Should I just eat at TDEE of goal weight?

If you use the TDEE method, you will need to subtract a certain percentage in order to continue to lose weight. The calorie amount MFP calculates already has a deficiency built in. With the TDEE method, you have to create it by subtracting from the initial amount generated.

This website will explain it better: http://iifym.com/tdee-calculator/

I did the math on this once. Let's say you're 5'8, 30 years old, and female. You're 180 pounds and you want to be 130. Let's further assume that your TDEE is 1.6 of BMR, and use the Harris Benedict equation to estimate BMR. Then your TDEE at 180 is about 2239 and at 130 it is about 2587.

So let's say you start eating at 2239. At first, this is a 348 calorie deficit - so you lose between half a pound and a pound each week. Not bad. As you lose, though, your TDEE also goes down - so your deficit gets smaller and smaller, and your loss gets slower and slower.

By the time you get to the last 10 pounds, you're only at a 70 calorie deficit. If you ate at a constant 70 calorie deficit, it would take 72 weeks to lose 10 pounds. But, your deficit continues to shrink - when you (after a very long time) get to five pounds over, you will be at a 35 calorie deficit, and by the time you eventually get to one pound over, you are at a 7 calorie deficit - so it would take you another 72 weeks just to lose that last pound.

If we treat it as a strict mathematical equation, you never actually get to 130 - although you get infinitely close, so the scale rounds it off and we don't care about the infinitesimal fraction. It takes a very long time to get there, though. If you have a scale that weighs to the nearest .2 of a pound, it will show 130.0 in 418 weeks, or a little over 8 years.

If you eat at TDEE for just a little bit lower - 120 pounds, or TDEE of 2169 - you'll get there in 129 weeks, or 2 and a half years - a big difference for a change of 70 calories per day.

(For the fellow math dorks who care, the relevant differential equation is w' = (c - 1333.79)/6.96 + k e^(-6.96 t / 500) , where w is weight at week t, c is calorie intake, 1333.79 and 6.96 are constants generated by the Harris Benedict equation for the assumed height, age, and gender, and 500 represents the daily deficit necessary to lose a pound a week. k is a constant of integration that works out to be the difference between the starting weight, and the weight at which c = maintenance.)

(For the fellow math dorks who care, the relevant differential equation is w' = (c - 1333.79)/6.96 + k e^(-6.96 t / 500) , where w is weight at week t, c is calorie intake, 1333.79 and 6.96 are constants generated by the Harris Benedict equation for the assumed height, age, and gender, and 500 represents the daily deficit necessary to lose a pound a week. k is a constant of integration that works out to be the difference between the starting weight, and the weight at which c = maintenance.)

As a fellow math nerd, I salute you.

...and I totally messed up that equation, as I switched midway into typing the solution to the differential equation instead of the Diff. Eq. itself. It should be w' = (c - 6.96 w - 1333.79)/500, which solves to w = (c - 1333.79)/6.96 + k e^(-6.96 t / 500). But the point stands.

I guess my thinking was that if I wanted to lose faster I could just increase my activity level, which I expect to be easier the more weight I lose. Hopefully.

This would work, but at that point you're no longer eating your TDEE at your new weight, unless you plan on decreasing your activity level again when you get there. You've just shifted to creating your deficit through exercise instead of food.

Please consider the fact that at 5'9" 135 lbs may be too light for your frame. Rather than putting a number on it right now, see how you feel when you get closer. Your body will change along the way and you may find another number is better for you.

All the best as you change your health for the better.

Oh, ya, that might be light. I'm 5'4, currently 140, and I'm quite happy at 135.

Regardless, the answer is still the same; yes, eating at goal weight TDEE works.

I did the math on this once. Let's say you're 5'8, 30 years old, and female. You're 180 pounds and you want to be 130. Let's further assume that your TDEE is 1.6 of BMR, and use the Harris Benedict equation to estimate BMR. Then your TDEE at 180 is about 2239 and at 130 it is about 2587.

