How do calorie deficits work?

ErickGP

I've been searching for the answer endlessly. I currently sit at 5'8, 221 pounds. I am obese, but luckily proportional. If I didn't exercise, I would need to eat 1,990 calories a day, because to maintain my weight, I would need 2490. This creates a 500 calorie deficit. Fitbit tracks the calories I burn, I think both naturally from metabolism and cardio. So if I eat that 1,990 calories, I met my goal. But If i burned 4k calories. I would need to eat that back because I'd be in more than just a 500-calorie deficit. 4,000 - 1,990= 2,010 calorie deficit. I don't know how in the world I can fit 2,010 more calories after already eating 1,990. I dont know any big healthy meals for that, nor do I have the budget or stomach space. Am I understanding calorie deficits correctly? If so, I would assume everyone is practically starving.

Lietchi

Where are you getting this 4000 calorie burn from? From your Fitbit? That number sounds very high, how active are you?

I think your theoretical grasp of calorie deficits is okay, but I think there might be something wrong with your calorie burn estimates from Fitbit.

One thing to keep in mind is that fitness trackers don't measure calorie burns, they estimate them based on your personal stats, heart rate,... So the number can be way off (and Fitbit does seem to be prone to that).

The best test of your actual calorie burns is to eat a certain amount of calories for 4 weeks and see if your weight behaves as expected or not. Theoretically, it's a 3500 kcal deficit to lose 1lb of bodyfat.

sollyn23l2

Yes, you are correct. However, unless you are running a literal marathon every day, you are almost certainly not burning 4000 calories in exercise.

tomcustombuilder

Dont rely on those smart watches for any real accuracy. If your weight has been stable then your calorie consumption is your maintenance calories so use that as a base number and deduct accordingly from there for fatloss.

AnnPT77

I'm another person who's questioning the 4000, if it's just for exercise.

There's a very, very narrow possibility that if you set MFP at sedentary/not very active, and you have an absolutely brutally active job, and you train like an Olympic/elite athlete in a cardiovascular sport on top of that, you might get that many added calories in MFP from the totality of all-day movement, but even that is very, very unlikely. (I put your stats in a TDEE calculator, assumed a young age to maximize the calorie estimate, and got an all-day total calorie estimate of at most 4156 for "Extremely Active, Very Heavy Physical Work or Exercise Every Day, Professional/Olympic Athlete" for a male of your size.)

High, high odds the Fitbit estimate is wrong.

We might be able to guess more accurately about what's going on if you tell us

• What kind of exercise you did, for how long, at what pace or intensity
• How old you actually are
• What your MFP 'activity level' setting is.

But I doubt the conclusion would change.

Research suggests that the average person gets around 5% of their daily calorie burn from intentional exercise. It may be up to 10-15% for very heavy exercisers, but it's unlikely to go beyond that for people who have to lead normal lives alongside, time for having a job, home chores, social life, etc.

I'm retired and a very active person for my demographic. I'd estimate I get around 13% of my total calorie expenditure from my cardiovascular exercise. There are probably some people around MFP who exceed the 15% level, because some people go all-out with exercise to lose weight . . . but there aren't many, and they don't exceed 15% by much, I'd bet. Moreover, excessive exercise tends to reduce calorie expenditure from daily life activity anyway. (Look up "calorie compensation" or "energy compensation for exercise" if you want to learn more.)

The above are the things that make me deeply question the 4000 calories, plus my decade of estimating exercise calories for a smaller body (during a year of loss and 9+ years of maintenance since, all successful), some academic knowledge about relative calorie expenditure during common exercise modalities, plus some theoretical knowledge about why fitness tracker calorie estimates can be wildly wrong for some people.

BTW, if you're relatively new to this type/intensity/duration of exercise, that increases odds that you'll get an overestimate. Other individual factors matter, too.

Your post implies that others of us must be starving when in a calorie deficit if we exercise because the exercise calories are so massive. I didn't starve; it wasn't even all that hard as long as I didn't try to lose aggressively fast. The exercise calories aren't massive, at least not remotely commonly. My exercise calories are less than a peanut butter sandwich on hearty bread most days. I could easily eat that sandwich, let alone that number of calories in a chocolate bar or cookies.

Cute cat, BTW!

Retroguy2000

1. You probably didn't burn 4,000 calories from exercise. Certainly not every day.
2. Your exercise estimate may have been total calories burned, not net. What you're really interested in is total calories burned in that time minus the calories you would regularly burn sitting around or whatever.
3. Even if you did burn 4,000, you don't get a 1:1 benefit. You don't need to eat 4,000 to offset it. Good luck even trying to consume that on top of your regular daily food. It's probably closer to 50% benefit on average.
4. How do you know that you maintain at 2,490? Have you been tracking all calories and weight for a while, or is that an online calculators estimate which includes a very vague estimate of your daily activity?

JonByrne6350

I am 175lb and this morning ran the equivalent of a half marathon, that burn was estimated by my Fitbit and my Garmin at just over 1600 calories. This matches online calculators too.

I am aiming for a 1700 net so it does feel like I am over eating to meet that target so I get what you are saying, it can seem counter intuitive.

I'm not sure if you where just using that number as an example however.

PAV8888

A lot of things influence the numbers your Fitbit comes up with and a lot of things influence how close or how far you're tracking from the Fitbit numbers in question.

The numbers are not random. But they are also not directly applicable to someone without testing how actual results align with expectations.

10 years later I have a much larger divergence from Fitbit data than I did when I first joined MFP part way through the process of losing from Class III to normal weight.

This is both because of my much looser logging of intake nowadays and partially because of health issues that can affect my HR which in turns can disproportionately affect Fitbit's Caloric burn estimations. Whereas my initial divergence was well under 5%, currently I am happy when I remain within the 10% range.

But, yes, you appear to understand the concept of deficit correctly.

But. Whether the precise level of deficit you believe is there truly is there will require evaluation after a few weeks of consistent logging to see how closely your expectations track to your actual results.

The level of deficit you can tolerate also varies based on how much extra fat mass you have available to lose and how long you've been eating at a deficit, in addition to the size of your recent deficits.

Stuffing yourself to avoid a large deficit every time you have one is probably silly and counter-productive.

Consistently ignoring (or celebrating) multiple multi-thousand Cal deficits because you're pushing both exercise/activity to the max and reducing intake to the min till you start fainting while cycling (yes, I've had an MFP friend who had that happen to her) is also counterproductive.

Can a 220lb 5ft 8" male hit 4000 Cal?

A 172.25 cm 158lb ~60yo male can come very close to it (remember my ~10% divergence)….

…given an EXTRAORDINARY high level of activity for the day (I "cheated" by going for walks on the "correct" side of midnight. So basically this was 2 days worth of activity logged in the one). The day clocked in a 41,152 steps and 162 zone minutes. I would normally engage in half of that, or less.