Your weight is affected by three major factors: your genetic makeup, what you eat, and your activity level.

Genetics

Your genetic makeup affects your basal metabolic rate, your appetite and point of satiety (feeling full), your weight range, how your body fat is distributed, and possibly the tendency to be active or inactive.

• Basal metabolic rate (BMR). BMR is the rate at which your body uses energy (calories) at rest, and therefore, it affects your total energy needs. Some people have higher BMRs than others (based on heredity, height, body composition, and age). A lower BMR makes it easier to gain weight. Your BMR can change slightly in response to certain conditions. For example, starvation or very low-calorie diets will decrease your BMR. Overeating increases BMR, as do fever and severe physical stress, such as recovery from surgery or from extensive burns.
• Body signals. Hunger, satiety, and appetite are body signals that tell you how much to eat. These signals can be influenced by your environment or ignored for short periods of time. However, they are powerful hormonal drives, and trying to ignore them for a long period of time (as in dieting behavior) can cause you to become obsessed with food.
• Fat distribution. Your weight distribution changes as you age. Aging leads to decrease of muscle mass and an increase in fat. Men store more fat in the abdomen as they age, and women store more fat in the hips and thighs. Repeated weight loss and weight regain can change the proportion of fat to lean tissue in your body and actually increase your percentage of body fat.

Nutrition

A balanced, healthy diet includes lots of fruits, vegetables, whole grains, protein (lean meats, eggs, legumes, and nuts), and low-fat dairy products. This supplies your body with the nutrition it needs and lowers your risk for some diseases, like heart disease, some cancers, and osteoporosis.³ In addition, you will generally feel better and have more energy if you practice healthy eating habits.

The average American diet contains too many calories and too much fat, cholesterol, animal protein, salt, alcohol, and sugar. Many of us don't get enough whole grains, fruits, and vegetables.

It can be hard to make healthy food choices. Factors that influence our food choices include lack of time to cook and easy access to fast foods and packaged snacks. In addition, sometimes foods that seem like a healthier alternative may not be. For example, a low-fat cookie may have less fat, but it is usually high in sugar and often has the same number of calories as a regular cookie. Potato chips labeled cholesterol-free are still a high-fat, high-calorie, low-nutrient snack food.

People who eat regular meals tend to be more successful at maintaining a healthy weight than people who eat on an irregular schedule or skip meals. More importantly, planned meals are usually more nutritious than meals grabbed on the go or at the last minute. Also, skipping meals may make it more likely that you will overeat at the next meal or eat a less-than-nutritious snack.

Physical activity