A widely accepted concept in mainstream nutrition is that weight loss or weight gain is strictly a matter of "calories in versus calories out”. If you "burn" more calories than you take in, you will lose weight regardless of the calorie source and if you eat more calories than you burn off each day, you will gain weight, regardless of the calorie source. In other words, “a calorie is a calorie” whether it comes from protein, fat or carbohydrates.
But in actual fact and practice, are all calories created equal? Well, let’s examine the question from the standpoint of science and from the practical viewpoint of empirical observation.
Common sense observation tells us that all calories are not created equal – or if in scientific jargon they are, then all foods are not created equal. Quite simply, if two groups of people maintain a daily intake of 2000 calories and group A derives the calories from toast, coffee with cream and sugar, hamburger and fries, pizza, ice cream and sugared soft drinks and group B obtains the calories from egg whites, oatmeal, chicken, fish, green vegetables, sweet potatoes, brown rice, and sugar free beverages, it doesn’t take a degree in rocket science (notice we didn’t say ‘nutrition’ as that can sometimes be a mixed bag) to figure out that group B will look better, feel better and perform better than group A.
Given the foregoing example, how is it that any number of registered dieticians, physicians and others in the medical community still hold to the all calories are equal mantra? Could it be that mainstream nutrition hasn’t caught up with modern science? Let’s look at what science says.
In scientific terms, a calorie (kilocalorie or kcal), is the amount of energy required to raise 1 gram of water 1 degree Celsius. According to that definition, bio-chemically speaking, calories from fat, protein or carbohydrates might all be considered equal. But when the physiological and psychological effect of calories from different foods are taking into consideration, the answer changes.
Protein, fats and carbohydrates have primary and secondary nutrient-specific purposes within the body. For example, proteins are used for cellular growth and repair, synthesis of hormones and enzymes, and as a secondary source of energy (proteins can be converted to a form of glucose via gluconeogenesis) while carbohydrates are the body’s primary source of energy. A growing body of research shows that fats, carbohydrates and proteins not only serve different purposes within the body but have different effects on the metabolism via numerous pathways such as their effects on hormones (e.g., insulin, leptin, glucagon, etc), hunger and appetite, heat production, and uncoupling proteins (UCPs) and via the other mechanisms such as thermic effect of food (the heat liberated from a particular food not only of its energy content but also of its tendency to produce heat).
The ‘a calorie is a calorie is a calorie’ school of thought also ignores the ever mounting volume of studies that provide data to indicate that diets with identical calorie intakes but different macro nutrient ratios have different effects on body composition, physical performance, cholesterol levels, oxidative stress, and a host of other physiological factors. Here's some information derived from such studies that show how different foods affect the calories in - calories out equation and the number you see on the scale.
"Let's take a pure food example," says Anne-Marie Nocton, MS, MPH, RD. "If someone were to eat all of her daily caloric requirement as fried onion rings, would the body respond the same way as if all of the calories came from raw spinach? No, because caloric absorption is affected by the composition of the food itself and by the amount of energy it takes the body to process that food. In this example, the body doesn't need to expend many calories to digest and store fat (in the onion rings) because the digestion and storage process isn't very complex. But the spinach contains fiber, and the structure of a fibrous food means that some of the calories will be 'lost' because the body cannot break it all down."
Dr. Rick Mattes, PhD, MPH, RD, professor of foods and nutrition at Purdue University, has similar views. He notes that the simple act of eating raises your metabolism, and eating certain foods raises metabolism even more. “The energy the body uses in the digestion process is called the thermic effect of food (TEF),” he explains. "Protein has a higher TEF relative to carbohydrate and fat.” (Editors note: the thermic effect of protein is about twice that of carbohydrate or fat).
Speaking at an American Dietetic Association conference in Anaheim, California, Dr. Mattes, explained that other factors, such as the form of a specific food, also play roles when you compare calories from different foods. Taking the perspective that calories are equal as chemically processed in the body, Mattes looks at the foods rather than just the calories. When comparing and counting calories, the delivery system matters. For example, are the calories in solid or liquid form? Researchers comparing fruit juice and fruit found that the fruit showed a blunting effect on hunger while juice resulted in only a small decline.
