An old rule-of-thumb suggests a pound of fat equates to 3500 calories. So if you want to lose a pound of fat, you’d need to have a deficit of 3500 pounds. Or, phrased another way, you would need to consume 500 fewer calories than you use every day for a week.
However, numerous studies have demonstrated that these numbers don’t quite accurately reflect reality.
Understanding Calorie Deficits
Perhaps the most important factor in weight loss is creating a consistent calorie deficit. This means you’re consuming fewer calories than you burn daily.
In a day of doing nothing at all, the average adult burns around 1800 calories (slightly more if you are bigger, maybe less if you are small). That equates to a little bit more than one calorie per minute to digest food, keep your heart pumping and your lungs breathing, and fuel all the other processes that keep you alive.
Gentle activity such as walking will burn about 5-8 calories per minute, while running and intense exercise can burn upwards of 10-15 per minute. This means that a person with an active lifestyle may use anywhere between 2000-3000 calories or more daily.
If you regularly eat more calories than you are spending, that extra energy will be stored, and you will gradually gain weight.
If you consistently eat fewer calories than you spend, your body will need to break down stored fat to use as fuel, gradually losing weight.
Slow Weight Loss
Commonly reported progress is around 1-2 pounds per week. This would generally equate to a deficit of 500-1000 calories each day, although this number will differ from person to person and will depend on various factors such as age, food types, and starting weight.
When you are inconsistent with your calorie deficit, or if you are only eating a very small amount less than you use, weight loss will be slow. In this case, you might only see 0.5-1 pound of weight loss each week, or even less.
Rapid Weight Loss
When you create a more significant calorie deficit, weight loss can occur much faster.
There’s no strong consensus on whether it is better to lose weight slowly or quickly, and there are pros and cons to both approaches. Slow weight loss is often considered the safest option, giving your body time to adapt to the new calorie intake. But rapid weight loss, using very low calorie diets, can also be safe and possibly more effective (with informed dietary choices involving nutrient-dense foods) and may lead to losses nearing one pound per day!