It is tempting to try to calculate one's goal Calorie consumption and by extension one's overall goal solid food calorie density. As I describe in the main article, I do not actually recommend doing any calculations or calorie counting when attempting to lose or maintain weight. Rather, it is best to use calorie density as a concept. Use it to more accurately understand the weaknesses in your current diet and to understand which foods are good for weight loss. Use it to combat the constant marketing messages telling you that unhealthy foods are healthy.
The problems with a quantitative approach are as follows:
1) The Calorie requirement varies widely from person to person. Michael Phelps consumes up to 12,000 Calories per day while training (117). His diet consists of things like fried eggs, french toast, and mayonnaise (117). He gets away with this due to his intense exercise regimen and ample muscle mass which contribute to a very high metabolic rate. An older, more modestly built, and less active person might have to be quite strict with dietary choices in order to maintain a healthy weight. There is no way to calculate metabolic rate with perfect accuracy.
2) The concept of calorie density is imperfect and has various limitations discussed here. Some potential chemical potential energy is lost in urine and stool (11), and digestion itself requires energy output and varies for different foods (57).
3) There is no way to accurately determine the total mass of food a person needs to achieve satiety thought the day. Factors other than mass affect satiety such as protein content, fiber content, and other factors (61, 62, 67, 58, 71, 64, 66, 72, 73).
Despite all of this, I will attempt to calculate goal calorie density, using an average 40 year old normal-weight male as an example. let us assume the following information:
height: 69 inches
weight: 155 lbs (BMI 22.9)
body fat%: 16%
activity level: sedentary.
We need to the know the total food intake, the basal metabolic rate, and the excess metabolic activity through exercise and the thermic effect of food.
Starting with the mass of food consumed, here a few pictures of meals I ate which were fairly filling....
These meals are 1.066kg and 0.985kg...so approximately 1kg. Lets say that our example subject has an appetite similar to mine and also eats about 1kg in total snacks throughout the day and drinks only calorie-free drinks such as water and black coffee. He then eats 4kg/day of solid food. Obviously, this is a rough estimate.
Next, lets estimate his basal metabolic rate. Basal metabolic rate can be estimated using the Muffin St Jeor equation as follows:
B = (10m + 6.25h - 5a + 5) where B is basal metabolic rate in Calories/day, m is mass in kilograms, h is the height in centimeters, and a is the age in years.
Which works out to 704 + 1094 - 200 + 5 = 1603 Cal/day
Next, we can estimate the additional Calorie requirement given the thermic effect of food, the energy required for digestion and absorption itself.
The following describes an estimate of the amount of energy which is lost in digestion for the three classes of macronutrients (57):
The recommended daily allowance for the macronutrients is 45g protein, 230g carbohydrates, and 70g fats which is 13% protein, 66.7% carbohydrate, and 20.3% fat. Using this ratio, the average thermic effect works out to about 8.75% or about 140.3 Calories in our subject.
Next, we have to estimate the excess metabolic activity through movement and exercise which can vary widely from person to person, but has been estimated at about about 20% of the basal metabolic rate in a sedentary individual (118). This works out to 400.6 Calories in our subject.
The total energy expenditure is then 1603 + 140.3 + 320.6 = 2063.9 Calories per day.
The estimate of the goal calorie density would then be 2063.9 Calories/4,000g = 0.52 Calories per gram.
So Our subject should be eating foods like this to maintain his weight...
He would theoretically have to minimize even lean meats or cancel them out with nonstarchy vegetables such as spinach or lettuce.
To play with is idea a little bit, I could make our subject physically active with about 60 minutes of intense exercise 5-7 days a week which would increase his total Calorie requirement to 2705 Calories per day and his goal calorie density to 0.68 Calories per gram. To go with this further, I can keep the same activity level but make our subject 20 years old and with a lesser appetite such that he only eats 2.5kg of food daily. Now, his requirement is 2874 Calories per day, and his goal calorie density is 1.15 Calories per gram. Now he can eat foods like these and still maintain his weight:
He can even eat a decent amount of refined carbohydrates, fatty meats, and refined oils so long as he adds some fruit and non-starchy vegetables.
Again, I want to make it clear that I don't think these calculations are accurate or useful for the individual, but going through these calculations makes the following points:
1) If you are older, have a modest lean body mass, and are not very active, you will have to be fairly strict with your diet in order to lose weight.
2) Even if you are young and active, you still have to eat somewhat sensibly to avoid gaining weight. This is why most Americans are overweight. Certain foods like refined carbohydrates, refined oils, and fatty meats are simply too dense in calories and should be excluded from the diet (unless perhaps you are Michael Phelps).
A ridiculous mathematical approach to calorie density