Have you been eating right and exercising but still not losing weight? It's easy to blame your metabolism. But is that really a valid excuse?

Have you been eating right and exercising but still not losing weight? It’s easy to blame your metabolism. But is that really a valid excuse? Metabolism is the entire process of converting calories to the energy needed to fuel body processes. There are three ways the body burns energy: 1) Major organs, such as the heart and lungs, require about 60 percent to 70 percent of the energy produced just to maintain basic functions. 2) Digestion uses about 10 percent of the calories we eat. 3) Muscles and activity account for the remaining 20 percent. Any extra calories are stored as fat. Everyone’s metabolism is different. Key factors that play into our metabolism include:

Muscle mass. Muscle requires more calories to maintain than fat. A pound of muscle burns about six calories per day, while a pound of fat burns about two calories a day. The more muscle you have, the more calories you burn. Men generally require more calories than women because their muscle-to-fat ratio is usually greater.

Age. The trend is that as we age, we more often gain weight in the form of fat than muscle, so we need fewer calories. We also tend to be less active, burning fewer calories. Hormone shifts also affect metabolism as we age.

Genetics. We all absorb calories differently. Some people are blessed to either absorb fewer calories or burn more.

Hormones. Hormones, including testosterone, estrogen and thyroid hormones — act like dials that turn your metabolism up or down depending on your body’s needs.

Overall health. Healing wounds or fighting an infection requires more calories. Stress can either cause your metabolism to speed up or slow down.

Given all the variables, calculating your exact calorie needs is difficult. There are lots of claims about products and strategies that boost metabolism for weight loss. But there are far more myths about metabolism than there are tactics that actually work. Following are a few of the most common misunderstandings.

•Eating small meals several times a day will burn more calories than eating three square meals daily. The truth is as long as the quantity and quality of food you eat is consistent, it doesn’t matter if you eat it all at once or split it into several meals. Frequency doesn’t seem to matter to your metabolism.

•Thinner people just have higher metabolisms. Actually, the bigger the body, the more calories it takes to maintain it.

•Drinking green tea will boost your metabolism. Several small clinical trials have suggested this is true, but the results have been inconsistent. Even when this effect is found, it is small, giving about a two-percent boost. To put that in perspective, if you consume 2,000 calories a day, you might burn 40 more calories in a day if you drink green tea.

•Late-night eating slows your metabolism. Your body works 24/7. It’s the extra calories often eaten at night that cause weight gain, not the time of day that you ate them.

•Skipping meals will lower your metabolism. An occasional skipped meal isn’t a problem, but severely restricting calories for a long period of time will slow your metabolism, and you may not be able to reset it back to normal. If you eat less than what the body needs for basic function, your body thinks it is entering famine mode, so it adjusts your metabolism to use fewer calories. This is why you should never embark on a weight-loss diet with fewer than 1,200 calories.

•You can boost your metabolism with caffeine, spicy foods, stimulants or other supplements. These can produce a small bump in energy, mainly due to an increased heart rate or increased internal heat production. But none of these will have a significant or lasting effect on your metabolism. However, they may cause harm by increasing blood pressure or causing insomnia or anxiety.

•You get what you get, and you can’t change your metabolism. There are a few things you can do to optimize your metabolism: Don’t over-restrict your calories; work on building more muscle mass; get adequate sleep to help regulate hormones and reduce stress; and stay hydrated. Mild dehydration can slow your metabolism, so try to drink around two liters of water daily.

Sustainable weight loss doesn’t happen overnight. There is no magic pill to boost your metabolism. Weight loss is difficult, without a doubt, and the only sure way to keep it off is by consistently eating a little less and exercising a little more.

Anita Marlay, R.D., L.D., is a dietitian in the Cardiopulmonary Rehab department at Lake Regional Health System in Osage Beach, Mo.