Today’s post is a follow up to last weeks discussion where I went over the basics of metabolism science. As we know, our metabolism is complex and there isn’t much we can do to greatly change it. However, today I wanted to talk about how gaining and losing fat can change the way your brain regulates your body weight. This is a complex area because our body composition can be influenced by a myriad of factors including sex hormone levels, macronutrient intake (especially protein), exercise style / frequency / intensity, age, medication use, genetic predisposition, and more. No ones body defies the laws of physics. So if the calories in calories out equation isn’t working for you, it’s because the equation is more complicated than it sounds.
This part is easy. You eat food, so you gain calories from that food… right? Well not exactly. For starters we aren’t very accurate at guessing how many calories are in foods. In fact, food labels can be off by up to 20-25%! Secondly, the amount of energy we absorb, store, and/or use isn’t even close to being uniform! For instance, processed foods (cooked, chopped, soaked, blended, etc.) are broken down plant and animal cells, which means we absorb more energy from them. Have a gut feeling that there’s something more to it? Well you’re right! The bacteria in your gut can also influence the amount of energy we take in from foods. In the end, don’t count on counting calories to correctly calculate the quantity of calories converted to energy. Say that three times fast and receive a free high five!
I would first like to make a correction to last weeks post where I stated “with digestion we use a maximum of 43% of energy from the foods we eat.” Although it is true that the thermic effect of eating consists of burning 0–3% from fat, 5–10% from carbs, and 20–30% from protein, these numbers actually only represent roughly 5-10% energy out. The point here remains that meat sweats are real. Protein requires a lot of energy to digest!
As a refresher, our resting metabolic rate (RMR) accounts for about 60% of our calories out per day. But guess what… that figure can be off by about 15%! That means while I’m a 200-pound guy with an RMR of 1905 calories, another guy just like me might burn 286 more (or fewer) calories each day with no more (or less) effort. Tack on variable from the last two sources of energy out (physical activity and NEAT), and now have a 50% disparity between what can be calculated to calories in and out vs. reality. Ultimately the Energy Balance Equation will look like this.
Because our bodies enjoy consistency (homeostasis), it will respond negatively when you restrict your calorie intake. So what happens when you go on a restrictive diet? The thermic effect of eating goes down because you’re eating less. Resting metabolic rate goes down because you weigh less. Calories burned through physical activity go down since you weigh less. Non-exercise activity thermogenesis goes down as you eat less. Calories not absorbed goes down and you absorb more of what you eat. Hunger signals increase, causing us to crave (and maybe eat) more. A rise in cortisol from the stress of dieting can cause our bodies to hold onto more water. Bad things also happen when you over exercise as well. For instance, over exercising can cause an increased appetite and more calories eaten, absorbing more of what we eat, decreased RMR, and decreased NEAT. YIKES! The good new is that losing weight won’t “damage” your metabolism. Your body simply makes adaptations in response to fat loss (to prevent that fat loss, in fact).
The Bottom Line
– How your metabolism reacts to changes in energy balance will be unique to you.
– Food labels are way off, so 1,600 calories eaten daily could really be 1,200… or 2,000.
– By eating a diet rich in whole, minimally processed foods, the number of calories you absorb can be significantly decreased and require more calories to digest.
– Eating lots of highly processed foods will increase the calories absorbed, burn fewer calories in the digestive process, be less filling, more energy dense, and more likely to cause overeating.
– Energy out for those who have lost significant weight will always be lower than for people who were always lean, so keep in mind that exercise provides tremendous health benefits and should be done for more than just weight loss purposes.
– Losing weight, and keeping it off, is accompanied by adaptive metabolic, neuroendocrine, autonomic, and other changes.
– Even if your body might defend against weight loss, you can still lose weight, gain muscle, and dramatically change your body.
– TAKE ACTION by eating plenty of protein, eat a wide variety of fruits, vegetables, quality carbs, and healthy fats, adjust portions as you plateau, or to prevent plateaus, create an environment that encourages good food choices, do a mixture ofresistance, HIIT, cardiovascular, and recovery activities, find ways to increase NEAT, create a nightly sleep routine and manage your stress, and eat slowly to enjoy your meals and decrease the total amount of calories consumed.