How does decreasing body mass impact caloric requirement?


Any good data on how decreasing body mass impacts caloric requirements? Obviously fat cells are less metabolically active than muscle, so require less energy, also given a negative energy balance in the longer term, metabolic rate will tend to slow. (Decreasing caloric requirements further). When I started on Soylent I was finding that the 2000 calorie per day point was about right for me, but as my weight loss has continued I’ve found I need less calories (the fact that this is noticeable is very interesting to me). I am familiar with various basal metabolic rate formulas (which pretty much all assume lean body mass), looking for more of the practical experience side of things.
Right now, my weight loss has somewhat stalled (after a pretty steady 30 lbs of loss). Trying to ‘troubleshoot’ it a little (one thing I find interesting is I feel like I’m sitting a lot in the ‘in between’ stage. Not hungry enough to really eat, but hungry enough to want something, meaning I’m snacking more, which I think throws things off.)


As a general rule of thumb, the more you weigh, the more calories you need to maintain that weight.

Sure, fat burns calories slower than muscle, but it still needs calories to continue as part of your body. There are of course additional considerations in your body adjusting to certain caloric limits and routines, but that gets into the complicated and speculative. Stick to the general rule of thumb and you’ll be fine.


Looking for more numbers based… like can I assume that the relationship is linear? (Interestingly, with an N of 1, If seems fairly close… taking my initial body weight to be 100%, I currently weight 88% of what I did, yesterday I had about 1600 calories of Soylent and a few ‘extras’. 0.88x2000=1771.)


I have seen numbers like “A pound of fat burns X calories per day, a pound of muscle burns Y calories per day,” but I’ve also heard that there a huge range from person to person in how many calories per day they need. Really the best way to find out is by experimenting on yourself. Your weight loss has stalled? Drop from 2000 cal/day to 1800. If your energy level drops or other bad things happen, go back to 2000, otherwise see whether you resume weight loss. Etc.


That’s pretty much what I’ve done. My Achilles heel has always been snacking though, and as I’ve cut down the Soylent I’ve found the ‘snacking drive’ goes up…but if I stay at ‘full soylent’, I’m way too stuffed…


Reading a little, looks like the numbers I can find aren’t really what I’m looking for. What I find is ‘base’ metabolic rate of fat, which is really not helpful. Obviously it takes energy to drag around 30 pounds everywhere you go, even if it were completely non metabolically active (I generally walk about an hour or so a day with the dog, and always have, so not like I live a really sedentary lifestyle…)


Yeah, snacking is the worst when trying to lose weight. I find that the only way for me to lose weight effectively is to totally eliminate snacking - no eating at all, unless at meals. If I have just a small snack then I always want more, so I have to do none at all. I know other people manage to incorporate snacking into their diet though, so it takes all kinds I guess. Hopefully you can find something that works for you.


Not to be too obvious, but you could snack on Soylent (or something similar)… I go through about 2800kcal/day which includes a full 2000kcal 1.8 packet. Sometimes I’ll “snack” on half a bottle of 2.0. Other times to mix it up I’ll make a serving of chocolate Schmilk.


I found this calculator to be a helpful guideline as I have lost weight. It isn’t perfect because it doesn’t take body fat percentage into account but I have used it a few times and found it to be helpful.


Weight is a factor in relation to how much energy you spend to move your body around also. (Besides the basal metabolic rate)


Interesting calculator…I’m WAY below the estimates for caloric requirements…


The estimates are based on a level of activity above Sedentary. Not sure which though.

Best way to check that you’re getting the right amount for your goals:

  1. check your bodyfat percentage. There are scales and hand-held devices that can measure this, and even though it might not be ultra-accurate, it’s generally good enough to get a useful estimate.

  2. calculate your lean body mass. In the following formula, LBM is lean body mass, and TBM is total body mass, and BFP is bodyfat percentage. BFP is a decimal, e.g. 50 percent = 0.5

        LBM = TBM - (BFP * TBM)
  3. Calculate your desired body mass (DBM). Say you want 13 percent bodyfat. You want 100% + 13% of your lean body mass. (Do this step with whatever you want as your target.)

