What is metabolism?
The word metabolism gets used a lot when talking about nutrition and weight loss, but at its core, metabolism is the term for all the chemical reactions taking place in the body. Metabolism can be subdivided into two categories - either anabolic reactions (building) or catabolic reactions (breaking down). As an example, building muscle is an anabolic reaction while using stored fat for fuel would be a catabolic reaction. (7, 8)
Unsurprisingly, nutrition is a crucial component in supporting a healthy metabolism and achieving weight loss success. The food we eat gets broken down into calories that fuel the pathways of metabolism. A normal, functioning metabolism is one that is able to adapt to change in order to maintain homeostasis. Our metabolism needs a plentiful nutrient supply to keep it running efficiently.
What is a calorie?
A calorie is another term for "unit of energy," and it comes from three primary macronutrients - carbohydrates, fat, and protein. Calories are required for the body to store and transfer energy to every cell in order to perform its life-sustaining functions such as breathing, blood circulation, body temperature regulation, brain and nerve function, cell growth, and muscle contractions. Metabolism is the term we use when we speak about burning carbs, fat, and protein. (9)
We consume calories in the form of:
- Protein (1 gram of protein = 4 calories)
- Fat (1 gram of fat = 9 calories)
- Carbohydrates (1 gram of carbohydrate = 4 calories)
- Alcohol (1 gram of alcohol = 7 calories)
The amount of calories you per burn day at baseline is known as basal metabolic rate, or BMR. Understanding BMR can help you understand your basic calorie needs, making sure you eat enough to perform your best and maintain a healthy weight. BMR is highly influenced by genetics, but other influencers include age, gender, lean body mass, stress, and current stage of life/health status. (10, 11)
We also use energy to digest the food we eat (TEF) and to fuel our movements, both intentional exercise (EAT) and incidental movement (NEAT), throughout the day. The combination of BMR plus NEAT, TEF, and EAT makes up our total daily energy expenditure, or TDEE for short. (12, 13)
TDEE determines the rate at which you burn calories, or your metabolic rate, and plays a key role in weight maintenance. Consider calories as your "gas" and metabolism as your "engine." (14)
It is important to maintain some caloric deficit to achieve weight loss, but there are nuances here. It may sound counterintuitive, but consistently eating well below your calorie budget is likely to have the opposite effect when it comes to moving closer to your desired body composition. (15)
By understanding your BMR, tracking meals and exercise, and monitoring glucose, we can better understand the caloric needs that are right for you. This is why logging meals and activities in the Nutrisense app is crucial - we can assess how your body is uniquely responding to meals and adjust over time. Monitoring your weight and measurements like waist/hip helps assess whether your current nutrition and expenditure are appropriate for your body. In other words, awareness is the first step! We can use specific formulas to calculate both BMR and TDEE. Your nutritionist here at Nutrisense has the expertise in this area to help determine an appropriate amount of calories and macronutrient distribution your unique body needs for weight loss.
Limitations of calorie counting
While understanding your individual caloric needs is crucial for starting any successful weight loss plan, it only gets us so far! Eating too many calories or too few calories can both negatively impact weight, but focusing on calorie intake alone fails to capture the full picture of metabolic health.
There are a few reasons for this, including:
- Nutrient density - Consider 150 calories from a soda and 150 calories from a handful of nuts. Even though the calories are equal, the way the body uses these calories may be different. Processed foods are less nutrient dense and can create more inflammation in the body, slowing down your weight loss progress. The appropriate macronutrient balance is critical beyond calorie intake.
- Flaws of the Calories In, Calories Out (CICO) model - The CIC0 model is a one-compartment model of weight loss. It states that all the food we eat gets broken down and put into one "sink" (the body). When the body needs energy, it pulls from the sink regardless of where the calories came from (what foods we are eating). This does not take into account the nuances of glucose/ insulin interplay and the way the body prefers to use different types of fuel (known as oxidative priority). (16)
- Hormonal balance - Have you ever tried to restrict calories but still struggled with weight loss, or maybe you might have even gained weight? This is a common experience for some people. This is because our hormones, such as insulin, estrogen, and cortisol, are intrinsically connected to our weight and may sometimes be negatively impacted by under-eating. We need healthy hormones for a healthy weight. Many things can negatively impact our hormones, including nutrient imbalances and other stressors we'll talk about more as we go. (15)
- Bio-individuality - Different foods with the same exact amount of calories can have dramatically different metabolic fates, largely dependent upon a host of factors outside of our control. These factors include genetics and microbiome composition, among others. (17)
In summary, we find that on the extreme ends of the spectrum (getting too few calories or far too many), calories really do matter. In both cases, this can result in weight gain for some people. That being said, it's important to consider other aspects of nutrition, starting with macronutrient balance.