You decided to you want to lose some weight, but you are trying to figure out how long it will take you to reach your goal. In this post, I'll explain what are some realistic expectations when it comes to how fast you can lose body weight and provide you with some basic calculations you can use to estimate your rate of weight loss.
First, we have to make a distinction between losing body fat and losing bodyweight. Our body weight consists of many other things in addition to body fat like muscles, bones, organs, body water, etc. So if we purely rely on the weight scale, drop in weight doesn't tell us whether we lost body fat, muscle or body water. In fact, most diets cause you to lose muscle and body water in addition to body fat which will result in a much more significant weight drop.
However, If you are more concerned about how you look, feel and perform, then you need to pay attention to body composition changes and not just bodyweight. Generally, the goal is to lose as much body fat as possible, while maintaining or building muscle and maintaining proper hydration (i.e. not dehydrating yourself with saunas, exercising in the heat and not drinking enough water).
Let's assume we have a person weighing 200 Ibs with a body fat percentage (BF%) of 30% who wants to lose 30 Ibs of fat. Being at 30% body fat means this individual is carrying 60 Ibs of fat (200 x 0.3). At this bodyweight, it's reasonable to expect an average weight loss of 1-2 Ibs/week. This means it will take 15-30 weeks to lose 30 Ibs and reach 170 Ibs weight. If we assume that most of the lost weight is fat*, we now have 30 Ibs of fat and body fat percentage of 17 % (30/170).
*at the beginning stages of weight loss, most of the lost weight will come from muscle, carbohydrate, and body water losses. After this initial stage, weight loss will come predominately from fat (~90%) with the rest (10%) coming from other components of body weight (muscle, water, protein loss, etc.). So really you are never losing only body fat, but using specific dieting and exercise techniques, we can force your body to predominately use body fat.
Let's use another example. We have a woman that weighs 130 Ibs, 25% body fat (BF%) with a goal of getting below 20% BF%. We are trying to calculate how long it will take her to get down to 20% body fat.
First, we are going to calculate her body fat mass - 130 x 0.25 = 32.5 Ibs. This means she is carrying 32.5 Ibs of fat. Compared to the previous individual, this woman is much leaner which means her rate of weight loss will be slower so we are going to use 1 Ibs of weight loss/week. If we assume that most of the weight is coming from body fat it will take her 12-weeks to lose 12 Ibs of body fat which will bring her body weight down to 118 Ibs and fat mass to 20.5 Ibs. In terms of body fat percentage that is 17% bodyfat (20.5/118).
However, things usually don't go this smooth. As you get leaner, metabolism slows down and you might get intense cravings at which point it would make sense to introduce a diet break. So if we add one week of diet break for every 4-weeks of dieting this brings total dieting period to 15 weeks which is around 3-4 months. For a more conservative approach, add another 2-3 weeks if you don't have perfect adherence to diet and training program and this prolongs dieting period to 4-5 months.
To ensure you are losing body fat and not just muscle and water, incorporate other tracking methods in addition to just body weight. For example:
With our clients, we use ultrasound body composition assessment machine that tells us exactly how much fat, muscle and body fat you are carrying on your body. It can also tell us what's your fat and muscle thickness at locations on your body that we want to specifically focus on. This allows us to better customize your program and gives us feedback whether we are on the right track or we need to make any adjustments.
Thank you for reading and we hope you found this article useful. If you have any questions don't hesitate to let us know how we can help.