Matte also noted that solid foods have greater compensatory responses than fluids. "Fluids add to the diet rather than replacing other foods,” he says. “This is called a weak compensatory response. And soda isn't the only problem drink - it's fluid calories in general, whether from juice or even milk. In other words, be careful of liquid calories, which may add to your total calorie intake rather than substituting for other foods.
Mattes stated that high-protein food has the highest satiety rating, therefore eating a high-protein diet could theoretically help you feel fuller and stay satisfied longer. While high-protein foods are valuable for their fullness factor, foods such as nuts that are rich in fat and protein have also garnered attention. Many studies have shown that nuts, though high in calories, have high dietary compensation and may even increase metabolism. Mattes illustrated one study that found subjects' resting energy expenditure was 11% higher after nut consumption.
Along these same lines, researchers at the City of Hope Medical Center in Duarte, California studied two groups of overweight people, both on medically supervised low-calorie liquid diets. One group added 3 ounces of almonds to their daily diet, while the other group added the same amount of calories from complex carbs like popcorn and Triscuit crackers. Both groups ate the same number of calories daily, about 1,000. During the 24-week study, the almond-eating group lost more weight even though they ate the same number of calories as the carb group. Same calories, different results.
Dr. David Ludwig, from Children’s Hospital Boston is another authority who debunks the ‘all calories are created equal’ theory. “The idea that ‘a calorie is a calorie is a calorie’ doesn’t really explain why conventional weight-loss diets usually don’t work for more than a few months,” says Dr. Ludwig. “Almost anyone can lose weight in the short-term but very few keep it off in the long-term. That’s given rise to the notion that the body has a ‘setpoint’ and that when you diet, internal mechanisms work to restore your weight to that setpoint.” Low-carb diets,” he continues, “may work better with these internal biological responses to create the greatest likelihood of long-term weight loss.”
“Our data suggest that the type of calories consumed - independent of the amount -can alter metabolic rate,” says Dr. Ludwig.
Finally, we like to reference the work of Richard Feinman, PhD, Professor of Biochemistry at the State University of New York Downstate Medical Center. In an article published in Nutrition Journal 2004, 3:9 with his colleague, Eugene Fine, MD, Dr. Feinman puts the all calories are equal issue to rest by addressing the first and second laws of thermodynamics. “The first law of thermodynamics is the one that's easy to understand, it's the conservation of energy," says Dr. Feinman. "There's a fixed amount of energy in the world, and in the context of nutrition it means that any energy that you take in in the form of food must either show up as work that you do, or heat that you generate, or the chemical transformation that you carry on in your body, making new protein, and so on; and the rest will be leftover as fat. So that's always true. The second law of thermodynamics, however, is a much more difficult law to understand, and it's a dissipation law. It's a law of efficiency. It says that not all processes are equally efficient."
Dr. Feinman, says getting the body's fuel – glucose - from protein is less efficient than getting it from carbs, which means low carb diets make the body use more energy. "Your brain and some cells in your body have to have glucose, and there are several ways they can get that glucose," he explains. "You take in sugar or starches, that's a direct supply of glucose. You can make that glucose from protein. If you do that, that's a very inefficient process, you're going to use energy to turn protein into glucose, and in the end you're going to have to get that energy from burning something, usually fat." Essentially, then, the more inefficient the diet is at turning calories into glucose, the more effective it should be for weight loss.
Now to the topic at hand. Dr. Feinman also states that not all calories are created equal. "For many years nutritionists have been saying, 'a calorie is a calorie,' " Feinman said. "That is, weight gained or lost only depends on the calories in the diet, regardless of the macronutrient composition, that is, protein, carbohydrate, fat. We knew this was not true, so we set out to show that this was not true. I think the bottom line is once you have the idea that all calories are the same, you're not going to try to find the best diet. And I think it's very important to try to find out what's going to be most effective. We don't know that yet, but unless we work at it, we won't find it."
According to Dr. Feinman, A calorie is a calorie" violates the second law of thermodynamics. And we don’t want to do that, do we?