Hello there. I have been using this article as a basis to set my deficit and those of my clients and referred to it in discussions for years, so first off thank for that.
Now, at the start of this year, Greg Nuckols published the following article:
In it, he brings up the question "How fast can I lose fat?" and gives the following answer/formula based on this study
With this information, we can use a nifty little formula that can tell you how fast you can shoot to lose fat without unnecessarily increasing your risk of losing much (or any) lean mass in the process. I’m using 25kcal/day per pound of fat because those 3kcal/day aren’t going to make a meaningful difference, and they’ll simplify the calculation a lot, as you’ll see in a second:
Body weight x bodyfat percentage = total body fat x 25kcal/day per pound of fat = daily caloric deficit x 7 = weekly caloric deficit ÷ 3500 (since there are roughly 3500kcal per pound of fat tissue) = pounds of fat you can lose per week
It may look messy, but here’s what it all simplifies to:
Body fat percentage ÷ 20 = percentage of your current bodyweight you should aim to lose per week.
So, for example, if you’re currently at 20% body fat, you should aim to lose about 1% of your bodyweight per week. If you’re 10%, you should only aim to lose about 0.5% of your body weight per week.
Now, you can certainly aim to lose weight faster than that, but you’ll almost certainly lose muscle in the process. If that doesn’t matter to you (since it’s much faster to gain back muscle you’d previously lost much faster than to build new muscle), then be my guest and crash diet, but your rate of fat loss probably won’t be much faster.
Saying this, especially the bolded parts, he implies that muscle loss at higher deficits than prescribed per his formular here are basically inevitable and fat loss won't be much improved. Of course, building that much decisionmaking on a single study is already problematic, but still, this made me unsure about how large (or not) to set my deficits and those of my clients.
Thank you for any insight you can give.