So let's say you start eating at 2239. At first, this is a 348 calorie deficit - so you lose between half a pound and a pound each week. Not bad. As you lose, though, your TDEE also goes down - so your deficit gets smaller and smaller, and your loss gets slower and slower.

By the time you get to the last 10 pounds, you're only at a 70 calorie deficit. If you ate at a constant 70 calorie deficit, it would take 72 weeks to lose 10 pounds. But, your deficit continues to shrink - when you (after a very long time) get to five pounds over, you will be at a 35 calorie deficit, and by the time you eventually get to one pound over, you are at a 7 calorie deficit - so it would take you another 72 weeks just to lose that last pound.

If we treat it as a strict mathematical equation, you never actually get to 130 - although you get infinitely close, so the scale rounds it off and we don't care about the infinitesimal fraction. It takes a very long time to get there, though. If you have a scale that weighs to the nearest .2 of a pound, it will show 130.0 in 418 weeks, or a little over 8 years.

If you eat at TDEE for just a little bit lower - 120 pounds, or TDEE of 2169 - you'll get there in 129 weeks, or 2 and a half years - a big difference for a change of 70 calories per day.

(For the fellow math dorks who care, the relevant differential equation is w' = (c - 1333.79)/6.96 + k e^(-6.96 t / 500) , where w is weight at week t, c is calorie intake, 1333.79 and 6.96 are constants generated by the Harris Benedict equation for the assumed height, age, and gender, and 500 represents the daily deficit necessary to lose a pound a week. k is a constant of integration that works out to be the difference between the starting weight, and the weight at which c = maintenance.)

Awesome reply. Very well done.

I faced something a bit similar. Back in Nov, I had a complex BF% analysis done on me. I think it had me at like 19%BF at 203. I said I wanted to get to approx 8% BF. So they figured out my lean body mass and spit out that I'd have to go down to 172.4. However, it failed to take into consideration that as one loses body weight, it's inclusive of both fat AND muscle. Even if you lift heavy and take in lots of protein. So while the majority is fat, there is some lean muscle lost. I found a website that worked this out as a 3 to 1 ratio. And long story short, it figured I'd have to hit an even 170 to be 8%. It may not seem like much difference, but at the single digit BF%, I can go up or down 1% with as little as 1.6lbs.

I'm definitely flexible on the weight goal. I just chose 135 because when I plugged various weights into the "Better Ideal weight" thing that was the weight around which women of my height stopped feeling like they needed to lose more weight. I'll go with whatever feels right as I get closer.

http://www.halls.md/ideal-weight/body.htm

Off-topic, but that thing is fascinating. I agree that it doesn't matter that much what your goal is now and that you should just revise based on how you feel as you start getting closer, but I just played around with it like you did, and at my weight (5'3) apparently women of my height want to be a lot thinner (so do I), but not especially so--more like a BMI of 25.1. But at that weight (142), they want to bemore like 130 and at 130 they want to be 125 and so on. I was curious whether the results would ever end up with them (on average) wanting to be heavier, and eventually they did. For my height (5'3), women wanted to be thinner (even if just a little bit) until they got to 116, and then lower than 116 they wanted to be heavier. 5'9 and 135 rounds to a 20 BMI and 5'3 and 116 is a 20.5. I wonder if they are all around 20?

okay I didn't look at the math it makes my head hurt...

How can someone predict TDEE of goal weight...TDEE is dependent on exercise and is a flucuting number.

And mine has gone up since I lost weight as my exercise levels have increased...

Sorry if I am missing something here but my logic brain part isn't computing this...

Oh, I should have read how it worked. For some reason I was assuming they did surveys, heh.

If I just eat at the TDEE of the goal weight (around 1650 calories a day) won't I just naturally end up there eventually?

Assuming you calculate it correctly, yep, that'll work. Most exercise burn numbers will be a function of weight - do the math right and you'll be golden.

"Fire and forget..."