Calories, calories and more calories. We have an obsession with counting calories. Look at any food label and right there at the top, usually bigger than anything else, are the calories. And we even have calories listed on restaurants menus. It’s as if food is only good for the calories it provides. And therefore it doesn’t matter where we get our calories from. But it does matter, because not all calories are created equal.
What is a calorie?
A calorie is a unit of energy. One calorie is the amount of energy needed to heat up one mL of water by one degree Celsius. However, calories on food labels are actually kilocalories. One food calorie (or kilocalorie) is the energy needed to heat up one litre of water one degree.
How many calories are in a food depends on what type of food it is, and for processed foods, what’s in the ingredients. There are three main macronutrients: fat, carbohydrates and protein. These macronutrients contain 9, 4 and 4 calories per gram, respectively. So fat provides the most calories per gram and has the biggest energy boost, making it an ideal way to store energy in the human body.
Despite everything that tells us to lower and watch our calories, we need the energy from calories to live. Calories aren’t something like cigarettes where the ideal amount is zero. How many calories an adult needs can vary based on body size, metabolism and activity levels, but many of us will require between 1500 to 2000 just to keep our body going.
But aren’t all calories equal?
The idea of all calories being equal comes from the weight loss field. At the core level, a person’s weight depends on how much energy in (dietary calories) and how much energy out (calories used in metabolism and activity). If you take in more calories than you burn, you will likely gain weight. Conversely, if you burn more calories than you take in, you will lose weight.
A number of studies, such as this one, have even demonstrated that it’s how many calories you eat that matters in terms of weight loss, not whether they come from fat, carbohydrates and protein. In this study, people were randomized to different diets- typical diet, high protein, high fat or low carbohydrate. After two years of nutrition counselling, the amount of weight loss was no different between the groups.
So from an energy perspective, yes, all calories are equal. There is no difference between the amount of energy in one calorie of fat from that in one calorie of protein. But if all calories were equal, we could just get away with eating sugar all day (plus the odd supplement). It’s cheap and packed with energy. But your body doesn’t see calories when you eat. It sees food. This is because different foods go through different biochemical pathways. And it’s those different pathways that determine whether that one calorie leads you to eat another or fills you up.
Not All Calories are Created Equal
This is easily realized when looking at food volume. A medium apple is about 100 grams and has 52 calories. To get the same amount of calories from table sugar, you only need to eat 13 grams of it. For chips, as little as 10 grams will get you 52 calories. As a result, the apple will make you feel fuller. This is because inside your stomach and intestines are stretch receptors. When you eat and the gut gets stretched, it sends out a signal to the brain to stop feeling hungry.
In the weight loss study above, it should be noted the foods were similar across the diets (just differing amounts) with a focus on plants and minimal processed foods. However, another study more reflective of the real world found when people ate a low-fat diet, with the ability to eat as much as they wanted, they ate nearly 700 calories less per day compared to when they ate a low-carb diet.
Neither of those studies included processed foods in their diet, which is important because ultra-processed foods (pop, some cereals, ready-to-eat foods) make up more than half of most people’s diets. And these foods can lead to eating more. A study comparing free access to either processed or unprocessed foods for two weeks found processed foods resulted in people eating 500 calories more per day.
Ultra-processed foods tend to have less volume per calorie and result in greater production of hunger hormones. They’re also more likely to result in a greater insulin release when metabolized (so-called high-glycemic index foods). This can result in the rapid clearing of glucose from the bloodstream making you feel hungry and likely to consume more calories. On the other hand, unprocessed foods are higher in fibre, which results in less insulin being released. They’re also better for your microbiome and can result in fewer calories metabolized.
So while one calorie from table sugar is equal in energy to one calorie from an apple or a steak, how that one calorie affects your metabolism and feelings of hunger can vastly differ. That one calorie from sugar (or other processed foods) will affect your body in a way that will keep you feeling hungry and may lead to you eating more calories.
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