The saying, “Calories in/calories out” is common shorthand for, “You have to burn all the calories you eat or you’re gonna be fat.” It sounds right. Our logical brains say, “Yes.” But (of course there’s a but), it’s not completely true. It's not about calories. It's about energy availability.

The problem is that the way calories are measured (in a lab) has nothing to do with how bio-available calories (energy) are. In a lab, a scientist burns the food and measures how much heat (energy) it creates.  A calorie is the amount of energy it takes to heat a gram of water one degree Celsius. Guess what, your body has no idea what that means. And your body isn’t nearly as efficient at creating energy from food as fire is. Sometimes calories are “stuck” in the fiber and your body can’t get it out. Sometimes it takes so much energy to remove the calories what’s left was hardly worth the work (a cup of celery nets you about four calories after digestion).

When I explained this phenomenon, I was asked this question:

“So exactly how is that bioavailability/bioconversion measured? And how should a person measure portions to lose/maintain/gain weight?”

This was my response:

"That's a great question. When I work with clients, we don't worry about calories directly. Instead we think about nutrient density versus volume. For example: yellow/green/red veggies have high nutrient density and high volume (meaning you get lots of good stuff and they make you feel full). Starches (like root veggies and beans) still great nutrition but less volume. Nuts and seeds, again great nutrition but WAY less volume. Processed foods, oils, and animal products are low nutrient and low volume (easy to "overeat" and little value).

So, eat as much of you want of the first group, a "reasonable" amount of the second and a bit of the third. Stay away from the fourth. (naturally, with a client there is an in depth conversation about what "reasonable" and "a bit" mean)

What I have found is that once people understand hunger eating vs emotional or Pavlovian eating (habit), they eat exactly the right amount to reach and maintain their ideal body weight based on their energy expenditure.

That's the rule of thumb I give my clients (of course it's more personalized to their situation). I hope it's helpful."

When calories are “easy” to access in small containers (honey is the easiest because it’s already been digested by the bees) it’s going to be super easy to eat too much. When calories that are harder to access and in bigger containers (like whole-food plants), we are less likely to over eat (it’s almost impossible).

It is also the case that some calories (like fat) are easier to turn into the fat you wear than others (whole-food carbohydrates for example).

Dr Robyn is a former competitive volleyball player turned psychologist with continuing education in nutrition. Russ is a former competitive bodybuilder and trainer on the Mr. Olympia Tour. They are the co-founders of Whole Food Muscle and the authors of How to Feed a Human The Whole Food Muscle Way. To work with them one on one to improve your health and fitness or to have them speak at your event or organization email them at