TDEE for the Curious (or Why Don't I Lose Weight Faster?)

Welcome to The Fast Diet The official Fast forums Body Benefits and side effects
TDEE for the Curious (or Why Don't I Lose Weight Faster?)

This topic contains 205 replies, has 61 voices, and was last updated by  MrsP2008 5 years, 11 months ago.

Viewing 50 posts - 1 through 50 (of 206 total)

  • A common question from those following 5:2 is ‘Why do I lose weight so slowly?’ Enter TDEE

    When I started roaming around 5:2 forums, I kept running into the term TDEE. People used it quite a bit, and it seemed to have some relevance. TDEE stands for ‘total daily energy expenditure’ (how many calories you burn in one day and so how much you would need to eat to maintain your weight).

    Under the ‘how?’ section at the top of this page you will find a TDEE calculator and it seemed to compute my TDEE for me. Being curious, I also looked for similar calculators on the web, and found several (a good one – … or/NU00598). Strangely, several gave me TDEE numbers quite different than that of this forum’s calculator. The variations seemed to center around my chosen activity level (and, I think, the formula used).

    To determine my TDEE, I decided it better to guess at my correct activity level, and then choose the activity level one level below that (if possible). My reasoning was as follows.

    First, TDEE is, after all, an estimate. So we are not talking precision here. Second, I know I usually overestimate how much activity I do over any given period of time (and studies have shown people usually overestimate their physical activity by 30% or more). And third, I figured that if by underestimating I turned out actually to be right, my estimated weight loss would fall in line with reality (more on this later), but if I was wrong, I would lose more than expected and be much happier for exceeding my weight loss expectations. In effect, I would gain happiness by underestimating my activity level. And I am all for being happy!

    So, how does TDEE help explain how 5:2 works?

    Let us say you are a female with a TDEE of 2000 calories per day (about average, but everyone’s is different) and are starting 5:2. Here is how you can compute your expected weight loss.

    For two days a week, you will eat only 500 calories, thus cutting 3000 calories out of your diet for the week (2000 – 500 = 1500 calories cut in each of two days). As there are around 3500 calories in a pound, you might expect to lose about 14 ounces for the week (3000 cut from diet divided by 3500 in a pound times 16 ounces in a pound equals 14 ounces, rounded). These numbers tend to explain a lot.

    First, they explain why the average weight loss is around a pound a week under 5:2.

    Second, they explain why men lose faster than women – because on average a man’s TDEE is 2400 calories per day (men often are bigger). So when they eat 600, they are cutting out 1800 calories from their diet and thus losing more each week than a woman cutting out 1500 calories.

    Third, they explain why so many people following 5:2 try to speed things up. 14 ounces a week is pretty slow for some people. Several typical attempts to speed things up include going to 4:3 (adding another fast day and deleting another 1500 calories from the week – this adds an additional 7 ounces of loss for the week), or not eating any calories on fast days (liquid fasting) – this cuts 1000 additional calories out, or produces a 5 ounce additional loss. Some people try to increase their calorie usage by exercising (trying to increase their TDEE). And, if they walk 25 miles each week, they will indeed burn an additional 3500 calories, thus upping their weekly loss to 30 ounces.

    (As an aside, if you are really in a hurry you can simply not eat for a week, something this Forum rightfully shuns. But if you run the numbers, at most you will cut 14,000 cal. out of your diet, or 4 pounds worth – lest you really think you lost 4 or more pounds of fat weight after your first week of 5:2.)

    Now, all of the above assumes that on your five non-diet days, you are eating 2000 calories per day on average. If you are eating more than your TDEE, on average, on your non-diet days each week, your weight loss will be less than expected. If you are eating less, your weight loss will be more. This explains why many people doing 5:2 experiment with dieting on top of the 5:2 way of eating as a way of speeding up their weight loss (ie. follow the Atkins diet on their 5 non-diet days). This also explains why people that think 5:2 means you fast for two days and then can eat as much of whatever you want for the remaining 5 are usually quite unhappy and complain they are not losing weight.

    Finally, all of these antiseptic numbers work with the background of normal fluid retention and dehydration in the body, either of which can overwhelm (or artificially supplement) any weight loss that is measured in ounces per week.

