Caloric Deficit vs. Net / Question about Net Calories Changing

[ceelliott]

Apologies if these have been answered elsewhere...

I have a couple of questions about caloric deficit vs. net. I'm female/26/150 pounds.

Question 1: My data from yesterday on my Alta shows that I burned 1973, including exercise (15 minute warm up jog and light strength training). I ate 1308 calories.

So, if I'm understanding net vs. deficit properly, my deficit is 665 (1973 minus 1308). Then what are my net calories? I've read that I need to net at least 1200 so my body doesn't explode and die, but I'm not sure how to figure out what that means and how that's different from net calories. 

Question 2: My TDEE (according to iifym.com) is 1690. So becasuse I burned 1973 yesterday, that's more than my normal "sedentary" existence. If I want a daily deficit of 500 calories to lose 1lb/week, I should eat 1190. Since I burned extra, should eat more than the 1190 calories so it's 500 less than 1973 (what I actually burned for the day)? Will it mess up my progress if I move my calories up and down every day to match my actual activity level? Or, should I pick a happy "middle ground" and eat a consistent number of calories every day regardless of extra activity?

Thanks in advance for all your help! 🙂 

[Knitknitfrog]

i think you have to move your calorie  allowance up and down to match your activity. i have lost 20+ kilos since julyn of last year, by running fitbits 500 cal deficit per day. by upping the proportion of  protien I ate I pretty much never went hungry ad. yet kept dropping the weight. I increased my excercise (not much - just to hit 10k steps per day) and as a result had to up what I ate. I think that if you are more active and dont eat a little more that day you risk being so hungry you give in and eat rubbish or eat too much. i think the fit bit system that cacluates how much you can eat based on how active you are is way more sucessful than restrictive set diets set by traditional systems. When people have a busy day, and get hungry, in a traditional diet you cant adjust for that so people get hungry, fall off their diet plan and blame themselves and think they have failed. 

[FitBeforeFifty · Accepted solution]

Regarding Question #1:

In your case, your estimated net calories is 1973 - 1308 = 665 ... theoretically.  For every 500 calories of deficit between your TDEE and what you eat you should lose 1 lb of fat ... theoretically. I bolded theoretically because measuring TDEE accurately is not something a fitbit (or any other cheap wearable for that matter) is really capable of doing. When these devices have been compared to indirect calorimetry in labs, the accuracy is not that great (they are off by several hundred calories: http://www.ncbi.nlm.nih.gov/pubmed/27232714). I would continue doing what you are doing and then compare your weight loss over a 3 week period (anything shorter is subject to error) and re-evaluate your calorie intake based on your actual results.

Regarding Question #2:

There is no need to consider TDEE estimates (your iifym.com number). You should only use these estimates if you aren't tracking your activity via some other means.

[JohnRi · Accepted solution]

Only thing I would add that hasn't been said, is you should never eat less than 1200-1300 calories a day. If you deficit wants you to eat less than that, you either need to reduce your deficit, or exercise more.

Net calories is the amount of total calories you want to burn that day.  So in your example your net calories was 1973.  Deficit has nothing to do with it.  Another way to look at it, say you wanted to eat 2000 calories, and have a 500 calorie deficit.  Then your net calories (IE target calories burned) would be 2500.

I would look at your weight loss.  With a 500 calorie deficit, you are expecting 1 lbs loss per week.  If you are losing less than a lbs, then I would increase your exercise more, while maintaining your diet at the same level.  IE creating a slightly higher deficit.  You'll find your balance between diet, calories burned, and weight loss per week.

Good luck and keep at it!