Knowing the basics of caloric energy usage is important for proper weight management.
We all know the term calorie. It gets bandied about everywhere these days. But what exactly is a calorie and how does caloric usage ultimately affect our body weight? Healthy weight is fundamental to good health and to avoiding many lifestyle diseases like cancer, heart disease, and type 2 diabetes. Understanding the process of energy production in the human body is important and will help us make smarter choices when it comes to maintaining ideal weight.
All animals live by converting food into energy to drive their body. Measured in kilojoules, or kilocalories (1 kj = 4.2 kc), energy is derived from foods through cellular respiration (aerobic and anaerobic.) 80% of energy is used for the metabolic requirements of organs and tissues, and about 20% is used by the brain. Macronutrients from carbohydrates, fats, and proteins are converted into energy in varying amounts depending on their weight. Fats provide the most 'weight' of energy, followed by proteins, then carbohydrates, and together these three groups contain 90% of all our food weight.
Energy delivered by the nutrients in food:
Carbohydrates - 3.8 kcal per gram
Protein - 4.1 kcal per gram
Fat - 9 kcal per gram
Alcohol - 7.6 kcal per gram
According to WebMD, humans require the following energy per day:
| Gender | Age (yrs) | Sedentary | Moderately Active | Active |
|---|---|---|---|---|
| Child | 2-3 | 1,000 | 1,000-1,400 | 1,000-1,400 |
| Female | 4-8 9-13 14-18 19-30 31-50 51+ | 1,200 1,600 1,800 2,000 1,800 1,600 | 1,400-1,600 1,600-2,000 2,000 2,000-2,200 2,000 1,800 | 1,400-1,800 1,800-2,200 2,400 2,400 2,200 2,000-2,200 |
| Male | 4-8 9-13 14-18 19-30 31-50 51+ | 1,400 1,800 2,200 2,400 2,200 2,000 | 1,400-1,600 1,800-2,200 2,400-2,800 2,600-2,800 2,400-2,600 2,200-2,400 | 1,600-2,000 2,000-2,600 2,800-3,200 3,000 2,800-3,000 2,400-2,800 |
We are all familiar with the equation calories out > calories in. For a static body weight, one's energy intake should equal energy output, which is the amount of kilojoules or kilocalories used by the body for sustaining life (i.e. breathing, pumping blood, digesting, etc) and from physical activity. More energy in than out means weight gain, and less energy in than out means weight loss. It's simple enough, but it has complex undertones.
Ultimately, the efficiency of energy converted from respiration to mechanical power is dependent on the type of food and on the type of physical usage (i.e. aerobic or an-aerobic activity, fast-twitch or slow-twitch muscle employment.) Although some foods contain more energy, or calories, per mass than others -- for instance, fat has almost twice the energy content of carbohydrate and protein, -- the body prefers to derive its energy primarily from carbs. If there are not enough carbs in your diet, the body will then use fat for energy, and then as a last resort, protein. We'll come back to this later.
The biggest problem we face today is our lifestyle. In our affluent societies, we tend to be both more sedentary and to consume more calories, which unbalances the energy equation, leading to weight gain and the obesity epidemic. As I just stated, when you ingest more calories than you expend, the result is that the excess is stored as body fat.
Energy Expenditure > Energy Intake
And that's basically the foundation of every approach to losing weight ever conceived of.
Forgive me for being overly reductive, but it helps to think about the equation when you are looking at the overall picture. Where and what to do will be based on your unique physiology, diet, and lifestyle. Simply put, if you are not maintaining or achieving your ideal weight, then you are failing to address one side or the other in the equation.
So what does this mean in practical terms?
First, let me say I am not advocating obsessively counting calories because ultimately food labels are often misleading and even inaccurate, and unless you completely prepare food for yourself and use a nutritional calorie guide, you are unlikely to be accurate in your estimations. Plus, it's a lot of work.
The goal is to achieve balance. You cannot get to a healthy state by just reducing caloric intake, or by exercising till you drop, or by focusing on specific foods to try to increase thermogenesis. Creating your healthy solution requires you to look carefully at all the components of each side and make judicious choices.
Let's consider the fundamentals on both sides of the energy equation.
On the intake side of the equation, we want to choose high quality food of the right kind (including thermic effect.) This means as we reduce caloric quantity we must increase caloric quality. Choose lean proteins, complex carbs, and heart-healthy fats. Choose to eat smaller portions and more often, but concentrated during a smaller part of the day so your body has a chance to utilize all its glucose stores. This is an important point I broached earlier. By keeping your carbs complex and fiber-rich, you maximize utilization versus storage.
By burning all your stores of carbs, your body will then use fat stores, and this is the key to effective weight control.
The process is two-fold: eating the right balance of carbs, proteins and fats, and then concentrating your meals into 8 hours during the day. By doing this, you optimize your body's energy usage, or metabolic efficiency, and thereby achieve your proper weight in a balanced manner. Also, choosing foods that have a high thermic effect (like peppers, spices, high-fiber foods, fatty fish, or lean proteins) helps fuel burning via thermogenesis. And finally, we can't forget to mention water. Water is actually a source of energy, but it is also central to every function in the body.
On the usage side of the equation, choosing the right kinds of activities and exercise, and when you do them is critical. Again you need to look at the big picture. If you have reduced caloric intake, you need to be careful with energy outgoings because there is compelling evidence that you may cause illness in the body if you over-exert with insufficient available energy.
Furthermore, whether you choose to do aerobic or an-aerobic exercise, and what time you do it, has an impact on calories burned. Studies show that as a result of insulin production (the hormone that governs carbohydrate use), if you delay eating for 45 minutes after exercising, you burn more fat than if you eat right away. If you exercise before eating, you may use more fat for energy, but in the end your body will compensate, and you also run the risk of hypoglycemia and difficulty recovering from metabolic stress.
Also, when you exercise for more than 40 minutes, you significantly increase cortisol levels, which may work against your efforts. In order to get the ideal program in place, you need an individual analysis of your physiology from your healthcare professional to understand the way your unique body functions and what choices are best for your needs.
Employ these basic processes to the balancing of the equation, and it will put you on the path for weight loss success.
Again, it bears stating that you cannot accurately quantify the exact numbers of either side of the equation. Even if you do prepare everything yourself and have an exact number for the foods ingested, you really cannot quantify energy usage in your body. Sure there are calorie-meters, but they are still generalizing, and you cannot fully know your resting energy expenditure, the actual thermic effect of foods, and the many variables like the fact that there is a peak in energy usage right after exercise, or that how hot or cold it is that day affects metabolism. If you are off in your calculations by just 10%, then the whole system is pointless (see post below.) The point is to understand the whole process so you can plan a balanced approach. That is being smart, and that is your solution to achieving ideal weight and ideal health.
References:
"Carbohydrates, Proteins, and Fats: Overview of Nutrition". The Merck Manual.
"Nutrient Value of Some Common Foods" (PDF). Health Canada, PDF p. 4. 1997.
Ross, K. A. (2000c) Energy and fuel, in Littledyke M., Ross K. A. and Lakin E. (eds), Science Knowledge and the Environment.
Calories: Overview of Nutrition: Merck Manual Home Edition
Energy requirements and energy expenditure of lean and overweight women; AJCN l987; Jana 0 de Boer, PhD; Aren JH van Es, PhD; Jop MA van Razj PhD; and Joseph GAJ Hautvast, MD
The opinions expressed in this article are of the author. Content and other information presented on the site are not meant to be medical advice or any substitute for professional advice, counseling, diagnosis, or treatment. Never delay or disregard professional medical or mental health advice from your physician or other qualified health provider.