    So, there we have it, TDEE in an (unscientific) nutshell. I guess all I can say is if you are having the results you want, ignore TDEE. If not, accurately determine your TDEE, insure your diet day calories do not exceed 5/600 and count calories on non-diet days to see if they average your TDEE or below. That will probably identify the problem. Otherwise


    It really does work over time. ๐Ÿ™‚


    I just noticed they changed the link to the Mayo Clinic TDEE calculator. Here is the new one:


    Great post. Thank you.

    Great information, thank you!

    Hello again simcoeluv,
    Fantastic information but can I add one point you forgot to mention, some people including Michael have low receptors to exercise. Sadly I am one. I burn a minimum of 3500 cals per week as measured at the gym apart from 1 hour badminton and 5 hours of fast dog walks. This makes not one jot of difference to my weight loss. I do it for toning and because I enjoy it. I keep detailed records and measure and weigh on fast and non fast days. I do 4 : 3 usually and stay under my TDEE which is underestimated to be 1200. As you say we are all different and not necessarily patient. If I am lucky I lose 6 pounds per month or sometimes 4. I am learning to live with it. I don’t want to cut further calories because it is depressing and therefore not sustainable as it will take me at least a year ( probably 18 months) to get to my goal. I plan to be 10 stone when I get to my 60 th birthday late next year. Wish me luck!
    Currently one stone down since January and feeling good about fasting even with side effects like headaches and sleeplessness, problems I am sure we will resolve between us forum writers.( new specs ordered so that’s a start and small bowl of cereal at bedtime helps sleep)

    This is a GREAT post. Very informative. I’ve worn an Exerspy (like a bodybugg) for 4 years now and I know what I burn daily when I’m sedentary. I also know what I burn when I do certain exercises. This knowledge has allowed me to figure out how many calories I want to eat on my nf days. I also know that there is NO way I can eat only 500 calories a day. I’m just too active (working out 7 days/wk). Some people can survive. Everyone is different. So, I’ve designed my 5:2 to be 1650cal on my nf days and 850cal(which I think I can sustain without going crazy) on my fasting days. My TDEE is about 2000 on average. There are days where it is higher of course. But I only reach that if I’m working out. When I’m not working out, my TDEE is around 1820…literally sitting all day. So, with my weekly caloric burn (TDEE) of 14,000 and weekly caloric intake of 9,950, I will be losing a little more than 1 lb which I would be really happy with! And I’m a newbie so I will be starting my second fast day on Monday. My first didn’t go so well and I hope to do better next time. Onward and upward!!! So glad I found this site. I want to take it nice and slow. I’ve done everything there is out there and I’m tired of sacrificing and getting nowhere. I’m ready for the slow, not so manic process….thanks for reading. Signing off from Sunny California ๐Ÿ™‚

    This is a great post. People forget that losing a pound a week is great, sustainable weight loss. Am I happy that it will take me a year to reach my goal? No. Is that silly, considering how many years I have been overweight, and how many more years I hope to live? Yes. I am just glad that I finally found something that I, personally, can actually follow through on that actually works. If I don’t exercise I can only lose about a half a pound a week, which I do find discouraging, but that just motivates me to exercise, which I need to do anyway!

    Thanks for this, I have a quick question for you. On this site I calculate my BMR and TDEE. My BMR is 1800 odd and TDEE is 2100odd. However on the link above it gives me 1850. Does this mean on my non fast days I shouldn’t be going over 1850? I have been floating between my BMR and TDEE that I was given from this site. I have never really hit my TDEE of 2100.



    Hi Amy:

    The question is are you losing weight? If you are happy with your progress, no problem. But if you are not losing weight as fast as you think you should you are probably eating a bit too much if you are eating to the 2100 level.

    TDEEs are estimates at best. You have to find a level of eating that gets you where you want to be.

    Thanks, I am only in my second week, just completed my fourth fast. I lost 2kg last week which was good for first week and I did jump on the scales although I am not meant to until next Monday and another 1kg has dropped off, obviously this will vary across the week a bit so not counting it until I weigh in Monday. I will monitor how I go up to the 3 week mark and then make adjustments if I need to. Going to introduce swimming a few times a week next week with some walking as well.
    Thanks for the advice simcoeluv.


