Calories (kilocalories… kcals)

The available energy contained within the caloric nutrients (carbohydrates, ethanol, fats, fiber, organic acids, polyols, and proteins) of different foods is measured in kilocalories (kcals). Food energy is released during cellular respiration (also known as oxidative metabolism). A kcal is a unit of food energy, and 1 kcal = 1 food calorie = the energy necessary to raise the temperature of 1 kg of water (~ 1 liter) by 1° Celsius (1.8 degrees Fahrenheit) = 4.1868 kilojoules (kJ). Food nutritional labels in some countries express food energy in kilojoules. One kilojoule is the approximate maximum amount of solar radiation received by one square meter of the Earth per second.

Carbohydrates not easily absorbed, such as fiber (2 kcal/g [8.37 kJ]), and lactose in lactose intolerant individuals… release less food energy than proteins, easily absorbed carbohydrates, and fats. The differing energy densities of caloric nutrients is due to their varying proportions of carbon atoms oxidized during cellular respiration (also called oxidative metabolism).

Cellular respiration: C6H12O6 + 6O2 arrow ATP + 6H2O + 6CO2

A single molecule of glucose oxidized to carbon dioxide and water also produces molecules of Adenosine-5′-triphosphate (ATP), the main intracellular energy transfer molecule.

The different energy densities of different foods is a basic concept behind some weight loss diets. To lose weight and feel full, eat foods that are less energy dense. Many fruits and vegetables are high in water content, so they have fewer calories by volume. For example, a grapefruit is approximately 90% water and has approximately only 80 calories.

#1 Secret to weight loss: Avoid energy dense foods. Read the top ten secrets to weight loss (coming soon).

See a List of Low Calorie Foods (coming soon).

High fiber foods (whole grains, and many vegetables and fruits) not only provide much fewer calories by volume, but they digest slower so they keep you feeling full longer and which keeps blood glucose levels lower, which in turn keeps levels of the hormone insulin lower.

In contrast, when glucose blood levels are elevated [by eating quickly digested foods… carbohydrates that rank high on the Glycemic Index (GI)], insulin spikes are triggered in order to decrease glucose blood levels. Insulin spikes can be a health risk in overweight individuals, especially when living a sedentary lifestyle; as insulin stimulates the body to uptake, utilize, and store glucose. In essence, insulin causes most cells to preferentially oxidize carbohydrates rather than fatty acids for energy, and causes accumulation of adipose tissue (fat)… the overall effect including a slowed down metabolism, which means fewer calories burned and weight gain.

#2 Secret to weight loss: Avoid carbohydrates that rank high on the GI Index. Read the top ten secrets to weight loss (coming soon).

On the other hand, a non-overweight individual eating high GI foods is a good idea after a workout intended to gain muscle mass, as insulin changes the body from a catabolic (muscle losing) state to an anabolic (muscle gaining) state. Insulin facilitates entry of glucose and amino acids into muscles; thereby replenishing the glycogen burned during exertion, and providing the muscle protein needed to repair and enlarge muscles.

Read more about the Glycemic Index (GI) & Glycemic Load (coming soon).

The human body needs a minimum number of calories per day depending on several factors, including body composition, weight, height, age, wellness or illness, and environmental temperature.

Basal Life Processes (~70%) + Activity [physical and mental] (~20%) + Digestion (~10%) = Total Energy Expediture

All basal life processes require an intake of oxygen along with water and macronutrients [carbohydrates, fats, and proteins] to provide energy for survival, and to expel carbon dioxide buildup.

Basal metabolic rate (BMR) is the amount of energy expended per day in a state of complete muscular repose in a neutrally temperate environment (the ambient temperature in which oxygen consumption is at a minimum and the lowest rate of heat is being produced by the body in maintaining normal body temperature), immediately after 8 hours of sleep, in the post absorptive state (the digestive system is inactive, which takes place after approximately 12 hours with no food). Temperatures significantly cooler or warmer than a neutrally temperate environment may lead to hypothermia or heat stress, respectively. BMR has been measured following the Harris-Benedict equation since 1918, and it the most popular equation used to find BMR.

For men: h = 66.4730 + 13.7516 w + 5.0033 s – 6.7550 a

For women: h = 655.0955 + 9.5634 w + 1.8496 s – 4.6756 a

where h = total heat production per 24 hours, w = weight in kilograms, s = stature in centimeters, and a = age in years. These equations have been tabulated for values of weight from 25.0 to 124.9 kgm., for stature from 151 to 200 cm., and for age from 21 to 70 years.

According to the Harris-Benedict equation, the average daily basal heat production of men is 1632 calories; and the average daily basal heat production of women is 1349 calories.

(For more information, refer to A Biometric Study of Human Basal Metabolism; Arthur Harris and Francis G. Benedict; October 1918.)

