The basic “law” is:
Calories consumed – Calories burned = (+) Fat storage or (-) Fat/Weight loss
Everyone has heard this mantra, but how straightforward is calorie tracking? It depends on how accurate you want to be.
Calories are units of energy (1 pound of fat stores 3500 calories). For example, if you normally eat 2000 calories per day and burn 2000 calories daily–you are in energy homeostasis. If you add 200 calories to your regular diet or reduce 200 calories from what you normally burn, you will put on a pound of fat after 17-18 days (3500 / 200 = 17.5 days). Conversely, if you cut your calorie intake (or add to the calories burned), you would lose weight (ideally, but not necessarily, fat) the same way. It’s worth pointing out that those who diet alone (without exercise) can lose muscle weight as well as fat weight. Not ideal!!!
As simple as that is, it’s NOT so easy to measure your own caloric input & calorie burn.
Caloric input is easier, but who is really going to measure out 3/4 cup cereal and 1/2 cup milk before eating?? I’m impressed if any of you has actually done that. And if you eat lots of the recommended “real” foods like fruits, veggies, anything homemade, or different cuts of meats bought from the butcher–there could be quite a lot of variation. I doubt you buy ground beef and ask the butcher what the exact fat content is (they probably don’t know). Even so, you can get a decent estimate of calories consumed per meal or per day.
As far as measuring Caloric expenditure, that is much more complex. Calories burned include those we all use for daily metabolic function (BMR), food processing, and exercise.
1) Basal metabolic rate (BMR) (60-75% of daily calories burned)-you may think you’re doing “nothing” just sitting there, but we each have our own resting rate of metabolism (BMR). You need energy for breathing, blood circulation, etc… There can be A LOT of variation among individuals due to:
a) Body composition: if you are larger or have more muscle mass–you will have a higher resting metabolism (10 lb of muscle burns ~50 calories per day at rest while 10 lb of fat burns ~20 calories/day).
b) Gender: males tend to have higher muscle mass and therefore higher metabolic rates
c) Age: unfortunately, we tend to add fat and decrease muscle mass as we get older (therefore older adults have slower metabolism)
2) Food processing(10% of daily calories burned)–digesting, processing, transporting and storing food takes energy, but this number is very stable and you can’t easily change it. Interestingly, I was reading up on meal frequency and its effect on metabolism…and my scientific interpretation of the literature is that there is no direct relationship. I’ve personally always liked eating many small meals daily, but there is no conclusive evidence that this alone changes your metabolism. Your body is way too good at regulating energy homeostasis to trick into burning more calories by changing eating frequency (assuming you still get the same total # of calories). It’s all about the basic equation up top (TOTAL calories in, no matter how you do it). So if you prefer 3 meals of 667 calories each, you will come out the same as if you eat 5 meals of 400 calories each. 3 x 667 = 2000 vs. 5 x 400 = 2000.
3) Exercise!!–YAY. This is the one you can change the most. The basic rule is that the more vigorous the exercise, the more calories you’ll burn. Sometimes this is hard to measure, but a quite a few online tools are out there where you can include some personal info to get an estimate of your BMR as well as your favorite form of exercise. I would just add +/- 10 % to any estimates you get online. If you want to lose weight, be conservative and subtract 5-10 % of those estimates & you will either be “right on”or happily surprised.
Here are a few options that I played around with from the web. Have fun!!
http://nutritiondata.self.com/tools/calories-burned
http://www.myfitnesspal.com/exercise/lookup
http://www.webmd.com/diet/healthtool-fitness-calorie-counter
Ultimately, if you do spend the time to measure all of these variables and your weight is NOT changing, there is a good chance you are mis-estimating your BMR or that you are not accurately counting your calories in.
Berkeley Underground Fitness blog 