What the terms mean
TDEE: Total Daily Energy Expenditure – how many calories you need each day to maintain your current weight. Your gender, age, weight, height and activity level all affect your TDEE which is why the daily ‘average’ guideline of around 1800-2000 calories for women and 2200-2400 for men may be wrong for you.
BMI: Body Mass Index – a basic calculation of whether you are a healthy weight or not. 18-25 is the number you are aiming for – lower, and you are underweight, higher and you may be running a health risk by being overweight or obese. (It ‘s a useful guideline but does have limitations see The 5:2 Diet Book or this NHS link for much more information)
BMR: Basal Metabolic Rate – the number of calories you need to keep the body’s MOST BASIC functions going each day. But use your TDEE as a guideline.
Real Life Examples
is 5ft/60inches/152cm tall – and weighs 157 pounds/11 stone 3 pounds/71.2kg – after a recent injury, she’s not very active and her BMI of 30.66 puts her just into the obese category. Her height, age and activity levels mean she’s burning less energy than average, so her TDEE is 1572, lower than the average for women of 1,800-2,000. It’s a good idea for her to aim for an average of around 1,600 or less so she doesn’t cancel out the calories she ‘saves’ on her Fast Days as it’s only by creating a deficit that she’ll lose weight.
is 6ft/72 inches/183cm tall and weighs 210lbs/15 stone/95.3kg – he works in a very physically active job on a building site. His age, height and physical activity levels mean his TDEE is higher than the average for men of 2,200-2,400 calories… so he can eat up to an average of 3917 on his non-fast days and still lose enough weight to bring him into a healthy BMI. That’s a pretty large allowance, but to speed up weight loss, he could easily aim for 3,000 and make very rapid progress.
is 5ft 8/68 inches/173cm tall and weighs 190lbs/13 stone 8/86.2kg – she’s started exercising at least four times a week to help her weight loss regime and her height, age, weight and activity levels mean her TDEE, at 2602, is higher than the average for women of 1,800-2000 calories. To help her weight loss, she could still aim for around 2,000 which will allow her plenty to eat, without feeling hungry, but speed up weight loss. But she certainly doesn’t need to count every calorie!
Should I adjust my calorie limit on Fast Days?
The limit of 500 for women and 600 for men is based on around 25% of the ‘average’ TDEE.
For most of us, the averages work just fine. If you’re much taller, heavier or more active than average, it may be worth allowing yourself slightly higher limits on a Fast Day – just divide your TDEE by four.
If your TDEE is lower than average, you can limit your Fast Day intake if you like, but it’s unlikely to make a significant difference to your weight loss if you cut your limit to 450, for example, rather than 500, and may make meal planning that bit harder.
Is the TDEE completely accurate?
It’s an estimate: in addition, there are different formulae used which may mean your estimate varies by up to 150-200 calories with different online calculators.
The trick with 5:2 is not to obsess, but to use the TDEE as a guideline on how much fuel your body needs. That, and learning to listen to your body, will help you make the best choices when it comes to staying in good, healthy shape.
- Your TDEE will reduce as you lose weight, so recalculate for every stone/7kg lost
- If in doubt, underestimate your activity levels – we can all be a little optimistic about how active we are
- Don’t be obsessive – learn to listen to your appetite, but use the TDEE as a helpful guideline.