You’ve probably heard that 3500-Calorie rule for fat loss that says if you eat 3,500 Calories less, you’ll lose 1 pound (0.45 kg) of body fat. I just talked about this when we were calculating our daily calorie targets. But have you ever wondered where that number actually came from?
Back in 1958, a scientist named Max Wishnofsky introduced this simple formula to estimate fat loss. It’s been used ever since as a rough starting point for calculating weight loss.
The Science Behind the Number
Let’s break it down with some simple math.
- 1 gram of pure fat contains about 9 Calories.
- But body fat tissue (what we carry on our bodies) isn’t 100% fat. Wishnofsky’s 1958 model used an estimated fat content of 87% (which we now know isn’t quite accurate).
So if we do the math:
- 1 lb = ~454 grams
- 454g × 0.87 (fat content) × 9 cal/g ≈ 3,500 Calories
That’s how we arrived at the idea that you need a 3,500-Calorie deficit to lose one pound of body fat, or about 7,700 Calories for 1 kg.
But, is This 3500-Calorie Rule Accurate?
Not entirely. It oversimplifies the entire fat loss process. While the math checks out, our bodies aren’t machines. The human body is more complex, and it adapts as we lose weight. Plus, not all weight lost will be purely fat. (It can include fat, water, muscle, and more.)
That’s why we still use the 3500-Calorie rule for fat loss as a starting point—not a perfect prediction. It’s a rough estimate to help you get started. From there, you can track your intake, monitor your progress, and adjust as needed.
If you’re curious about the history behind this idea and why it’s considered outdated, check out this research paper that explores Wishnofsky’s theory and how our understanding has evolved.
References:
- Wishnofsky, M. (1958). Caloric equivalents of gained or lost weight. The American Journal of Clinical Nutrition, 6(5), 542-546. https://doi.org/10.1093/ajcn/6.5.542
- Thomas, D. M., Gonzalez, M. C., Pereira, A. Z., Redman, L. M., & Heymsfield, S. B. (2014). Time to correctly predict the amount of weight loss with dieting. Journal of the Academy of Nutrition and Dietetics, 114(6), 857. doi: 10.1016/j.jand.2014.02.003
