Absolutely not. Our metabolism is a complex system of organs working together that dictate how food is used, disposed of, etc. Not to mention, based on your goals and body type, different manipulations to your diet are indeed necessary.
A NIH-funded study tried to suss out the associations between specific foods, lifestyle factors, and weight gain. Its conclusion?
Specific dietary and lifestyle factors are independently associated with long-term weight gain, with a substantial aggregate effect and implications for strategies to prevent obesity.
Other studies are finding similar results (for instance). Our metabolism is too complex to follow the adage, "a calorie is a calorie".
In other words, calories are not the only important aspect of diet. Total caloric intake has an effect, but the foods you're eating and activities you're partaking of will affect your health and weight gain. Perhaps more importantly, the foods you choose to eat will affect how many calories you feel like eating.
The Washington Post summarizes more of the ramifications of this study:
[There are] striking differences in how various foods and drinks — as well as exercise, sleep patterns and other lifestyle choices — affect whether people gradually get fatter.
...[G]etting heavier is not just a matter of “calories in, calories out," and...the mantra: “Eat less and exercise more” is far too simplistic. Although calories remain crucial, some foods clearly cause people to put on more weight than others, perhaps because of their chemical makeup and how our bodies process them. This understanding may help explain the dizzying, often seemingly contradictory nutritional advice from one dietary study to the next.
The problem with focusing solely on Calories is the foods people tend to keep versus cut when they start restricting them.
When you look at Jenny Craig and Weight Watcher's practitioners, the first thing to go is the protein source because they are "high in points" or take up a significant portion of the volume of food the people can eat. This is bad on many points:
- Protein keeps you satiated longer, so you don't need as much volume
- Protein is necessary to protect existing muscle mass, or build more muscle mass
- Excess protein (more than what your body will use) takes a lot of energy to process, in essence raising your metabolism a bit.
Another problem we have is the overemphasis of carbohydrates in western diets. I'll go on a limb and say that carbs are necessary, but definitely not in the quantities most people eat them. For active people (and we are designed to be active), carbs are an important part of recovery and a source of energy. However, they have some negative impacts, and worse if your sedentary:
- Carbs have the most glycemic impact, and the more processed the carb, the sharper that insulin response is.
- Insulin prepares your body's cells to accept glycogen, which for active people helps put energy in the muscles. However, in sedentary people, or in great quantities, when the body's cells become saturated, the carbs can only be stored as fat. When this condition exists for extended periods the person becomes insulin resistant, and ultimately diabetic.
- We are designed to process carbs, but think more in terms of peppers, green vegetables, and fruits.
Our bodies need energy, and it really doesn't matter whether that energy comes from fat or from carbs. The USDA gave fats a bad name, and then later the scientific community had to come back to the defense of certain fats. Most unnatural fats have "trans-fats" which are harmful to the body. However, mono-unsaturated fats like olive oil and fish oil have many good properties that are helpful to the body. Not to mention that certain vitamins we need are fat soluble.
Calories are important, but not as important as a proper balance of the macro-nutrients. Greatly exceeding the number of calories your body burns in a day (through normal metabolism and through activity) forces your body to do something with the excess.
- Excess protein will get converted to glycogen through a very slow process, but that excess glycogen can cause an insulin spike and ultimately convert it to fat.
- Carbs are broken down to glycogen immediately, and take a bit less energy to process than protein--but it is most readily turned into body fat.
- Dietary fat packs the most calories per gram, and takes the least amount of energy to process. However, dietary fat does not necessarily translate to body fat.
Bottom line is that the more active you are, the higher your metabolism gets, and the more Calories you need. Part of this is due to the increased muscle mass that accompanies activity, and part of that is due to how quickly you go through your energy reserves.
Different body types have different challenges, and treating everyone the same is a recipe for disaster.
- Mesomorph: the stereotypical genetically blessed individual. Hourglass shape for women, perfect V for men. These folks tend to be sensitive to fats, but they can usually work it off pretty quickly.
- Ectomorph: the pencil shaped body. These folks seem to be able to eat what they want without gaining a pound. A common complaint from these folks is that they can't gain wait. The only way to fix that is to eat copious amounts of food and protein and work hard to turn it into muscle. They just can't seem to hold on to fat.
- Endomorph: the round bodied person. These folks can't seem to get weight off. They sniff a brownie and gain a pound. Carbs are the endomorph's enemy--especially those highly processed and delicious dessert carbs.