Following a conversation with my mother Saturday night, I have been trying to articulate the importance of different types of calories, if for no other reason than so I can formulate a standard answer to the question, "Does it matter where calories come from?" Yes, it does. But not simply for reasons of weight gain.
There are calories from protein, calories from fat, and calories from sugar (or carbs). They are listed separately on a nutrition panel, because they are separate. And that matters.
The number of calories you take in, relative to the number of calories expended, ultimately determines your overall body mass. "A calorie is a calorie."
But calories are not bad things. A "calorie" is a unit of measurement for energy (it's used in electricity, too). We need calories, and the average adult needs between 1800-2400 in order to maintain his/her weight. To lose weight, the consumption of 1200-1800 calories is recommended. This, of course, depends on your level of physical activity.
All that aside, however, there is a national guideline regarding the percentage of calories that "should" come from protein, fat, and carbohydrates. Carbohydrates are the body's preferred source of energy (longest-sustained and most efficiently utilized). But you want complex carbs (fruits, vegetables, grains), not simple carbs (refined sugars, starches). And this is where most calories should come from for optimal health. Calories from simple carbs are stored as fat, while calories from complex carbs are burned as energy and used to build muscle and tissue.
Next are calories from protein. But again, there is a difference between animal protein and plant protein. The beauty of plant protein is that it is also packed with micronutrients that animal protein doesn't have (fiber being an important one in weight loss, both because it helps burn calories AND helps curb hunger by filling you up quickly and for a long time). Animal protein is devoid of micronutrients, but comes complete with fat (mostly saturated) and cholesterol (which is not found in plant foods). So, if you take in 100 calories from protein in a burger, you're also getting an additional whopping serving of calories from fat, plus dietary cholesterol. If you take in 100 calories from plant protein, those are the only calories you're getting (so you can eat a lot more!), no dietary cholesterol, and, depending on the veggies you eat, an insignificant amount of fat (if any). It's simply more bang for your buck.
Last should be calories from fat. About 10% of your calories should come from unsaturated fat (not saturated or trans). Animal products are mostly saturated, and processed foods often have transfats (synthetic).
So in short (finally), the reason "it matters where your calories come from" is that it's not just about balancing intake with outflow for weight loss/maintenance, it's about being healthy and feeling good and, above all, being satisfied. Knowing that I can eat all day, every day, without ever feeling stuffed,l and without ever consuming more than a reasonably healthy amount of calories, gives me an unmatched sense of freedom in my food choices.
Vegans never count calories. Ask them. They don't have to. We get really full long before we've reached our maximum calorie intake.
In conclusion, if you are on a whole foods, plant-based diet, you'll eat more bulk and less calories. You'll eat more fiber and other vital micronutrients, and less fat and cholesterol. And that's why it matters
