Theoretical Background

This article provides an explanation for the importance of calorie density in weight loss dieting.

Calorie density is only one aspect of nutrition, and I do not mean to imply on this website that it is the only important factor.  Other important factors include...

1) Micronutrient nutrition (vitamins and minerals)

2) Dietary balance/diversity of foods

3) Type of fats (saturated fats, polyunsaturated fats, monounsaturated fats, omega 3/omega-6 fatty acids et cetera)

4) Salt content

5) Food allergies/intolerances

6) The effect of food on gut flora

7) Tailoring of the diet to specific medical problems

8) Risk of food borne illness and toxin exposure

Also, I do not mean to suggest that body fat content and maintaining a healthy weight are the only keys to overall good health.  Other limitations discussed here.

However, this website attempts to provide a practical approach for individuals with limited time, nutritional science knowledge, and motivation.  I think it is ridiculous to worry about whether olive oil is better than butter if you are 60 lbs overweight. Stop eating both of them.  I also find it questionable to concern yourself with low level organophosphate exposure from non-organic fruit when your fasting blood glucose is 250 and you can't run one mile at age 35.  Put down the fig newtons and pick up the pear.  I don't care if it's drenched in Raid; just put it in your mouth (just kidding  :)  )

Focus on the changes which will make a large and proven difference in your health.  Don't bother seeking out the theoretically optimal human diet.  Who cares.  I don't drive long distances to farmers markets or specialty restaurants.  It's too inconvenient.

There is significant evidence that "diets" are usually ineffective in the long term (26, 28), so it is of the upmost importance that you make reasonable and practical changes which can be maintained.

So what is so important about calories anyways?

Weight deals with mass, and a calorie is a unit of energy.  A "calorie" (with a lower case "c") is the amount of energy required to increase the temperature of one gram of [liquid] water by one degree Celsius.  a "Calorie" (with an upper case "C") is the kind of Calorie seen on the back of packages and is 1 kilocalorie or 1,000 calories.

When used to describe food, calories describe the chemical potential energy in foods which can be used by your body to perform various cellular activities or used to make and store fat.  The complicated biochemistry of metabolism is beyond the scope of this article, but suffice it to say that the chemical potential energy of food is extracted with remarkable efficiency.  Only about 5% of calories from food are lost in stool and urine (11) (note: this is slightly influenced by fiber intake, body weight, and other factors).

In order to lose body fat, you [for the most part] must consume less chemical potential energy ("Calories") than your body requires ("metabolic rate"), forcing your body to catabolize (eliminate) fat.

In case you are curious, the actual mass of fat lost is lost in the form of water and carbon dioxide.  There is an entire Ted talks lecture on this subject to your right.

What determines metabolic rate?(6)

Metabolic rate is influenced by the following factors (The first three factors constitute "basal metabolic rate"):

1) Body weight.  Metabolic rate increases with increasing body weight by about 4.5 Calories per pound (more influenced by lean body mass than fat unfortunately)

2) Height.  Metabolic rate increases with increasing height by about 1.2 Calories per inch of height

3) Age.  Metabolic rate decreases with age by about 5 Calories per year of age

4) Exercise.  Exercise increases metabolic rate

5) Luck.  everyone is different.  Some people have a lower metabolic rate than others (7).  This isn't your problem.  Read the section on psychology.

The steady state effect

Many individuals with a given lifestyle will tend to maintain a stable body weight for long periods of time.  People tend to gain weight as they age due to decreasing metabolic rate (which does occur naturally with age) and a decrease in activity level.  However, people often have a steady weight for several years.  The reason for this is that caloric intake equals caloric expenditure.  For instance, if your metabolic rate is 2,000 kcal/day and you consume 2,000 kcal/day, you will maintain your body weight.  If you eat 2,200 kcal/day, you will gain weight until your metabolic rate increases (due to weight gain) to 2,200 kcal/day.  

There are various quantitative estimates for basal metabolic rate which can be  applied.  For instance, I would estimate that if you increase your Caloric intake by 200 kcal/day, you will slowly gain about 20kg (44 lbs) over months to years.  This is not a very accurate estimate because you will probably increase your Caloric expenditure through normal daily activity (more work is required to complete the same activity or walk the same distance if you are heavier).  There are other factors as well.

You may or may not be currently at a steady state weight.  If you are currently gaining weight (within the last 3-6 months), you are probably not at steady state, and you will probably continue to gain weight slowly if you do not change your lifestyle.  You would have to improve your diet just to maintain your current weight.

Here is an interesting corollary.  Let us say that you are 5’7 and weigh 300 lbs.  Obviously, you are overweight.  Let us say that you are a 40 year old male, and that your weight is stable over the last year.  You are probably consuming at least 2675 kcal/day to maintain your body weight.  What if I could magically snap my fingers and make you 150 lbs?!

You would look in the mirror and look lean and ripped.  You would be ecstatic!  But what would happen?  Could you maintain your magical losses?

Doubtful if you don’t change your lifestyle.  Why?  Because your basal metabolic rate has plummeted (54), and you are now consuming far more calories than you burn, and you will slowly gain weight…and eventually, you will be 300 lbs once again.

That is why “dieting” often doesn’t work.  You simply gain the weight back when you go off the diet.  You have to actually change your lifestyle to one that you can maintain in the long run.  That is why I don’t want to tell you exactly what to eat.  I want you to UNDERSTAND the principle of calorie density and tailor it to your lifestyle and dietary preferences.

So how do I cut calories?

There are many ways to lose weight.  For instance, you can simply starve yourself. In the short run, starvation is a highly effective weight loss technique, and many commercial products are essentially based on starvation.  For instance, with the “48 hour miracle diet” (which can be obtained on amazon for about 20 bucks), you are consuming only 800 calories and only 160mg of sodium in two days, so you can easily lose about ten pounds due to salt and glycogen depletion, leading to a loss of water retention.

This is great if you are trying to make weight for a wrestling match, but you will gain the weight back within a few days when you resume your normal diet.  Try it if you don’t believe me. The problem with any diet based on starvation is that we are essentially programmed to be hungry and to seek out tasty foods aggressively.  Our ancestors commonly died of starvation during tough winters or other periods of scarcity.  Now, this isn’t much of a problem, but we are left with their genes.  We are left with their tendency to hold on to extra fat for an energy reserve and to pursue food aggressively when we are hungry. If you starve yourself, you are constantly fighting against your biology.  You are constantly fighting against your desire for satiety.  Most people cannot maintain this level of discipline in the long run.

Another strategy is to count calories explicitly and limit them strictly.  Various studies have found that when people are asked to estimate the number of calories they consume, they will systematically underestimate. The reason for this is that food products are often marketed in a deceptive way to make us think that they are healthier.  Also, food product labeling systematically underestimates the number of calories in foods! (10)

If you continue eating the same foods but in lesser amounts to cut calories, you will surely feel hungry, and you will constantly fight the urge to eat, the urge to be satiated.  You will likely reach your goal weight and lose motivation or succumb to other stressors in life.

So what causes satiety?

The biology behind hunger and satiety is very complex.  I won’t discuss it extensively here.  One of the primary mechanisms of satiety is physical distension of the stomach by food and the ability of the stomach to detect nutrients.  Vagal nerve pathways carry information from the gastrointestinal tract to the area of the brain that mediates satiety (8), the ventromedial nucleus of the hypothalamus.

The video to the right is a brief explanation of this phenomenon from the "Forks over Knives" movie:

Other factors include the following:

1) Blood levels of glucose, amnio acids, and fatty acids (9)

2) Horome levels such as insulin and cholecystokinin

3) The hormone Leptin released by fat cells which decreases hunger (8, 51, 52)

4) The hormone Ghrelin

One thing to note is that the mechanisms of satiety are delayed somewhat, so if you eat very quickly, you can bypass these mechanisms to some extent.  If you eat more slowly, you are less likely to overeat. The dieting strategy based on calorie density exploits the stretch receptors in your stomach, giving you the same satiety with less calories.  Eating something lower in calorie density and drinking water 20-30 minutes before a meal can help to prevent you from overeating.  For instance, if you eat an apple and drink a glass of water 30 minutes before dinner, you will probably end up consuming less calories overall because the apple/water will fill up part of your stomach.

What mediates calorie density?

Many things influence calorie density:

1) The distribution of macronutrients.  

Roughly speaking, proteins and carbohydrates have 4 Calories per gram and fats have 9 Calories per gram.  Hence, a diet with relatively more carbohydrates and proteins relative to fats is preferred.  As a side note, carbohydrate consumption results in insulin release, an anabolic hormone.  Many fad diets such as the zone diet and atkins diet are based on reducing carbohydrate consumption and changing your glucagon to insulin ratio.  This strategy does work, but I don’t recommend it because it is difficult to maintain and can cause unintended consequences.  The distribution of macronutrients has some importance, but the other factors are much more important.

2) Fiber content.

Insoluble fiber cannot be absorbed through the gastrointestinal tract and has no calories.  It binds water and fills up the stomach, causing satiety and diluting the calorie density of foods.  It turns out that the structural characteristic of fiber has some importance, and a stick of celery binds more water and causes more satiety than a comparable amount of fiber in a fiber supplement powder or even pureed celery.

3) Foods high in water content have lower calorie density simply because the water dilutes the calorie density of the macronutrients.  Watermelons are sweet and sugary, and the sugar in the water melon is effectively the same as the sugar in a lollipop, but the watermelon has water and fiber to dilute the calorie density.

[side note-there are differences between different types of sugars and other carbohydrates which are beyond the scope of this article]

4) Alcohol- Alcohol has about 7 calories per gram.  It is high in calorie density.  Use in moderation.

The scatter plots which you see to the right are from a cross sectional study looking to evaluate the relationship between individual factors and overall calorie density of foods (20).  As you can see, water and fat consumption have a clear relationship with calorie density.  Protein and carbohydrate content appears uncorrelated with calorie density, though they Converge on 4 Calories per gram as the content of the macronutrient reaches 100%.  Fiber may have a modest effect, but it is masked by other factors as most foods do not have high insoluble fiber content.

For a more detailed description of the calorie density of foods and how to implement this principle into your diet, please read the main article.

Ancillary benefits:

In addition to weight loss, there are other benefits to changing your diet to one with lower calorie density:

1)  Better control of blood sugar

By avoiding processed/refined starches and sugars, you are reducing the glycemic index (the tendency for foods to spike blood glucose) of your foods and improving blood sugar control.  If you are diabetic or prediabetic, I suggest you incorporate the principle of glycemic index into your dietary plan.

2)  Reduced sodium intake

The typical American diet has much more salt than is needed due to the high sodium content of processed and preserved foods and due to added salt.  Salt can increase blood volume and cause or exacerbate hypertension.  I can also worsen other medical conditions such as congestive heart failure and edema.

If you exercise regularly, live in a hot/dry climate, or have a tendency towards low blood pressure, you may need to add some salt. 

Tip for endurance athletes:  For long runs/cycles over several hours, consider taking about 300mg of sodium and 20mg of potassium per hour in the form of a salt tablet or other source to prevent excessive sodium losses and muscle cramps (often related to low potassium).  The amount can be varied based on intensity of exercise and heat, but avoid over consumption of salt as well, as it can be dangerous.

3) Improved micronutrient nutrition

By increasing fruit and vegetable intake relative to processed food intake, you may correct or prevent micronutrient deficiencies.

4) Avoidance of prolonged satiety

Heavy calorie dense meals are very satiating, but they can cause a stuffed feeling for several hours that may make it difficult to be productive or exercise.  Generally speaking, fruits and vegetables provide satiety but allow for recover after a few hours if you a prefer an evening workout after dinner.