Eating less calories than your BMR. Good or Bad?

First, make sure you're clear on the difference between BMR and TDEE.

BMR = the number of calories your body needs to keep itself alive
TDEE = the number of calories you burn doing all the things you do in a day.

TDEE includes your BMR and a bunch of other things, so it's higher.

To lose weight, you have to eat less than your TDEE. It's not a good idea to eat less than your BMR, and it's not necessary. The goal is to aim for a reasonable number that is in between the two.

I'm not sure I truly believe in the numbers we get from the calculators anyway. At 64 years of age and 6 feet tall, the BMR calculator says that I have a BMR of just over 1700. When I add in the 240 minutes per week of moderate exercise I try to get, it adds another 500 calories a day or so. So how come the goals page tells me to eat 1700 calories a day to lose 1 pound per week, and after weighing everything I consume, I'm averaging about 1700 calories a day. That's calories, not net calories, and I've gained 1 1/2 pounds in the last month. Anyone got any ideas? Not exactly new at this, but it's always been a continuing thing.

cdsuggs2014 wrote: »

I'm not sure I truly believe in the numbers we get from the calculators anyway. At 64 years of age and 6 feet tall, the BMR calculator says that I have a BMR of just over 1700. When I add in the 240 minutes per week of moderate exercise I try to get, it adds another 500 calories a day or so. So how come the goals page tells me to eat 1700 calories a day to lose 1 pound per week, and after weighing everything I consume, I'm averaging about 1700 calories a day. That's calories, not net calories, and I've gained 1 1/2 pounds in the last month. Anyone got any ideas? Not exactly new at this, but it's always been a continuing thing.

I just peeked at your profile and saw that you had gastric bypass. One of the possible side effects of WLS is loss of muscle mass. If you have lower muscle mass than average for a man with your other stats, you'd expect to see a slightly lowered BMR, so that could be a contributing factor.

Camo_xxx wrote: »

I'd love to see some sort of medical authority's explanation of why it is bad. I see people claim that it is on a frequent basis.
Doesn't make sense to me as the calories needed to sustain life are readily available from fat stores in your body.

Calories, yes. Other nutrients, no. Eating under your BMR puts most people at a really low intake, so they're not as likely to be getting adequate nutrition. The issue is the low intake, which doesn't tend to be sustainable or allow for a well-rounded diet.

AliceDark wrote: »

Camo_xxx wrote: »

I'd love to see some sort of medical authority's explanation of why it is bad. I see people claim that it is on a frequent basis.
Doesn't make sense to me as the calories needed to sustain life are readily available from fat stores in your body.

Calories, yes. Other nutrients, no. Eating under your BMR puts most people at a really low intake, so they're not as likely to be getting adequate nutrition. The issue is the low intake, which doesn't tend to be sustainable or allow for a well-rounded diet.

While it may be harder, it doesn't necessarily mean it's not possible. If you use the calculators, mine is over 2000 caloires and I am pretty sure I can eat a fairly nutrient dense foods on that number of calories. There is no evidence out there that would suggest that eating below your BMR is bad. Keeping in mind that calculators are just estimates.

Having said that, I would be more concerned with creating large deficits as research would suggest it's harder to maintain your metabolic functions and muscle mass.

These are all just generalizations. Only you, playing with the numbers, are going to come up with your true BMR or TDEE.
To answer your question, you're not going to melt into a puddle.

There isn't a problem with going below your BMR. Your body will make up the difference from fat stores, which is what we want it to do when we are trying to lose weight.

Your body doesn't care if the calories are used to just keep you alive or to fuel other activity, so the differentiation between BMR and TDEE seems pointless in terms of weight loss. As long as you are getting the nutrient you need you will be fine.