Fac­tor in the rest­ing meta­bolic rate while try­ing to burn off en­ergy

The Weekend Australian - Travel - - Health - SHARON NA­TOLI

‘ IT must be my me­tab­o­lism’’ is a phrase I of­ten hear in prac­tice as clients search for an ex­pla­na­tion to the some­times frus­trat­ing ex­pe­ri­ence of aiming to change their weight and im­prove their health.

But to what ex­tent can a per­son’s meta­bolic rate be to blame for their cur­rent weight sta­tus? Af­ter test­ing the rest­ing meta­bolic rate of hun­dreds of clients over the past few years, ex­pe­ri­ence shows it can make a huge dif­fer­ence.

Rest­ing meta­bolic rate is the amount of en­ergy a per­son burns up at rest just to keep their body alive, in­clud­ing the en­ergy needed for func­tion­ing of vi­tal or­gans, breath­ing, cir­cu­la­tion and con­trac­tions of the gas­troin­testi­nal tract.

Rest­ing meta­bolic rate ac­counts for 60-70 per cent of a per­son’s to­tal daily en­ergy needs, and as a re­sult, a change to this can mean a sig­nif­i­cant change in weight over time.

For ex­am­ple, re­search in the Jour­nal of Clin­i­cal En­docrinol­ogy and Me­tab­o­lism (1997;82(10):3208-3212) shows that rest­ing meta­bolic rate de­creases by about 10 per cent in post-menopausal ver­sus pre-menopausal seden­tary women.

If a wo­man in this age group ate the same amount of kilo­joules over the next 10 years with­out ad­just­ing for a lower rest­ing meta­bolic rate, they would gain around 10kg a year.

Rest­ing meta­bolic rate com­bined with an es­ti­mate of how many kilo­joules a per­son burns daily through ac­tiv­ity and ex­er­cise, en­ables a rea­son­ably pre­cise mea­sure of to­tal daily kilo­joule re­quire­ments to be made.

This in turn as­sists with how much a per­son needs to eat in a day for weight main­te­nance, weight loss or weight gain.

While it’s com­monly be­lieved that over­weight peo­ple have a ‘‘ slow me­tab­o­lism’’ and thin peo­ple who can eat the side of a house and still not put on weight have a fast me­tab­o­lism, the op­po­site is more of­ten the case.

The lighter you are, the less en­ergy your body needs daily in or­der to keep it func­tion­ing, while the heav­ier you are, the harder your body has to work and the higher the num­ber of kilo­joules you will need in a day.

How­ever, rest­ing meta­bolic rate is just one com­po­nent of a per­son’s to­tal daily en­ergy needs — the re­main­der be­ing made up of the ther­mic ef­fect of food (en­ergy used dur­ing di­ges­tion to ab­sorb, trans­port and metabolise food) plus phys­i­cal ac­tiv­ity. Gen­er­ally, around 10 per cent of daily en­ergy re­quire­ments are used up dur­ing di­ges­tion.

The third com­po­nent of to­tal en­ergy ex­pen­di­ture, phys­i­cal ac­tiv­ity, is the most vari­able and the re­sult­ing in­flu­ence on to­tal en­ergy needs for the day can range from quite small (seden­tary peo­ple) to sig­nif­i­cant (ath­letes).

Rest­ing meta­bolic rate can be af­fected by a num­ber of fac­tors, and those that in­crease me­tab­o­lism in­clude a higher body weight, a higher amount of mus­cle in the body, younger age, male gen­der, nico­tine, caf­feine, ill­ness and stress.

Fac­tors that de­crease rest­ing meta­bolic rate in­clude lower body weight, fe­male gen­der, higher per­cent­age body fat, older age, weight loss and kilo­joule re­stric­tion. Cer­tain med­i­ca­tions can also in­crease or de­crease rest­ing meta­bolic rate.

Most peo­ple would like a higher rest­ing meta­bolic rate as this means you can eat more and not gain weight.

So to keep your me­tab­o­lism tick­ing along, the best ad­vice is to ex­er­cise reg­u­larly, par­tic­u­larly in­clud­ing ac­tiv­i­ties that as­sist with the gain­ing of lean mus­cle tis­sue, and to avoid very low kilo­joule di­ets.

If you’re aiming to lose weight, do so grad­u­ally and en­sure you in­clude reg­u­lar ex­er­cise to as­sist with re­ten­tion of mus­cle tis­sue.

To burn more kilo­joules over­all, it’s also im­por­tant to eat reg­u­larly so you keep your di­ges­tion sys­tem work­ing for you in more ways than one.

Sharon Na­toli is an ac­cred­ited di­eti­tian and di­rec­tor of Food & Nu­tri­tion Aus­tralia.


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