Weight Loss and Metabolism: How Your Body Burns Calories

I think you'll agree with me that losing weight is not easy. Not only does it require a long-term commitment, but it also involves sifting through all the advice that is out there (some good, some bad) and deciding which weight loss program is right for you.

If you've ever been on a diet, you're probably familiar with the advice to "eat less and exercise more". It's one of the most cited strategies for weight loss. However, it's also one that might have left you feeling hungry, tired, and frustrated when the weight wasn't coming off. Or perhaps you even lost some weight, but it took a reeeaaally long time.

Well, maybe you should have eaten even less and pushed through a few more hours of exercise each day. Or maybe ... you have followed the wrong advice.

In this article, I'll debunk the three most common myths concerning weight loss and explain how your body actually burns calories.

Well, not really. The truth is, your body doesn't follow formulas. Yes, calories do matter when it comes to weight loss, but they aren't the be-all and end-all of weight loss success.

Metabolism and Calories:

Energy balance is a complex process. It's regulated by metabolism, which refers to an entire range of biochemical reactions happening within every living organism. Metabolism consists of two pathways:

• Anabolism: synthesis of small molecules into complex molecules, requiring energy in the process.
• Catabolism: break down of complex molecules into smaller molecules, producing energy in the process.

Anabolism consumes the energy catabolism creates. If catabolism produces more energy than anabolism requires, there is excess energy. This energy is either immediately used as a fuel or stored as fat for a later use. In this sense, calories do matter when it comes to weight loss. If you have ever lost weight, you have necessarily expended more calories than you consumed.

Metabolism and Hormones

Both catabolism and anabolism have also their own sets of hormones that turn these processes on and off. Catabolic hormones, such as adiponectin, adrenaline, cortisol, and glucagon are fat-burning. Anabolic hormones, such as estrogen, growth hormone, insulin, and testosterone, are muscle-building. The hormonal anabolic-catabolic balance in your body plays a crucial role in fat loss and muscle building.

In fact, it's your hormones that determine whether you burn or store fat, remain full or get hungry easily, feel satiated or crave certain foods. If your hormones are imbalanced, weight loss will be a struggle regardless of how much you restrict your calorie intake. Advocates of the "eat less exercise more" way of thinking suggest that the only thing that matters when it comes to weight loss is calories. However, they completely disregard the metabolic and hormonal impact of food. The truth is that different food effects your body in a different way. (1)

Calories vs. Hormones: The Intricate Interplay

So what's more important when it comes to weight loss: calories or hormones? Well, they are equally important because they affect each other.

Consuming 100 calories from carbohydrate has a completely different hormonal effect than consuming 100 calories from protein. Protein stimulates production of hormones that help to reduce appetite and normalize blood sugar levels. Carbohydrates, on the other hand, stimulate production of hormones that increase appetite, cravings, and spike blood sugar levels.

Let's look at a practical example. Say you eat a doughnut. All the sugar in the doughnut spikes your blood sugar. That tells your pancreas to release a hormone called insulin to bring your blood sugar levels back down. Insulin also increases your appetite and blocks an appetite-controlling hormone called leptin. As a result, your brain becomes incapable of signaling to your body that you are full and should stop eating. You are now up against one of your most basic drives - hunger - and the chances of you winning are pretty slim.

So while it's true that weight gain is a direct result of consuming excess calories, calories don't tell the whole story. The culprit of excess calorie consumption is a hormonal imbalance.

Myth #2 - Hitting The Gym Is Necessary For Weight Loss

There is no question that exercise is a crucial part of any successful weight loss program. However, there are two ways you can expend calories: go to the gym or build movement into your lifestyle. To see which one is more important, we need to first understand how your body burns energy.

