Question: Should I use lean body mass or total weight to set my caloric intake?
Or should I use goal weight?
Answer: First off let me address the second question, using goal weight. With few exceptions I don’t recommend using goal weight to set anything for the simple reason that most people tend to pick a goal weight that is exceedingly unrealistic and this tends to make them set calories very strangely. That is, unless someone sets a goal weight that is perhaps 10-20% below their current weight, using goal weight will tend to do odd things. So I don’t recommend it.
As to the first question, as usual it depends and there are pros and cons to each method. Let’s look at them and then I’ll explain why I tend to use total weight regardless.
Part of the complication is that total daily energy expenditure has several components to it; classically these included resting energy expenditure (REE), the thermic effect of food (TEF), and the thermic effect of activity (TEA).
Recently, interest in non-exercise activity thermogenesis (NEAT) and spontaneous physical activity (SPA) has also been generated based on the observation that people differ greatly in their ability to burn off excess calories through NEAT/SPA. This topic is discussed in more detail in Metabolic Rate Overview.
And while a good deal of work shows that resting energy expenditure is related primarily to lean body mass. It’s worth noting that lean body mass includes a lot more than muscle mass, something that is often forgotten. I’m not aware of any work linking the thermic effect of food to lean body mass specifically. The calories burned during activity tends to be related to total body weight (since you’re moving the entirety of you weight) and, depending on how active someone is, this can actually make up a fairly large portion of total energy expenditure. So while part of daily energy expenditure is certainly related to lean body mass, not all of it is.
As an additional complication, there is the issue of getting an accurate measurement of lean body mass in the first place, a topic that I discussed recently in Problems with Measuring Body Composition. Admittedly this is a minor issue as many body composition methods can get you within 3-5% of true body composition and any variance in lean body mass based on that inaccuracy will be fairly small.
As a final issue, there is the simple fact that no matter how you estimate your starting calorie levels, it’s never more than an estimate (this is something that is altogether too often forgotten) and it will always have to be adjusted based on real world changes in body weight and body fat.
For this reason, I tend to simply use current total body weight and go from there. It’s faster and easier, and unless you’re dealing with extremes (e.g. of age, body composition, activity) tends to get most people within shooting distance anyhow.
So, as I discussed in How to Estimate Maintenance Caloric Intake, for someone engaging in about an hour of moderate intensity activity per day, I will tend to assume a maintenance caloric intake of between 14-16 calories per pound current body weight. Is this a perfect value correct for everyone? No. Is it pretty close most of the time? Yes.
I’d note that, in recent years, due to drastically decreasing daily activity (outside of the gym), this value is often turning out to be a bit too high and many people are ending up towards the lower end (or lower than 14 cal/lb) as often as not. Sitting in front of the computer all day burns squat for calories, even being on one’s feet burns significantly more.
So an individual weighing 170 pounds would have an estimated maintenance caloric intake between
- 170 pounds X 14 calories per pound = 2380 calories
- 170 pounds X 16 calories per pound = 2720 calories
Just to simplify the math, let’s split the middle and assume a maintenance level of about 2500 calories for this person.
Depending on the goals, I’d make adjustments to caloric intake based on that starting point. A fairly standard moderate deficit fat loss diet might be a 20-25% reduction from maintenance. Or 500-625 calories per day for an intake of 1875-2000 calories per day.
Which, as it turns out is about 11-12 calories per pound total weight. And, as I discussed in How to Estimate Maintenance Caloric Intake, a very common moderate deficit calorie level is ~10-12 calories per pound anyhow. So we could have saved a lot of time by just using that value in the first place.
More extreme diets would use larger deficits, of course. For example, the low-calorie phase of my Ultimate Diet 2.0 uses a full 50% reduction from maintenance which would bring our subject to 1250 calories per day. But that’s a different kind of diet since there are only 4 low-calorie days before raising them again.
Of course for muscle gain, you’d go the opposite direction, perhaps increasing calories by that same 20-25% (depending on a host of factor). So you might end up at 3000-3125 calories per day or 17.5-18 calories per pound. I typically use 16-18 cal/lb as a starting point for muscle gain and, as you can see, even using a slightly more complicated method yields an identical value. So I tend to just use the fast one (with total weight) and then make adjustments from there.
Again, let me reiterate that these are all only rough estimates; they should only be treated as such rather than as holy writ. While I don’t have the space to go into the approach I use to adjust calories (both are discussed in the final chapters of both The Rapid Fat Loss Handbook and A Guide to Flexible Dieting), the key is that those values must be adjusted based on real world changes in body weight and/or body fat levels.
And since this is true whether or not you use lean body mass or total weight, I tend to just use faster estimates using total weight and then adjust from there. Outside of extreme situations, this typically works well enough and since you have to adjust things anyhow, I don’t see much of a benefit to using the more complicated approaches.
I hope that answers the question.