Advice commonly given to people who are trying to lose weight is "Calories in, calories out." It's actually more complicated. Calories don't always count.
Weight watchers count calories in the food they consume. They believe that slimming down is simply a matter of eating less. At first glance, this approach seems to make sense. However, gaining weight is driven by biochemical processes that respond more to the
type of food rather than the amount eaten.
There are 3 main sources of calories in the human diet, also known as macronutrients. Digestible carbohydrates, made up of sugars and starches, contain 4 calories per gram. Proteins, made up of amino acids, also contain 4 calories per gram. Fats contain 9 calories per gram. Alcohol also contains calories but is not a primary source of fuel.
Macronutrients must be broken down during digestion in order to pass from the gut into the bloodstream. Through the action of enzymes, sugars and starches are converted mainly into glucose. Fiber is also a carbohydrate, but humans cannot digest it so fiber passes through the body. Proteins separate into constituent amino acids. Dietary fats in the form of triglyceride break apart into glycerol and free fatty acid chains.
Glucose, amino acids and fatty acids all enter into the Krebs Cycle. Through this process, complex molecules are converted into adenosine triphosphate (ATP), a form of energy that can be used directly by the cells during respiration.
What is a Calorie?
A calorie is a unit of measure of energy. However, there is a disconnect between the physics view and the foodie view of calories. A dietary calorie represents the amount of energy needed to raise the temperature of 1 kg of water by 1o Celsius when food is burned in a closed container called a calorimeter.
Unfortunately, materials behave very differently in a calorimeter than in the human body. For example, if wood is burned in a calorimeter, heat will be produced and the temperature of the water will rise. However, the human body lacks digestive enzymes to break down cellulose so that it can be absorbed into the bloodstream. Thus, wood contains calories, but no dietary calories.
When is a Calorie not a Calorie?
Another flaw in the calorie-counting approach is that the total amount of macronutrients ingested is not necessarily also absorbed by the body. Carbohydrates are easy to digest and therefore absorbed more efficiently than fats or proteins. As a result, some fat and protein (and calories therein) pass through the digestive system and are eliminated.
Another issue is that food contributes building blocks as well as energy. Almost every atom in the body comes from food. Cell membranes, the protective layers surrounding every cell in the body, are composed mainly of fats. The cytoplasm inside every cell is made largely of protein. Fats and proteins also are used in the manufacture of hormones, antibodies, and enzymes. In contrast, carbohydrates play much more limited structural roles in the body.
Because of these differences in how the body uses various macronutrients, the concept of
isocaloric intake commonly compared in many diet studies is flawed from the outset. Two menus may ostensibly contain the same number of calories, but the body may not receive the same amount of usable energy from each.
Eat Less, Move More?
Health experts routinely state that more exercise is the key to weight loss. But consider another way of looking at energy use. In order to drive a car somewhere, its owner must put gasoline in the tank. Does the owner then drive the car with no purpose other than to burn up all the fuel that has just been paid for? Of course not - that would be pointless. And yet exercise is viewed as way to rid ourselves of unwanted calories. But what drives people to eat too many calories to begin with?
Why People Gain Weight
While some people do ingest more calories than their bodies need, gaining weight is not so much a problem of over-consumption as it is of over-storage. Rather than being used to meet energy requirements, macronutrients are converted to triglyceride and stored as adipose tissue. This happens because of the action of insulin.
Insulin is a
hormone made in the pancreas. When the concentration of glucose in the bloodstream (known as “blood sugar”) rises, insulin is released from the pancreas to counteract the damaging effects. It accomplishes this in several ways. The first is to move glucose into cells to be used as fuel. Second, insulin converts some glucose to glycogen (a kind of starch) for storage in the muscles and liver.
At this point, any excess glucose is converted to glycerol which combines with free fatty acids to produce triglyceride. High levels of triglyceride in the bloodstream are a risk factor for heart disease. In a protective response by the body, triglycerides are moved into vacuoles inside fat cells, leading to an increase in adipose tissue.
When dietary fat is ingested without significant amounts of carbohydrate, there is no insulin spike and no conversion of free fatty acids to triglyceride. Fatty acid chains are then available to be used for energy, hormone production or cellular repair. In contrast, when insulin is present, the body is robbed of both usable energy and necessary building materials.
Weight Loss without Calorie Restriction
In order to liberate stored fat so that it can be used for energy and other needs, it’s necessary to limit the action of insulin. As long as insulin is present at elevated levels in the bloodstream, stored triglycerides will not be released. Exercise will result in
increased hunger, not fat loss.
If insulin levels are low, triglyceride molecules break apart into free fatty acids that can be used by the body as fuel. Exercise will result in fat loss without hunger because the body has a ready supply of
available energy. Dietary carbohydrates are not needed because glycerol will be converted to glucose to maintain appropriate levels of blood sugar.
Disclaimer: This information is for educational purposes only and should not be considered as medical advice. It does not replace the advice of the physician who cares for you. All medical advice and information should be considered as incomplete without a physical exam, which is not possible without a visit to your doctor