    Here are some tips for those just starting:

    You may find your weight loss slows over time, but enjoy it as long as it falls this fast!

    Thanks heaps. I know it will slow down and I am looking at this as a long-term change and love the health benefits that I have read about. I have a bit to lose so I am not surprised it is falling off initially and I will take it while I can. I love this site and the forums. Definitely keeps the motivation up!

    Very interesting posts, and certainly interesting to understand how the figures work. Having a few friends that have been doing the 5:2 diet over the past few months, without doubt the more weight you want to lose, the easier it is to begin with. One (male) friend has lost 12kgs very easily in 3 months, but has slowed down now trying to lose the last 5kgs. I wanted to lose 5kgs, basically to drop a dress size, I have lost 4kgs so I am nearly there, but the last couple of weeks I have only lost 200g each week, but at least it is going down! I think the understanding of how many calories you need to consume for your age, weight and height is interesting having just done the calculation on the Mayo clinic website. Using various apps and gadgets it is easy to get a good understanding of exactly how many calories you consume each day and burn each day. MyFitnessPal app for calories and a Fitbit (for monitoring exercise) seem to be pretty accurate. I think it is the underestimating the calories that we consume on our non fast days that is the real eye opener. I know for me a few glasses of wine, and exactly how many mls are in each glass is where I seem to get carried away at the weekend! I think that I have not realised exactly how many calories I need daily and why I was unable to lose weight before the Fast Diet, I obviously needed to have the two Fast Days to balance out my calorie intake over a weekly period, despite the fact that I thought playing golf 3 days a week and 3 pilates classes a week would be enough.

    For the people who are new to this, keep going with your fast days you will be surprised as to how much easier they become, I can now go all day until 6pm with only 3 cups of tea, and I never would have believed that on day one!

    I am still confused by the difference in TDEE on this site and then then Mayo TDEE. The Mayo TDEE seems to be BMR. I guess it is a case of find which works best but I see on a few posts you send people to this thread and I wonder why it is that you think the Mayo clinic calculation is the best one over and above what is on this site?

    I just ask as it says to eat over your BMR and around your TDEE or your body goes into starvation mode. I also know some days I struggle to reach my BMR. I also know that other people’s BMR (Mayo TDEE) are quite low.

    Just trying to work it all out


    Excellent read: summed up exactly how I’m finding my dieting with 5:2. I quickly took on 4:3 method, 1200 cals on non-fast days & two sessions of Zumba to shift the flab at a more acceptable rate. In 12 weeks I lost 26lbs and now for my last 16lbs desired loss, I am not stressing over the non-fast days cals if they climb towards 1500 (Max for me as TDEE states 1700).

    Keep going everyone and consider the whole week not just TWO days until you are at your target weight/BMI

    Thank you!

    Great info from Simcoeluv! Thanks so much!

    Hi might be a stupid question but used to have tea with 2 sugars yikes since starting FD 3 weeks ago I swapped to black coffee with canderel will this have an effect on weight loss re artificial sweetener ..?

    Great info above tho thank you


    I started out by erring on the side of caution and not taking anything in my coffee. Now I use Tesco’s brand of Stevia (which I believe is a derivative of a South American plant). No idea why Morrison’s version is so much more expensive!) I haven’t touched anything with aspartame in it for years now, believing it to be a toxin. (And I don’t think sucralose is much better). Informed opinion is stevia and something (hope I have the spelling right) called xylotol are the only ‘safe’ sweeteners. I take one spoonful, which probably isn’t enough to sate my sweet tooth, but better safe than sorry. Still don’t use milk, though. Hope that helps.

    Thank you I will try the stevia version and see what it’s like , appreciate your reply


    There seems to be some confusion around TDEE and BMR. BMR (Basic Metabolic Rate) is the very-much-theoretical amount of energy you use doing NOTHING. Literally lying around. TDEE (total daily energy expenditure) takes your BMR as a baseline with an allowance for how much exercise you do. So if you are a complete couch potato your TDEE won’t be much more than your BMR. Whereas if you are an olympic athlete you’re TDEE will be much, much more. But life is never that simple ! For example, if you’ve been on a diet for a significant length of time and lost say 5% of your starting weight, then your BMR slows down PERMANENTLY by up to 10%. So your BMR and TDEE may be 10% less than the theoretical value.

