Welcome to the ROOTS series: a source for education on all things nutrition and wellness. We’ll dig though the fad diets, buzzwords, and confusion to get to the roots of healthy living, which will help you make educated, confident decisions about your food and lifestyle. I am a self-declared nutrition nerd, and I love understanding the ins and outs of how the body works, so be prepared to get a little science-y. This will be an expanding section of information, so check back periodically for new topics. Let’s dig in!
We’ll start with the basics. There are two categories of nutrients in our food supply: macronutrients and micronutrients. If you’ve remembered your Latin root words, you might be able to figure out that macronutrients are needed in large amounts and contribute to the bulk of our diets, and micronutrients are needed in smaller amounts. The three macronutrients are carbohydrates, proteins, and fats. These are the components of food that provide energy (calories). Micronutrients include vitamins and minerals and do not provide calories but do provide other benefits.
This should raise the question, “what is a calorie?” A calorie is simply a measurement unit – much like inches, ounces, or grams – that denotes the amount of energy that a food can provide. Scientifically speaking, it is the energy needed to raise the temperature of one gram of water by one degree Celsius. Macronutrients (carbohydrates, proteins, and fats) are the components of our food that provide calories. Carbohydrates and proteins provide 4 calories per gram, and fats provide 9 calories per gram. [Side note: alcohol provides 7 calories per gram. I haven’t included alcohol in micronutrients since it’s kinda its own thing.] This means that when you hear someone say, “There are 60 calories in 1/2 cup of this juice,” the calories are coming from one or more macronutrients in the juice.
Calories are not to be feared! Much like gasoline fuels your car, calories provide fuel for the body. Believe it or not, it takes a lot of fuel to make a body run smoothly and optimally. The human body has three main uses for fuel: resting metabolic rate (RMR – this is the energy needed to support basic organ functions such as breathing and a heartbeat), thermic effect of food (TEF – the energy needed to digest food and convert it to fuel), and thermic effect of activity (TEA – this includes any movement like shivering, brushing your teeth, or running).
A healthy individual’s RMR is influenced by age, gender, stature, body composition, and genetics. Generally speaking, a person’s RMR is roughly 10 calories per pound of body weight and constitutes 40-75% of their daily energy needs. This means a 140-pound person will need 1400 calories per day just to support basic life processes like breathing, maintaining a heartbeat, filtering blood through your kidneys, and transmitting brain messages. That’s 1400 calories per day just to exist! Here’s how those 1400 calories would be used by the body in a given day:
Heart: 12% (168 calories)
Kidneys: 12% (168 calories)
Liver: 23% (322 calories)
Brain: 23% (322 calories)
Skeletal muscle: 30% (420 calories)
The thermic effect of food (TEF) is the energy used by digestion. Just like your muscles need fuel to get through a workout, your gastrointestinal tract needs fuel to take the food you eat and digest it, convert it to usable energy, and store it for later use. TEF constitutes about 10% of your total energy needs per day.
Activities of daily living (ADL) is the energy we expend doing our normal daily tasks, such as cooking a meal, getting dressed, sitting up straight in a chair, driving to work, etc. Those tasks, as small and insignificant as they may seem, require energy as well! The calories required for ADL are generally equal to 50% of RMR.
The thermic effect of activity (TEA) is the most variable use of energy and can constitute 15-30% of the calories your body needs in a day. It’s easy to think about activity in terms of purposeful exercise – after all, running uses about 100 calories per mile, cycling uses about 50 calories per mile, and weightlifting uses 200-600 calories per hour. For a more comprehensive list of calories burned by activity, Fitness Partner is a great resource. However, the majority of our activity is much less obvious. It takes energy to produce any movement: shivering, fidgeting, tossing and turning in bed, sitting up straight, answering your phone, scrolling through your internet browser… it all uses energy!
To put all of these numbers together, let’s say our 140-pound example runs 2 miles and does moderate-intensity weightlifting for 60 minutes each day. How many calories will her body need to fuel her day?