Although, the Harris-Benedict equation is inaccurate (it overestimates by 5% or more) for the following reasons:

  • According to today’s BMR test standards which include that the test subjects spend the night at the test facility, the Harris-Benedict equation does not estimate BMR, but rather it estimates resting metabolic rate (RMR).
  • The test subjects used to develop the Harris-Benedict equation did not include an adequate representation of obese individuals, nor of young or old individuals.

A number of studies have attempted to improve upon the Harris-Benedict equation since it was first published in 1919. “The Mifflin standard provided an accurate estimate of actual resting metabolic rate in the largest percentage of nonobese and obese individuals and therefore deserves consideration as the standard for calculating resting metabolic rate in obese and nonobese adults.” (For more information, refer to The Journal of the American Dietetic Association, Volume 103, Issue 9, Pages 1152-1159, September 2003; "Validation of several established equations for resting metabolic rate in obese and nonobese people", David C. Frankenfield, MS, RD, William A. Rowe, MD, J.Stanley Smith, MD, R.N. Cooney, MD.)

The Mifflin REE (resting energy expenditure; synonymous with RMR) equation is a more representative and accurate measurement than the Harris-Benedict equation, is taken under less restricted conditions, and does not require that the subject spend the night sleeping in the test facility prior to testing, so the subject might not be in a state of complete muscular repose. The following equations for BMR and RMR should be thought of as approximations ONLY of how many calories the human body needs to stay alive while awake at complete rest at ideal temperature on an empty stomach, and this amount of energy is ONLY sufficient for continued functioning of the vital organs, and therefore do not take into consideration the energy requirements of any kind of physical activity whatsoever. They are dependent upon weight, height, and age, and do NOT take into consideration activity levels.

As a rule of thumb, the smaller or older a person is, the lower that person’s RMR.

RMR (or REE) is estimated using the Mifflin standard equation:


P = RMR,
m = weight in kilograms (1 pound [lb] = 0.4536 kg),
h = height in centimeters (1 inch [“] = 2.54 cm),
a = age,
and s = +5 for males and −161 for females.

The Mifflin equation does not take into account individual body composition or type, which is a measure of the percentages of bone, fat, and muscle that comprise the body. Therefore it is less accurate if you have a greater or lesser amount of muscle or bone than most individuals. This is because muscle and bone tissue is metabolically active and fat cells are comparatively not. So, an individual with an above average amount of muscle will have a higher RMR than equated; while an individual with a below average amount of muscle will have a lower RMR than equated.

(for more information, refer to The American Journal of Clinical Nutrition, Volume 51, Pages 241-247, 1990; "A new predictive equation for resting energy expenditure in healthy individuals", MD Mifflin, ST St Jeor, LA Hill, BJ Scott, SA Daugherty and YO Koh)

Other equations use lean body mass (LBM) to estimate basal metabolic rate (BMR) and resting metabolic rate (RMR).

  • The Katch-McArdle Equation (equates for BMR):

spaceimageBMR = 370 + (21.6 × LBM), where LBM is the lean body mass in kg.

spaceimageBMR = 370 + (9.79759519 × LBM), where LBM is the lean body mass in lbs.

  • The Cunningham Equation (equates for RMR):

spaceimageRMR = 500 + (22 × LBM), where LBM is the lean body mass in kg (1 lb = 0.45359237 kilogram).

Since the Katch-McArdle and the Cunningham equations take into account the difference in metabolic activity between lean body mass and body fat (requires minimal energy to maintain), these formulas tend to be more accurate for individuals who have above average lean body mass and less body fat, but they are still only estimations. In order to find LBM, you need the following equations, N1 and N2 for men; and N1, N2, N3, N4, and N5 for women.

Body Fat Equations Abbreviations:

TBW = Total Body Weight
LBM = Lean Body Mass
BFW = Body Fat Weight

Body Fat % Equations for Men

N1 = (TBW x 1.082) + 94.42
N2 = Waist measurement (at naval) x 4.15

LBM = N1 – N2


Body Fat Percentage = (BFW x 100) divided by TBW

Body Fat % Equations for Women

N1 = (TBW x 0.732) + 8.987
N2 = Wrist measurement (at fullest point) divided by 3.140
N3 = Waist measurement (at naval) x 0.157
N4 = Hip measurement (at fullest point) x 0.249
N5 = Forearm measurement (at fullest point) x 0.434

LBM = N1 + N2 – N3 – N4 + N5


Body Fat Percentage = (BFW x 100) divided by TBW

Total Daily Energy Expenditure (TDEE)

To calculate a rough estimate of your daily calorie needs, or total daily energy expenditure (TDEE), your basal metabolic rate (BMR) or resting metabolic rate (RMR) value is multiplied by a factor with a value depending on your activity level… from 1.2 to 1.9.

