“I’ve been using a body fat scale to let me know if I’m losing fat or muscle,” wrote one reader.
“But I’m not sure how much I can trust it, as the results seem to vary wildly.”
“How can I be sure that I’m losing fat rather than muscle?”
The honest answer is that you can’t. Not with any degree of accuracy anyway.
Body fat scales are largely a waste of time. Skinfold calipers can be useful in some circumstances, but even they have their problems. Even “high tech” methods like DEXA and underwater weighing can’t be trusted.
Tracking changes in waist size can be useful. But it’s a method that does have a few limitations.
Some people find it difficult to get the tape measure in the exact same position from one week to the next. Using some kind of anatomical reference point, such as your belly button, can make it easier to get a consistent reading.
But if you’re carrying a lot of abdominal fat, the belly button will often point downwards, which makes waist circumference very difficult to measure. As fat is lost, the angle of your belly button is going to change, which has the potential to skew the results.
Even just a small change in the amount of tension applied to the tape measure can affect the accuracy of the results.
So what are you supposed to do?
Rather than spending a bunch of money on expensive body fat tests, I think you’re much better off using two simple metrics — your weight on the scales and your performance in the gym.
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The argument against using your scale weight to track your progress is that any loss in fat will be offset by a gain in muscle.
That is, if you lose 5 pounds of fat and gain 4 pounds of muscle, the scales will show that you’ve lost only 1 pound in weight.
While the theory sounds good, it doesn’t always work that way in practice.
Once you’ve moved past the “overweight beginner” stages of training, you won’t be building muscle at anything like the same speed at which you’re losing fat.
While you can lose fat and gain muscle at the same time, you won’t do so at the same rate. The best that most people can hope for is to gain a relatively small amount of muscle while losing a much larger amount of fat.
For example, you might lose 6 pounds in weight over the course of a month. In reality, you might have lost 7 pounds of fat and gained 1 pound of muscle.
While the scales aren’t a completely accurate way to track your progress, they will tell you if you’re moving in the right direction.
I also recommend that you weigh yourself every day, rather than every week or every month.
Some advise against the practice of weighing yourself daily, mainly on the basis that your weight fluctuates from day to day.
But when you think about it, this is really an argument IN FAVOR of daily weighing.
Let’s say that you weigh yourself once a week, and that you stepped on the scales first thing this morning. Let’s also assume that the scales show that you’re one pound lighter than you were last week.
“Great,” you think to yourself. “Things are moving in the right direction.”
But are they really?
How do you know that today isn’t one of those days when your weight happened to fluctuate downwards? And that if you weighed yourself again tomorrow morning, it won’t have shifted upwards again?
A single weekly data point isn’t particularly useful when it comes to guiding your decisions about what to eat and how to exercise.
So instead of weighing yourself once a week, weigh yourself every day. Then take an average at the end of the week.
Any daily fluctuation in weight will be “averaged out” over time. Over a period of several weeks, you’ll be able to see a trend. If the trend isn’t downwards, you’ll know that some aspect of your diet and training program needs to change.
Provided your training program is set up properly, your performance in the gym is also a good way to gauge your progress.
When you cut back on your carbohydrate intake, it’s not unusual to see some kind of decline in performance during certain types of exercise.
Your performance in this “lowered glycogen” state then serves as a benchmark against which to track your results.
If your performance in the gym is improving, there’s a good chance that — at the very least — you’re holding on to the muscle you have.
And by an improvement in performance, I’m talking about doing more reps with the same weight, or lifting a heavier weight for the same number of reps.
Muscle size and strength are not 100% correlated, and there are other factors (such as your nervous system doing a better job of using the available fibers in a given muscle) that contribute to gains in strength.
But for our purposes, the link is strong enough. If you’re gaining strength, you’re on the right track. Even just maintaining your performance in the gym while losing weight is a good sign that what you’re doing is working.
Someone who is very overweight and new to lifting weights will find it relatively easy to gain strength while dropping fat. As you get leaner, the rate at which you gain strength will slow down.
Eventually you’ll reach the point where the best you can hope for is to simply maintain your strength. It’s not uncommon for competitive bodybuilders to lose strength in preparation for a contest .
What this means is that you’ll need to modify your expectations as your body composition changes. All other things being equal, you’ll find it easier to gain strength while losing fat when you’re going from “overweight” to “lean” than you will going from “lean” to “ripped.””
That doesn’t mean you should stop trying to get stronger. But it’s not something you should necessarily expect, especially once you’ve moved past the beginner stages of training.
Tracking your weight on the scales and your strength levels in the gym is not a particularly accurate way to quantify actual changes in body composition. But it will tell you if you’re on the right track and moving in the right direction. Most of the time, that’s all you really need to know.
1. Rossow LM, Fukuda DH, Fahs CA, Loenneke JP, Stout JR. (2013). Natural bodybuilding competition preparation and recovery: a 12-month case study. International Journal of Sports Physiology and Performance, 8, 582-592
2. Hulston CJ, Venables MC, Mann CH, Martin C, Philp A, Baar K, Jeukendrup AE. (2010). Training with low muscle glycogen enhances fat metabolism in well-trained cyclists. Medicine and Science in Sports and Exercise, 42, 2046-2055
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