Weight Loss vs. Fat Loss: Is BMI or Body Fat Percentage More Important?


Let’s start with weight loss since most people are focused on the scale. Some days the scale can be your best friend; other days it’s your worst enemy. Personally, my weight fluctuates by up to 3-4lbs day-to-day. Why is there so much variability? It’s all about water retention. If you perform carb cycling like I do, then be prepared to weigh more after high carb days and less after low carb days. If you have a simple weight loss goal, you could follow the Atkins approach, reduce carbs, and watch the pounds (of water weight!) melt off. Guess what though, when you inevitably start eating carbs again, your weight will spike back up.

The other problem with focusing exclusive on weight loss is that you don’t account for muscle gain. This is especially true for those who are new to resistance training. Just because your weight goes up doesn’t necessarily mean you’re getting fatter. In fact, if you replace fat with muscle, you’ll find that your weight remains unchanged despite a positive change in health and appearance.

Fat Loss

Hopefully the above flaws make it obvious that weight loss shouldn’t be the primary goal…it should be fat loss. While there may be a general correlation between weight loss and fat loss, it’s far better to focus on fat loss to the extent possible. How can you effectively track your fat loss though? You could start by trying a body fat scale or caliper. The problems with body fat scales are that they are also influenced by water retention and a variety of other factors. I’ve seen my body fat fluctuate by 1-2% day-to-day because of this. Calipers are marginally better. The challenge is that you’re measuring within millimeters and it’s hard to measure the same exact area every time. What about using a tape measure? Again, a tape measure can be just as inaccurate as anything else because you’re trying to measure within fractions of inches sometimes.

With all these flawed methods, it’s often best to gauge yourself by looking in the mirror, taking before/after pictures, and/or seeing how your clothes fit. If you’re training for looks, this is probably what’s most important to you anyway.

BMI vs. Body Fat Percentage

What if you’re training for health purposes though? Is BMI or body fat percentage more important? You might think that BMI is more important since it seems to be used as a general indicator of potential health risks. However, the use of BMI is prevalent because it’s an easy calculation. It only requires your height and weight. The problem is that two people could be the same height and weight but have different levels of body fat. Those people probably don’t have the same health risks, especially if one has extra body fat stored around the waist.

So maybe body fat percentage is more important then. How many times has someone ever told you to have your body fat measured though (vs. the number of times that you’ve been weighed)? Personally, I don’t ever recall being asked about my body fat percentage so it may not be the most critical determinant of overall health either. In my opinion, a better determinant than BMI or body fat percentage may be waist circumference. It’s a pretty simple measurement and really does account for both weight and fat since a decrease in those factors tends to lead to a smaller waist. Additionally, excess stomach fat, especially visceral fat which surrounds your organs, can result in a higher risk of heart disease or diabetes. If you’re male with a waist in excess of 40” or a female with a waist in excess of 35”, you have an elevated risk. If you have a high BMI in conjunction with a large waist, you have an even higher risk.

Weight Loss vs. Fat Loss

Summing everything up, it’s good to focus on weight loss since there is a correlation between losing weight and losing body fat. However, if you have a reasonable means to track your body fat, it’s really best to put your effort toward losing fat since the scale may be deceptive. With either method, it’s best to track trends over time. Frankly, as long as you’re happy with your appearance, don’t be overly concerned with arbitrary readings from a scale or body fat tester. Finally, if health is your focus, BMI, body fat percentage, and waist circumference can all be used in conjunction with each other to determine your overall health and risk factors.

As for my wife, based on the methods above, it actually appears that she lost around 2lbs of fat while adding 2lbs of muscle in 3 weeks which makes sense because she’s relatively new to resistance training and has been eating well and performing cardio in line with the recommendations from Visual Impact for Women. It’s early but with this knowledge, it’s much more encouraging for her to feel like she’s making progress rather than focusing on the scale and worrying that her hard work isn’t leading to any results.