The activity multipliers take into account the “thermic effect of food”, which is the energy expended (calories burned) by our bodies in order to consume (bite, chew, and swallow) and process (digest, transport, metabolize, and store) food. Protein requires the greatest energy expenditure, as high as 30%. Dietary fat is very easily processed and turned into body fat and has a very little thermic effect of 2 or 3%. The energy expenditure required to process carbohydrates is between that of protein and fat.

Be aware that if your TDEE is below ~1300 to ~1500 for a man, and below ~1000 to ~1200 for a woman, and if that is all the calories you consume, your body might go into starvation mode. In starvation mode, the body slows metabolism down in an attempt to gain weight by converting protein from the muscles into glycogen and burning it instead of the body’s fat reserves. The body burns muscle when in starvation mode because muscle requires many more calories to maintain than fat does.

Increasing your activity level will demand a higher caloric intake and consuming them will avoid the slowed metabolism of starvation mode. This is what the “experts” mean when they say “Stay active!” It is estimated that most men should be burning between ~2000 to ~2500 calories per day, and women slightly less. Children, the inactive, and the elderly obviously need even less.

Total Daily Caloric Need For Fat Loss (TDEE – 500 to 750)

There are 3500 calories in 1 lb (0.45 kg) of body fat. If your weight loss strategy consists only of calorie reduction… in order to only lose fat and not muscle tissue when reducing caloric intake, be patient and limit your fat loss goals to no more than 1 to 1.5 pounds per week. TDEE – 500 will give an average loss of one pound per week, as 500 X 7 days = 3500 calories.

Why BMI?

The Body Mass Index (BMI, also called the ‘Quetelet Index’) was invented by Belgian mathematician Lambert Adolphe Quetelet (1796-1874) as one of his many attempts to determine and show how individual behavior could be compared to that of an “average man” (a term coined by Quetelet to represent the average characteristics of a population) by arraying the facts of life as bell shaped curves.

Quetelet intended the BMI to serve only as a way to classify sedentary (physically inactive) individuals that have average body compositions as being “underweight”, “overweight” or “obese”. There are the following example exceptions: athletes, children, the elderly, and the infirm.

For example, as such, since most people under the age of 20 are still growing; and since older people typically become shorter and less muscular with time:

  • BMI is only valid for individuals over the age of 20.
  • BMI often underestimates the amount of body fat in older individuals.

Because the BMI ranges are valid only as statistical categories, they should not be thought of as accurate predictors of individual health.

Some people like to equate for BMI (body mass index) to get a quick estimate of body fat, but the BMI equation does not account for the fact that fat does not weigh the same as muscle or bone, so larger very athletic individuals with very little body fat may be calculated as obese. Keep in mind that the BMI equation was developed to estimate for obesity in populations not individuals so it is only an average, even though it is often used in the latter capacity. There is some good information associated with the BMI though, so it is not entirely useless so long as it is understood that it is not meant to be used as reliable diagnosis.

Here are three different BMI equations using different systems of measurement:

Different cultures have different perceptions for BMI, but the BMI chart below is oriented toward helping to determine potential negative health risks that may accompany overweight and obese BMI’s.

BMI Prime (BMIP) is the ratio of an individual’s calculated BMI to upper limit BMI (currently defined as BMI 25 [23 in Asian populations]). BMIP can be useful as it gives an easy visual of what percentage an individual may be deviating over from their upper weight limits. For instance, an individual with a BMI 31 has a BMIP of 31/25 = 1.24 = 24% overweight.


To correctly measure your waist, standing, hold a tape measure level around your middle, just above your hipbones, and measure just after you exhale.

Again, the BMI ranges are valid only as statistical categories, and therefore they should not be thought of as accurate predictors of individual health.

That said, higher BMI’s may have increased risk for diseases that can occur with more body fat, such as breathing problems, cardiovascular disease, diabetes (type 2), gallstones, high blood pressure, hypertension, and certain cancers. Being overweight and having two or more risk factors may significantly increase your risk of developing cardiovascular disease or other conditions.

Risk Factors:

  • High blood pressure (hypertension)
  • High LDL cholesterol (“bad” cholesterol)
  • Low HDL cholesterol (“good” cholesterol)
  • High triglycerides
  • High blood glucose (sugar)
  • Family history of premature heart disease
  • Physical inactivity
  • Cigarette smoking

More on the limitations of the BMI… the BMI doesn’t account for different body frame sizes, the loss of height and muscle loss in the elderly, that muscle is heavier by volume than fat, or the varying proportions of bone, cartilage, fat, water weight, etc. within different individuals. For example, according to the BMI, both these guys are obese; Lou Ferrigno weighing in at 316 lbs and 6’5″ tall… and wannabe sex stud on the couch weighing in at… well we won’t even go there, but you can see where the BMI errors: