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Eating below BMR: why not?


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Dear calorie-counters,

one piece of advice that is very often given here is that people should not eat below their BMR.

It is said to be unhealthy, unsustainable, bad for weight loss, and sometimes I have the impression that eating below the BMR is considered evil... . The consensus seems to be: eat at or above your BMR, and create a deficit with other activity. This deficit will eventually be your weight loss. 

Now I would like to discuss the scientific basis for this advice. To be honest, I do not understand it, so I hope that by explaining my doubts, someone here might be able to explain why eating below the BMR is not good for me.

First, for weight loss, all sources that I am aware of say that it is the energy equation that matters. If I expend more energy than I eat, there will be weight loss. Nothing is being said about the BMR here. However, it is known that when people severely undereat, then their metabolism goes into starvation mode and fat loss will be difficult. There is still no sign of the BMR here, though. I have yet to find a source that says you go into starvation mode when you eat below your BMR.

Now, let us take the standard advice: eat at your BMR and let activities create a deficit. The reason for this advice, so people write, is that the BMR is the absolute minimum for your body to function properly, and eating less than that is bad for you. For me, this does not make sense at all. Consider the following two scenarios: the BMR is 2000, say. In scenario A, I eat 1500, which creates a 500 cal deficit. In scenario B, I eat 2000 and create a 500 cal deficit with some activity. Where is the difference?

The advice "eat at BMR and create a deficit with activity" seems to assume that my body automatically uses all calories for functioning. However, to put it bluntly, suppose I do the activity first thing in the morning, and I also eat all my calories before my activities first thing in the morning. It is my understanding that the body will use some of the energy derived from the food to accommodate the activity. However, "at the end of the day", there is a 500 cal deficit, i.e. there is energy missing to maintain the standard body functions etc. (which is then taken from stored energy, which is the point of it all...). I don't see how this deficit is different from the one in which I eat less and don't do any activity.

I hope you see that there is something in the consensus advice here that I do not understand, and I hope that some of you might be able to shed some light on this issue. Hopefully, my confusion is delineated sufficiently above, so that some of you can see what I am missing. I would really appreciate an explanation, and it would be awesome if some of you had sources!

Thanks in advance!

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Original Post by lamasshu:

I hope you see that there is something in the consensus advice here that I do not understand, and I hope that some of you might be able to shed some light on this issue.

I'm so glad you asked, because I have not got a clue why people are advising this either! I have never seen any reference materials to explain it either, so have no idea why its such a big deal and what your intake level really should be. People have tried to explain it to me, but it just doesn't make sense to my feeble noggin.

Thanks for asking!!

"Consider the following two scenarios: the BMR is 2000, say. In scenario A, I eat 1500, which creates a 500 cal deficit. In scenario B, I eat 2000 and create a 500 cal deficit with some activity. Where is the difference?"

Here is one major difference:  In scenario B you gave your body 500 calories containing vitamins, minerals, nutrients, fiber, etc.  In scenario A, you deprived your body of those important items.

Yes, the "bottom line" may come out to 1500, but clearly they are not of equal value to the body.

You shouldn't have a deficit below your BMR, anyway.

I have a deficit under my BMR and according to this site am getting all nutrients I need. I don't see the problem with this.I understand the advice of not cutting calories below 1200 because it becomes almost impossible to get all the nutrients that you need but other than that I don't get it either.

Not eating below your BMR is a good rule of thumb, particularly for people in the normal BMI range. People that are obese can often eat under their BMR without a problem, one of the reasons is that their BMR is actually lower than what an online calculator will tell them.

The main reason to not under-eat is that your body needs nutrition for normal body functions such as cell repair. Another reason is that there is a limit to how fast your body can burn fat. So if you lose 50 pounds by under-eating, and 60% was fat, you would have lost 30 pounds of fat. But if you lose 50 pounds not under-eating, and 90% was fat, you would have lost 45 pounds of fat.

 

Ok, first let's clarify.  Your BMR is the amount of calories your body requires to just exist.  It is the calories to make your heart pump, brain work, breathe, etc.  The things that if you were in a coma, your body would still do for you.  The reason against eating below the BMR is that it puts a strain on each of these organs. 

Your burn rate is the amount that you specifically burn every day.  So, by brushing your teeth, going to the bathroom, walking around the house, watching tv, working, etc (any activity you actually do including sitting doing nothing), you burn more calories above your BMR.  The burn rate is what causes the deficit.  So when you add up all these activities you do every day, you have your burn rate.  Instead of actually measuring everything, there is a calculation for a person based on the general activity they do.  I have an office job and do limited exercise, so when I choose sedentary, I'm close enough.  So, your BMR is always lower than the burn rate.  If your burn rate is 2300 and BMR is 1800, you'd burn 500 calories every day just by eating your BMR (1 lb a week average).  So, you don't have to exercise to create the deficit.  Exercise can make the deficit larger so that you lose more.  So if you burn an additional 500 calories through exercise, and still eat your BMR, you'd create an 1000 cal deficit, 2 lbs a week loss.

Thanks everyone for your answers so far. I have to admit, though, that I am not completely convinced. Maybe I can quickly answer to your replies and you see how I think, and what might be wrong with that.

The overall gist seems to be this: the BMR is "the amount of calories your body requires to just exist.  It is the calories to make your heart pump, brain work, breathe, etc.  The things that if you were in a coma, your body would still do for you.  The reason against eating below the BMR is that it puts a strain on each of these organs."

While I agree with everyone on the meaning of the BMR, I disagree on the conclusion. I have the impression that people believe that eating below the BMR is bad for your body as the body will not have enough energy to maintain its body functions, which is what I still fail to see.

If I eat below my BMR, my calorie intake is below my BMR, but my body will still have enough energy to maintain its body functions because it has so much energy stored in fat cells. This is what fat cells are for! However, if there is evidence that eating below the BMR causes the body to attack its own organs before the majority of its fat cells are gone, I would be very grateful if someone provided this evidence.

However, there are also differences among the proponents of the "not-below BMR"-strategy. topeze seems to be fine with a deficit "below" the BMR as long as I have eaten my BMR, whereas armandounc suggests to eat so many calories that calorie intake minus activities is still at least as large as BMR. The latter seems more logical to me, but I still don't understand it thoroughly. Again, if I eat below my BMR, I claim that my body will not be harmed (please prove me wrong here). It will use the energy stored in fat cells, just like my body does when I eat just above my BMR but my overall energy expenditure is higher than my calorie intake.

My two cents worth.

I guess the advice of not eating below BMR is for sound health and for a sustainable loss of body fat. Losing weight to improve health would not be sensible if, as you lose the weight, your body is getting increasingly endangered, health wise, by declining nutrients denied to the body.

So in a nutshell, consistently eating below BMR would ideally lead to of body mass but in the long run, it is not a sustainable venture since other health complications would naturally step in

Original Post by lamasshu:
Consider the following two scenarios: the BMR is 2000, say. In scenario A, I eat 1500, which creates a 500 cal deficit. In scenario B, I eat 2000 and create a 500 cal deficit with some activity. Where is the difference?

In scenario A, you don't have a 500 cal deficit. You would be burning at least 2400 if sedentary, and so your deficit would be 900, and that's if you aren't exercising at all.  There's a huge difference between A) eating 1500 with a 900 cal deficit and no exercise, and B) eating 2000 with a 500 cal deficit and exercise.

 

Eating your BMR is a good rule of thumb. The world won't end if you eat less, but many people, most especially those who are within a normal weight range, have reported that they lose more steadily and with fewer plateaus if they eat at least that much, and keep their deficit at a reasonable amount.  Generally, it ensures that people are getting more nutrition than they would otherwise, and getting more of their deficit from being active, which is always a good thing.

If my BMR is 2000 and I burn 2400 daily, then there is no big difference between eating 1500 with a 900 deficit and eating 2000 and doing some additional activity that burns 500 calories (2400+500=2900, so that the deficit is still 900). Of course, it will affect the composition of lean body mass and fat, but that is not the point of this discussion.

The point is: why does the BMR show up so frequently as a reference point? The arguments so far are kind of similar, but you could also say people should never eat below 80% of their BMR, or 120% of their BMR. By browsing through this forum, I got the impression that the BMR seems to be a very well established threshold in the scientific community, but from the arguments so far I get the impression it is but an arbitrary number someone once came up with and people followed blindly. Yet, here in this forum it is often sold as if it was established that people should "never" eat below their BMR.

Please don't misunderstand me: I don't want to make a case for eating below the BMR. I just want to understand why people here are so convinced that eating below this threshold is bad. The advice that is given here is often sound and can quite often be validated with scientific results, but in this case the reference to the BMR seems arbitrary, and I haven't found any scientific papers or even articles supporting this strategy (and I have been looking). It seems to me that instead of BMR, we could equally well say 1500 calories (like CC does). Or we could say 120% of BMR, or 80% of BMR. All the arguments that have been brought forward to support the BMR threshold can also be made for these numbers, so I wonder: is there any more specific reason that people use the BMR?

Even the nutrition argument is more about what to eat, not so much about how much to eat. I could be deficient in important nutrition with an huge calorie intake, and if it is about nutrition, it would seem more plausible to me to recommend watching the nutrition values, instead of eating at the BMR.

BMR is the amount of energy your body will expend at rest for the maintenance of vital organs. So you need to meet that energy requirement or your health will be impaired. Some of that energy can come from stored fat, but there is a physical limit to how fast you can burn fat. Once you reach that limit, your body will have to resort to getting that energy elsewhere.

There are more accurate ways of determining the absolute minimum you can eat and still be healthy. You could measure your true BMR through calorimetry, your total body fat through hydrostatic weighing, calculate how much fat you can burn per day, and then derive your absolute minimum calories. But that's not very practical.

There are a lot of variables: what is your true BMR? how much body fat do you have? How much nutrition is in the food you are eating? Do we even know all the nutritients that are required for good health? How much are you really burning through activity? With all those variables, I don't think anyone can say accurately what the absolute minimum is.

In general, the closer you eat to maintenance the better. You'll have an easier time sticking to a diet, you'll be more likely to get all the nutrition your body needs, you'll keep the lean mass loss to a minimum, etc.

 

Your BMR is the number of calories you would need if you lay in bed whole day. When saying this the unsaid part is that this consumption should be from a balanced diet so this many calories would give your body the requored nutrients. Eating at your BMR getting all ypur calories from say sugar would not acheive the purpose of eating at your BMR.

Secann above has a valid point. If you can eat below your BMR n get ypur full nutrition requirement you should be fine BUT you cannot possibly be counting every single nutrient you require so room for not getting some required nutrients eating too low is not a risk worth taking. For example if you were counting n getting your required calcium but not getting your required vitamin D you would have calcium deficiency as your body needs Vitamin D to use the calcium. This is why you are also advised not to try to get all you nutrients taking supplements. Eat a balanced diet diet of healthy foods at your BMR n you leave far less room for error. It would be even better if you ate above your BMR n maintained a deficit. Malnutrition causes damage slowly from inside n can be too late by the time you realise it.

Here is another post where it was discussed pretty thoroughly.

Thanks everyone for your replies so far. This is indeed quite an interesting debate, and I think an important one. For my own understanding, I would like to raise two more questions:

BMR and nutrients: We already agreed that the BMR measures the energy the body needs to keep the basic functions going. So, the BMR is a concept related to the body and gives us a calorie value. The BMR is hence not a concept about the nutritional value of food. I doubt very much that there is any close relationship between caloric content of food and the nutritional value. Just take junk food: high in calories, low in nutrients. This raises the question: why do you believe that the BMR secures the nutrients that the body needs? Why not, say, half of the BMR? Or 120% of the BMR? Or, as one poster above pointed out, 1500/1200 as a minimum? While I understand the argument, it still seems a bit arbitrary to me. :(

Conversion of Fat into Energy: The most convincing argument so far has been that there is an upper bound on the body's ability to convert fat into energy, so that by undereating, the body may indeed use energy from other sources than fat to maintain the body functions since the conversion of fat is not quick enough. I have now looked around for a while, but I could not really find anything elaborating on this speed. Does anyone here know a source where I can read up on this? That is, does anyone know an article / paper elaborating on how quick the body can mobilize the energy stored in fat cells?

try   bodyrecomposition.com

 

You may find something there. I'm too lazy to search through all the articles atm to find it

Original Post by lamasshu:

