A calorie is a calorie is a calorie, at least from a thermodynamic point of view. It is defined as the amount of energy required to raise the temperature of 1 kilogram of water by 1 degree Celsius (2.2 pounds per 1.8 degrees Fahrenheit).
But when it comes to your body’s health and energy balance, not all calories are created equal.
For instance, some studies have reported this diets that are high in protein, low carb or a combination of both give greater weight loss than diets with other levels of fat, protein and carbohydrates.
If every calorie in food were the same, you wouldn’t expect to see differences in weight loss between people consuming the same number of calories distributed in different types of food.
Dieticians like me Know that there are many factors that influence what a calorie means to your body. Here’s what we understand so far about calories and nutrition.
The energy actually available to your body
In the late 1800s, chemist WO Atwater and his colleagues devised a system to determine the amount of energy, or number of calories, in various foods. Basically, he burned food samples and recorded how much energy they gave off as heat.
However, not all of the energy in food that can be burned in the lab is actually available to your body. What scientists call metabolizable energy is the difference between the total energy of food eaten and the energy that leaves your body, undigested, in feces and urine. For each of the three macronutrients – protein, carbohydrates and fat – Atwater devised a percentage of the calories they contained that would actually be metabolizable.
According to the Atwater system, one gram of each macronutrient is estimated to provide a certain number of calories. The United States Department of Agriculture still uses these calculations today to propose a official calorie count for each food.
How much energy do you use
What you eat can affect what scientists call your body energy costs. It’s the amount of energy it takes to keep you alive – the energy you use to breathe, digest, circulate your blood, etc. – as well as what you exercise to get your body moving. You may have heard of something called metabolism.
The quality of the diet can alter the body’s energy expenditure, also called thermic effect of food. For example, in one study, people consuming the same number of calories per day but following either a low-carb or low-fat diet had differences in total energy expenditure about 300 calories a day. Those on very low-carb diets used the most energy, while those on low-fat diets used the least.
In another study, high-fat diets reduced total energy expenditure than high carbohydrate diets. Other researchers have reported that although substituting carbohydrates for fats did not alter energy expenditure, people who increased their protein intake to 30%-35% of their diet used more energy.
In general, diets high in carbohydrates, fat or both produce a 4% to 8% increase in energy expenditure, while meals high in protein causes an increase of 11% to 14% above the resting metabolic rate. Proteins have a higher thermic effect because they are harder for the body to break down. Although these variations are not huge, they could contributing to the obesity epidemic by encouraging a slight average weight gain.
Quality of the calories you consume
Dietitians pay attention to a glycemic index of foods and glycemic load – i.e. how fast and how much it will raise your blood sugar. An increase in blood sugar triggers the release of insulin, which in turn influences energy metabolism and the storage of excess energy as fat.
Foods like white rice, cakes, cookies, and chips all have a high glycemic index/load. Green vegetables, raw peppers, mushrooms and legumes all have a low glycemic index/load. Some evidence suggests that foods drop in glycemic index/load Perhaps best for keeping blood sugar regulated – regardless of the calories they contain.
Reward centers in the brain light up when people eat high glycemic index/load foods, highlighting the pleasant and addictive effect foods like sweets or white breads.
The fiber content of food is another thing to consider. Your body can’t digest fiber — found in plant foods like fruits, vegetables, whole grains, and beans — for energy. Thus, high fiber foods tend to have less metabolizable energy and can help you feel fuller with fewer calories.
Empty calories — those from foods with minimal or no nutritional value — are another factor to consider. Things like white sugar, soft drinks, and many ultra-processed snacks don’t provide much, if any, benefit in the form of protein, vitamins, or minerals with their calories. The opposite would be nutrient rich foods that are high in nutrients or fiber, yet relatively low in calories. Examples are spinach, apples and beans.
And don’t think of empty calories as neutral. Nutritionists consider them harmful calories because they can have a negative effect on health. Foods that contribute the most to weight gain are potato chips, potatoes, sugary drinks and meats, both processed and unprocessed. On the other hand, foods that are inversely associated with weight gain are vegetables, whole grains, fruits, nuts, and yogurt.
More for health than calories and weight
It is indisputable that for weight loss, the difference between the number of calories consumed and the number of calories exerted by exercise is the most important factor. But make no mistake. Although weight plays a role in health and longevity, weight loss alone does not equate to health.
Yes, some high protein diets seem to promote weight loss at least in the short term. But epidemiologists know that in areas where people live the longest – almost 100 years on average – they having a mainly plant-based dietwith very little or no protein of animal origin and little or moderate fat in the form of mono- and polyunsaturated fats.
I often hear friends or clients say things like “these carbs are making me fat” or “I need to go on a low carb diet”. But these complaints are driving dietitians like me, well, nuts. Carbohydrates include foods like Coca-Cola and candy canes, but also apples and spinach. Reducing simple carbs like soft drinks, baked goods made from refined flour, pasta, and sweets will definitely have a positive impact on your health. But cutting out carbs like vegetables and fruits will have the opposite effect.
A plant-based diet rich in vegetable proteins and carbohydrates mainly from vegetables, fruits, nuts and legumes is the healthiest food researchers know for longevity and the prevention of chronic diseases like heart disease, cancer, hypertension and many other conditions.
The modern Western diet suffers from a increase in the amount of calories consumed with a competitor decrease in the quality of calories consumes. And researchers now know that calories from different foods have different effects on satiety, insulin response, the process of conversion of carbohydrates into body fat and metabolic energy expenditure.
When it comes to your health, rely more on the quality of the calories you eat than on the number of calories.
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