In our never-ending search for effective diets, several weight loss programs have adopted the principle that what really matters is not the foods you eat, but how many calories you actually take in.
In other words, it doesn’t matter if you eat pizza and ice cream or salmon and vegetables. As long as you stay within an allotted number of calories—or certain amount of “points”—allowed per day, you will lose weight.
In essence, this type of diet espouses the belief that “a calorie is a calorie,” whether it comes from a healthy source like a vegetable, or an unhealthy source like a cookie. And it doesn’t matter what you eat, because as long as you cut back on the number of calories you consume, you will lose weight.
But is this true? Let’s take a look at both sides of the story.
The “Calorie Is a Calorie” Argument
By definition, a calorie is the amount of heat needed to raise the temperature of one liter of water by one degree.1 So, the amount of calories in food is a measure of the stored energy in that food.
Knowing this, perhaps the “calorie is a calorie” theory is sound. After all, it’s been beaten into our heads that to maintain your weight, you need to eat the same number of calories you burn in a day. And to lose weight, you need to burn more calories than you take in—simple as that.
In fact, to lose one pound of body fat in one week, you need to create a calorie deficit of about 3,500 calories.2 People who believe that all calories are the same say that you can create that calorie shortfall by eating less carbs, less fat, less protein or less of all three. It really doesn’t matter.
And research has shown that perhaps this is true, at least in some respect. In a review published in the American Journal of Clinical Nutrition, researchers examined nine studies that involved individuals following high-protein and/or low-carb diets compared to those following high-carb and/or low-fat diets.
After assessing the results, researchers stated that, while the diets high in protein and/or low in carbs produced a slightly greater weight loss, “the difference in energy expenditure is small and can potentially account for less than one-third of the differences in weight loss that have been reported between high-protein or low-carbohydrate diets and high-carbohydrate or low-fat diets. As such, a calorie is a calorie.”3
Basically, the law of thermodynamics applies here, which states that energy cannot be created or destroyed, only transformed. Thus, the body is constantly transforming food to produce heat. It doesn’t matter what the food is, because the transformation happens regardless. To this point, there are also those people who lose weight by counting calories, even while indulging in unhealthy cravings on a more-than-occasional basis.
So, on a basic level, this makes sense. However, there are a few problems with this idea. If all calories are equal, this means that the carbohydrates, proteins and fats you consume have the exact same effect on your body and on your weight. Not true.
Calories from all three of these macronutrients may be equal in terms of their energy content, but the body processes each of these substances differently, which can have dramatic effects when it comes to weight loss and management. For this reason, losing weight in a healthy manner involves much more than believing that “a calorie is a calorie.”
All Calories Are Not Equal
The more we learn about how the body metabolizes food, the more apparent it becomes that carbs, proteins and fats are processed differently, with the body using varying amounts of energy to metabolize each. In other words, we have to look at foods not just for their calories, but how they are used and how they affect the body as a whole.
This point was illustrated in a recently published JAMA study that included 21 obese individuals who were divided into three diet groups:
- Low-fat diet (60 percent carbs, 20 percent fat, 20 percent protein);
- Low-glycemic index diet (40 percent carbs, 40 percent fat, 20 percent protein); and
- Very low-carb diet (10 percent carbs, 60 percent fat, 30 percent protein).
All three groups consumed the same number of calories for the study duration. At the end of the study, the results showed that, compared to the low-fat dieters, the low-carb dieters burned 350 more calories per day and the low-glycemic dieters burned 150 more calories per day.4
These results make sense, considering proteins tend to make you feel full for longer periods of time, while also reducing appetite longer than fats and carbohydrates.
In another study, this one from the University of Washington School of Medicine, 19 participants were fed three different diets, one after the other. For the first two weeks, they followed a weight-management diet that consisted of 15 percent protein, 35 percent fat and 50 percent carbs. The following two weeks, they followed a same-calorie diet that consisted of 30 percent protein, 20 percent fat and 50 percent carbs. After those two weeks, they were told to follow the same 30/20/50 diet, but with no calorie restrictions, for a duration of 12 weeks.
The researchers reported that, upon switching from the low-protein diet to the higher-protein diet, the participants felt fuller longer, despite the fact that they were eating the same number of calories. And during the unrestricted calorie, high-protein diet portion of the study, the participants actually reduced their caloric intake voluntarily by almost 450 calories per day… and they lost an average of 11 pounds.5
Now let’s take a look at carbohydrates.