        DBM = LBM * (1.13)

To use this information …

  1. Using the BMR calculator of your choice, but I recommend one that includes activity level and gender to be sure. Then find out what the target Calories are for that DBM at your actual activity level. Your current caloric intake SHOULD be above that number. If not, you have a depressed metabolism and you’ll need to fix that, and that process is beyond the scope of this answer and you need a doctor to help. Otherwise, you have some juggling to do. First, if the difference between your target and your current is more than 500 Calories a day, you’ll need to approach this in stages. Typically this is true if your target bodyfat is more than 6 percent (0.06) from your current bodyfat percentage. If that’s the case, choose a new target that’s no more than 6 percent away and do the calculation with that, knowing that when you reach that level you will change it again. Step by step.

(I chose that number from a range. You can experiment to find your best difference. It should be a number where you can go without feeling like you’re starving and must snack.)

Once you have the target Calories, eat that many Calories a day. NOTE this may be more than 500 Calories below what your current requirement says – so you may be forced to do it in stages. If it’s less than 500 Calories difference, and you want to make it happen a bit faster subtract 100 Calories. You want to feel slightly but not annoyingly hungry but not right after you eat.
Keep track of your weight once every two or three days, at the same time every day. Stay hydrated but don’t overdo it. The purpose of this process is to make your body composition go to what you want it to be. So keep up exercise levels, because exercised muscles respond better to insulin and teach organs to respond better as well. But don’t go crazy unless you want to do the calculation over again for the higher activity level.

Don’t sweat it if you go over once a week or so, after you’ve got the eating pattern set. And, according to the dieticians I’ve known, that will cause a slow, steady loss (or gain) until you reach the body composition that you targeted. Losing more than 2 pounds a week is stressful on your body and can actually cause more harm that it fixes, so be careful.

This process does rely on activity above ‘sedentary’ because ‘sedentary’ also makes the body’s famine-detection mechanisms switch on more easily, as people who are starving become less active. Feedback. Yay. So if you’re not more active, then walk for a half hour a day, if you can.

And if you insist on asking – yeah, this works when I can get myself to do it. Having my insulin changed (increased) knocked me for a loop and I have to get back into it again… because the insulin made me gain back the weight I had lost doing this process before. (Avoid diabetes, if you can. I am told it’s possible.)

… there was something missing here that I noticed when I was doing another reply but I can’t remember what it was.
Oh well. Someone is sure to point it out. OH RIGHT.

The USDA site says that 500 Calories deficit is a good number to choose as the daily caloric deficit, so my initial 100 Calories deficit recommendation might be too slow. Personally I think 500 might make you feel too hungry, but that’s up to you. Just don’t go much beyond that 500 Calorie deficit. So I’ve adjusted my answers above to fit that recommendation.


Two simple things you might try are more exercise and fasting after 8pm. I am not even talking about hitting the gym. I just put in earphones and listen to podcasts while I walk. When I want to drop weight I just dial it up over 10,000 steps a day.


I generally walk about an hour a day, and my job keeps me on my feet most of the day, so not like I’m living a really sedentary lifestyle.

On the plus side, my weight loss seems to have started up again (no changes to what I’m doing…)


Excellent news. May it keep dropping safely. Perhaps your body was consolidating itself.

A quick explanation for why you need to change your numbers when you lose weight:

All your cells are metabolically active. Even fat cells are not inert and inactive; they do have metabolic requirements, however small. And some fat cells (called ‘brown fat’ for their apparent color) are much more active, transforming fat into usable metabolites. The problem is, when your bodyweight drops, so does your caloric requirement, unless you have increased the amount of muscle much more than the offset loss of weight from fat. So you may have new requirements.

If you’re eating what you need to support a specific target bodyweight, then you don’t need to adjust things. If you’re eating the amount to support your current bodyweight minus 500 Calories, then you don’t need to mess with it until you either stop losing or your current intake has matched your Daily Caloric Requirement. In the latter case, if you are done losing and happy, then just keep at that. Otherwise you’re going to need to drop more, but if it takes you below 2000 Calories, it’s probably not a good thing…