    Please confirm! My TDEE is 1800. So on a fast day should I eat 450 or 500 cals ?

    Theoretically, you should aim for a quarter of your TDEE therefore 450 cals. On normal days you should aim for somewhere between your BMR and TDEE for a steady weight loss. This is not a fast way to lose wieght just a way to lose weight which includes fasting and has a load of other benefits for your body ๐Ÿ˜€

    Ok thanks, my weight loss has stopped after loosing over a stone, so maybe thats why, I need to reduce to 450 on fast days….

    As you lose weight you do need to re-adjust your calculations or increase your activity levels to continue weight loss. ๐Ÿ™‚


    Research shows many people overestimate their activity level. If they do that, they get a higher TDEE than it should be. If they eat to the higher TDEE, they either lose weight more slowly than they think they should, or don’t lose at all.

    There are some very general guidelines to help figure out your activity level. As most overweight people don’t start with strenuous exercise levels, walking is a good initial guideline.

    Generally, walking on level ground, you burn about one calorie for every 20 steps. So 10000 steps will burn 500 calories. 10000 steps equals five miles. So if you walk five miles a day you will burn 3500 calories in a week walking. (As an aside, an average walking pace is about three miles per hour, so five miles comes out to around one hour, 40 minutes of walking.)

    For TDEE purposes, you need to put in an activity level. The McKinley Health Center at the University of Illinois at Urbana-Champaign indicates that 2,500 steps or less per day is very inactive, up to 5,000 steps in inactive, 5,000 to 7,500 steps is moderately active, 7,501 to 10,000 steps is active and more than 10,000 is very active.

    So, as an example, if you walk five miles three times a week, you will walk 30,000 steps. 30,000 divided by 7 days in a week equals 4285 steps a day, or ‘inactive’. Of course, you are probably walking more than that number of steps because of steps taken on ‘non-walking’ days, but that might get you up to ‘moderately active’.

    Hope this helps when choosing an activity level for your TDEE calculation.

    I have nearly finished my first week and have found the comments on this site are very helpful. I have looked at mayo clinic calculator and the levels are quite close for my stats. TDEE is 1633 and mayo clinic suggest 1750 so I will make sure I don’t go above 1500 on the non-fast days. Think I must increase my exercise!!

    Hi, my TDEE on this website says I should eat 2214 per non-fast day, but the calculator on the Mayo Website says 1850?? which one do I use? this is only my second day on 5:2 so I’d like to start out right

    Hi shoe and welcome:

    I think you should use the Mayo number. They are both estimates and it is best to use the lowest to start.

    If you begin to lose weight too fast, you can go to the higher number to slow yourself down.

    Good Luck!

    Thanks simcoeluv, I’ll do that – I’ve never had the problem of losing weight too quickly, so if that did happen, I think I’d be in shock! I’ll stick to the Mayo numbers and see how that goes.

    Some fat science as additional background:

    One pound = 454g
    Fat is 9 kcal per gram (carb is 4, alcohol 7, protein 4)
    “Body fat” (adipose tissues) is 87% lipids (fats), the rest is other cellular matter
    One pound of body fat = 87% x 454g = 395g of caloric fat
    Energy in a pound of body fat: 395g x 9 = 3,555 calories … hence the 3,500 often quoted

    But that’s not the full story and why some of you don’t lose weight despite fasting. A few additional facts to consider:

    The liver stores approximately 90 – 110g of liver glycogen
    The muscles store another ~400g of muscle glycogen
    You have another ~25g of glucose flowing around in your blood

    Altogether, you have an energy store of around 530g of glycogen / glucose
    530g x 4 calories per g = 2,120 calories (glycogen is a carb and thus 4 cal /g)
    Your body needs to use up most of that storage before it starts to burn any fat

    If you use less than those ~2,000 calories on fasting days you will not lose fat

    The calculation of (TDEE x 2) / 3500 = pounds lost per week on 5:2 will not give you your expected weight loss

    Implication 1:
    You will lose NOTHING if your TDEE is less than 2,000 kcal on a fasting day … unless you are in a glycogen deficit.