Carbs provide the quickest form of energy for the body. But not all carbohydrates are the same. The differences between carbs can be seen in their glycemic index (GI) scores.
The glycemic index is a scaling system that goes from 0 to 100, and indicates how quickly a food raises blood sugar levels. The higher the GI, the more it affects blood sugar levels. This is a big deal when it comes to weight loss or maintenance because an abundance of high-GI carbohydrates in the system triggers the release of insulin. One of the primary functions of insulin is to move these carbs into the cells, where they can be stored as fat.
This idea of high-GI carbs causing weight gain was shown in a study of 572 adults. Researchers collected data on these participants’ food consumption and exercise habits over a four-year span. They determined that weight gain or loss was associated with glycemic index, but not daily carbohydrate intake or the percentage of calories the individuals got from carbs. The high-GI carbs increased insulin production and fat storage.6
Foods with lower GIs (55 or less) don’t elicit as much of an insulin response, so they don’t lead to the fat deposits that high-GI foods (70 or higher) do.
Basically, this boils down to eating healthy carbohydrates over unhealthy ones. The majority of vegetables and fruits are low on the GI chart, while foods such as bread, pastas and processed foods—especially those made from refined white flour—are high GI.
Another benefit of carbohydrates—particularly vegetables, whole grains (not refined) and legumes—is that they are high in fiber. Fiber contributes to satiety without increasing caloric load, because fiber is not absorbed in the body. So, eating 150 calories worth of high-fiber vegetables is going to stick with you way longer than eating 150 calories worth of high-GI, fiber-void potato chips or soda. So choose your carbs wisely!
The final macronutrient—fat—has gotten a bad rap over the past several decades due to its link to heart disease and stroke. But numerous studies have found no evidence to corroborate this link.7
In reality, eating a certain amount of the right kinds of fat—mainly monounsaturated and polyunsaturated fats found in olive oil, avocado, seafood and raw nuts like almonds and walnuts—can play an important role in weight management and preserving lean muscle mass.8 These types of fat provide a great source of fuel, and actually reduce cholesterol and the risk of cardiovascular disease. So eliminating them completely would be a mistake.
However, avoiding artery-clogging trans fats is critical to good health and weight loss and maintenance. Trans fats provide no nutritional value and lead to a variety of health problems, not the least of which are obesity and cardiovascular disease.9 In fact, in one study, monkeys fed a Western-style diet that contains trans fat had a 7.2 percent increase in body weight, compared to a 1.8 percent increase in body weight observed in monkeys fed a same-calorie diet rich in monounsaturated fats.10
Even more concerning was that the extra weight the trans fat-fed monkeys gained went straight to their abdomen. Those monkeys deposited 30 percent more fat in their abdominal area than the monkeys fed the healthy monounsaturated fats. This type of abdominal, or visceral, fat has been shown to raise the risk of cardiovascular disease, diabetes and even cancer.
Given the research, it’s pretty safe to say that all calories are not equal.
We recommend approaching your diet with a well-balanced view when it comes to calories and what you’re eating. Eliminate all high-GI carbohydrates, including sugary foods, processed foods and anything made with refined white flour.
Instead, eat a Mediterranean-style diet that focuses on foods rich in fiber, essential fatty acids, antioxidants and protein to promote health as well as satiety. This includes plenty of high-quality, unsaturated fats like olive oil, proteins such as fish and chicken, legumes, vegetables, fruits and low-GI carbs. Adopting this sensible approach to dieting, and avoiding blatantly unhealthy foods, will go a long way in helping you maintain a healthy weight.
3. Buchholz AC and Schoeller DA. Am J Clin Nutr. 2004;79(suppl):899S-906S.
4. Ebbeling CB, et al. JAMA. 2012 Jun 27;307(24):2627-34.
5. Weigle DS, et al. Am J Clin Nutr. 2005 Jul;82(1):41-8.
6. Ma Y, et al. Am J Epidemiol. 2005 Feb 15;161(4):359-67.
7. Siri-Tarino PW, et al. Am J Clin Nutr. 2010 Mar;91(3):535-46.
8. Clifton PM, et al. J Nutr. 2004;134(7):1741-5.
9. Mozaffarian D. N Engl J Med. 2006 Apr 13;354(15):1601-13.