatty tissue to lean tissue, like muscle -- also affects your metabolism. Muscle burns about 6 calories per pound per day, while fat uses just 2 calories per pound per day, so the more muscle tissue you have, the more calories you'll burn. If you lose muscle when you lose weight and then regain some of this weight, the gains will be fat tissue, so you could end up at the same weight you started, but with a slower metabolism. Make sure to do some resistance training while you're dieting to help limit the amount of muscle you lose, and don't forget that as you slim down, you need to eat fewer calories to fuel your new, smaller body and avoid regaining what you worked so hard to lose.
Aging, Muscle Loss and Metabolism
Your metabolism may also slow down as you age; typically, it slows by about 1 to 2 percent every 10 years, which is why people tend to gain weight more easily as they get older. The most likely reason for this decrease is because of changes in body composition since people often lose muscle and gain fat with age. This muscle loss averages between 3 and 8 percent every decade after you turn 30, according to a review article published in Current Opinions in Clinical Nutrition and Metabolic Care in 2010. You can limit this muscle loss by exercising regularly and eating about 25 to 30 grams of protein per meal. You can get this amount of protein by eating a 4-ounce serving of tuna, pairing a 3-ounce chicken breast with 1/4 cup of peanuts, or having a cup of cooked lentils with a glass of skim milk as part of your meal.
How Sleep Affects Metabolism
Cutting back on sleep won't just leave you tired the next day, it can also decrease your metabolism. People who get less sleep don't metabolize glucose, or sugar, as well as those who get sufficient sleep, according to a review article published in 2010 in the International Journal of Endocrinology. This is most likely a result of sleep's effect on growth hormone, which affects muscle growth and helps control your metabolism. Growth hormone levels typically peak soon after you fall asleep, but when you're sleep-deprived, you don't experience that growth hormone spike.
Not getting enough sleep can also increase your appetite and lower your calorie burn throughout the day, which increases your risk of weight gain and obesity. Aim for at least 7 hours of sleep per night to limit this risk.
Chemical Effects on Metabolism
A number of chemicals, called obesogens, may interfere with your metabolism and make you more likely to gain weight, notes a review article published in Environmental Health Perspectives in 2012. About 20 different chemicals are in this group, including a substance called tributyltin, which is used as a preservative in wood; phthalates, in many personal care products and air fresheners; monosodium glutamate in processed foods and the BPA in some canned goods and cash register receipts. Using plastics less frequently, eating organic food and filtering your water can help minimize your exposure to these chemicals.