    When you use up your store of glycogen and glucose, your body goes to fat cells for energy, converting the lipids stored there into ketone bodies (ketones for short) – you enter into a “ketogenic” state.

    This is where the story gets interesting. Not all of those ketones fro your fat are used up as energy by your body – some are excreted from the body in urine (why the test strips will measure ketones) and some will exit from your breath (as acetone). As much as 30% is excreted.

    Implication 2:
    You use up more than one pound of fat to generate those same 3,500 calories when you are ketogenic.

    1) TDEE is most relevant for fasters if you are above or below 2,000 TDEE. If you are above it, you will convert some fat on a fasting day. If you are below it, you will not convert any fat unless …
    2) you enter your fasting day with a glycogen deficit and you become ketogenic at less than 2,000 calories or you increase your TDEE above 2,000 on fasting days by doing exercise
    3) some of your fat is “wasted” when ketogenic so you use more fat weight for the same amount of energy and therefore one pound of fat does not equal 3,500 calories when you are losing fat weight.

    I’m getting confused!
    Haven’t started yet (tomorrow) but I am a 1200 cal kind a gal. My TDEE is 2000. Does this mean I should UP my calorie intake for effective loss or keep it at 1200?

    Hi MissFitz:

    I have no idea what you mean by being a ‘1200 cal kind a gal’. If your TDEE is 2000 and you eat 1200, you should be losing weight quite quickly. Did you compute your TDEE at 2000, or are you using some kind of average?

    To answer your question, the less you eat, the more you lose. The guideline is to eat to your TDEE or less. If you want to eat 1200 cal on your non diet days, that is fine.

    But do compute your TDEE again – hitting exactly 2000 would be unusual.

    Good Luck!

    If you are truly taking in only 1,200 calories a day, then you would be quite thin and losing weight already.

    I’ve been eating an average of 1200 calories for a couple of years, hit a plateau and a few extra kilos. Hence why I want to shift my dot into another gear.
    My question was –
    On non fast days, Should I be eating my recommended TDEE (which is 2200 ish) or stick with my 1200?

    TIA ๐Ÿ™‚


    “To answer your question, the less you eat, the more you lose. The guideline is to eat to your TDEE or less. If you want to eat 1200 cal on your non diet days, that is fine.”

    The more you eat, the less you lose.

    Depends on your goal.

    Good Luck!

    Thank you – between this and your wonderful trousers account, I feel much better. Have a great weekend.

    I got a tip from a person that really stays within her TDEE (she’s dieting not on 5:2 but she did have 215 pounds to lose a year ago she now has 74 pounds to go) but it’s worth a thought. Calculate your TDEE at your goal weight and eat to that. When you reach your goal weight you won’t have to change a thing in your eating habits.

    Myself I don’t count calories. I refuse to that’s “dieting” I’m not dieting I’m just changed my eating format/formula. I know the calories in a lot of the foods I eat having gone through “diets” which required calorie counting. I gained every pound back plus some.

    I don’t eat during fast days and I try to eat healthier during my normal eating days but I don’t deny myself my goodies either. My weight gain has come about due to health issues and portion size.

    I’m doing 5:2 for health reasons if I lose weight that will be great but my health conditions are my reason for changing my eating format.

    My BMR is 1750 & TDEE 2407. I put in lightly active in the calculator as some weeks I can exercise more than others depending on work. When I exercise I can burn anywhere between 400-900 cals depending on what I activity I do. Do I need to eat back calories or adjust my calories in any way when I exercise. Or am I ok to eat between my BMR &TDEE & ignore cals burned thru exercise.

    I did lose my weigh quite rapidly by eating up to my BMR calories on non-fasting days and drinking only non-caloric liquids on fasting days, doing 5.2. I did adjust my BMR according to how smaller I was getting. I did not pay much attention to the calories lost during exercise (it was a bonus!). All in all, I managed to lose more than 10kgs in about 2 months and I got to circa 19 BMI.

    I guess it depends on how easy or hard you want to do it for yourself!

    Good luck!