RMR = 140 lbs x 10 calories/lb = 1400 calories
+ ADL = 1400/2 = 700 calories
+ TEA(running) = 100 calories/mile x 2 miles = 200 calories
+ TEA(weightlifting) = 400 calories/hour x 1 hour = 400 calories
= 2700 calories/day for RMR + activity
+ TEF = 2700 x 0.1 = 270 calories
= 2770 calories/day for RMR + TEA + TEF
As you may know, your weight is a reflection of a constant exchange of calories. If the calories you take in (food) are more than the calories your body uses (RMR + TEA + TEF), weight gain will result. If the calories you use are more than the calories you eat, weight loss will result. If you are in energy balance (calories in = calories out) your weight will stay the same. Please keep in mind that this is a very simplistic and general explanation – our bodies are much more complex than this, and we don’t work like cash registers. Eating more than your needs on one occasion does not lead to overnight weight gain; weight change is a reflection of long-term trends. In other words, you would need to consistently eat more calories than your body needs to experience weight gain, and you would need to consistently eat fewer calories than your body needs to experience weight loss. Even though this adds a layer of complexity to weight management, this is good news. This means we can have flexibility with our food intake and not live in fear of indulging every once in awhile. [Note: Another layer of complexity comes from the Set Point Theory – a theory that each person has a genetically-determined set weight that the body strives to maintain, even with calorie excess or deficiency. That’s a topic for another day.] No matter whether your goal is to lose, gain, or maintain, you can benefit from following a few simple guidelines:
- Focus on health. Focus on eating real, healthful foods and not on counting calories. This is a simple and beneficial attitude to have toward food, and a healthy body will result from healthy habits.
- Change your habits. Crash dieting never benefitted anyone, and weight loss achieved by severe calorie restriction is mostly water and glycogen, which means it will return when you begin eating normally again. Instead, focus on improving yourself one habit at a time. This will make it much easier to turn your actions into a lifestyle and maintain your healthy self for the long haul.
- Be active. Regular exercise (in moderation) can help improve mood, reduce stress, and improve your physical health. In addition to purposeful exercise, make it a point to be active throughout the day. It has been said that sitting is the smoking of our generation, and research shows that prolonged sitting – even when accompanied by daily exercise – increases mortality risk. This is easier said than done, particularly if you work a desk job. Take breaks every hour to walk around, or better yet, look into a standing desk. On the other hand, if you struggle with compulsivity or obsessiveness around exercise, talk to a professional (therapist or eating disorders dietitian) about whether or not incorporating exercise is a wise choice for you.
- Accept yourself. Some people were built to be tall and slender, others were built to be athletic and strong. There is no right or wrong, and this is no different than one person being business-minded and another having artistic talent. Our unique qualities make us who we are, and we can only change ourselves to a certain degree without becoming unhealthy and extreme. Learning to embrace and celebrate our bodies’ distinctive abilities can be incredibly freeing.
There is an often-neglected flip side to the weight issue. Our bodies are amazing machines, and we can survive even when we don’t fuel ourselves adequately. Under-eating can be just as dangerous to our health as over-eating. Unhealthy calorie restriction, which is considered under 1200 calories per day for women and under 1500 calories per day for men, results in the metabolism sloooowing doooown as an energy-conserving survival strategy. This means your body will become more energy efficient, using less fuel to power its essential tasks. This can cause gradual damage to the body if calorie restriction continues long-term. Remember all those important organs and their fuel requirements listed above? Without adequate calories to support the body’s basic needs, heart rate will slow, dizziness and low blood pressure will occur, digestion becomes less efficient, deterioration of bone may occur, hair and skin suffer, brain matter is lost, and anxiety and depression may result. At best, eating under 1200 calories per day is an unhealthy crash diet that likely will not result in a person meeting their health and lifestyle goals. At worst, it could be a sign of a larger problem at hand. If you feel you may be struggling with restrictive eating, you feel guilt following meals, or you find yourself compensating for calories eaten via exercise or other behaviors, please inform someone you trust or contact me – I’m happy to point you in the direction of non-judgmental help. Life’s too short to be spent worrying about weight and calories all the time. Food is fuel!