Calories
What's the magical formula to achieve your weight goals?
In order for your weight to stay the same, the energy (or calories) you consume must equal the energy (or calories) you expend. In most cases, it’s really a simple matter of energy balance: “Calories In” must equal “Calories Out.” “Calories In” includes what you eat and drink. “Calories Out” includes your resting metabolic rate, thermic effect of food, and physical activity. Your personal calorie requirement depends on these three factors.
Read on to learn…
  • What you can do to rev up your metabolism.
  • Whether fat burner supplements are worth your money.
  • How many calories you can burn during different physical activities.
  • Exactly how many calories you need to meet your weight and fitness goals.
Resting Metabolic Rate
Resting metabolic rate (RMR) is the number of calories it costs for you to maintain all your internal physiological functions at complete rest. In other words, it’s the amount of energy required to keep your heart beating, your lungs breathing, your brain and liver functioning, and all your cells alive and well at complete rest. RMR accounts for approximately 65% of your total daily calorie needs. 

Several factors affect RMR. Some of these factors you cannot control because they are part of your genetic make up. As examples, males and/or tall individuals often have higher RMRs. Having a fever, growing (i.e. during puberty or pregnancy), living in a cold climate, and the premenstrual period in a women’s monthly cycle all increase RMR and calorie needs. Meanwhile, having low levels of thyroxin (thyroid hormone) or leptin (a metabolism-regulating protein) in your body decrease RMR and calorie needs.

So what factors can you control? What can you do to rev up your metabolism?
Two things: 1) build lean body mass and exercise and 2) avoid restrictive diets. Read on to learn why.

1. Build lean body mass and exercise.
Of the factors you can control, the main one that affects your RMR is the amount of lean body mass you have. Lean body mass (which includes muscle tissue) is very metabolically active and accounts for 75-80% of your RMR. At rest, one pound of muscle burns about three times more calories a day than a pound of fat (and during exercise, the metabolic rate of muscle increases substantially more!). So, people who have more muscle on their bodies burn more calories just sitting in class than people who have more fat on their bodies. 

Of course, your lean body mass is somewhat determined by your genetic make-up and your age (things you cannot control). Genes dictate what body type you have and whether you tend to carry more muscle or fat on your body. Also, as you get older, your body naturally shifts towards more fat and less muscle, which results in a 2-5% decline in RMR (about 75-100 fewer calories per day) every decade past age 30, unless you do something to combat muscle loss.

What can you do to combat muscle loss and keep your metabolism revved up?
You can partly control your lean body mass and prevent the age-related body composition shift by regular resistance training 2 to 3 times per week. In fact, older women and older men can recover 1 to 2 decades of loss, respectively, with just 2 months of resistance training 3 times per week. That’s a metabolic boost of up to 10%! Resistance training may include lifting weights, doing push ups and sit ups, or holding up your own body weight in yoga poses. When it comes to aging and muscle loss, "if you don't use it, you're going to lose it." So, use it! 

In addition to building muscle (which is more metabolically active tissue), very intense exercise sessions can speed up your RMR for several hours after you stop working out. So, people who have more muscle AND are training very hard most days of the week need a lot more calories just to maintain their internal physiological functions at rest. 

2. Avoid restrictive diets.
Restrictive dieting, on the other hand, slows down RMR. Your body slows down in order to adapt to the lower calorie intake (so it can function with less fuel). Your body is very smart, and it wants to protect you. So, it actually begins holding on to every calorie you eat and storing it as fat (since it’s not sure you will feed it later). This is one possible reason why people who diet usually gain back their weight (and then some!) once they return to their normal eating patterns. Click here for more info on “Do diets work?”

What about fat burner supplements?
Many dietary supplements are marketed as “thermogenic agents,” claiming to speed up metabolism and burn fat. These substances usually contain ephedra, synephrine, caffeine, and/or green tea extract, and they do have some stimulating effects. They can increase heart rate, increase blood pressure, and increase metabolism slightly. But, looking at the big picture, their effect is relatively minor. And some products can cause serious health problems. There is no magical pill that can shed pounds without some life-long adjustments in eating and activity patterns. If something sounds too good to be true, it probably is. Click here for more info about fat burner supplements. 

Thermic Effect of Food
The thermic effect of food is the amount of calories it costs to digest, absorb, transport, and store nutrients in your body. Every time you eat, your RMR goes up slightly and stays up for about 5 hours to fuel these metabolic activities. This may be why you’re more likely to maintain a healthy weight and keep your metabolism revved up if you eat smaller, more frequent meals throughout the day (instead of skipping breakfast and lunch and then stuffing yourself late at night). 

In reality, the thermic effect of food plays only a minor role in your total calorie expenditure (maybe 5-10% of your total needs), so it probably has minimal effect on your weight. But, eating smaller, more frequent meals certainly won’t hurt. If anything, your brain and muscles will appreciate the steady supply of nutrients throughout the day, and you are likely to feel better and perform better in school and physical activities. 