    It’s been too cold for me to do any fast days this week so I tried to keep within my TDEE and I did lose a little bit of weight which is very encouraging. I am using the TDEE for my current weight and like the comment about using the TDEE for the goal weight so will now calculate that!

    Hi Rae and welcome:

    Your TDEE includes exercise, so you do not eat back calories. If you do, you will be ‘overeating’.

    The thing to do is to eat 5/600 cal. on your diet days and to your TDEE or less on your non diet days. Your BMR is irrelevant, and there is no need to eat ‘between’ your TDEE and BMR – that just introduces a mathematical challenge that is totally unnecessary. If you eat below your BMR it will not hurt you.

    Here are some tips:

    Good Luck!

    Blimey this is all very interesting stuff TDEE etc etc , must try harder me thinks, dont like mathematical challenges, but i do need to cut down on non fast days,
    started 7th Jan, will keep at it!!!!

    Hi, I have been doing 5:2 for three weeks now. My Tdee is 1586 which is a lot lower than most posts I have read. I try to eat around 390 cals on my fast days but unless I calorie count on my ‘feast’ days, I go over my Tdee. Would I be better off doing a 4:3 week (I would prefer 5:2!). Also, as weight loss will be very slow, will I still loose inches any quicker?

    Hi Bubbly and welcome:

    With your low TDEE you will not lose weight quickly with either 5:2 or 4:3. I suggest you do 5:2 but stay within your TDEE on your non diet days. If you can’t do that, you will not be successful with 4:3 either.

    There is no relationship between weight and ‘inches’. You can lose weight without losing inches, and vice versa.

    Good Luck!

    hi Bubblyboo: I have the same TDEE as you and have been doing 5:2 for three weeks. I have lost 4 lbs and 2.5″ off my waist in that time. I downloaded the myfitnesspal free app which is great for calculating calories easily. Their calculation of TDEE is a lot less than FD so I keep between the two. I feel I eat healthily (retired chef) so know a bit about food for health etc. however I was gobsmacked at the calories I was putting away, mainly due to the amount I was eating. Now I cook less, don’t go back for seconds, and eat very little protein or carbs, but fill up with veg and salads. Am hoping for a good weight loss before big hols in May, but figure it took a long time to put this fat in my body, so it will take a while to unload! Good luck with it.

    Hi Third time lucky, thank you for your reply. I feel a little disheartened as I feel I can do the fast days but can’t seem to stay within my Tdee on feast days. I have cut down on portion sizes and have cut out treats but don’t feel that I will be able to sustain this long term. I’m not sure if I have lost weight but do feel better in myself. I will keep plugging away and hope that I will loose something in time. Good luck with your journey.

    Thanks for the detailed posts… I’m just going into week 5 on the 5:2, and overall I love it. I feel good, and I’m not really finding it that challenging.
    My BMR is 1237 and my TDEE is 1485. On fast days I’m eating between 400/500 calories, never over. And on non fast days I eat around the 1100 cals mark. (This is normal for me). I keep reading that you should eat between your BBM and TDEE, and obviously I’m not. Am I doing something wrong? And could this be a reason I’ve not lost any weight? I know that technically 5:2 isn’t a ‘diet’, but lots of people do lose excess weight on it. I just want to shift around 8lb. I’m not in any hurry, but wonder if I’m getting in my own way by doing something incorrectly. Also I know that I am not drinking enough water, so maybe this isn’t helping?
    Any advice would be a huge help! ๐Ÿ™‚

    Hi misspricy and welcome:

    You are not doing anything wrong – there is no need to eat ‘between your BMR and TDEE’.

    If your TDEE is 1485, you will be cutting about 2000 cal. per week from your diet. That means you will only be losing about 8 oz. a week.

    Its going to take awhile to lose the weight you want to lose, but if you keep going, you will lose it eventually.

    As for water, there is no ‘required’ amount. Drink what your body asks for and you will be fine.

    Good Luck!

    Hi simcoeluv, thanks so much for the quick reply. And for the advise.
    I’ll keep going… Happier now that I know I’m on the right track. I was starting to panic, I think I got lost in my own head there for a while.
    Thanks again, I really appreciate it!! ๐Ÿ™‚

Viewing 50 posts - 1 through 50 (of 206 total)

You must be logged in to reply.