Thanks everyone for your replies so far. This is indeed quite an interesting debate, and I think an important one. For my own understanding, I would like to raise two more questions:

BMR and nutrients: We already agreed that the BMR measures the energy the body needs to keep the basic functions going. So, the BMR is a concept related to the body and gives us a calorie value. The BMR is hence not a concept about the nutritional value of food. I doubt very much that there is any close relationship between caloric content of food and the nutritional value. Just take junk food: high in calories, low in nutrients. This raises the question: why do you believe that the BMR secures the nutrients that the body needs? Why not, say, half of the BMR? Or 120% of the BMR? Or, as one poster above pointed out, 1500/1200 as a minimum? While I understand the argument, it still seems a bit arbitrary to me. :(

Conversion of Fat into Energy: The most convincing argument so far has been that there is an upper bound on the body's ability to convert fat into energy, so that by undereating, the body may indeed use energy from other sources than fat to maintain the body functions since the conversion of fat is not quick enough. I have now looked around for a while, but I could not really find anything elaborating on this speed. Does anyone here know a source where I can read up on this? That is, does anyone know an article / paper elaborating on how quick the body can mobilize the energy stored in fat cells?

Thermodynamics.  I don't know of anyone who found an experimental yield for how fast one can metabolize fat into energy, but the theoretical yield is around 33kcal/lb of fat/day.  I have never looked into the math behind this, because I don't care enough.

@armandounc: I have tried to find something there. In fact, I contacted Lyle and asked him to explain the below-BMR strategy to me. His response was ambiguous and non-informative, but I got the impression that he does not share the belief that eating below the BMR is bad. This is what caused me to open this thread.

When you eat below the BMR, it will start to slow down your metabolism.  This means that you won't burn as many calories, shrinking the deficit as well.  It's counterproductive. The reason for this is that when you don't eat enough, the body tries to find more efficient ways to preserve itself.  That's about the only way that works.  You can google it, but there are actual reasons for this. 

Original Post by lamasshu:

BMR and nutrients: I doubt very much that there is any close relationship between caloric content of food and the nutritional value. 

Conversion of Fat into Energy:  does anyone know an article / paper elaborating on how quick the body can mobilize the energy stored in fat cells?

First, let me commend you on staying with this. It is very much human nature to take on board a viewpoint and champion it without having reviewed the evidence for the viewpoint - and that can lead to a whole bunch of folk meandering nowhere in particular, while being convinced that they know the way.

Based on the discussion so far it seems that there is no nutritional reason for eating a higher calorie amount once nutritional needs are met. In fact, eating like that would be a uniquely western concept, the more I think about it! :)

You will not find evidence on any limitations to mobilization of fat. I've been into the fat burning data very deeply, and I don't think I missed that.

You will, however, find plenty of evidence that suggests that thermal dynamics is an inadequate theory to explain human metabolics. One line of research, in fact, suggests that there are internal processes that affect calorie utilization and storage. There is some hope that this processing difference may lead to a medication to treat maladaptive metabolization.

http://zafgen.com/

I think you may be on to something here. You'll still have to figure out a caloric intake level that promotes optimal functioning and does not overly hasten the metabolic adaptation process, but I'm guessing the BMR isn't necessarily that level.

Somewhere in my reading I saw that you set your intake level by taking the caloric level required to maintain your goal weight. That's arbitrary too, but to my befuddled mind it almost makes some intuitive sense. The BMR idea never did.

Original Post by divasnote:

Based on the discussion so far it seems that there is no nutritional reason for eating a higher calorie amount once nutritional needs are met. 

And how would one go about determining that nutritional needs have been met? Would one just have to meet some level of the most common known micronutrients? What about antioxidants and phytochemicals? What about nutrients that have not yet been discovered? How would the average person go about creating a diet plan without a Herculean effort?

Nobody is suggesting that as long as you eat your BMR it doesn't matter what types of food you eat. Paying attention to nutrition is essential. But making sure you eat a certain quantity of nutritious foods is a simple way to plan your diet and ensure that you stay healthy.

I am confused why there appears to be a great need to find the ultimate low threshold. If it is for intellectual curiosity, that is fine. But as far as a practical method for ensuring healthy weight loss, I think it is misguided. Taking a little longer to get to your weight loss goal is a small price to pay for good health.

 

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