There are two ways to lose weight. You either have to decrease the input of calories coming from food, or increase the output of calories coming from exercise. If the amount of calorie input (food) is less than the amount of calorie output (basal metabolic rate + exercise), then a calorie deficit leads to weight loss Your question asked about how best to decrease this woman’s calorie input to achieve weight loss. However, it’s important to remember that weight can also be lost by increasing calorie output through exercise!
Figuring out calorie deficit per day:
The first thing you will need to think about is how large this woman’s calorie deficit will need to be each day to achieve the loss of 20 lbs. over 257 days. A pound is roughly equal to 3,500 kcal, meaning that a calorie surplus of 3500 kcal will lead to a pound of weight gain and a calorie deficit of 3500 kcal will lead to a pound of weight loss.
20 lbs. is equal to 70,000 calories. Knowing that this woman will need to create a 70,000 kcal deficit over 257 days, how much of a calorie deficit will she need each day?
Figuring out energy expenditure (basal metabolic rate + exercise):
The next thing you will need to figure out is this woman’s daily energy expenditure. This you can find by adding her basal metabolic rate (BMR) with her calories burned through activity (exercise).
A basal metabolic rate simply means the amount of calories she burns per day just from the chemical work of sustaining life! In other words, it is the minimum amount of calories burned per day at rest, or the number of calories you would still burn if you were completely bedridden.
A basal metabolic rate can be roughly estimated by this formula: 655 + (4.35 x weight in pounds) + (4.7 x height in inches) – (4.7 x age in years). Since we don’t have most of this information, we will not be able to get a particularly accurate estimate of her BMR.
This problem also didn’t give us this women’s daily calories burned through activity. Normally, we would add this together with her BMR to find her total daily energy expenditure. Since we are at such a loss for information, let’s go with a very rough estimate of 2,000 kcalfor energy expenditure—a fairly typical number for non-athletes.
Decreasing calorie input to create a calorie deficit:
This woman will need to create a calorie deficit of 272 kcal per day to hit her weight loss goal (70,000 kcal/257 days). How many calories per day will she need to limit herself to assuming her daily energy expenditure is 2,000 kcal?
(Hint: take the daily calorie deficit and subtract it from her daily energy expenditure)