Losing 40 pounds in a single month is possible but not healthy, and according to Web MD, it is best to lose a maximum of 3 to 5 pounds of fat per week. Trying to lose more requires consuming a dangerously low amount of calories.
Weight loss happens when a person creates a caloric deficit by eating less calories and expending more energy, states WebMD.
To lose 1 pound of fat, a person must burn 3,500 more calories than they consume in a week, however, it is important to eat at least 1,050 calories a day in order to preserve muscle mass and metabolic function. When planning a weight loss diet, choosing the right foods is paramount to success. It is best to eat nutrient-rich foods such as fruits, vegetables, nuts, whole grains and lean proteins, as recommended by Nutrition.gov.
In addition to eating less food, weight loss can be achieved by increasing activity levels to burn more calories. This can be accomplished by exercise at the gym, walking, biking or any activity that gets the body moving. It is possible to use an online-based metabolic-rate calculator to determine how many calories are required to sustain a person's current weight, and then subtract from this number to establish a daily caloric target, according to About.com.