How Your Body Burns Energy

The amount of energy your body burns in a day is called metabolic rate, also referred to as the Total Daily Energy Expenditure (TDEE). TDEE can be further divided into Resting Energy Expenditure (REE) and Non-Resting Energy Expenditure (NREE). (2)

Components of REE

• Basal Metabolic Rate (BMR) refers to the amount of energy your body needs to sustain its most basic functions, such as breathing, circulating blood, maintaining body temperature, growing and repairing cells, etc. BMR is determined primarily by the amount of your lean body mass, that is, your total weight minus fat weight. While BMR varies from person to person, it generally accounts for about 60% of TDEE in a sedentary person and about 80% of TDEE in a physically active person. (2, 3, 4)

Components of NREE

• Non-Exercise Activity Thermogenesis (NEAT) is the energy expended for everything you do that isn't sleeping, eating, or sports-like exercise. It includes normal daily activities, such as reading, writing, cooking, performing yard work, or simply fidgeting. (5) Most of the variance in NEAT between people is associated with differences in occupation. NEAT accounts for about 15% of TDEE.
• Thermic Effect of Food (TEF) encompasses the energy expended in the process of ingesting, absorbing, metabolizing, and storing nutrients from food. About 6% to 12% of TDEE is attributed to TEF. (6, 4)
• Exercise Associated Thermogenesis (EAT) refers to a sports-like exercise and only accounts for about 5% of TDEE. (2)

Myth #3 - If You Have Slow Metabolism, Your Are Destined To Be Overweight

When people talk about "slow metabolism", they usually refer to their basal metabolic rate (BMR). In this article, I'll use these two terms interchangeably as well.

BMR accounts for 60% - 80% of TDEE and is the biggest factor in determining metabolic rate. There are several aspects that determine how fast or slow your BMR is.

Factors That Influence BMR

1. Age: BMR slows down with age. This is a consequence of a loss of muscle tissue and hormonal changes. (7, 8, 9). Metabolism is the highest during periods of rapid growth. At the age of 30, metabolism is only approximately 70% of its value at the first birthday. (8)
2. Body size: BMR increases in direct proportion to body mass. The bigger your body, the higher the energy requirements for heat production and oxygen consumption. (8, 10)
3. Body composition: BMR increases in direct proportion to the percentage of muscle mass. (11) Muscle requires more energy to function than fat. Lean body mass, which is your total body weight minus fat weight, is usually viewed as the main determinant of BMR. (8)
4. Diet: severely restricting calories puts your body into starvation mode. Starvation mode slows down your BMR as your body tries to conserve as much energy as it can by reducing the amount of calories it burns. (12) This amounts to 12.8 calories for each kilogram of weight loss. (13) Moreover, your body starts burning muscle tissue to conserve its valuable fat stores, which further reduces your BMR. (14)
5. Environmental temperature: if the outside temperature is very low or very high, your body has to work extra hard to maintain its normal body temperature, which increases BMR. (15, 16)
6. Gender: BMR is higher in men than in women of the same age and height. Different hormonal patterns, affecting both body size and body composition, seem to be the major reason. (8, 17)
7. Genetics: some people are born with higher BMR than others. (18)
8. Hormones: hormones that affect metabolism include adiponectin, adrenaline, cortisol, estrogen, ghrelin, human growth hormone, incretins, insulin, leptin, neuropeptide Y, progesterone, testosterone, and thyroid hormones.
9. Illness: sickness, fever, and infections increase BMR due to a higher than normal body temperature. (19) Your body also has to work harder to fight off the illness and create an immune response.
10. Medical conditions: in some cases medical conditions are the underlying reason for weight gain. Such conditions include underactive thyroid, diabetes, Cushing’s syndrome, polycystic ovary syndrome, steroid treatment, or fluid retention. (20)

Is Your Metabolism The Reason You Are Not Losing Weight?

Unless you're suffering from a certain endocrine disorder, the answer is no - slow metabolism doesn't usually cause weight gain.

Your metabolism is a natural process and balances itself to meet your individual energy needs. It operates as fast or as slow as your body requires it to. In fact, larger people - both overweight and more muscular - have usually faster metabolisms than lean people. (21) This is because the larger your body is, the more energy it needs to function properly.

A simple example would be dieting. If you restrict your calorie intake, your body unconsciously slows down its metabolizing processes to conserve energy. The opposite is true as well. If you consume more calories than your body needs, your body speeds up its metabolizing processes to burn off excess calories and slow down weight gain. Essentially, your body is like a thermostat, trying to regulate its weight by either expending more or less energy.

Do Overweight People Have A Broken Metabolism?

If your body naturally balances itself, why do some people become overweight? Excess calorie intake, low quality food, and insufficient exercise over a longer period of time override your body's natural tendency to stay at its healthy weight. (22) The good news is that this "damage" is completely reversible. (23) There are many things you can do to keep your metabolism working the way it was designed to.