Interestingly, researchers have found that the thermic effect of food varies between obese and lean people. When lean people eat a meal, energy use speeds up for a while and then drops back to normal (as expected). Many obese people, on the other hand, do not experience any change in energy use after eating (i.e. food has no thermic effect for them). So, while thermic effect of food contributes little to our overall daily energy needs, this small amount of energy probably adds up over a lifetime and may explain why some people stay lean while others gain weight, despite similar calorie intake.

Physical Activity
Physical activity includes the calories you spend during normal daily activities (such as walking to school, brushing your teeth, fidgeting in class), as well as the calories you spend during purposeful exercise sessions (like jogging, swimming, and kick-boxing). As you may suspect, there is huge variability in the number of calories different people spend in physical activity. Do you take the stairs or the elevator? Do you walk to school or drive? Are you fast-moving and fidgety all day, or do you move slowly and prefer to stay still and relaxed? Do you enjoy sports, weight lifting, hiking, and aerobics in your free time or do you prefer reading, painting, or writing? The calories burned in physical activity vary widely, but it usually accounts for about 25-35% of your total daily calorie needs. 

The exact number of calories you personally burn during different activities depends on your size (it costs more calories for a larger person to do the same task as a smaller person), your fitness level (it takes more calories for a beginner to do the same exercise as an experienced athlete), and the intensity of the activity (it takes more calories to run for 30 minutes than to walk for 30 minutes). Click here to see how many calories your burn during 30 minutes of different activities (based on your body weight).

Calculate Your Total Calorie Needs
There are many equations to estimate your total calorie needs based on your RMR and level of physical activity (NOTE: the thermic effect of food is usually not accounted for since its role is so minor). It is important to realize that all these equations are just estimates. You may need more or less depending on genetic differences in RMR and your body composition. Consult a qualified health professional for more information about your personal calorie needs. 

Step 1: Estimate RMR
Men Healthy body weight x 11 calories
Women Healthy body weight x 10 calories

IMPORTANT NOTE: This is just an estimate of what your body requires at rest. If you have more muscle than the average person, you probably require more calories at rest than this equation suggests. If you have more fat than the average person, you probably require fewer calories at rest than this equation suggests. Remember, muscle tissue is more metabolically active than fat tissue. If you are 30 lbs. or more overweight (and that excess weight is mostly fat, not muscle), you can use your desired body weight instead of your actual body weight when calculating your RMR.

Step 2: Multiply RMR by Activity Factor Activity Factors
 
 
Activity Factors
Very Light/Sedentary (sitting or standing all day) e.g. lab/computer work, typing, painting. 1.20 - 1.30
Light (walking and some movement throughout day)
e.g. student, teacher, homemaker, child care worker
1.30 - 1.45
Moderate (work at a job with some physical work or 
moderate intensity exercise 4-5 x/wk. for about one hour)
e.g. gardening, carrying loads, most recreational exercisers
1.45 - 1.65
Heavy (work at a job with heavy manual labor or 
vigorous intensity exercise 5-6 x/wk. for one or more hours)
e.g. roofer, carpenter, many athletes
1.65 - 1.90
Exceptional (intense physical training for many hours every day) e.g. professional or collegiate athletes during their seasons 1.90 - 2.20
 
What if you want to lose weight?
The only way to lose weight is to create a calorie deficit. One pound of fat equals 3500 calories. So in theory, to lose ½ pound to 1 pound a week, you have to create a deficit of 250 to 500 calories per day (either by eating fewer calories or burning more in physical activity). Of course, genetic differences determine how easy it is for you personally to lose weight. In one study, researchers overfed a group of people 1000 extra calories every day for 8 weeks and found that there was a huge difference in the amount of weight gained (ranging from 3 to 16 pounds)! The researchers concluded that the people who gained less weight “wasted” the extra calories by fidgeting more and giving off more body heat. The people who gained more weight, on the other hand, had bodies that were more efficient in storing the extra calories. For more tips on healthy weight loss, go to “Eating Strategies for Permanent Fat Loss.” To maximize fat loss, minimize the drop in your metabolism, energy, mood, and grades, and increase the chances that you won't gain it back, lose weight slowly! Decrease your intake slightly by 250-500 calories per day and increase your exercise level. Aim for about 0.5-2 lb. weight loss per week. If you are very overweight, 2 lb. per week is acceptable. But, if you only have a few pounds to drop, the rate should not exceed 0.5-1 lb. per week. 

What if you want to gain weight?
The only way to gain weight is to create a calorie excess. So, in theory, to gain ½ pound to a pound a week, you have to create an excess of 250 to 500 calories per day. Whether or not those extra calories go towards building muscle or body fat depends on whether or not you exercise. Of course, as with weight loss, genetic differences make it easier for some people to gain weight and harder for others. If your metabolism speeds way up every time you eat more, you may have to consume many more calories before you’ll achieve results. For more tips on weight gain, go to “Eating Strategies to Gain Weight” and “Frequently Asked Questions about Bulking Up.” Also, click here for more tips on what to eat before, during, and after workouts for maximal results.
 
Sheri Barke, MPH, RD
COC, Student Health & Wellness Center
Rev. 2005