Weight loss: It’s more than ‘Calories In vs. Calories Out’


KIRTLAND AIR FORCE BASE, N.M. — One frequently hears “calories in vs. calories out” when discussing weight loss. The idea behind this is simple; in order to lose weight, calories in must be less than calories out.

The reality is a bit more complicated. Let’s start with the “calories out” component, which is daily energy expenditure, or DEX. DEX consists of resting metabolic rate (RMR,) thermic effect of food (TEF,) and physical activity (PA).

What is RMR? Let’s use an analogy; if you think of your body as a car, RMR is your car’s idiling speed; it’s the amount of gas in calories your “car” is burning while operating, but not going anywhere. RMR is about 60 to 70 percent of total DEX.

The primary contributors to RMR are the brain, heart and liver. Those organs are not big percentages of body weight. However, those organs run “hot” they have very high idling speeds. The thermic effect of food is the amount of calories burned as a product of digesting what you eat. The TEF is approximately 10 percent of DEX. Foods which are higher in protein have a higher TEF than carbohydrates or fat and also decrease appetite more rapidly. Another factor which increases TEF is chewing food. TEF may increase by up to 50 calories per meal if the meal is thoroughly chewed versus swallowed without chewing. Remember when your mother told you to chew your food as a kid? Well, mom was right.

The final piece of DEX is physical activity (PA). There are many factors that influence the contribution of PA to DEX. For example, the type of PA (weight bearing vs. non-weight bearing, resistance training vs. cardio), differences in lean body mass and total body fat mass. Other factors that influence DEX include genetics, muscle fiber type, exercise intensity, exercise economy, gender and excess post-exercise oxygen consumption, or EPOC. EPOC represents the exercise “afterburn”, or the calories expended from exercise after the exercise is over. Some of these factors can be modified. For example, increases in exercise duration and/or intensity will increase DEX.

Another way to increase DEX is resistance training. Resistance training increases muscle mass, which in turn increases RMR plus DEX. Adding 10 pounds of muscle will increase RMR, and therefore DEX, by 60 calories per day. That may not seem to be a large difference, but over one year, that’s an additional 21,000 calories burned sitting on the couch. Physical activity also alters TEF; individuals with high levels of aerobic fitness have a higher TEF than individuals who are sedentary.

The “calories in” component is also more complicated. To illustrate, nuts are high in fat, and one might think people who consume nuts regularly are at a higher risk of becoming overweight/obese as a result. The reality is that regular nut consumers are not at higher risk of obesity. Why? Nuts are high in protein, which promotes a sensation of fullness; the high fiber content of most nuts has the same effect. The really interesting part is that in some nuts (almonds, peanuts and walnuts have been studied), 20 to 25 percent of the fat calories are so tightly bound to the nut fiber that even after chewing, the calories stay locked to the fiber and pass all the way through the digestive tract without being used. Processing of nuts does affect this; peanut butter is more completely digested than whole peanuts. This same mechanism likely contributes to observations that diets high in whole grains, fruits and vegetables lead to greater weight loss than processed foods; another reason to consume plant foods as close to unprocessed as possible.